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  • Articles  (929)
  • Springer  (871)
  • Blackwell Science Ltd  (58)
  • 1995-1999  (929)
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  • 1995-1999  (929)
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  • 1
    Electronic Resource
    Electronic Resource
    The influence of elevated CO2 on species phenology, growth and reproduction in a Mediterranean old-field community (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We studied the effects on the phenology, growth and reproduction of 19 Mediterranean species, of elevating the atmospheric CO2 concentration ([CO2]) to twice-ambient. Intact monoliths were taken from an old-field and put, during a six month growing season, into growth chambers in which external climatic conditions were mimicked and [CO2] was regulated. Fruit set time was significantly changed in six species under elevated [CO2] and leaf and branch senescence accelerated in most species. Grasses had fewer leaves and legumes were more branched at peak production under elevated [CO2] than under ambient. Plant seed number was not significantly changed under elevated [CO2], whereas the reproductive effort of grasses was significantly depressed. Reproductive and vegetative characteristics showed related responses to [CO2], as species with enhanced biomass had a hastened fruit set time, a higher number of fruits per plant and a higher reproductive biomass under elevated [CO2] than under ambient conditions, while species with depressed biomass had a delayed fruit set time, a lower number of fruits per plant and a lower reproductive biomass. Our results also show a high interspecific variability in [CO2] response, but some trends emerged at the family level: the production of vegetative and reproductive modules were depressed in grasses and slightly stimulated in legumes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00092.x
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  • 2
    Electronic Resource
    Electronic Resource
    Wildlife and climate change: assessing the sensitivity of selected species to simulated doubling of atmospheric CO2 (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We explored, using computer simulations, the sensitivity of four mammal species (elk, Cervus canadensis; white-tailed deer, Odocoileus virginianus; Columbian ground squirrel, Spermophilus columbianus; and chipmunk, Tamias striatus) within the continental USA to the effect of anticipated levels of global climate change brought about by a doubling of atmospheric CO2. Sensitivity to the direct effects of climate change were evaluated using a climate-space approach to delineate the range of thermal conditions tolerable by each species. Sensitivity to indirect effects were evaluated by quantifying the association of each species to the current vegetation distribution within the continental USA and using this association to assess whether wildlife species distributions might shift in response to vegetation shifts under climate change. Results indicate that altered thermal conditions alone should have little or no effect on the wildlife species’ distributions as physiological tolerance to heat load would allow them to survive. Analyses of the effects of vegetation change indicate that deer and chipmunks should retain their current distributions and possibly expand westward in the USA. For Elk and ground squirrels, there is a possibility that their current distributions would shrink and there is little possibility that each species would spread to new regions. This work emphasizes that the distributions of the four mammalian species are likely to be influenced more by vegetation changes than by thermal conditions. Future efforts to understand the effects of global change on wildlife species should focus on animal–habitat and climate–vegetation linkages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00093.x
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  • 3
    Electronic Resource
    Electronic Resource
    Methane emission from Texas rice paddy soils. 2. Seasonal contribution of rice biomass production to CH4 emission (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Measurements focused on seasonal contribution of rice productivity to methane emission were made in three experiments conducted in Texas flooded paddy soils during 1994 and 1995 growing seasons. A total of five rice cultivars representing two distinct groups in methane emission were involved. Over a 10-week period after permanent flooding, total seasonal methane emission was positively correlated with rice above-ground biomass (r2 = 0.845, n = 11). A very strong dependence of daily methane emission on above-ground vegetative biomass (r2 = 0.887, n = 93) and on root biomass (r2 = 0.816, n = 33) was also observed. Calculation from three developmental periods (vegetative, reproductive and ripening) of rice plant indicated that more than 75% of total seasonal methane was emitted during the last 5-week period in concert with reproductive and ripening stages, while rice biomass production during the same period amounted to ≈ 50% of the seasonal total. According to the correlation of cumulative methane emission with above-ground biomass increment between every two-week interval (r2 = 0.490, n = 93, P = 0.000), the carbon released as methane is approximately equivalent to 3% and 4.5% of photosynthetically fixed carbon in the biomass for low and high emission cultivars, respectively. A further investigation showed that these fractions are related to plant growth and development. The carbon ratio of methane emitted to net photosynthetic production during vegetative, reproductive, and ripening periods averaged 0.9%, 3.6% and 7.9%, respectively, for low emission cultivars, and 2.0%, 5.0% and 8.3%, respectively, for high emission cultivars. Moreover, the ratio was strongly dependent on plant biomass, resulting inr2 values from 0.775 to 0.907.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00106.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of elevated atmospheric CO2 in agro-ecosystems on soil carbon storage (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Increasing global atmospheric CO2 concentration has led to concerns regarding its potential effects on the terrestrial environment. Attempts to balance the atmospheric carbon (C) budget have met with a large shortfall in C accounting (≈1.4 × 1015 g C y–1) and this has led to the hypothesis that C is being stored in the soil of terrestrial ecosystems. This study examined the effects of CO2 enrichment on soil C storage in C3 soybean (Glycine max L.) Merr. and C4 grain sorghum (Sorghum bicolor L.) Moench. agro-ecosystems established on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). The study was a split-plot design replicated three times with two crop species (soybean and grain sorghum) as the main plots and two CO2 concentration (ambient and twice ambient) as subplots using open top field chambers. Carbon isotopic techniques using δ13C were used to track the input of new C into the soil system. At the end of two years, shifts in δ13C content of soil organic matter carbon were observed to a depth of 30 cm. Calculated new C in soil organic matter with grain sorghum was greater for elevated CO2 vs. ambient CO2 (162 and 29 g m–2, respectively), but with soybean the new C in soil organic matter was less for elevated CO2 vs. ambient CO2 (120 and 291 g m–2, respectively). A significant increase in mineral associated organic C was observed in 1993 which may result in increased soil C storage over the long-term, however, little change in total soil organic C was observed under either plant species. These data indicate that elevated atmospheric CO2 resulted in changes in soil C dynamics in agro-ecosystems that are crop species dependent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.d01-173.x
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  • 5
    Electronic Resource
    Electronic Resource
    Host plant effects on the performance of the aphid Aulacorthum solani (Kalt.) (Homoptera: Aphididae) at ambient and elevated CO2 (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: In future elevated CO2 environments, chewing insects are likely to perform less well than at present because of the effects of increased carbon fixation on their host plants. When the aphid, Aulacorthum solani was reared on bean (Vicia faba) and tansy (Tanacetum vulgare) plants under ambient and elevated CO2, performance was enhanced on both hosts at elevated CO2. The nature of the response was different on each plant species suggesting that feeding strategy may influence an insect’s response to elevated CO2. On bean, the daily rate of production of nymphs was increased by 16% but there was no difference in development time, whereas on tansy, development time was 10% shorter at elevated CO2 but the rate of production of nymphs was not affected. The same aphid clone therefore responded differently to elevated CO2 on different host plants. This increase in aphid performance could lead to larger populations of aphids in a future elevated CO2 environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.t01-1-00087.x
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  • 6
    Electronic Resource
    Electronic Resource
    Free Air CO2 Enrichment of potato (Solanum tuberosum, L.): design and performance of the CO2-fumigation system (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Free Air CO2 Enrichment (FACE) systems are used to fumigate unconfined field plots with CO2. As these installations can treat a sufficiently large area without interfering with natural climatic conditions, they are considered important tools for global change research worldwide. However, there is general consensus that elevated capital costs of existing FACE systems as well as high running costs may prevent their application at the required level of scale. A new and small FACE system that was designed to reduce both capital costs and CO2 use, is described in this paper. Due to its intermediate size (8 m diameter) between the smaller Mini-FACE systems that were developed in Italy and the larger systems designed by the Brookhaven National Laboratory in the USA, it was named Mid-FACE. The Mid-FACE was at first developed as a prototype and then used to enrich field grown potato crops in a CO2 concentration gradient experimental design. Technical details of a Mid-FACE prototype and of the operational set-up are presented in this paper together with performance data in terms of temporal and spatial control of CO2 concentrations within the experimental area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00076.x
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  • 7
    Electronic Resource
    Electronic Resource
    Interannual variability of seasonal succession events in a temperate lake and its relation to temperature variability (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The assessment of possible implications of anthropogenic climate change requires the evaluation of results obtained with complex climate models. Here we considered the problem of assessing the impact of climate variability on successional events in a lake (Plußsee) of the temperate region between January and May. We first established a statistical link between large-scale air temperature, at about 1500 m height, and the local temperature, in order to bridge the spatial gap of information obtained from global climate models and local climate which forces processes in the lake. Secondly, the local temperatures were statistically related to biologically induced dynamic features in the lake, derived from Secchi depths readings (as integrated measures). The observed relationships were compared with results from a phyto- and zooplankton population-dynamic model run under different temperature regimes. The local temperatures approximated closely the large-scale temperature. The timing of phyto- and zooplankton maxima (clearwater phase) were negatively related to the temperature. Thus, with a temperature increase both occurred earlier. The intensity of the spring algal maximum was negatively related to its timing, whereas no clear relation between the timing and intensity of the clearwater phase (zooplankton maximum) could be obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00080.x
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  • 8
    Electronic Resource
    Electronic Resource
    Biomass of primary and secondary vegetation in Rondônia, Western Brazilian Amazon (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Biomass estimates of primary and different ages of secondary vegetation are reported for a tropical forest region in Rondônia, Western Brazilian Amazon. The estimates are based on published allometric equations, and on vegetation composition and allometric data collected in areas of primary forest and secondary vegetation of ages 2, 3, 5, 9, 11, 16 and 18 years. Primary forest biomass estimates varied from 290 to 495 t ha–1. Secondary vegetation biomass estimates accounted for 40–60% of the primary forest biomass after 18 years of abandonment. Secondary growth rates in lightly used areas are estimated to have varied from 6.6 to 8.7 t ha–1 y–1 between the third and the eighteenth years after abandonment. CO2 sequestration by regrowing vegetation is discussed for two scenarios of land abandonment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00081.x
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  • 9
    Electronic Resource
    Electronic Resource
    The biogeochemistry of nitrous oxide in permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: This manuscript presents an overview of published work on nitrous oxide in the permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica. One of these lakes contains the highest concentration of nitrous oxide reported for natural aquatic systems (??bg 500 000% with respect to the global average mixing ratio in air). Recent data on nitrous oxide from the major lakes in this region of Antarctica are used to draw general conclusions regarding sources and sinks for this gas within the liquid water column, and to estimate exchanges with the atmosphere. Nitrous oxide maxima are usually found in regions where oxygen concentrations and redox potentials are decreasing (i.e. where high gradients exist); nitrous oxide is virtually absent in anoxic, and very low redox zones. These trends, together with positive relationships between apparent oxygen utilization (AOU) and apparent nitrous oxide production (ANP) indicate that nitrous oxide is primarily a product of nitrification; experiments showed that denitrification is a sink for this gas in anoxic water. ANP/AOU ratios are several orders of magnitude higher than that for the ocean. Yield ratios for nitrous oxide [ANP/(NO2–+NO3–)] averaged 4.2% (i.e. 1 atom of N appears in nitrous oxide for every 24 atoms appearing in oxidized N), greatly exceeding existing reports for pelagic systems, being similar to that from reduced sediments. Production and consumption rates, computed with a one-dimensional diffusion model, ranged from 0 to 5.3 nM-N d–1 and 0–2.7 nM-N d–1, respectively. Rates were usually greatest in the region of largest oxygen and inorganic nitrogen gradients. Turnover times averaged 2917 and 1277 years for production and consumption which is in the range of the mixing times for the lakes. Areal flux from the lakes to the atmosphere (6.17 gN m–2 y–1) is several hundred times greater than areal fluxes reported for oceanic systems. Owing to the relatively small combined surface area of these lakes, absolute atmospheric transfer (1.2 × 105 gN y–1) is only a small fraction of annual global emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00147.x
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of elevated CO2 on rhizosphere carbon flow and soil microbial processes (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Direct effects of increased above-ground CO2 concentration on soil microbial processes are unlikely, due to the high pCO2 of the soil atmosphere in most terrestrial ecosystems. However, below- ground microbial processes are likely to be affected through altered plant inputs at elevated CO2. A major component of plant input is derived from litter fall and root turnover. Inputs also derive from rhizodeposition (loss of C-compounds from active root systems) which may account for up to 40% of photoassimilate. This input fuels the activity of complex microbial communities around roots. These communities are centrally important not only to plant–microbe interactions and consequent effects on plant growth, but also, through their high relative activity and abundance, to microbially mediated processes in soil generally. This review focuses on approaches to measure C-flow from roots, in particular, as affected by increased atmospheric CO2 concentration. The available evidence for impacts on microbial communities inhabiting this niche, which constitutes an interface for possible perturbations on terrestrial ecosystems through the influence of environmental change, will also be discussed. While methodologies for measuring effects of increased CO2 concentration on plant growth, physiology and C-partitioning are abundant and widely reported, there is relatively little information on plant-mediated effects on soil microbial communities and processes. Importantly, many studies have also neglected to recognize that any secondary effects on microbial communities may have profound effects on plant parameters measured in relation to environmental change. We critically review approaches which have been used to measure rhizodeposition under conditions of increased atmospheric CO2 concentration, and then consider evidence for changes in microbial communities and processes, and the methodologies which have been recently developed, and are appropriate to study such changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.t01-1-00088.x
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  • 11
    Electronic Resource
    Electronic Resource
    Microbial decomposition at elevated CO2 levels: effect of litter quality (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The decomposition of senesced plant litter represents an important intermediate step in the cycling of nutrients between above- and below-ground systems. The rate of decomposition of plant litter is sensitive to fluctuations in a number of parameters, including environmental conditions, and particularly to changes in the quality of the litter. Increased C: N ratios of litter are thought to be one possible consequence of growth of plants under elevated [CO2]. This response is likely to reduce the rate of decomposition of the litter.Evidence from the growth of plants in both pot and field studies suggests that growth of C3 plants in elevated atmospheric [CO2] (600–700 μmol mol–1) may lead to a significant increase in either/both the C: N and the lignin: N ratios of litter. Short-term decomposition of litter from plants showing this response in elevated [CO2] has confirmed that decomposition occurs at a significantly lower rate. The limited studies of both the response of C4 plants to elevated [CO2] and the subsequent degradability of the senescent litter suggest that no differences in litter quality or degradability occur. In terms of litter quality the response of plants therefore appears to be dependent upon photosynthetic type; the C:N and lignin:N ratios of litter from C3 plants exposed to elevated [CO2] are increased, leading to lower degradation rates, while the nutrient ratios and degradation rates of litter from C4 plants grown in elevated [CO2] remain unchanged.To date, very few ecosystem studies of decomposition have been carried out. Further work is required at the ecosystem level to determine whether the effects observed in laboratory, pot and field studies are also observed in long-term, complex ecosystem studies. Clearly if these results are repeated at the ecosystem level then significant changes in the cycling of C and N in important terrestrial ecosystems may occur as a results of elevated [CO2].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.t01-1-00089.x
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  • 12
    Electronic Resource
    Electronic Resource
    Nitrogen cycling in microcosms of yellow birch exposed to elevated CO2: simultaneous positive and negative below-ground feedbacks (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: This study investigated simultaneous plant and soil feedbacks on growth enhancement with elevated [CO2] within microcosms of yellow birch (Betula alleghaniensis Britt.) in the second year of growth. Understanding the integrated responses of model ecosystems may provide key insight into the potential net nutrient feedbacks on [CO2] growth enhancements in temperate forests. We measured the net biomass production, C:N ratios, root architecture, and mycorrhizal responses of yellow birch, in situ rates gross nitrogen mineralization and the partitioning of available NH4+ between yellow birch and soil microbes. Elevated atmospheric [CO2] resulted in significant alterations in the cycling of N within the microcosms. Plant C/N ratios were significantly increased, gross mineralization and NH4+ consumption rates were decreased, and relative microbial uptake of NH4+ was increased, representing a suite of N cycling negative feedbacks on N availability. However, increased C/N ratios may also be a mechanism which allows plants to maintain higher growth with a constant or reduced N supply. Total plant N content was increased with elevated [CO2], suggesting that yellow birch had successfully increased their ability to acquire nutrients during the first year of growth. However, plant uptake rates of NH4+ had decreased in the second year. This discrepancy implies that, in this study, nitrogen uptake showed a trend through ontogeny of decreasing enhancement under elevated [CO2]. The reduced N mineralization and relatively increased N immobilization are a potential feedback which may drive this ontogenetic trend. This study has demonstrated the importance of using an integrated approach to exploring potential nutrient-cycling feedbacks in elevated [CO2].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00070.x
