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  • 1
    Electronic Resource
    Electronic Resource
    Rainfall and drought in equatorial east Africa during the past 1,100 years (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 403 (2000), S. 410-414 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Knowledge of natural long-term rainfall variability is essential for water-resource and land-use management in sub-humid regions of the world. In tropical Africa, data relevant to determining this variability are scarce because of the lack of long instrumental climate records and the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35000179
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  • 2
    Electronic Resource
    Electronic Resource
    Marked recent increases of colonial scaled chrysophytes in boreal lakes: implications for the management of taste and odour events (2004)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 49 (2004), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Lake managers suspect that taste and odour-causing algal blooms are increasing in frequency and intensity, although long-term monitoring records are scarce, and a number of critical scientific and management questions remain unanswered.2. In nutrient-poor lakes and reservoirs, these events are caused primarily by sporadic outbreaks of some chrysophyte algae, which leave identifiable markers in lake sediments. We examine the siliceous remains of these organisms in more than fifty boreal lakes at broad temporal and spatial scales.3. Colonial scaled chrysophytes, including the taste and odour-causing Synura petersenii, have increased markedly in more that 90% of the lakes examined since pre-industrial times.4. Detailed stratigraphic analyses of two lakes show a rise in the abundance of colonial taxa in the 1930s to 1950s, with a sharp increase over the past two decades.5. An examination of biogenic silica and biological ratios in Crosson Lake, Ontario, Canada, indicate that these changes represent true increases in the absolute abundance of colonial chrysophytes.6. Rapid increases over the past two decades indicate that these trends are the result of one or more anthropogenic stressors that are operating at a broad, regional scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01170.x
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  • 3
    Electronic Resource
    Electronic Resource
    A landscape approach to examining spatial patterns of limnological variables and long-term environmental change in a southern Canadian lake district (2003)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. We explored patterns of limnological variables (physical, chemical and biological) with relation to landscape position (expressed as lake order) in 86 study lakes located on shield bedrock in south-central Ontario, Canada.2. Using anovas with lake order as the categorical variable, landscape position explained significant amounts of variation in major ion chemistry, physical and catchment characteristics, hypolimnetic oxygen, and community composition in algal (diatom, chrysophyte) and invertebrate (chironomid) assemblages preserved in surficial sediments. Several nutrient variables (TP, total phosphorus and TN, total nitrogen) and dissolved organic carbon did not have significant relationships with lake order.3. The strongest relationships with lake order (as a fraction of variation explained in anovas) included silica concentrations (r2 = 0.40) and SO4 (r2 = 0.29) concentrations, surface area (r2 = 0.50) and hypolimnetic oxygen (r2 = 0.29).4. Bedrock geology (carbonate metasedimentary versus non-carbonate bedrock) had strong influences on spatial gradients of pH and major ion chemistry. It was difficult to separate geological influences from spatial influences on limnological variables in this study, as drainage patterns in the region are highly influenced by surface features of underlying geological formations because of the very thin glacial till or exposed bedrock that exists in most catchments.5. Patterns of limnological variables indicated that low-order, headwater lakes had the lowest concentrations of major ions, and, from algal inferences of pH change, had been most susceptible to acidic deposition. High-order, downstream lakes were larger and deeper, and had higher concentrations of hypolimnetic oxygen, indicating that optimal lake trout habitat was primarily located in high-order lakes.6. Variance partitioning analyses indicated that lake order as a metric of landscape position explained comparable portions of community variation in algal and invertebrate assemblages compared with geographic position (latitude, longitude) and Cartesian coordinate position (e.g. x, y, x2, y2, etc.) metrics. Lake order explained more community variation in chironomid assemblages compared with other landscape metrics, possibly because of the strong relationships between lake order and lake morphometry variables.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01105.x
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  • 4
    Electronic Resource
    Electronic Resource
    Tracking Recovery Patterns in Acidified Lakes: A Paleolimnological Perspective (1998)
    Cambridge, MA, USA : Blackwell Science, Inc.