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  • 13
    Electronic Resource
    Electronic Resource
    Acclimation of photosynthesis to elevated CO2 and temperature in five British native species of contrasting functional type (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Acclimation of photosynthesis to growth at elevated CO2 concentration varies markedly between species. Species functionally classified as stress-tolerators (S) and ruderals (R), are thought to be incapable, or the least capable, of responding positively in terms of growth to elevated [CO2]. Is this pattern of response also apparent in leaf photosynthesis of wild S- and R-strategists? Acclimatory loss of a photosynthetic and growth response to elevated [CO2] is assumed to reflect limitation on capacity to utilize additional photosynthate. The doubling of pre-industrial global [CO2] is expected to coincide with a 3 °C increase in mean temperature which could stimulate growth; will photosynthetic capacity at elevated [CO2] be greater when the concurrent temperature increase is simulated? Five species from natural grassland of NW Europe and of contrasting ecological strategy were grown in hemispherical greenhouses, environmentally controlled to track the external microclimate. Within a replicated design, plants were grown at (i) current ambient [CO2] and temperature, (ii) elevated [CO2] (ambient + 340 μmol mol–1) and ambient temperature, (iii) ambient [CO2] and elevated temperature (ambient + 3 °C), or (iv) elevated [CO2] and elevated temperature. After 75–104 days, the CO2 response of light-saturated rates of photosynthesis (Asat) was analysed in controlled-environment cuvettes in a field laboratory. There was no acclimatory loss of photosynthetic capacity with growth in elevated [CO2] or elevated temperature over this period in Poa alpina (S), Bellis perennis (R) or Plantago lanceolata (mixed C-S-R strategist), and a significant (P ??bl 0.05) increase in capacity in Helianthemum nummularium (S) and Poa annua (R). Photosynthetic rates of leaves grown and measured in elevated [CO2] were therefore significantly higher than rates for leaves grown and measured in ambient [CO2], for all species. With the exception of Poa alpina, stomatal conductance and stomatal limitation on Asat showed no acclimatory response to growth in elevated [CO2].Carboxylation efficiency, determined from the initial slope of the response of Asat to intercellular CO2 concentration was significantly increased by elevated [CO2] and elevated temperature in H.nummularium, implying a possible increase in in vivo RubisCO activity. Increased carboxylation efficiency of this species was also reflected by an increase in the CO2- and light-saturated rates of photosynthesis, indicating an increased capacity for regeneration of the primary CO2 acceptor in photosynthesis. The results show that R-strategists and slow-growing S-strategists, are inherently capable of large increases in leaf photosynthetic capacity with growth in elevated [CO2] in contrast to expectations from growth studies. With the exception of P.annua, where there was a significant negative interaction between CO2 and temperature, concurrent increase in growth temperature had little effect on this pattern of response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00071.x
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  • 14
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    Electronic Resource
    Yield of wheat across a subambient carbon dioxide gradient (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Yields and yield components of two cultivars of day-neutral spring wheat (Triticum aestivum L.) were assessed along a gradient of daytime carbon dioxide (CO2) concentrations from about 200 to near 350 μmol CO2 (mol air)–1 in a 38 m-long controlled environment chamber. The range in CO2 concentration studied approximates that of Earth’s atmosphere since the last ice age. This 75% rise in CO2 concentration increased grain yields more than 200% under well-watered conditions and by 80–150% when wheat was grown without additions of water during the last half of the 100-day growing season. The 27% increase in CO2 from the pre-industrial level of 150 years ago (275 μmol mol–1) to near the current concentration (350 μmol mol–1) increased grain yields of ‘Yaqui 54’ and ‘Seri M82’ spring wheats by 55% and 53%, respectively, under well-watered conditions. Yield increased because of greater numbers of grains per spike, rather than heavier grains or numbers of spikes per plant. Water use increased little with CO2 concentration, resulting in improved water use efficiency as CO2 rose. Data suggest that rising CO2 concentration contributed to the substantial increase in average wheat yields in the U.S. during recent decades.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00074.x
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  • 15
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    Carbon balance and water use efficiency of frequently cut Lolium perenne L. swards at elevated carbon dioxide (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The impact of doubled atmospheric [CO2] on the carbon balance of regularly cut Lolium perenne L. swards was studied for two years under semi-field conditions in the Wageningen Rhizolab. CO2 and H2O vapour exchange rates of the swards were measured continuously for two years in transparent enclosures. The light utilization efficiencies of the swards ranged between 1.5 g CO2 MJ–1 global radiation (high light, ambient [CO2]) and 2.8 g CO2 MJ–1 (low light, doubled [CO2]). The above-ground net primary productivity (NPP) in the enclosures was greater by 29% in 1994 and 43% in 1995 in the doubled [CO2] treatments, but only 20% and 25% more carbon was recovered in the periodical cuts. Thus, NPP increased significantly more than did the harvested above-ground biomass. The positive [CO2] effect on net carbon assimilation is therefore associated with a preferential allocation of extra carbon to the roots and soil.In addition to higher canopy photosynthesis and leaf elongation rates, a small part of the positive [CO2] effects on NPP could be attributed to a decrease of the specific respiration of the shoots. On a canopy basis however, respiration was equal or slightly higher at doubled [CO2] due to the higher amount of standing biomass.Comparison of NPP and carbon recovered in different harvests showed that allocation to roots and soil was highest in spring, it was low in early summer and increased again in late summer and autumn.The total gross amount of carbon partitioned to the roots and soil during the two year period was 57% more at doubled [CO2]. The total amount of carbon that was sequestered in the soil after subtraction of the respiratory losses was 458 g m–2 and 779 g m–2 in the ambient and doubled [CO2] treatments, respectively.The average water use efficiency (WUE) of the swards was increased by a factor 1.5 at doubled [CO2]. Both WUE and its positive interaction with [CO2] varied between years and were positively correlated with global irradiance. At doubled [CO2], the higher WUE was fully compensated for by a higher leaf area index. Therefore, total transpiration on a canopy basis was equal for the ambient and the doubled [CO2] concentrations in both years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00099.x
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    Effects of long-term atmospheric CO2 enrichment on the growth and fruit production of sour orange trees (1997)
    Oxford BSL : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: In July of 1987, we planted eight 30-cm-tall sour orange tree seedlings in a field of Avondale loam at Phoenix, Arizona and enclosed them in pairs in clear-plastic-wall open-top chambers. Since 18 November of that year, we have continuously pumped ambient air of ≈400 ppmv [CO2] through two of these enclosures, while through the other two we have continuously pumped air of ≈700 ppmv [CO2]. By the end of the second year of the study, the trunk plus branch volume of the [CO2]-enriched trees was ≈2.75 times greater than that of the ambient-treatment trees. Three years later, this factor had dropped to ≈2.0; but the decline in the [CO2]-enriched/ambient-treatment ratio of trunk plus branch volume was nearly perfectly offset by the relative fruit production advantage enjoyed by the [CO2]-enriched trees over that period. In Years 6, 7 and 8, however, there was a moderate drop in total productivity enhancement. This decline may be a delayed acclimation response, or it could be due to enhanced self-shading in the [CO2]-enriched trees or to the fact that, starting early in Year 6, many branches of the [CO2]-enriched trees grew all the way to the walls of their enclosures, so that many blossoms and young fruit were destroyed by intermittent physical trauma produced by the action of wind against the taut plastic in that year and in all succeeding years. Hence, we will have to maintain our experiment for several more years for this lateral growth obstruction to occur to the same degree in the ambient-air chambers as it has in the [CO2]-enriched chambers, in order to determine the long-term equilibrium effects of atmospheric [CO2] enrichment in a spatially confined environment.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00053.x
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  • 17
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    Rice responses to drought under carbon dioxide enrichment. 1. Growth and yield (1997)
    Oxford BSL : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Projections of future climate change include a strong likelihood of a doubling of current atmospheric carbon dioxide concentration ([CO2]) and possible shifts in precipitation patterns. Drought stress is a major environmental limitation for crop growth and yield and is common in rainfed rice production systems. This study was conducted to determine the growth and grain yield responses of rice to drought stress under [CO2] enrichment. Rice (cv. IR-72) was grown to maturity in eight naturally sunlit, plant growth chambers in atmospheric carbon dioxide concentrations [CO2] of 350 and 700 μmol CO2 mol–1 air. In both [CO2], water management treatments included continuously flooded (CF) controls, flood water removed and drought stress imposed at panicle initiation (PI), anthesis (ANT), and both panicle initiation and anthesis (PI & ANT). The [CO2] enrichment increased growth, panicles plant–1 and grain yield. Drought accelerated leaf senescence, reduced leaf area and above-ground biomass and delayed crop ontogeny. The [CO2] enrichment allowed 1–2 days more growth during drought stress cycles. Grain yields of the PI and PI & ANT droughts were similar to the CF control treatments while the ANT drought treatment sharply reduced growth, grain yield and individual grain mass. We conclude that in the absence of air temperature increases, future global increases in [CO2] should promote rice growth and yield while providing a modest reduction of near 10% in water use and so increase drought avoidance.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00058.x
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  • 18
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    Rice responses to drought under carbon dioxide enrichment. 2. Photosynthesis and evapotranspiration (1997)
    Oxford BSL : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Future climate change is projected to include a strong likelihood of continued increases in atmospheric carbon dioxide concentration ([CO2]) and possible shifts in precipitation patterns. Due mainly to uncertainties in the timing and amounts of monsoonal rainfall, drought is common in rainfed rice production systems. The objectives of this study were to quantify the effects and possible interactions of [CO2] and drought stress on rice (Oryza sativa, L.) photosynthesis, evapotranspiration and water-use efficiency. Rice (cv. IR-72) was grown to maturity in eight naturally sunlit, plant growth chambers in atmospheric carbon dioxide concentrations [CO2] of 350 and 700 μmol CO2 mol–1 air. In both [CO2], water management treatments included continuously flooded controls, flood water removed and drought stress imposed at panicle initiation, anthesis, and both panicle initiation and anthesis. Potential acclimation of rice photosynthesis to long-term [CO2] growth treatments of 350 and 700 μmol mol–1 was tested by comparing canopy photosynthesis rates across short-term [CO2] ranging from 160 to 1000 μmol mol–1. These tests showed essentially no acclimation response with photosynthetic rate being a function of current short-term [CO2] rather than long-term [CO2] growth treatment. In both long-term [CO2] treatments, photosynthetic rate saturated with respect to [CO2] near 510 μmol mol–1. Carbon dioxide enrichment significantly increased both canopy net photosynthetic rate (21–27%) and water-use efficiency while reducing evapotranspiration by about 10%. This water saving under [CO2] enrichment allowed photosynthesis to continue for about one to two days longer during drought in the enriched compared with the ambient [CO2] control treatments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00061.x
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  • 19
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    Changes in carbon isotope discrimination in grain cereals from different regions of the western Mediterranean Basin during the past seven millennia. Palaeoenvironmental evidence of a differential change in aridity during the late Holocene (1997)
    Oxford BSL : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Carbon isotope discrimination (Δ) was determined for kernels of six-row barley and durum wheat cultivated in the western Mediterranean basin during the last seven millennia. Samples came from different archaeological sites in Catalonia (north-east Spain) and in the south-east of Spain (mainly eastern Andalusia). Samples from the present were also analysed. Mean values of Δ for barley and durum wheat grains decreased slightly from Neolithic (7000–5000 BP) to Chalcolithic-Bronze (5000–3000 BP) and Iron ages (3000–2200 BP) both in Catalonia and in south-east (SE) Spain. Values were consistently lower in SE Spain than in Catalonia throughout these five millennia, which suggests that Catalonia was less arid than SE Spain in this period. Within a given region, current discrimination values for kernels of the same cereal species cultivated under rainfed conditions were lower than those of archaeological grains, which implies more arid conditions at present. Furthermore, an empirical relationship between Δ of mature kernels and total precipitation (plus irrigation where applicable) during grain filling (r2 = 0.73, N = 25) was established for barley, currently cultivated at different locations in the western Mediterranean basin in Spain. The resulting relationship was applied to the Δ data for barley kernels from 10 archaeological sites in Catalonia and 10 sites in SE Spain, to estimate the precipitation during grain filling at the time the kernels were produced. For both regions, current climatic conditions are consistently more arid than those inferred for the Neolithic, Bronze and Iron ages. In addition, although Catalonia was estimated to have had consistently wetter conditions (about 20% more precipitation) than SE Spain throughout these millennia, differences in precipitation between these two regions have recently increased, with 79% more precipitation in Catalonia. Results indicate a more rapid increase in aridity in SE Spain than in Catalonia, probably produced during the last few centuries, and due to anthropogenic causes.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00056.x
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    Possibilities for carbon sequestration in tropical and subtropical soils (1997)
    Oxford BSL : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Soil organic matter is a key component of all terrestrial ecosystems, and any variation in its composition and abundance has important effects on many of the processes that occur within the system. The role of soil organic matter in soil nutrient cycling and soil gaseous emissions is discussed in the context of agricultural sustainability and global environmental change. Recent data on organic carbon and nitrogen reserves in the soils of the world are presented, with special reference to the subtropical and tropical regions. Possibilities for long-lasting, enhanced sequestration of carbon in the soil through management of the land and water resources are reviewed. Finally, the need is stressed for an up-to-date database on soil resources and for a global monitoring system in order to permit the study of changes in soil organic matter quantity and quality over time, as determined by changes in land-use and climate.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00062.x
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  • 21
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    Open-top designs for manipulating field temperature in high-latitude ecosystems (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Passive open-top devices have been proposed as a method to experimentally increase temperature in high-latitude ecosystems. There is, however, little documentation on the efficacy of these devices. This paper examines the performance of four open-top chambers for altering temperature at six sites in the Arctic and Antarctica. Most of the heating effect was due to daytime warming above ambient; occasional night-time cooling below ambient, especially of air temperatures, depressed mean daily temperature. The mean daily temperatures at four arctic sites were generally increased by 1.2–1.8 °C; but occasionally, temperature depressions also occurred. Under optimal conditions at the antarctic site (dry soils, no vegetation, high radiation) mean daily soil temperatures were increased by +2.2 °C (–10 cm) to +5.2 °C (0 cm). Protection from wind may play a more important role than temperature per se in providing a favourable environment for plant growth within open-top devices. Wind speed had a generally negative impact on mean daily temperature. Daily global radiation was both positively and negatively related to chamber temperature response. The effect of chambers on snow accumulation was variable with the Alexandra Fjord site showing an increased accumulation in chambers but no difference in the date of snowmelt, while at Latnjajaure in a deep snowfall site, snowmelt occurred 1–2 weeks earlier in chambers, potentially increasing the growing season. Selection of a passive temperature-enhancing system requires balancing the temperature enhancement desired against potential unwanted ecological effects such as chamber overheating and altered light, moisture, and wind. In general, the more closed the temperature-enhancing system, the higher is the temperature enhancement, but the larger are the unwanted ecological effects. Open-top chambers alter temperature significantly and minimize most unwanted ecological effects; as a consequence, these chambers are a useful tool for studying the response of high-latitude ecosystems to warming.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb136.x
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  • 22
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    Responses to natural climatic variation and experimental warming in two tundra plant species with contrasting life forms: Cassiope tetragona and Ranunculus nivalis (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Two circumpolar tundra plant species, the evergreen dwarfshrub Cassiope tetragona and the perennial herb Ranunculus nivalis, were studied at Latnjajaure in northern Swedish Lapland during three consecutive growing seasons (1993–95) as a contribution to the ITEX programme. Open-top chambers (OTCs) were used in a passive heating experiment, and the performance of the plants in unmanipulated controls was correlated with climatic fluctuations among the years. Phenological, vegetative, and reproductive variables were measured. In both species phenological responses were controlled mainly by ambient air temperature. In the evergreen C. tetragona vegetative growth was controlled mainly by the influx of global solar radiation and was not temperature-dependent, whereas the opposite applied in the herbaceous R. nivalis. Vegetative growth in C. tetragona was rather stable among years as well as between treatments, whereas it was strongly influenced by annual climate in R. nivalis. Both species increased their reproductive success with increasing temperature, but R. nivalis was also radiation-dependent in this case, probably because of its green, photosynthetic nutlets. Ovule number in R. nivalis increased steadily in the experimentally heated plots during the study in response to the constant temperature amelioration above the ambient. At the community level, evergreen C. tetragona seems to have low competitive ability under warmer conditions. The situation for vernal low-growing herbs like R. nivalis is more complex; despite a strong positive response to increased temperature, they may exhibit decreased reproductive success if overgrown by a vigorous graminoid canopy.
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    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb138.x
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  • 23
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    Experimental manipulations of snow-depth: effects on nutrient content of caribou forage (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We investigated the potential effects of global climate change on arctic tundra vegetation used as caribou forage. A total of 96 experimental plots was established at six sites on the coastal plain of the Arctic National Wildlife Refuge, Alaska, in 1993 and 1994. We erected snow-fences to increase the amount of snow deposition, and therefore delay the date of the snowmelt on 48 plots (referred to as increased snow/late melting plots). We used black mesh netting on the surface of the snow to increase the rate of melting on 24 plots; the remaining 24 plots served as controls. In July 1994, we collected green leaves from Eriophorum vaginatum, Salix planifolia, and Betula nana and analysed these samples for total carbon and total nitrogen content. Ratios of carbon to nitrogen differed among treatments for all three species. Generally, C:N ratios for B. nana and E. vaginatum on increased snow/late melting plots were lower than on control plots. C:N ratios for S. planifolia on increased snow/late melting plots did not differ from controls, but were lower than on plots which started to melt early. These results may be due to the timing of nitrogen translocation from leaf and stem tissue into storage organs, or due to an increase in available nitrogen input to the system. Further sampling is needed to adequately determine the mechanism responsible for increased nitrogen content of caribou forage in areas with increased amount of snow and delayed snowmelt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb142.x
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  • 24
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    Exsertion, elongation, and senescence of leaves of Eriophorum vaginatum and Carex bigelowii in Northern Alaska (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The seasonal patterns of leaf exsertion, elongation, and senescence were described and compared for two of the most abundant graminoid species of Alaskan moist tussock tundra, Eriophorum vaginatum and Carex bigelowii. In addition the responses of both species to NPK fertilizer and to variation in site fertility (water track vs. non-track areas) were also assayed and compared. The research was done over two full growing seasons at two sites near Toolik Lake, Alaska, where other aspects of the ecology of both species have been the subject of intensive and ongoing research.Both species showed the typical graminoid pattern of sequential leaf growth, in which the exsertion and elongation of new leaves is coincident with the senescence of old leaves. However, the rates of these processes were much slower and steadier in Eriophorum than in Carex, with much greater overlap in the life histories of individual leaf cohorts. The total and green leaf lengths of whole tillers in Eriophorum were also less variable over the entire year than in Carex. The conclusion is that leaf growth in Carex should depend more on external storage of carbon and nutrients than Eriophorum, with a much greater seasonal variation in demands on storage and retranslocation to and from leaves.The effects of fertilizer and the water track on leaf growth dynamics and turnover rates were largely nonsignificant, despite major effects on total tiller size and productivity. This is in contrast to previous research on evergreen leaf dynamics, but similar to results of previous research on overall production and biomass regulation in Eriophorum. It is concluded that the graminoid response to increased nutrient availability in the Arctic is to dilute the greater amounts of nutrient uptake by greater growth, so that nearly the same metabolic homeostasis is achieved as under low nutrient availability, but at a higher biomass.
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    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb141.x
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  • 25
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    Response to experimental warming in a population of Papaver radicatum in Greenland (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: In an attempt to simulate the effect of a global climatic change, temperature manipulations were carried out in a natural population of Papaver radicatum from a low arctic area on Disko Island, West Greenland. The manipulations were carried out by means of ITEX corners, which are angular plexiglass screens placed around individual plants. The corners were placed with openings towards four directions and different microclimatic conditions were obtained. The corners increase the summer temperature to different degrees in the four directions. In addition they are windscreens and eventually accumulate snow, dependent on the wind directions.Dataloggers in a set of corners measured temperatures at the end of one growing season and at the beginning of the next. Spring was delayed in all corners due to increased snow cover duration, especially in those facing East and North. Nevertheless, temperatures were increased in the corners during the season, and highest temperature sums were obtained in those facing South and West. No temperature increase was found in the North-facing corners.No effect was seen on the plants the first year after application of the ITEX corners. In the second year an increased biomass was observed in corners facing West and South in accordance with the higher temperatures experienced in these directions. In the third biomass year plants in corners facing West decreased and those facing North slightly increased compared to previous years. After 4 years plants in corners facing West, South and East had attained significantly higher biomass than the control plants and the plants in corners facing North.An earlier onset of flowering was seen in the corners compared to control, and South-facing corners had more flowers. An early onset of the growth period is an advantage to flowering, more so than increased temperatures during the season. Flowering was prolonged in the corners compared to controls, but there was a higher risk of frost damage to the flowers in the corners.
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    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb140.x
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    Response of Saxifraga oppositifolia L. to simulated climate change at three contrasting latitudes (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Saxifraga oppositifolia, a widespread circum-arctic and alpine plant species, was exposed to increased temperature at three ITEX sites of different latitudes: Val Bercla in the Swiss Alps (46°N), Latnjajaure in mid-alpine Northern Sweden (68°N), and Alexandra Fjord, Ellesmere Island (79°N) in the Canadian High Arctic. Phenology, growth, and reproduction were monitored for 2 or 3 consecutive years. Increased temperature had little influence on the phenology of S. oppositifolia, although flowering period was somewhat longer and pollination earlier in the experimental plots. A decrease in the density of flowers on each plant was noted at two sites over 3 years, with a slightly larger decrease in the warmed plots. The few changes observed in reproductive variables (e.g. fruit : flower ratio) are mostly assigned to increased shading by taller growing neighbouring plants of other species, thus limiting performance of the shade-intolerant S. oppositifolia. It is assumed that survival of this species, especially at the lower limits of its altitudinal and latitudinal distribution, will depend on seed dispersal to new, open habitats.
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    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb144.x
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  • 27
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    Responses of Dryas octopetala to ITEX environmental manipulations: a synthesis with circumpolar comparisons (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We have examined organismic responses of Dryas octopetala to simulated changes in the summer climate at four tundra sites as part of the International Tundra Experiment (ITEX). Our study sites are located in the High Arctic, on Svalbard, Norway, in the Low Arctic at Abisko, Sweden, and at Toolik Lake, Alaska, USA and our temperate alpine site is at Niwot Ridge, Colorado, USA. These sites represent a range of tundra temperature and precipitation regimes, being generally cold and dry in the High Arctic and warmer and wetter at Toolik Lake and Niwot Ridge. Results from our studies indicate organismic attributes such as flowering shoot length varies by 30% between low and high arctic populations and that experimental warming results in significant increases in shoot height at three of four sites. We find that phenological development of Dryas is accelerated under experimentally warmed conditions which corresponds with a lengthening of the growing season in autumn, greater degrees of seed set and a higher likelihood of colonization of bare ground. We also observe that Dryas dominated ecosystems which are exposed to experimental manipulations are capable of exhibiting net carbon sequestration in late autumn, and that Dryas photosynthesis and green leaf biomass is significantly greater under warmer as opposed to ambient temperature conditions. Dryas leaf nitrogen is also significantly lowered under warmer conditions resulting in senescent leaves having a higher C:N ratio than those under ambient conditions. Together these findings indicate that Dryas phenology and carbon flux may be altered to the greatest degree in spring and again in autumn by higher summer temperatures and that simultaneously both positive and negative feedback effects may result from changes in plant and ecosystem performance.
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    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb143.x
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  • 28
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    Methane emission from Texas rice paddy soils. 1. Quantitative multi-year dependence of CH4 emission on soil, cultivar and grain yield (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Methane emissions at different rice productivity levels were observed from Texas rice paddy soils during the years 1991–95. Analysis of field measurements showed that seasonal methane emission (E) was strongly dependent on soil, cultivar, and rice grain yield. The relationship can be quantitatively described by E (g m–2) = 0.048 × SI × VI × GY. SI is a soil index to characterize the relative effect of soil texture on emission and is linked with soil sand percentage. VI is a variety index to identify the intervarietal difference in methane emission and is related to the amount of methane emission per unit grain yield. GY is grain yield (g m–2). Constant 0.048 was derived from the measurements of 10 cultivars planted in 1993. Computed emission applying the relationship is well matched with measured data. The comparison of computed with measured seasonal methane emission over an 80-day period using a total of 32 data sets yields a correlation coefficientr2 of 0.800. In addition, the ratio of seasonal methane emission to net primary productivity was calculated on a carbon to carbon basis, which produces an average value of 2.8%, ranging from 1.2% to 5.4%. A further investigation indicated that the ratio is soil and variety dependent and can be quantitatively explained by C[CH4]/C[NPP] (%) = 3.21 × SI × VI + 0.12 (r2 = 0.738, n = 32). Under the condition of 30% soil sand, this ratio is ≈ 3% for the majority of cultivars.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00083.x
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  • 29
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    Phenological and growth responses of Papaver radicatum along altitudinal gradients in the Canadian High Arctic (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Phenology and growth of Papaver radicatum Rottb. was monitored over four summers (1990–1993) at 12 sites, along a dolomitic and a granitic altitudinal gradient (330 m a.s.l.–770 m a.s.l.) at Sverdrup Pass, central Ellesmere Island, Canada. The gradients provided substantial differences in environmental characteristics. Three of the four seasons (1990, 1991 and 1993) had more than 400 thawing degree-days (TDD) in the valley, while the 1992 season had less than 300. The granitic sites had consistently higher temperatures than the dolomitic sites, despite their northerly aspect. Increasing elevation reduced total degree-day accumulation (c. 40 degree-days/100 m) and length of potential growing season. The proportion of the population producing flower buds was similar at all sites in any given year, but there were differences among years. Production of flowers and fruits per site, decreased with altitude along the dolomitic gradient in 1991 and 1992. There was no difference in the number of buds or flowers produced per plant with increasing altitude, although larger plants with multiple flowers were found only on low elevation granitic sites. Plants from the dolomitic sites were smaller and flowered, on average, after the site accumulated 150 degree-days, while plants on the granitic sites were larger and bloomed after 200 degree-days. Papaver is able to grow and reproduce over a wide range of environmental conditions and moderate climate warming would likely promote its growth and establishment, unless other factors, especially snow-free periods and water availability, become limiting.
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    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb145.x
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    Effects of elevated CO2-grown loblolly pine needles on the growth, consumption, development, and pupal weight of red-headed pine sawfly larvae reared within open-topped chambers (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Seedlings of loblolly pine, Pinus taeda, were grown in open-topped chambers under four levels of CO2: two ambient and two elevated. Larvae of the red-headed pine sawfly, Neodiprion lecontei, were reared from early instar to pupation, primarily on branches within chambers. Larval growth and mortality were assessed and leaf phytochemistry samples of immature and mature leaves collected weekly. Mature leaves grown under elevated CO2 had significant reductions in leaf nitrogen and increases in non-structural carbohydrate contents, resulting in foliage being a poorer food source for larvae, i.e. higher carbohydrate:nitrogen ratio. Nutritional constituents of immature needles were unaffected by seedling CO2 treatment. Volatile mono- and sesquiterpenes were unrelated to plant CO2 treatments for either leaf age class. Larval consumption of immature needles significantly increased on seedlings grown under CO2 enrichment, while mature needle consumption was not different between the treatments. The average weight gain per larva significantly declined in late instar larvae consuming elevated CO2-grown needles. In spite of this reduced growth, neither the days to pupation nor pupal weights were different among the CO2 treatments. This study suggests that enriched CO2-induced alterations in pine needle phytochemistry can affect red-headed pine sawfly performance. However, compensatory measures by larvae, such as choosing to consume more nutritious immature needles, apparently helps offset enriched CO2-induced reductions in the leaf quality of mature needles.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00086.x
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    Contribution of transpiration to forest ambient vapour based on isotopic measurements (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Using a simple isotope mixing model, we evaluated the relative proportion of water vapour generated by plant transpiration and by soil evaporation at two sites in the Amazon basin. Sampling was carried out at two different soil covers (forest and pasture), in a seasonal tropical rainforest at eastern Amazon where major deforestation is the result of land-use change, and compared to a less seasonal central Amazon forest. In both forests, vapour from transpiration was responsible for most, if not all, of the water vapour generated in the forest, while it could not be detected above the grassy pastures. Thus the canopy transpiration may be a major source of water vapour to the forest and perhaps to the atmosphere during the dry season. The results are discussed in relation to predictive models based on net radiation that usually are not able to distinguish between transpiration and evaporation.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00082.x
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    Using stable isotopes to determine soil carbon input differences under ambient and elevated atmospheric CO2 conditions (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Quantitative estimates of soil C input under ambient (35 Pa) and elevated (60 Pa) CO2-partial pressure (pCO2) were determined in a Free-Air Carbon dioxide Enrichment (FACE) experiment. To facilitate 13C-tracing, Trifolium repens L. was grown in a soil with an initial δ13C distinct by at least 5‰ from the δ13C of T. repens grown under ambient or elevated pCO2. A shift in δ13C of the soil organic C was detected after one growing season. Calculated new soil C inputs in soil under ambient and elevated pCO2 were 2 and 3 t ha–1, respectively. Our findings suggest that under elevated CO2 conditions, soil C sequestration may be altered by changes in plant biomass production and quality.