    Restoration ecology 6 (1998), S. 0 
    Details
    ISSN: 1526-100X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Long-term data are often lacking to effectively assess patterns of lake acidification and recovery. Fortunately, paleolimnological techniques can be used to infer past changes in lakewater acidity and related variables by means of biological indicators, such as diatom valves and chrysophyte scales, preserved in 210Pb-dated sediment cores. We summarize paleolimnological data that we have gathered from 36 Sudbury (Ontario) and 20 Adirondack Park (New York) lakes to estimate the magnitude of lake acidification and any subsequent recovery in these lake systems. In both regions, many lakes were shown to have acidified considerably, some over two pH units, since the 1850s. Although some recovery was noted in both lake regions, Sudbury lakes generally showed larger increases in inferred lakewater pH with recent declines in sulfur emissions. Possible explanations of these differences include the greater decrease in sulfate deposition in the Sudbury area, as well as generally longer residence times of lakes in Sudbury, perhaps allowing for more in-lake alkalinity generation. In addition, Sudbury lakes generally had higher pre-industrial pH levels, suggesting that lakes with higher natural buffering capacities are more likely to recover more quickly with declines in deposition, even if they had been acidified to a great extent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1526-100X.1998.06402.x
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  • 5
    Electronic Resource
    Electronic Resource
    The relationship between zooplankton, conductivity and lake-water ionic composition in 111 lakes from the Interior Plateau of British Columbia, Canada (1996)
    Springer
    International journal of salt lake research 5 (1996), S. 1-15 
    Details
    ISSN: 1573-8590
    Keywords: conductivity ; relative abundance ; saline lakes ; zooplankton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geography
    Notes: Abstract Zooplankton collected from vertical net tows were related to the environmental variables from 98 lakes from the Interior Plateau of British Columbia. Canonical correspondence analysis showed that both salinity and ionic composition (pH and Mg) of the lake-water made major and significant contributions to the first two ordination axes (λ=0.42 and 0.11 respectively,P〈0.05). BothArtemia franciscana andMoina hutchinsoni had their highest relative abundance in meso-hypersaline waters. However,Artemia franciscana preferred waters that were higher in Mg and Ca, whileMoina hutchinsoni was found in waters that were lower in Mg and Ca. Similarly, at intermediate salinities,Daphnia pulex and the calanoid copepods preferred waters slightly lower in Mg and Ca, whereasCeriodaphnia laticaudata andSimocephalus spp. were relatively more common in waters higher in Mg and Ca. Because the freshest lakes studied varied much less in ionic composition, the zooplankton in these lakes did not show a preference to ionic composition. As expected, multi-generic groups, such as the calanoid copepods, cyclopoid copepods and nauplii, had wider tolerances to conductivity than groups identified to lower taxonomic levels. Significant weighted-averaging regression and calibration models of conductivity were developed based on zooplankton species composition from the study lakes (r 2=0.56,P〈0.05). Samples composed largely of multi-generic taxa yielded the worst estimates of salinity in the reconstruction model. This study suggests that zooplankton community composition may be developed into a useful proxy for paleosalinity reconstruction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01996032
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  • 6
    Electronic Resource
    Electronic Resource
    Greater drought intensity and frequency before AD 1200 in the Northern Great Plains, USA (1996)
    [s.l.] : Nature Publishing Group
    Nature 384 (1996), S. 552-554 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The present-day climate of the Northern Great Plains (NGP, shaded area in Fig. 1) is highly variable as a result of its continental location and the changing influence of major air masses of differing characteristics: (1) warm dry flow from the Pacific, (2) cold dry air from the Arctic, and (3) ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/384552a0
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  • 7
    Electronic Resource
    Electronic Resource
    Conference announcement The 8th International Symposium on Paleolimnology will be held at Queen's University, Kingston, Ontario, Canada during the week of August 20, 2000 (1999)
    Springer
    Journal of paleolimnology 22 (1999), S. 225-225 
    Details
    ISSN: 1573-0417
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008197218951
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  • 8
    Electronic Resource
    Electronic Resource
    Diatom assemblages from Adirondack lakes (New York, USA) and the development of inference models for retrospective environmental assessment (1993)
    Springer
    Journal of paleolimnology 8 (1993), S. 27-47 
    Details
    ISSN: 1573-0417
    Keywords: Diatoms ; Adirondack Park ; detrended canonical correspondence analysis ; canonical correspondence analysis ; weighted-averaging ; lake acidification ; pH ; monomeric aluminum ; dissolved organic carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Detrended canonical coreespondence analysis (DCCA) was used to examine the relationships between diatom species distributions and environmental variables from 62 drainage lakes in the Adirondack region, New York (USA). The contribution of lakewater pH, Alm (monomeric Al), NH4, maximum depth, Mg, and DOC (dissolved organic carbon) were statistically significant in explaining the patterns of variation in the diatom species composition. Twenty-three and sixteen diatom taxa were identified as potential indicator species for pH and Alm, respectively (i.e. a taxon with a strong statistical relationship to the environmental variable of interest, a well defined optimum, and a narrow tolerance to the variable of interest). Using weighted-averaging regression and calibration, predictive models were developed to infer lakewater pH (r 2=0.91), Alm (r 2=0.83), DOC (dissolved organic carbon) (r 2=0.64), and ANC (acid neutralizing capacity; r 2=0.90). These variables are of key importance in understanding watershed acidification processes. These predictive models have been used in the PIRLA-II (Paleoecological Investigation of Recent Lake Acidification-II) project to answer policy-related questions concerning acidification, recovery, and fisheries loss.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210056