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    Satellite inventory of human settlements using nocturnal radiation emissions: a contribution for the global toolchest (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Time series data from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) have been used to derive georeferenced inventories of human settlements for Europe, North and South America, and Asia. The visible band of the OLS is intensified at night, permitting detection of nocturnal visible-near infrared emissions from cities, towns, and villages. The time series analysis makes it possible to eliminate ephemeral VNIR emission sources such as fire and to normalize for differences in the number of cloud-free observations. An examination of the area lit (km2) for 52 countries indicates the OLS derived products may be used to perform the spatial apportionment of population and energy related greenhouse gas emissions.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00115.x
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    Thirty years of in situ tree growth under elevated CO2: a model for future forest responses? (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Rising concentrations of atmospheric carbon dioxide have been predicted to stimulate the growth of forest trees. However, long-term effects on trees growing to maturity and to canopy closure while exposed to elevated CO2 have never been examined. We compared tree ring chronologies of Mediterranean Quercus ilex which have been continuously exposed to elevated CO2 (around 650 μmol mol–1) since they were seedlings, near two separate natural CO2 springs with those from trees at nearby ambient-CO2‘control’ sites. Trees grown under high CO2 for 30 years (1964–93) showed a 12% greater final radial stem width than those growing at the ambient-CO2 control sites. However, this stimulation was largely due to responses when trees were young. By the time trees were 25–30 y old the annual difference in tree ring width between low and high CO2 grown trees had disappeared. At any given tree age, elevated CO2 had a relatively greater positive effect on tree ring width in years with a dry spring compared to years with more rainfall between April and May. This indicates a beneficial effect of elevated CO2 on tree water relations under drought stress. Our data suggest that the early regeneration phase of forest stands can be accelerated in CO2-enriched atmospheres and that maximum biomass per land area may be reached sooner than under lower CO2 concentrations. In our study, high CO2 grown Q. ilex trees reached the same stem basal area at the age of 26 y as control trees at 29 y, i.e. three years earlier (faster turnover of carbon?). Reliable predictions of the future development of forests need to account for the variable responses of trees over their entire lifetime. Such responses to elevated CO2 can presently only be assessed at such unique field sites.
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    Brown Tide blooms in Long Island’s coastal waters linked to interannual variability in groundwater flow (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: There has been a widespread increase in the reporting of harmful and ‘nuisance’ algal blooms in the coastal ocean over the past few decades. On the global scale this is suspected to be a consequence of coastal eutrophication, however, on a case-by-case basis there is usually insufficient evidence to discriminate between the effects of human and natural causal factors. Intense blooms of the ‘Brown Tide’ unicellular algae (Aureococcus anophagefferens) have occurred sporadically since 1985 in coastal waters of Eastern Long Island and have devastated the local commercial scallop fishery. Analysis of an 11-year time-series dataset from this region indicates that bloom intensity is correlated with higher salinities and inversely correlated with the discharge of groundwater. Laboratory and field studies suggest that whereas salinity is unlikely to represent a direct physiological control on Brown Tide blooms, the addition of inorganic nitrogen tends to inhibit Brown Tide blooms. Budget calculations indicate that the inorganic nitrogen supply from groundwater is 1–2 orders of magnitude higher than any other external source of nitrogen for this ecosystem. Biweekly time series data collected in 1995 demonstrate that Brown Tide blooms utilize dissolved organic nitrogen (DON) for growth, as evidenced by a large decrease in DON parallel with an increase in cell abundance. On an interannual basis, bloom intensity was also positively correlated with mean DON concentrations. We hypothesize that bloom initiation is regulated by the relative supply of inorganic and organic nitrogen, determined to a large extent by temporal variability in groundwater flow. The 1980s and 1990s were characterized by exceptionally high and interannually variable groundwater discharge, associated with a large-scale climate shift over the North Atlantic. This, coupled with the time-lagged discharge of groundwater with high nitrate concentrations resulting from increased fertilizer use and population increase during the 1960s and 1970s, may have been a key factor in the initiation of Brown Tide blooms in 1985.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00117.x
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    Temperature-controlled open-top chambers for global change research (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: To enable experiments on the interactive effects of elevated atmospheric CO2 and increased air temperature on physiological processes in trees to be carried out, we altered the standard design of open-top chambers by replacing blowers with evaporative coolers and in-line heaters, with a feedback control system to maintain ambient or elevated air temperatures within the chambers. Ambient and elevated (+ 4 °C) temperature regimes were attained consistently and reliably throughout the growing season, with high reproducibility between chambers. From May through December the average of nearly 300,000 temperature measurements was 18.5 °C in ambient air, 18.9 ± 0.6 °C in six ambient chambers, and 22.4 ± 0.9 °C in six elevated temperature chambers. The difference in soil temperature between ambient and elevated chambers was 1.2 °C. Absolute humidity (vapour pressure) in the chambers was higher than that of ambient air, but it was generally similar between temperature treatments. Vapour pressure deficit therefore was higher in elevated temperature chambers than in ambient chambers, and this difference is considered an inseparable part of the temperature treatment. The addition of a temperature control system to open-top chambers removes what has been an important flaw in this important tool for global change research.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00072.x
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    Soil microbial responses to increased concentrations of atmospheric CO2 (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Terrestrial ecosystems respond to an increased concentration of atmospheric CO2. While elevated atmospheric CO2 has been shown to alter plant growth and productivity, it also affects ecosystem structure and function by changing below-ground processes. Knowledge of how soil microbiota respond to elevated atmospheric CO2 is of paramount importance for understanding global carbon and nutrient cycling and for predicting changes at the ecosystem-level. An increase in the atmospheric CO2 concentration not only alters the weight, length, and architecture of plant roots, but also affects the biotic and abiotic environment of the root system. Since the concentration of CO2 in soil is already 10–50 times higher than that in the atmosphere, it is unlikely that increasing atmospheric CO2 will directly influence the rhizosphere. Rather, it is more likely that elevated atmospheric CO2 will affect the microbe–soil–plant root system indirectly by increasing root growth and rhizodeposition rates, and decreasing soil water deficit. Consequently, the increased amounts and altered composition of rhizosphere-released materials will have the potential to alter both population and community structure, and activity of soil- and rhizosphere-associated microorganisms. This occurrence could in turn affect plant health and productivity and plant community structure. This review covers current knowledge about the response of soil microbes to elevated concentrations of atmospheric CO2.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00078.x
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    CO2-mediated changes in aspen chemistry: effects on gypsy moth performance and susceptibility to virus (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We investigated the effects of long-term CO2 enrichment on foliar chemistry of quaking aspen (Populus tremuloides) and the consequences of chemical changes for performance of the gypsy moth (Lymantria dispar) and susceptibility of the gypsy moth to a nucleopolyhedrosis virus (NPV). Foliage was collected from outdoor open-top chambers and fed to insects in a quarantine rearing facility. Under enriched CO2, levels of leaf nitrogen declined marginally, levels of starch and phenolic glycosides did not change, and levels of condensed tannins increased. Long-term bioassays revealed reduced growth (especially females), prolonged development and increased consumption in larvae fed high-CO2 foliage but no significant differences in final pupal weights or female fecundity. Short-term bioassays showed weaker, and sex-specific, effects of CO2 treatment on larval performance. Correlation analyses revealed strong, negative associations between insect performance and phenolic glycoside concentrations, independent of CO2 treatment. Larval susceptibility to NPV did not differ between CO2 treatments, suggesting that effects of this natural enemy on gypsy moths are buffered from CO2-induced changes in foliar chemistry. Our results emphasize that the impact of enriched CO2 on plant–insect interactions will be determined not only by how concentrations of plant compounds are altered, but also by the relevance of particular compounds for insect fitness. This work also underscores the need for studies of genetic variation in plant responses to enriched CO2 and long-term population-level responses of insects to CO2-induced changes in host quality.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00077.x
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    Effects of temperature elevation on the population dynamics of the upland heather psyllid Strophingia ericae (Curtis) (Homoptera: Psylloidea) (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: 1 Cloches permeable to gas and water were used to simulate the effect of climate warming on upland populations of the heather psyllid Strophingia ericae at Moor House National Nature Reserve in the North Pennines, UK.2 The cloches produced an average warming of about 1 °C in the heather canopy over a period of one year.3 The density of S. ericae increased markedly in cloches within a few months of erection.4 Species composition and numbers of potential predators were similar inside cloches and in control plots.5 In the two year life-cycle of S. ericae, the warming effect advanced the phenology from the second to third instar in the first winter, but in the second winter, fifth instar nymphs did not moult prematurely to adult.6 The density of S. ericae was higher on Calluna vulgaris at its boundary with Juncus squarrosus than in the pure C. vulgaris sward (in both cloched and control plots).
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    Water vapour fluxes and their impact under elevated CO2 in a C4-tallgrass prairie (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We measured leaf-level stomatal conductance, xylem pressure potential, and stomate number and size as well as whole plant sap flow and canopy-level water vapour fluxes in a C4-tallgrass prairie in Kansas exposed to ambient and elevated CO2. Stomatal conductance was reduced by as much as 50% under elevated CO2 compared to ambient. In addition, there was a reduction in stomate number of the C4 grass, Andropogon gerardii Vitman, and the C3 dicot herb, Salvia pitcheri Torr., under elevated CO2 compared to ambient. The result was an improved water status for plants exposed to elevated CO2 which was reflected by a less negative xylem pressure potential compared to plants exposed to ambient CO2. Sap flow rates were 20 to 30% lower for plants exposed to elevated CO2 than for those exposed to ambient CO2. At the canopy level, evapotranspiration was reduced by 22% under elevated CO2. The reduced water use by the plant canopy under elevated CO2 extended the photosynthetically-active period when water became limiting in the ecosystem. The result was an increased above- and belowground biomass production in years when water stress was frequent.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00084.x
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    Elevated CO2 and moisture effects on soil carbon storage and cycling in temperate grasslands (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: In grassland ecosystems, most of the carbon (C) occurs below-ground. Understanding changes in soil fluxes induced by elevated atmospheric CO2 is critical for balancing the global C budget and for managing grassland ecosystems sustainably. In this review, we use the results of short-term (1–2 years) studies of below-ground processes in grassland communities under elevated CO2 to assess future prospects for longer-term increases in soil C storage.Results are broadly consistent with those from other plant communities and include: increases in below-ground net primary productivity and an increase in soil C cycling rate, changes in soil faunal community, and generally no increase in soil C storage. Based on other experimental data, future C storage could be favoured in soils of moderate nutrient status, moderate-to-high clay content, and low (or moderateIy high) soil moisture status. Some support for these suggestions is provided by preliminary results from direct measurements of soil C concentrations near a New Zealand natural CO2-venting spring, and by simulations of future changes in grassland soils under the combined effects of CO2 fertilization and regional climate change.Early detection of any increase in soil C storage appears unlikely in complex grassland communities because of (a) the difficulty of separating an elevated CO2 effect from the effects of soil factors including moisture status, (b) the high spatial variability of soil C and (c) the effects of global warming. Several research imperatives are identified for reducing the uncertainties in the effects of elevated atmospheric CO2 on soil C.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00094.x
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    CO2 effects on the water budget of grassland microcosm communities (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Experimental grassland ecosystems, in microcosms 0.2 m in diameter and with a 0.95 m soil column, varied in their responses to elevated partial pressure of CO2 (pCO2) and altered moisture inputs. Ecosystems on moderately fertile sandstone soil and with a typical mix of moderately fast-growing sandstone species, responded to elevated pCO2 with decreases in mid-season evapotranspiration of nearly 50%. This pattern reversed at the end of the growing season, and sandstone ecosystems under elevated pCO2 continued active transpiration farther into the summer drought. The sandstone ecosystems appeared to convert mid-season water conservation into increased late-season growth. Effects of increased pCO2 on ecosystem evapotranspiration were much smaller in ecosystems with very infertile serpentine soil and a diverse mixture of slow-growing serpentine species.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.t01-1-00096.x
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    Elevated CO 2and water supply interactions in grasslands: a pastures and rangelands management perspective (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Water is a key variable driving the composition and productivity of pastures and rangelands, and many of the ecosystems in these grasslands are highly sensitive to changes in water supply. The possibility that elevated CO2 concentrations may alter plant water relations is therefore particularly relevant to pastures and rangelands, and may have important consequences for grassland ecosystem function, water use, carbon storage and nutrient cycling. The planning of effective research to better understand these changes requires attention to both: (i) gaps in knowledge about CO2 and water interactions, and (ii) knowledge of how precisely the effects of CO2 must be understood in relation to other factors, in order to predict changes in grassland structure and production. A recent microcosm experiment illustrates that non-linear effects of CO2 and water stress could perturb primary production by triggering changes in grassland community composition. The magnitudes of the effects of CO2 on key grassland ecosystems remain to be precisely determined through ecosystem-level experiments. A simplified simulation of the impact of different levels of productivity change in a water-limited Australian rangeland system was conducted by varying effects of CO2 on radiation and water use efficiency. The results indicate that direct effects of CO2 may be moderated at the enterprise scale by accompanying changes in adaptive management by farmers. We conclude that future research should aim to construct quantitative relationships and identify thresholds of response for different grassland systems. The sensitivity of these systems to management (such as grazing pressure) should also be considered when developing integrated predictions of future effects of CO2 on water supply to grassland ecosystems.
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    Modelling the effects of elevated atmospheric CO2 on crown development, light interception and photosynthesis of poplar in open top chambers (1997)
    Oxford BSL : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: An open-top chamber experiment was carried out to examine the likely effects of elevated atmospheric [CO2] on architectural as well as on physiological characteristics of two poplar clones (Populus trichocarpa × P. deltoides clone Beaupré and P. deltoides × P. nigra clone Robusta). Crown architectural parameters required as input parameters for a three-dimensional (3D) model of poplar structure, such as branching frequency and position, branch angle, internode length and its distribution pattern, leaf size and orientation, were measured following growth in ambient and elevated [CO2 ] (ambient + 350 μmol mol–1) treated open-top chambers. Based on this information, the light interception and photosynthesis of poplar canopies in different [CO2] treatments were simulated using the 3D poplar tree model and a 3D radiative transfer model at various stages of the growing season. The first year experiments and modelling results showed that the [CO2] enrichment had effects on light intercepting canopy structure as well as on leaf photosynthesis properties. The elevated [CO2] treatment resulted in an increase of leaf area, canopy photosynthetic rate and above-ground biomass production of the two poplar clones studied. However, the structural components responded less than the process components to the [CO2] enrichment. Among the structural components, the increase of LAI contributed the most to the canopy light interception and canopy photosynthesis; the change of other structural aspects as a whole caused by the [CO2] enrichment had little effect on daily canopy light interception and photosynthesis.
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    Systematics of the ITEX species (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: ITEX research was begun to develop generalizations on the growth of tundra plants through synthesis of data from distant arctic and alpine sources gathered by strict protocols. Target species have been selected from among widely distributed ones with attention to those without serious unresolved taxonomic problems, since valid comparisons and generalizations rest on data reported consistently from the same species. The consortium of researchers must firmly establish the identity of the experimental subjects to preserve the integrity of the ITEX synthesis. Documentation is possible only when voucher specimens are conserved. Notes on taxonomy and biology are provided as background for 14 primary, five secondary, and three additional candidate ITEX species.
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    Responses of the clonal sedge, Carex bigelowii, to two seasons of simulated climate change (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The effect of enhanced temperature was studied in open-top chambers on the arctic clonal sedge Carex bigelowii Torr. ex Schwein. at Latnjajaure Field Station, Swedish Lapland for two growing seasons. The flowering phenology of C. bigelowii accelerated during the first field season that the open-top chambers were erected. After the second season of perturbation the sexual reproductive investment was higher in the open-top chambers than in the controls and flowering phenology was still accelerated. Leaf phenology and the growth of vegetative tillers followed the same pattern in the open-top chambers as in the controls, but the leaves were longer in the open-top chambers from the end of June until the end of August. The results suggest that relatively late flowering clonal graminoids may be favoured by warmer climate, at least in the short term.
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    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb134.x
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    Response to simulated climatic change in an alpine and subarctic pollen-risk strategist, Silene acaulis (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The aim of this study was to test if early flowering species respond with increased seed production to climate warming as is predicted for late-flowering seed-risk strategists. Experimental climate warming of about 3°C was applied to two populations of the cushion-forming plant Silene acaulis (L.) Jacq. The experiment was run at one subarctic site and one alpine site for 2 years and 1 year, respectively, using open-top chambers (OTC).The 2-year temperature enhancement at the subarctic site had a marked effect on the flowering phenology. Cushions inside the OTC started flowering substantially earlier than control cushions. Both the male and female phases developed faster in the OTCs, and maturation of capsules occurred earlier. The cushions also responded positively in reproductive terms and produced more mature seeds and had a higher seed/ovule ratio. After 1 year temperature enhancement at the alpine site there was a weak trend for earlier flowering, but there was no significant difference in seed production or seed/ovule ratio.
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    Tundra plants and climate change: the International Tundra Experiment (ITEX) (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The International Tundra Experiment (ITEX) was established in late 1990 at a meeting of arctic tundra ecologists as a response to predictions that the human-enhanced greenhouse warming would occur earliest and most intensely at high latitudes. The initial objective of ITEX was to monitor phenology, growth and reproduction in major circumpolar vascular plant species in response to climate variations and environmental manipulations at sites throughout the tundra biome. The manipulations involve passive warming of tundra plots in open-top chambers (OTCs), and manipulating snow depth to alter growing season length. Standard protocols were developed for measurements, experimental design and statistical analyses, and published in an ITEX Manual. The standard methods ensure comparable data are collected at all sites. This special issue of Global Change Biology is based on papers developed from the 6th ITEX Workshop, held at the University of Ottawa, Ottawa, Canada, 7–11 April 1995. The papers compare short-term responses (1–3 years) of common species to climate variations and manipulations at ITEX sites. The OTCs increase mean near-surface temperatures by 1–3°C during the growing season, simulating predictions from global circulation models. All species investigated responded to the temperature increase, especially in phenology and reproductive variables. However, these short-term responses were individualistic, and no general pattern in type or magnitude of response was noted for functional types or phenology class. Responses were generally similar among sites, although the magnitude of response tended to be greater in high Arctic sites. Early snowmelt increased carbon:nutrient ratios in plants. Sustained growth and reproductive responses to warming will depend on nutrient supply, and increased carbon:nutrient ratios in litter could buffer nutrient cycling, and hence plant growth. Ongoing, long-term research at ITEX sites, linked to other global change initiatives, will help elucidate probable effects of climate change at the ecosystems level in arctic and alpine tundra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb132.x
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    Arctic soils and the ITEX experiment (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The objectives of this paper are broadly to examine arctic soils and specifically to examine soil properties at ITEX sites. The Arctic is dominated by cold, wet, shallow soils often characterized by surficial organic horizons. Seven of 11 soil orders in Soil Taxonomy are present in the circumarctic and alpine zones of the ITEX Project. Soil organic matter is highly correlated to soil carbon (sink or source of atmospheric CO2), soil moisture (surficial energy balance), and soil nitrogen (plant limiting nutrient). Because of these vital roles, soil organic matter is a keystone that will influence the future response of arctic ecosystems to climate change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb137.x
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    Effects of experimental warming on arctic willows (Salix spp.): a comparison of responses from the Canadian High Arctic, Alaskan Arctic, and Swedish Subarctic (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Three species of dwarf, prostrate willow (Salix arctica, S. rotundifolia and S. herbacea) were subjected to experimental summer warming in high arctic Canada, arctic Alaska, and subarctic Sweden, respectively, as part of the International Tundra Experiment. Phenological and growth responses of these species were compared for the second season of the experiment. Stigmas became receptive and pollen dispersal occurred significantly earlier for S. rotundifolia and S. herbacea in the ITEX open-top chambers, but not for S. arctica. Warming had no effect on the timing of seed dispersal, leaf yellowing, or leaf senescence. The length and dry weight of the largest leaves were greater for warmed plants, and was significant for S. rotundifolia. The number of catkins/plot did not differ among species or treatments, but the fruit : flower ratio was reduced in the experimental plots.
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    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb135.x
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    Short-term effects of simulated environmental change on phenology, leaf traits, and shoot growth of alpine plants on a temperate mountain, northern Japan (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: In order to assess the responses of circumpolar and semicircumpolar plants growing around their southern distribution margins to artificial warming, we set up 11 open-top chambers (OTCs) on a fell-field (1680 m a.s.l.) in the Taisetsu Mountains, northern Japan. The OTCs increased mean air temperature by 1.3°C through the growing season (June–September) and extended the length of the growing season. We examined phenology and leaf traits of plants in the OTCs and control plots during the first season under artificial warming treatment using two deciduous and three evergreen species. Ledum palustre (evergreen shrub), Vaccinium uliginosum, and Arctous alpinus (deciduous shrubs) showed earlier leaf emergence and/or flowering in the OTCs. Deciduous shrubs had longer individual leaf longevity and an extended foliage period in the OTCs than in the control plots. There were no significant differences in specific leaf area and leaf size for many species between the OTCs and the control plots. Vaccinium vitis-idaea (evergreen shrub), L. palustre, A. alpinus, and Empetrum nigrum (evergreen shrub) had lower leaf nitrogen concentration in the OTCs than in the control plots, whereas it was higher in V. uliginosum. Only E. nigrum showed larger annual shoot growth in the OTCs. No clear differences in response to the warming effect were detected between evergreen and deciduous species in the first season. Circumpolar plants growing in temperate alpine regions may be more affected by season length rather than temperature itself.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.1997.gcb146.x
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    Soil fungal-arthropod responses to Populus tremuloides grown under enriched atmospheric CO2 under field conditions (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We investigated the influence of elevated CO2 and soil N availability on the growth of arbuscular mycorrhizal and non-mycorrhizal fungi, and on the number of mycophagous soil microarthropods associated with the roots of Populus tremuloides. CO2 concentration did not significantly affect percentage infection of Populus roots by mycorrhizal or non-mycorrhizal fungi. However, the extra-radical hyphal network was altered both qualitatively and quantitatively, and there was a strong interaction between CO2 and soil N availability. Under N-poor soil conditions, elevated CO2 stimulated hyphal length by arbuscular mycorrhizal fungi, but depressed growth by non-mycorrhizal fungi. There was no CO2 effect at high N availability. High N availability stimulated growth by opportunistic saprobic/pathogenic fungi. Soil mites were not affected by any treatment, but collembolan numbers were positively correlated with the increase in non-mycorrhizal fungi. Results indicate a strong interaction between CO2 concentration and soil N availability on mycorrhizal functioning and on fungal-based soil food webs.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00085.x
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    The potential for feedback effects induced by global warming on emissions of nitrous oxide by soils (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: About 65% of all emissions of nitrous oxide, N2O, are from soils, and are caused by aerobic nitrification and anaerobic denitrification. Tropical forest soils are probably the most important single source, followed by cultivated soils. Emission rates in natural systems are related to the rate of N mineralization from organic matter, and N deposition; in agricultural systems they are related to the quantities of N used as fertilizers and, where relevant, to recent land use change. The global budget for N2O is not well balanced, and sources may still be underestimated. Direct evidence of a positive feedback of global warming on N2O emissions comes from studies of air in ice cores. One of the projected effects of future global warming is a lowering of water tables in northern peatlands; experiments suggest that this would lead to increased emissions, but that the effect on total emissions would be small. The results of many experiments with non-peatland soils indicate that the effect of temperature on soil emissions is generally positive, and that the rate of increase may be very steep when denitrification is the principal process involved. Process-level modelling suggests that the reason is increased soil respiration, which causes an increase in anaerobic volume in which denitrification can take place, in addition to the increased denitrification rate per unit anaerobic volume brought about directly by the rise in temperature. These results imply that generally a positive feedback on emissions from soils is likely. However, in some environments, a large proportion of total annual emissions can occur during freeze–thaw cycles; such cycles may become more or less frequent, depending on the climatic zone, and this may result in either a positive or negative feedback effect due to global warming. Models of global and regional trends give very conflicting predictions of the direction and the magnitude of climatic impacts on fluxes, but the prediction of a positive feedback seems to be the more soundly based.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00100.x
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    Responses of atmospheric methane consumption by soils to global climate change (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Soils consume about 40 Tg methane from the atmosphere annually. Thus, soils contribute significantly to the atmospheric methane budget. However, responses of atmospheric methane consumption to climate change are uncertain. Predicting these responses requires an understanding of the effect on methane consumption of specific variables (temperature and soil water content) as well as interactions among parameters (methane, ammonium, water content). Key considerations involve the limitations of diffusive transport and controls of methane diffusivity; limitation of methanotrophic activity by water stress; relatively slow growth rates of methane-oxidizing bacteria on atmospheric methane; ammonium toxicity. Interactions among these parameters may be particularly important, and lead to responses contrary to those predicted from changes in temperature and water content alone. Results from a number of analyses indicate that atmospheric methane consumption is especially sensitive to anthropogenic disturbances, which typically decrease activity. Continued increases in wet and dry ammonium deposition are likely to exacerbate inhibition resulting from changes in land use. Changes in hydrological regimes could further decrease activity if dry periods increase water stress at soil depths currently colonized by methanotrophs. Future trends in the soil methane sink are likely to lead to enhanced accumulation of atmospheric methane.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00090.x
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    Detection of methanogens and methanotrophs in natural environments (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
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    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The role of methane as a greenhouse gas and the contribution of bacteria to the production (methanogenesis) and destruction (methane oxidation) of methane is described. Using experimental approaches based on DNA sequences identifying either methanogen-specific or methanotroph-specific gene sequences methods were developed to broaden the detection and identification of methane metabolizing bacteria in natural environments. These methods were focused on blanket bog peat but are suitable for other environments. In addition to group specific 16S rRNA DNA sequences, specific functional gene probes based on methane coenzyme reductase sequences for methanogens and methane monooxygenase sequences for methanotrophs, were developed. These sequences were used in PCR-based protocols to detect and amplify specific gene sequences from the total DNA isolated from transverse sections of blanket bog peat. This permitted the analysis of the vertical distribution of methanogen and methanotroph populations, discrimination between different sub-sets of these populations, and the identification of novel organisms not previously detected by culture-based methods.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00104.x
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    Nitric oxide production in agricultural soils (1997)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Numerous papers on nitric oxide have been published covering various aspects ranging from its solution and gas-phase chemistry, biochemical and physiological functions and atmospheric processes. This review emphasizes recent developments in the literature relating to NO/NOx production in agricultural soils. We have tried to minimize overlap with other recent and relevant review articles. Emission measurements that have been made since 1992 are tabulated and discussed in terms of variability, fertilization effects, and advances made in monitoring fluxes. We describe attempts made by a number of authors to utilize ecological markers such as aeration, water, ammonium, nitrate content, etc. in order to distinguish between nitrification and denitrification as the primary source of production and/or consumption in natural field situations. This may allow a rational accounting for the high spatial and temporal variability observed, and the formulation of reliable predictive models. Factors such as diffusion, oxygen, water, and carbon (content and quality) that regulate or significantly influence production, consumption and emission are discussed. Finally some important implications of recent research relating to nitrification and denitrification is presented showing the chemical oxidation of NO which could occur when the acetylene inhibition technique is used.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00113.x
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    Growth and reproduction of aphids and levels of free amino acids in Scots pine and Norway spruce in an open-air fumigation with ozone (1997)
    Oxford BSL : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: To estimate the susceptibility of conifer seedlings to aphids under future tropospheric ozone levels, Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings were exposed to ambient and elevated ozone levels in an open-air exposure system. Growth and reproduction of the aphids Schizolachnus pineti and Cinara pinea on Scots pine and Cinara pilicornis on Norway spruce were monitored. Levels of free amino acids in foliage and young shoots were used as indicators of host plant quality. In elevated treatment plots the ozone doses were between 1.2 and 1.7 times the dose in ambient plots in 1990–93. Half of the seedling material in 1992–93 was subjected to nitrogen fertilization treatment to evaluate the effects of increased N deposition.In 1990, population density of S. pineti on pine did not differ between ambient and elevated ozone treatments during growing season, but remained higher in the elevated ozone plot than in the ambient plot at the end of the growing season. This was associated with elevated levels of glutamic acid in foliage. In August 1992, the numbers of S. pineti were consistent between the two ambient ozone plots, but deviated highly between the two ozone-fumigated plots. Glycine concentration in pine foliage was elevated by ozone, but free amino acid concentrations were not related to aphid performance. In 1993, ozone and nitrogen did not significantly affect the relative growth rate (RGR) of S. pineti or C. pinea nymphs on Scots pine, but glutamic acid concentration in foliage was increased by nitrogen fertilization. On Norway spruce, fecundity of C. pilicornis females was higher in elevated ozone treatment, but RGR of nymphs was not affected in 1992. In 1993, RGR of C. pilicornis nymphs was increased by nitrogen fertilization in June, but not affected by ozone. Nitrogen fertilization increased the levels of total free amino acids, aspartic acid, glutamic acid and proline in elongating shoots of Norway spruce, and ozone reduced the concentrations of valine and γ-butyric acid.Our results suggest that availability of nitrogen from soil has a stronger impact on the concentrations of free amino acids in conifer seedlings than ozone. Some episodes of high ozone concentration may increase free amino acids in foliage. Aphid response to ozone was extremely variable, in agreement with previous laboratory experiments. The expected 20–70% increase in ambient concentrations of tropospheric ozone may in some occasions enhance aphid performance on Scots pine and Norway spruce seedlings, but in most cases the ozone effect on the susceptibility of conifer seedlings to sucking insect pests is not important.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00067.x
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    Growth response of Trifolium repens L. and Lolium perenne L. as monocultures and bi-species mixture to free air CO2 enrichment and management (1997)
    Oxford BSL : Blackwell Science Ltd
    Global change biology 3 (1997), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Trifolium repens L. and Lolium perenne L. were grown in monocultures and bi-species mixture in a Free Air Carbon Dioxide Enrichment (FACE) experiment at elevated (60 Pa) and ambient (35 Pa) CO2 partial pressure (pCO2) for three years. The effects of defoliation frequencies (4 and 7 cuts in 1993; 4 and 8 cuts in 1994/95) and nitrogen fertilization (10 and 42 g m–2 y–1 N in 1993; 14 and 56 g m–2 y–1 N in 1994/95) on the growth response to pCO2 were investigated.There were significant interspecific differences in the CO2 responses during the first two years, while in the third growing season, these interspecific differences disappeared. Yield of T. repens in monocultures increased in the first two years by 20% when grown at elevated pCO2. This CO2 response was independent of defoliation frequency and nitrogen fertilization. In the third year, the CO2 response of T. repens declined to 11%. In contrast, yield of L. perenne monocultures increased by only 7% on average over three years at elevated pCO2. The yield response of L. perenne to CO2 changed according to defoliation frequency and nitrogen fertilization, mainly in the second and third year. The ratio of root/yield of L. perenne increased under elevated pCO2, low N fertilizer rate, and frequent defoliation, but it remained unchanged in T. repens. We suggest that the more abundant root growth of L. perenne was related to increased N limitation under elevated pCO2.The consequence of these interspecific differences in the CO2 response was a higher proportion of T. repens in the mixed swards at elevated pCO2. This was evident in all combinations of defoliation and nitrogen treatments. However, the proportion of the species was more strongly affected by N fertilization and defoliation frequency than by elevated pCO2. Based on these results, we conclude that the species proportion in managed grassland may change as the CO2 concentration increases. However, an adapted management could, at least partially, counteract such CO2 induced changes in the proportion of the species. Since the availability of mineral N in the soil may be important for the species’ responses to elevated pCO2, more long-term studies, particularly of processes in the soil, are required to predict the entire ecosystem response.