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  • 9
    Electronic Resource
    Electronic Resource
    Diatom-salinity relationships in 111 lakes from the Interior Plateau of British Columbia, Canada: the development of diatom-based models for paleosalinity reconstructions (1994)
    Springer
    Journal of paleolimnology 12 (1994), S. 197-221 
    Details
    ISSN: 1573-0417
    Keywords: diatoms ; paleolimnology ; paleoclimatology ; salinity ; athalassic ; British Columbia ; CCA ; transfer function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatoms were identified and enumerated from the surface sediments of 111 lakes, 45 from the Kamloops region and 66 from the Cariboo/Chilcotin region, located on the southern Interior Plateau of British Columbia, Canada. This paper is an extension of another study which investigated the relationship of diatoms to salinity and ionic composition in 65 lakes from the Cariboo/Chilcotin region. The 111 lakes spanned a large gradient in salinity, ranging from fresh through hypersaline (late-summer salinity values ranged from 0.04 to 369 g l−1), and included both carbonate- and sulphate-dominated lakes with sodium and magnesium as the dominant cations. The Kamloops region had more sulphate-dominated, hypersaline lakes and fewer carbonate-rich lakes than the Cariboo/Chilcotin region. Most lakes had higher salinities in the late-summer compared to the spring. Both salinity and brine-type were important variables that could explain the different diatom assemblages present in the lakes. The majority of diatom taxa had salinity optima in the freshwater to subsaline range (〈3 g l−1), and the taxa displayed a range of both narrow and broad tolerances along the salinity gradient. Weighted-averaging regression and calibration, and maximum likelihood techniques were used to develop salinity inference models from the diatom assemblages based on their relationship to the spring, late-summer and average lakewater salinity measurements. Simple weighted-averaging (WA) models generally produced the same or lower bootstrapped RMSEs of prediction than weighted-averaging with tolerance downweighting (WA(tol)) in the two regional and the combined datasets. Weighted averaging partial least squares (WA-PLS) showed little or no improvement in the predictive abilities of the datasets, as judged by the jackknifed RMSE of prediction. In all cases, the combined dataset of 102 lakes performed better than either of the smaller regional datasets, with relatively little difference between spring, average and late-summer salinity models. The maximum likelihood models gave lower apparent RMSEs of prediction in comparison to other methods; however, independent validation of this technique using methods such as bootstrapping were not undertaken because of the computer intensive nature of such analyses. These diatom-based salinity models are now available for reconstructing salinity and climatic trends from appropriately chosen closed-basin lakes in the Interior region of British Columbia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00678021
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  • 10
    Electronic Resource
    Electronic Resource
    Variability in diatom and chrysophyte assemblages and inferred pH: paleolimnological studies of Big Moose Lake, New York, USA (1991)
    Springer
    Journal of paleolimnology 5 (1991), S. 267-284 
    Details
    ISSN: 1573-0417
    Keywords: variability ; diatoms ; chrysophytes ; acidification ; paleolimnology ; Adirondacks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We measured variability in the composition of diatom and chrysophyte assemblages, and the pH inferred from these assemblages, in sediment samples from Big Moose Lake, in the Adirondack Mountains of New York. Replicate samples were analyzed from (1) a single sediment core interval, (2) 12 different intervals from each of 3 separate cores, and (3) 10 widely spaced surface sediment samples (0–1 cm). The variability associated with sample preparation (subsampling, processing, and counting) was relatively small compared to between-core and within-lake variability. The relative abundances of the dominant diatom taxa varied to a greater extent than those of the chrysophyte scale assemblages. Standard deviations of pH inferences for multiple counts from the same sediment interval from diatom, chrysophyte, and diatom plus chrysophyte inference equations were 0.04 (n=8), 0.06 (n=32), and 0.06 (n=8) of a pH unit, respectively. Stratigraphic analysis of diatoms and chrysophytes from three widely spaced pelagic sediment cores provided a similar record of lake acidification trends, although with slight differences in temporal rates of change. Average standard deviations of pH inferences from diatom, chrysophyte and diatom plus chrysophyte inference equations for eight sediment intervals representing similar time periods but in different cores were 0.10, 0.20, and 0.09 pH unit, respectively. Our data support the assumption that a single sediment core can provide an accurate representation of historical change in a lake. The major sources of diatom variability in the surface sediments (i.e., top 1.0 cm) were (1) differences in diatom assemblage contributions from benthic and littoral sources, and (2) the rapid change in assemblage composition with sediment depth, which is characteristic of recently acidified lakes. Because scaled chrysophytes are exclusively planktonic, their spatial distribution in lake sediments is less variable than the diatom assemblages. Standard deviations of pH inferences for 10 widely spaced surface sediment samples from diatom, chrysophyte and diatom plus chrysophyte inference equations were 0.21, 0.09, and 0.16 of a pH unit, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00200350
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