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    URL: http://dx.doi.org/10.1046/j.1365-2486.1997.00073.x
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    A bivariate meta-Gaussian density for use in hydrology (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 17-31 
    Details
    ISSN: 1436-3259
    Keywords: Bivariate density ; meta-Gaussian density ; normal quantile transform ; likelihood ratio dependence ; correlation coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Convenient bivariate densities found in the literature are often unsuitable for modeling hydrologic variates. They either constrain the range of association between variates, or fix the form of the marginal distributions. The bivariate meta-Gaussian density is constructed by embedding the normal quantile transform of each variate into the Gaussian law. The density can represent a full range of association between variates and admits arbitrarily specified marginal distributions. Modeling and estimation can be decomposed into i) independent analyses of the marginal distributions, and ii) investigation of the dependence structure. Both statistical and judgmental estimation procedures are possible. Some comparisons to recent applications of bivariate densities in the hydrologic literature motivate and illustrate the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02428423
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    Reliability analysis of hydraulic structures considering unit hydrograph uncertainty (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 33-50 
    Details
    ISSN: 1436-3259
    Keywords: Unit hydrograph ; uncertainty analysis ; linearly constrained Monte-Carlo simulation ; reliability analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Unit hydrographs (UHs), along with design rainfalls, are frequently used to determine the discharge hydrograph for design and evaluation of hydraulic structures. Due to the presence of various uncertainties in its derivation, the resulting UH is inevitably subject to uncertainty. Consequently, the performance of hydraulic structures under the design storm condition is uncertain. This paper integrates the linearly constrained Monte-Carlo simulation with the UH theory and routing techniques to evaluate the reliability of hydraulic structures. The linear constraint is considered because the water volume of each generated design direct runoff hydrograph should be equal to that of the design effective rainfall hyetograph or the water volume of each generated UH must be equal to one inch (or cm) over the watershed. For illustration, the proposed methodology is applied to evaluate the overtopping risk of a hypothetical flood detention reservoir downstream of Tong-Tou watershed in Taiwan.
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    URL: http://dx.doi.org/10.1007/BF02428424
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    Estimation for rainfall-runoff modeled as a partially observed Markov process (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 1-16 
    Details
    ISSN: 1436-3259
    Keywords: Nash cascade reservoir model ; rainfall-runoff ; EM algorithm ; filtering ; maximum likelihood estimation ; martingale estimating function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Abstract: Linear continuous time stochastic Nash cascade conceptual models for runoff are developed. The runoff is modeled as a simple system of linear stochastic differential equations driven by white Gaussian and marked point process noises. In the case of d reservoirs, the outputs of these reservoirs form a d dimensional vector Markov process, of which only the dth coordinate process is observed, usually at a discrete sample of time points. The dth coordinate process is not Markovian. Thus runoff is a partially observed Markov process if it is modeled using the stochastic Nash cascade model. We consider how to estimate the parameters in such models. In principle, maximum likelihood estimation for the complete process parameters can be carried out directly or through some form of the EM (estimation and maximization) algorithm or variation thereof, applied to the observed process data. In this research we consider a direct approximate likelihood approach and a filtering approach to an algorithm of EM type, as developed in Thompson and Kaseke (1994). These two methods are applied to some real life runoff data from a catchment in Wales, England. We also consider a special case of the martingale estimating function approach on the runoff model in the presence of rainfall. Finally, some simulations of the runoff process are given based on the estimated parameters.
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    URL: http://dx.doi.org/10.1007/BF02428422
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    Regionalization of unit hydrograph Parameters: 2. Uncertainty analysis (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 173-192 
    Details
    ISSN: 1436-3259
    Keywords: Uncertainty analysis ; unit hydrograph ; regression analysis ; probabilistic point estimation methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Hydrologic model parameters obtained from regional regression equations are subject to uncertainty. Consequently, hydrologic model outputs based on the stochastic parameters are random. This paper presents a systematic analysis of uncertainty associated with the two parameters, N and K, in Nash's IUH model from different regional regression equations. The uncertainty features associated with N and K are further incorporated to assess the uncertainty of the resulting IUH. Numerical results indicate that uncertainty of N and K from the regional regression equations are too significant to be ignored.
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    URL: http://dx.doi.org/10.1007/BF02427914
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    Regionalization of unit hydrograph parameters: 1. Comparison of regression analysis techniques (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 145-171 
    Details
    ISSN: 1436-3259
    Keywords: Hydrologic regionalization ; unit hydrograph ; regression analysis ; multivariate regression ; seemingly unrelated regression ; validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Hydrologic regionalization is a useful tool that allows for the transfer of hydrological information from gaged sites to ungaged sites. This study developed regional regression equations that relate the two parameters in Nash's IUH model to the basin characteristics for 42 major watersheds in Taiwan. In the process of developing the regional equations, different regression procedures including the conventional univariate regression, multivariate regression, and seemingly unrelated regression were used. Multivariate regression and seeming unrelated regression were applied because there exists a rather strong correlation between the Nash's IUH parameters. Furthermore, a validation study was conducted to examine the predictability of regional equations derived by different regression procedures. The study indicates that hydrologic regionalization involving several dependent variables should consider their correlations in the process of establishing the regional equations. The consideration of such correlation will enhance the predictability of resulting regional equations as compared with the ones from the conventional univariate regression procedure.
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    URL: http://dx.doi.org/10.1007/BF02427913
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    An analysis of the characteristics of rough bed turbulent shear stresses in an open channel (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 193-210 
    Details
    ISSN: 1436-3259
    Keywords: Turbulence ; sediment ; fluvial ; river ; bursting process ; statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Entrainment of sediment particles from channel beds into the channel flow is influenced by the characteristics of the flow turbulence which produces stochastic shear stress fluctuations at the bed. Recent studies of the structure of turbulent flow has recognized the importance of bursting processes as important mechanisms for the transfer of momentum into the laminar boundary layer. Of these processes, the sweep event has been recognized as the most important bursting event for entrainment of sediment particles as it imposes forces in the direction of the flow resulting in movement of particles by rolling, sliding and occasionally saltating. Similarly, the ejection event has been recognized as important for sediment transport since these events maintain the sediment particles in suspension. In this study, the characteristics of bursting processes and, in particular, the sweep event were investigated in a flume with a rough bed. The instantaneous velocity fluctuations of the flow were measured in two-dimensions using a small electromagnetic velocity meter and the turbulent shear stresses were determined from these velocity fluctuations. It was found that the shear stress applied to the sediment particles on the bed resulting from sweep events depends on the magnitude of the turbulent shear stress and its probability distribution. A statistical analysis of the experimental data was undertaken and it was found necessary to apply a Box-Cox transformation to transform the data into a normally distributed sample. This enabled determination of the mean shear stress, angle of action and standard error of estimate for sweep and ejection events. These instantaneous shear stresses were found to be greater than the mean flow shear stress and for the sweep event to be approximately 40 percent greater near the channel bed. Results from this analysis suggest that the critical shear stress determined from Shield's diagram is not sufficient to predict the initiation of motion due to its use of the temporal mean shear stress. It is suggested that initiation of particle motion, but not continuous motion, can occur earlier than suggested by Shield's diagram due to the higher shear stresses imposed on the particles by the stochastic shear stresses resulting from turbulence within the flow.
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    URL: http://dx.doi.org/10.1007/BF02427915
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    Parameter estimation for 2-parameter generalized pareto distribution by POME (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 211-227 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The principle of maximum entropy (POME) was employed to derive a new method of parameter estimation for the 2-parameter generalized Pareto (GP2) distribution. Monte Carlo simulated data were used to evaluate this method and compare it with the methods of moments (MOM), probability weighted moments (PWM), and maximum likelihood estimation (MLE). The parameter estimates yielded by POME were comparable or better within certain ranges of sample size and coefficient of variation.
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    URL: http://dx.doi.org/10.1007/BF02427916
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    Evaluation of kernel density estimation methods for daily precipitation resampling (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 523-547 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Kernel density estimators are useful building blocks for empirical statistical modeling of precipitation and other hydroclimatic variables. Data driven estimates of the marginal probability density function of these variables (which may have discrete or continuous arguments) provide a useful basis for Monte Carlo resampling and are also useful for posing and testing hypotheses (e.g bimodality) as to the frequency distributions of the variable. In this paper, some issues related to the selection and design of univariate kernel density estimators are reviewed. Some strategies for bandwidth and kernel selection are discussed in an applied context and recommendations for parameter selection are offered. This paper complements the nonparametric wet/dry spell resampling methodology presented in Lall et al. (1996).
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    Simulation of normal distributed smooth fields by Karhunen-Loéve expansion in combination with kriging (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 459-482 
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    ISSN: 1436-3259
    Keywords: Karhunen-Loéve expansion ; Empirical Orthogonal Functions ; stochastic simulation ; gaussian fields ; analytical covariance functions ; eigenfunctions ; kriging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Simulation of multigaussian stochastic fields can be made after a Karhunen-Loéve expansion of a given covariance function. This method is also called simulation by Empirical Orthogonal Functions. The simulations are made by drawing stochastic coefficients from a random generator. These numbers are multiplied with eigenfunctions and eigenvalues derived from the predefined covariance model. The number of eigenfunctions necessary to reproduce the stochastic process within a predefined variance error, turns out to be a cardinal question. Some ordinary analytical covariance functions are used to evaluate how quickly the series of eigenfunctions can be truncated. This analysis demonstrates extremely quick convergence to 99.5% of total variance for the 2nd order exponential (‘gaussian’) covariance function, while the opposite is true for the 1st order exponential covariance function. Due to these convergence characteristics, the Karhunen-Loéve method is most suitable for simulating smooth fields with ‘gaussian’ shaped covariance functions. Practical applications of Karhunen-Loéve simulations can be improved by spatial interpolation of the eigenfunctions. In this paper, we suggest interpolation by kriging and limits for reproduction of the predefined covariance functions are evaluated.
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    Chowdhury and Stedinger's approximate confidence intervals for design floods for a single site (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 51-63 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A basic problem in hydrology is computing confidence levels for the value of the T-year flood when it is obtained from a Log Pearson III distribution in terms of estimated mean, estimated standard deviation, and estimated skew. In an important paper Chowdhury and Stedinger [1991] suggest a possible formula for approximate confidence levels, involving two functions previously used by Stedinger [1983] and a third function, λ, for which asymptotic estimates are given. This formula is tested [Chowdhury and Stedinger, 1991] by means of simulations, but these simulations assume a distribution for the sample skew which is not, for a single site, the distribution which the sample skew is forced to have by the basic hypothesis which underlies all of the analysis, namely that the maximum discharges have a Log Pearson III distribution. Here we test these approximate formulas for the case of data from a single site by means of simulations in which the sample skew has the distribution which arises when sampling from a Log Pearson III distribution. The formulas are found to be accurate for zero skew but increasingly inaccurate for larger common values of skew. Work in progress indicates that a better choice of λ can improve the accuracy of the formula.
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    Stochastic analysis of multiphase flow in porous media: II. Nummerical simulations (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 94-94 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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    URL: http://dx.doi.org/10.1007/BF02428427
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    Structure in fluctuations of large-scale soil moisture climate due to external random forcing and internal feedbacks (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 95-114 
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    ISSN: 1436-3259
    Keywords: Soil moisture ; time scale ; non-Gaussian ; colored-noise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Large-scale fields of soil moisture are forced by atmospheric precipitation and radiative forcing. When these forcing factors are themselves influenced by surface and soil moisture processes, the result is a nonlinear land-atmosphere system with inherent feedback mechanisms that may strongly modulate variability in climate. Given such feedbacks, simple randomness in the forcing factors may be manifested as a complex statistical signature in the surface hydrology. In this paper, we investigate the impacts of non-Gaussian and colored-noise on the probability distribution of soil moisture resulting from the statistical-dynamical land-atmosphere interaction model of Rodriguez-Iturbe et al. (1991). Persistence of hydroclimatologic anomalies as characterized by the correlation time scale of soil moisture is discussed.
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    Rain-fall modeling: An Application of Bayesian forecasting (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 115-127 
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    ISSN: 1436-3259
    Keywords: Rainfall-runoff modeling ; transfer response ; dynamic non-linear models ; normal and gamma observational distribution ; predictive performance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The rainfall-runoff modeling is very useful for forecasting purposes. A good methodology for forecasting the future stream flow is a key requirement for designers and operators of water resources systems. A compromise between conceptual and classical time series modeling is applied to model the relationship between rainfall and runoff. The dynamic nonlinear model is composed of a probability distribution describing the observation, a link function relating its mean to the so called state parameters and a system of equations defining the evolution of these parameters. Its Bayesian nature permits to take into account subjective information, making forward intervention, defining monitoring schemes and introducing smoothing facilities. An application using the data of Fartura river's basin is reported. The assessment of the prior distribution is discussed and the predictive performance of the linear and the non-linear models is reported.
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    The role of moisture fluctuations in unsaturated transport (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 129-143 
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    ISSN: 1436-3259
    Keywords: Stochastic analysis ; perturbation methods ; unsaturated transport ; heterogeneous porous media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Within the framework of stochastic theory and the spectral perturbation techniques, three-dimensional dispersion in partially saturated soils with a finite correlation scale of log-hydraulic conductivity is analyzed. The effects of spatial variability of the moisture distribution parameter on the asymptotic spreading behavior of a unsaturated solute plume are assessed. This is accomplished by comparing two asymptotic macrodispersivities and two variance of solute concentration, obtained for a constant moisture content and spatially varied moisture, respectively.
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    Multivariate nonparametric resampling scheme for generation of daily weather variables (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 65-93 
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    ISSN: 1436-3259
    Keywords: Nonparametric ; Monte Carlo ; precipitation ; weather
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A nonparametric resampling technique for generating daily weather variables at a site is presented. The method samples the original data with replacement while smoothing the empirical conditional distribution function. The technique can be thought of as a smoothed conditional Bootstrap and is equivalent to simulation from a kernel density estimate of the multivariate conditional probability density function. This improves on the classical Bootstrap technique by generating values that have not occurred exactly in the original sample and by alleviating the reproduction of fine spurious details in the data. Precipitation is generated from the nonparametric wet/dry spell model as described in Lall et al. [1995]. A vector of other variables (solar radiation, maximum temperature, minimum temperature, average dew point temperature, and average wind speed) is then simulated by conditioning on the vector of these variables on the preceding day and the precipitation amount on the day of interest. An application of the resampling scheme with 30 years of daily weather data at Salt Lake City, Utah, USA, is provided.
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    A mean behavior model of aerobic biodegradation in heterogeneous formation (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 255-266 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract It has been observed that the field biodegradation rates for soluble hydrocarbon plumes are significantly smaller than the aerobic rates observed in the laboratory. It is believed that this difference is related to the fact that in the field oxygen and hydrocarbon must be mixed before the biodegradation reaction can occur, and that the effective degradation rate is controlled by the actual, not mean, concentrations of oxygen and hydrocarbon. In this work, we present a conceptual model of oxygen-mixing limited biodegradation, which indicates that the effective degradation rate should depend on the cross correlation between the oxygen and hydrocarbon concentration fluctuations. This is followed by a development of a rigorous, field-scale model.
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    On the problem of model validation for predictive exposure assessments (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 229-254 
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    ISSN: 1436-3259
    Keywords: Model validation ; analysis of uncertainty ; model verification ; quality assurance ; system identification ; model calibration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The development and use of models for predicting exposures are increasingly common and are essential for many risk assessments of the United States Environmental Protection Agency (EPA). Exposure assessments conducted by the EPA to assist regulatory or policy decisions are often challenged to demonstrate their “scientific validity”. Model validation has thus inevitably become a major concern of both EPA officials and the regulated community, sufficiently so that the EPA's Risk Assessment Forum is considering guidance for model validation. The present paper seeks to codify the issues and extensive foregoing discussion of validation with special reference to the development and use of models for predicting the impact of novel chemicals on the environment. Its preparation has been part of the process in formulating a White Paper for the EPA's Risk Assessment Forum. Its subject matter has been drawn from a variety of fields, including ecosystem analysis, surface water quality management, the contamination of groundwaters from high-level nuclear waste, and the control of air quality. The philosophical and conceptual bases of model validation are reviewed, from which it is apparent that validation should be understood as a task of product (or tool) design, for which some form of protocol for quality assurance will ultimately be needed. The commonly used procedures and methods of model validation are also reviewed, including the analysis of uncertainty. Following a survey of past attempts at resolving the issue of model validation, we close by introducing the notion of a model having maximum relevance to the performance of a specific task, such as, for example, a predictive exposure assessment.
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    A stochastic model of low flows (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 303-321 
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    ISSN: 1436-3259
    Keywords: Simulation ; hydrograph rise and recession ; rainfall process ; probability distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A model is developed for annual low flow hydrographs. Its two primary components reflect the fact that hydrologic processes during streamflow rise (function of water input) and recession (function of basin storage) are different. Durations of periods of rise (wet intervals) and recession (dry intervals) are modelled by discrete probability distributions — negative binomial for dry intervals and negative binomial or modified logarithmic series for wet intervals depending on goodness of fit. During wet intervals, the total inflow is modelled by the lognormal distribution and daily amounts are allocated according to a pattern-averaged model. During dry intervals, the flow recedes according to a deterministic-stochastic recession model. The model was applied to three Canadian basins with drainage area ranging from 2210 to 22000 km2 to generate 50 realizations of low flow hydrographs. The resulting two standard-error confidence band for the simulated probability distribution of annual minimum 7-day flows enclosed the probability distribution estimated from the observed record. A sensitivity analysis for the three basins revealed that in addition to the recession submodel, the most important submodel is that describing seasonality. The state of the basin at the beginning of the low flow period is of marginal importance and the daily distribution of input is unimportant.
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    Stochastic analysis of spatiotemporal solute content measurements using a regression model (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 267-295 
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    ISSN: 1436-3259
    Keywords: Space/time processes ; stochastic analysis ; regression model ; solute contents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A regression model is used to study spatiotemporal distributions of solute content ion concentration data (calcium, chloride and nitrate), which provide important water contamination indicators. The model consists of three random and one deterministic components. The random space/time component is assumed to be homogeneous/stationary and to have a separable covariance. The purely spatial and the purely temporal random components are assumed to have homogenous and stationary increments, respectively. The deterministic component represents the space/time mean function. Inferences of the random components involve maximum likelihood and semi-parametric methods under some restrictions on the data configuration. Computational advantages and modelling limitations of the assumptions underlying the regression model are discussed. The regression model leads to simplifications in the space/time kriging and cokriging systems used to obtain space/time estimates at unobservable locations/instants. The application of the regression model in the study of the solute content ions was done at a global scale that covers the entire region of interest. The variability analysis focuses on the calculation of the spatial direct and cross-variograms and the evaluation of correlations between the three solute content ions. The space/time kriging system is developed in terms of the space direct and cross-variograms, and allows the separate estimation of the regression model components. Maps of these components are then obtained for each one of the three ions. Using the estimates of the purely spatial component, spatial dependencies between the ions are studied. Physical causes and consequences of the space/time variability are discussed, and comparisons are made with previous analyses of the solute content dataset.
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    A test sensitive to extreme hidden periodicities (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 323-330 
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    ISSN: 1436-3259
    Keywords: Kolmogorov-Smirnov test ; identification of periodic component ; goodness-of-fit test for white noise ; periodogram ; residuals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A modified version of the widely used Kolmogorov-Smirnov (K-S) test of null hypothesis is constructed, that a given time series is Gaussian white noise, against the alternative hypothesis that the time series contains an added or multiplicative deterministic-periodic component of unspecified frequency. The usual KS test is treated as a special case. The proposed test is more powerful than the ordinary K-S test in detecting extreme (low or high) hidden periodicities. Computational procedure necessary for implementation are also given.
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    Solutions to the stochastic transport problem of O(σ V N ) for conservative solutes (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 297-302 
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    ISSN: 1436-3259
    Keywords: Perturbation ; conservative chemical ; velocity variance ; eulerian
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A recursive perturbation solution to the eulerian transport problem for a conservative solute in a random conductivity field is reported. The stochastic concentration is given to arbitrary order inσ ν, the variance of fluctuating velocity. The result gives the stochastic concentration as a perturbation to the deterministic concentration for constant mean flow. The closed form solution is easy to implement numerically via FFT.
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    Analytical solutions for the coefficient of variation of the volume-averaged solute concentration in heterogeneous aquifers (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 331-348 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Under the assumption that local solute dispersion is negligible, a new general formula (in the form of a convolution integral) is found for the arbitrary k-point ensemble moment of the local concentration of a solute convected in arbitrary m spatial dimensions with general sure initial conditions. From this general formula new closed-form solutions in m=2 spatial dimensions are derived for 2-point ensemble moments of the local solute concentration for the impulse (Dirac delta) and Gaussian initial conditions. When integrated over an averaging window, these solutions lead to new closed-form expressions for the first two ensemble moments of thevolume-averaged solute concentration and to the corresponding concentration coefficients of variation (CV). Also, for the impulse (Dirac delta) solute concentration initial condition, the second ensemble moment of thesolute point concentration in two spatial dimensions and the corresponding CV are demonstrated to be unbound. For impulse initial conditions the CVs for volume-averaged concentrations axe compared with each other for a tracer from the Borden aquifer experiment. The point-concentration CV is unacceptably large in the whole domain, implying that the ensemble mean concentration is inappropriate for predicting the actual concentration values. The volume-averaged concentration CV decreases significantly with an increasing averaging volume. Since local dispersion is neglected, the new solutions should be interpreted as upper limits for the yet to be derived solutions that account for local dispersion; and so should the presented CVs for Borden tracers. The new analytical solutions may be used to test the accuracy of Monte Carlo simulations or other numerical algorithms that deal with the stochastic solute transport. They may also be used to determine the size of the averaging volume needed to make a quasi-sure statement about the solute mass contained in it.
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    Tidal flow forecasting using reduced rank square root filters (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 349-368 
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    ISSN: 1436-3259
    Keywords: Data assimilation ; Kalman filter ; Square root filter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The Kalman filter algorithm can be used for many data assimilation problems. For large systems, that arise from discretizing partial differential equations, the standard algorithm has huge computational and storage requirements. This makes direct use infeasible for many applications. In addition numerical difficulties may arise if due to finite precision computations or approximations of the error covariance the requirement that the error covariance should be positive semi-definite is violated. In this paper an approximation to the Kalman filter algorithm is suggested that solves these problems for many applications. The algorithm is based on a reduced rank approximation of the error covariance using a square root factorization. The use of the factorization ensures that the error covariance matrix remains positive semi-definite at all times, while the smaller rank reduces the number of computations and storage requirements. The number of computations and storage required depend on the problem at hand, but will typically be orders of magnitude smaller than for the full Kalman filter without significant loss of accuracy. The algorithm is applied to a model based on a linearized version of the two-dimensional shallow water equations for the prediction of tides and storm surges. For non-linear models the reduced rank square root algorithm can be extended in a similar way as the extended Kalman filter approach. Moreover, by introducing a finite difference approximation to the Reduced Rank Square Root algorithm it is possible to prevent the use of a tangent linear model for the propagation of the error covariance, which poses a large implementational effort in case an extended kalman filter is used.
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    Diagrammatic theory of effective hydraulic conductivity (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 369-395 
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    ISSN: 1436-3259
    Keywords: Random fields ; diagrams ; perturbation ; non-local ; effective conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This work presents a stochastic diagrammatic theory for the calculation of the effective hydraulic conductivity of heterogeneous media. The theory is based on the mean-flux series expansion of a log-normal hydraulic conductivity medium in terms of diagrammatic representations and leads to certain general results for the effective hydraulic conductivity of three-dimensional media. A selective summation technique is used to improve low-order perturbation analysis by evaluating an infinite set of diagrammatic terms with a specific topological structure that dominates the perturbation series. For stochastically isotropic media the selective summation yeilds the anticipated exponential expression for the effective hydraulic conductivity. This expression is extended to stochastically anisotropic media. It is also shown that in the case of non homogeneous media the uniform effective hydraulic conductivity is replaced by a non-local tensor kernel, for which general diagrammatic expressions are obtained. The non-local kernel leads to the standard exponential behavior for the effective hydraulic conductivity at the homogeneous limit.
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    Conceptually-based shot noise modeling of streamflows at short time interval (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 483-510 
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    ISSN: 1436-3259
    Keywords: Conceptual-stochastic models ; shot noise ; streamflow simulation ; time aggregation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A conceptual-stochastic approach to short time runoff data modelling is proposed, according to the aim of reproducing the hydrological aspects of the streamflow process and of preserving as much as possible the dynamics of the process itself. This latter task implies preservation of streamflow characteristics at higher scales of aggregation and, within a conceptual framework, involves compatibility with models proposed for the runoff process at those scales. At a daily time scale the watershed response to the effective rainfall is considered as deriving from the response of three linear reservoirs, respectively representing contributions to streamflows of large deep aquifers, with over-year response lag, of aquifers which run dry by the end of the dry season and of subsurface runoff. The surface runoff component is regarded as an uncorrelated point process. Considering the occurrences of effective rainfall events as generated by an independent Poisson process, the output of the linear system represents a conceptually-based multiple shot noise process. Model identification and parameter estimation are supported by information related to the aggregated runoff process, in agreement to the conceptual framework proposed, and this allows parameter parsimony, efficient estimation and effectiveness of the streamflow reproduction. Good performances emerged from the model application and testing made with reference to some daily runoff series from Italian basins.
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    Direct probabilistic description of arrival times of Runoff events within the year (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 511-521 
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    Keywords: Runoff events ; arrival times ; partial duration series ; arid areas ; Israel ; probabilistic modeling ; Pearson III distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Present descriptions of arrival times of runoff events are based upon modeling of interarrival intervals. Maintaining the traditional assumption that arrival times are independent random variables, these times can be directly described through a continuous distribution fitted to recorded data. A case study for the arid Negev region in Israel indicates that the Pearson type III distribution satisfactorily achieves this goal. The direct description can apply nonuniform functions, respond to multi-modal distributions, and be extended to regional modeling.
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    Advection-diffusion in spatially random flows: Formulation of concentration covariance (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 397-422 
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    ISSN: 1436-3259
    Keywords: Random flow field ; diffusion ; concentration ; fluctuations ; covariance ; variance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The concentration c(x,t) of a nonreactive solute undergoing advection and diffusion in a spatially random divergence-free flow field is analyzed. A leading order formulation for the spatial covariance of the concentration field, $$\overline {c'\left( {x,t} \right)c'\left( {x,t} \right)} $$ , is made. That formulation includes the velocity variability induced macrodispersive flux of the covariance field, and the smoothing effects of diffusion. Previous formulations of the concentration covariance had dropped at least one of these effects. It is shown that both these effects need to be included to obtain a qualitatively correct description of the concentration fluctuations.
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    Effect of class-interval size on entropy (1997)
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    Stochastic environmental research and risk assessment 11 (1997), S. 423-431 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The value of Shannon entropy for a given set of data depends on the class interval chosen to compute the relative frequency of each class. For three data sets, expressed in dimensional as well as nondimensional form, the entropy value was computed for different class-interval sizes. Entropy was found to decrease with increasing class interval as well as with increasing sampling interval. It is suggested that these intervals should be selected with care.
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    URL: http://dx.doi.org/10.1007/BF02427927
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    A stochastic approach to model bottom boundary conditions and compute efficiency in a settling tank (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 449-457 
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    ISSN: 1436-3259
    Keywords: Settling tank ; diffusion in open sets ; elastic reflection ; boundary conditions ; efficiency ; exit time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract When the diffusion term is supposed not to be zero at the boundary of a settling tank, we show that an alternate (and equivalent) description to the basic advection-diffusion equation for the concentration of micro pollutant consists in modelling the micro pollutant particles' trajectories as a diffusion stochastic process. Indeed, the density of this latter satisfies the same Pde as the advection-diffusion equation. Our emphasis here is on the computation of the so called tank efficiency and on the bottom boundary conditions. We claim that our interpretation in terms of a diffusion process helps to enlighten the choice of the appropriate mathematical boundary conditions. What is more, we introduce a scouring parameter and give its range as well as its physical interpretation.
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    URL: http://dx.doi.org/10.1007/BF02428428
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    Incorporating inflow uncertainty into risk assessment for reservoir operation (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 433-448 
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    ISSN: 1436-3259
    Keywords: Risk ; uncertainty ; reservoir operation ; sedimentation ; computer application
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract An attempt of using stochastic hydrologic technique to assess the intrinsic risk of reservoir operation is made in this study. A stochastic simulation model for reservoir operation is developed. The model consists of three components: synthetic generation model for streamflow and sediment sequences, one-dimensional delta deposit model for sediment transport processes in reservoirs, and simulation model for reservoir operation. This kind of integrated simulation model can be used to simulate not only the inflow uncertainty of streamflow and sedimentation, but also the variation in operation rules of reservoirs. It is herein used for the risk assessment of a reservoir, and the simulation is performed for different operation scenarios. Simulation for the 100-year period of sediment transport and deposition in the river-reservoir system indicates that the navigation risk is much higher than that of hydropower generation or sediment deposition in the reservoir. The risk of sediment deposition at the river-section near the backwater profile is also high thereby the navigation at the river-segment near this profile takes high risk because of inadequate navigation depth.
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    URL: http://dx.doi.org/10.1007/BF02427928
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    High-speed rail in Europe: experience and issues for future development (1997)
    Springer
    The annals of regional science 31 (1997), S. 21-38 
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    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. The development of High-Speed Rail has been one of the central features of recent European Union transport infrastructure policy. This paper reviews the developments which have taken place in a number of countries and assesses the outcome. It identifies the lack of genuine network development which has taken place, criticises the failure to provide a more integrated framework between modes and questions the assumptions of improved regional development and cohesion which are claimed for the policy. Instead there is evidence of increasing concentration into the main metropolitan centres served by the emerging network.
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    URL: http://dx.doi.org/10.1007/s001680050037
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    Labor markets and regional transportation improvements: the case of high-speed trains An introduction and review (1997)
    Springer
    The annals of regional science 31 (1997), S. 57-76 
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    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. Labor market issues are reviewed in terms of mobility and policy resulting from transportation improvements. Research on Meso level regional adjustment versus micro level search processes are reviewed. A spatial interaction approach to assessing changes in regional access and regional industrial mix is outlined. Hypotheses with respect to transportation and labor markets are discussed. Empirical evidence of the impact of high-speed rail on labor markets and their structure is reviewed. Conclusions are drawn and new research questions are identified.
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    URL: http://dx.doi.org/10.1007/s001680050039
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    Justifying a high-speed rail project: social value vs. regional growth (1997)
    Springer
    The annals of regional science 31 (1997), S. 155-174 
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    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. This article establishes a relationship between the net present value (NPV) of a High-Speed Rail (HSR) project and its social value, its transportation consumers‘ surplus (TCS) and its regional economic impact in terms of growth. First, it is shown that if the NPV is positive, it may generate growth even if no bottleneck exists. Second, when shadow-pricing and externalities are included in the calculations, and the HSR demand has been forecasted by a multinomial logit model, the NPV differs from its net economic impact. For instance, one variant of the project, though acceptable, reduces growth elsewhere in the economy. Decision-making is then in a quandary.
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    URL: http://dx.doi.org/10.1007/s001680050043
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    Product differentiation and cartel stability: Chamberlin versus Hotelling (1997)
    Springer
    The annals of regional science 31 (1997), S. 259-271 
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    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. This paper contrasts the implications, for cartel stability, of the non-spatial (‘Chamberlinian’) and the spatial (‘Hotelling’) models of product differentiation. Using the special case of a linear demand framework, we show that whereas the former approach suggests that cartel stability is non-monotonic but predictable in the degree of differentiation, the outcome is very much more ambiguous when the latter formulation is employed. We examine also the implications for stability when demand shocks occur, and show that even in the case of linear demand, when differentiation is modelled in spatial terms the results are consistent with non-linear non-spatial demand functions, as well as with those obtained in more complicated models of firm behaviour.
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    URL: http://dx.doi.org/10.1007/s001680050048
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    A price-responsive framework for interregional input-output (1997)
    Springer
    The annals of regional science 31 (1997), S. 285-298 
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    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. In interregional analysis, supply models are based typically on defined sets of ‘representative firms’ with given ‘averaged’ technological and cost coefficients, such that, when aggregated as identical units into both sectors and regions, they reproduce the total output of each sector in each region. Then, deterministic models obtain profit-maximising patterns of input demands and corresponding output, prior to aggregating these quantities as if the firms were truly identical and homogeneous. In this paper, the above optimisation models are replaced by a probabilistic framework, which nevertheless guarantees convergence to the above classical deterministic solutions in the limit. The models are estimated on ‘observed’ flows, technological coefficients and prices, and a CES function (optionally) handles substitution between primary factors. These new input-output models become explicitly price-responsive, allowing tâtonnement with spatial models of final demand.
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    URL: http://dx.doi.org/10.1007/s001680050050
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    Traffic, transportation, infrastructure and externalities A theoretical framework for a CGE analysis (1997)
    Springer
    The annals of regional science 31 (1997), S. 369-389 
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    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. In Europe traffic congestions make it impossible to estimate travel time. The increasing number of cars calls for a transportation policy towards an improved efficiency of the transportation system. However, extending road infrastructure to reduce the congestion externality implies another type of externality, air pollution. Designing a transportation policy in industrialized countries one has to consider this trade-off. Our objective is to investigate the role of transportation services and their pricces within an interindustry framework. The authority wishes to minimize total cost of production with respect to the provision of infrastructure subject to an emission standard. By omitting a financial constraint to finance infrastructure we determine the size of infrastructure where no congestion occurs. The productivity effect of infrastructure and the cost savings from a dissolved congestion determine the optimal stock of infrastructure. Our congestion index is unity in that case of no financial constraint. If the extension of infrastructure has to be paid for by taxation, we obtain a lower level of infrastructure. In view of the trade-off between the benefit of a productivity gain from a dissolved congestion and the deadweight loss from taxation this lower level of infrastructure will result in an index of congestion higher than unity, implying a negative externality to the economy.
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    URL: http://dx.doi.org/10.1007/s001680050054
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    Job and housing tenure and the journey to work (1997)
    Springer
    The annals of regional science 31 (1997), S. 451-471 
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    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. Tenure at jobs and houses, along with commuting patterns between home and work, were studied for residents of metropolitan Washington. Two alternative potential outcomes were considered: (1) because moving or switching jobs can be used as an opportunity to reduce commuting duration in an era of rising congestion, those who recently moved or changed jobs should have shorter than average commutes; and (2) because most new residential construction is at the urban fringe, an area of longer commutes, those who recently moved to new homes should have longer commutes. Evaluation of the effect of commuting duration on job and housing tenure suggests that those who move, on average, maintain commute duration rather than having a major increase or decrease. This corroborates the idea that there are offsetting factors, where increases in commute lengths due to suburbanizing residences are counteracted by the correlated process of suburbanizing jobs.
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    URL: http://dx.doi.org/10.1007/s001680050058
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    A numerical study of barotropic vortex motion near a large-scale mountain range with application to the motion of tropical cyclones approaching the Sierra Madre (1997)
    Springer
    Meteorology and atmospheric physics 64 (1997), S. 1-19 
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    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary The motion of an idealized vortex near a large-scale mountain range is examined by numerically integrating the single-layer shallow-water equations on an equatorial beta plane. Modification of the asymmetric circulation by divergent vorticity generation as the air is forced across the ridge greatly affects the motion of the vortex. Attention is focused on the role of the vortex structure, the mountainrange width and orientation, and the stratification of the model atmosphere in influencing the motion of the vortex. A scale analysis is used to explain the sensitivity of the vortex track to changes in the model's external parameters. The sensitivity of the model vortex track to the slope and orientation of the mountain range is used to help explain some features of the observed tracks of hurricanes that make landfall on the east coast of Mexico.
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    URL: http://dx.doi.org/10.1007/BF01044127
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    Measurements of solar radiation and estimation of optical depth in the high Andes of Peru (1997)
    Springer
    Meteorology and atmospheric physics 64 (1997), S. 51-59 
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    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary During an expedition to the high Andes of Southern Peru in June–July 1977, measurements of direct solar radiation in four spectral bands (0.270–0.530–0.630–0.695–2.900 μ) were conducted at six sites in elevations ranging from sea level to 5645 m. These measurements were evaluated in Langley plots to determine total optical depths (τ) and irradiances at the top of the atmosphere. In addition, water vapor optical depths (τwv) were calculated from the mean radiosounding over Lima during the expedition, and Rayleigh (τray) and ozone (τoz) optical depths were obtained from published tabulations. Subtracting τray, τoz, and τwv from τ yielded estimates of aerosol optical depth τaer. The components τray and τoz decrease from the shorter towards the longer wavelength bands and from the lower towards the higher elevation sites; τaer also decreases towards the higher elevations. Particularly pronounced is the decrease of τaer and τ from the lowlands of the Pacific coast to the highlands of the interior, reflecting the effect of a persistent lower-tropospheric inversion and the contrast from the marine boundary layer to the clear atmosphere of the high Andes.
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    URL: http://dx.doi.org/10.1007/BF01044129
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    Mesoscale data assimilation and prediction of low stratus in the Alpine region (1997)
    Springer
    Meteorology and atmospheric physics 64 (1997), S. 21-50 
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    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary A number of problems related to mesoscale numerical prediction of low stratus in the Alpine region are formulated, and addressed in a series of experiments for two wintertime cases. These problems include modelling aspects and issues of data assimilation which are relevant particularly in relation to the observation nudging technique. A focus is on the influence of orography. A comparison of operational optimum interpolation, and nudging of routine rawinsonde and surface-level data reveals that nudging often yields better analyses and forecasts of low stratus, and notably of the sharp vertical temperature and humidity gradients. However, the humidity advection scheme of the model and, near steep terrain, particularly the horizontal diffusion along the model's σ-levels are identified to contribute to spurious vertical smoothing which can result in erroneous cloud dissipation. On occasions, forecasts succeeding a nudging period are more sensitive to this process due to the sharper initial vertical gradients. Specific problems of representiveness arise when low-level rawinsonde information is spread laterally along the sloping σ-levels from low to high terrain. A new concept for σ-layer models is introduced by speading the observational information along isentropic surfaces, and this tends to improve the low stratus prediction over steep and even moderate orography. A partly successful attempt to take advantage of the steep Alpine orography is made by applying this concept to surface-level humidity data from a high-resolution network of Alpine surface stations which are distributed relatively uniformly in the vertical.
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    URL: http://dx.doi.org/10.1007/BF01044128
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    On the impact of divergent part of the wind computed from INSAT OLR data on global analysis and forecast fields (1997)
    Springer
    Meteorology and atmospheric physics 64 (1997), S. 61-82 
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    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary In this paper, a procedure for the computation of the divergent part of wind from Outgoing Longwave Radiation (OLR) data is described. This divergent part is included in the global analysis scheme and its impact is studied by computing the vertical velocity, velocity potential etc., using the analysed fields with and without modifying the divergent part and also making 24 hr and 48 hr rainfall forecasts. Results show that magnitudes of vertical velocity were increased when the divergent part was modified in the wind analysis. There were also changes observed in the analysed wind field over convective regions and the changes over the oceanic regions were higher, suggesting that the impact of divergent part is more pronounced over data sparse regions. Marginal increase was observed in 24 hr and 48 hr rainfall forecast over the Indian region. The area averaged rainfall forecast at each time step in the first 6 hours of model integration was also higher in the case when the wind field contained the divergent part. To sum up, it can be stated that the inclusion of the divergent part from OLR data in the initial wind field has brought out positive impact on the wind analyses and rainfall forecast.
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    URL: http://dx.doi.org/10.1007/BF01044130
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    Measurements of diurnal heat exchange on the Quelccaya Ice Cap, Peruvian Andes (1997)
    Springer
    Meteorology and atmospheric physics 62 (1997), S. 71-78 
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    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary Measurements of the surface heat budget were conducted on an ice cap in the Andes of Southern Peru at 5645 m during an expedition in July 1977. Because of the high surface albedo, net software radiative gain is nearly offset by the longwave loss in the average over the diurnal cycle. The diurnal temperature wave has at the surface an amplitude of about 5°C, and by 50 cm depth this is nearly dampened out. During the day, the shortwave radiative gain is in part used to balance the longwave loss, some heat is stored in the top snow layer and lost by sensible heat transfer to the overlying atmosphere, and the greater part fuels the sublimation. At night, the longwave radiative loss is not completely compensated by heat depletion and downward directed sensible heat transfer. This deficit is made up by the downward transfer of latent heat, resulting in heat release at the surface and deposition. Regarding the mass balance, the nighttime deposition approximately cancels the daytime sublimation. At lower elevations of the ice cap, albedo is much less, allowing larger absorption of solar radiation. As a consequence, more energy is available for ablation. Melting occurs during the day, so that re-freezing and concurrent latent heat release can help to compensate the longwave radiative loss at night.
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    URL: http://dx.doi.org/10.1007/BF01037480
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