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  • 1
    ISSN: 1573-515X
    Keywords: Dinitrogen fixation ; nitrogen ; phosphorus ; competition ; legumes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract An analysis of data compiled from the literature confirms a strong inverse relationship between annual rates of nitrogen fixation and the soil nitrogen content in agricultural and pastoral ecosystems. However, this inverse relationship is strongly modified by the rate of application of phosphorus fertilizer, which strongly influences the activities of both symbiotic and non-symbiotic nitrogen fixing organisms. In the case of symbiotic legumes, the response of N-fixation to N and P is in part a result of changes in legume dominance within the plant community. These results, as well as supporting data presented from a review of experiments on nitrogen fixation in a variety of other terrestrial and aquatic ecosystems, provide important support for the hypothesis that phosphorus availability is a key regulator of nitrogen biogeochemistry.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 18 (1992), S. 37-51 
    ISSN: 1573-515X
    Keywords: carbon dioxide ; microhabitat ; peat ; temperature ; water table
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Soil surface CO2 flux was measured in hollow and hummock microhabitats in a peatland in north central Minnesota from June to October in 1991. We used a closed infrared gas exchange system to measure soil CO2 flux. The rates of CO2 evolution from hummocks (9.8 ± 3.5 g m−2 d−1, [mean ± SE]) were consistently higher than those from hollows (5.4 ± 2.9 g m−2 d−1) (the hummock values included the contribution of moss dark respiration, which may account for 10–20% of the total measured flux). The soil CO2 flux was strongly temperature-dependent (Q10 ≈ 3.7) and appeared to be linearly related to changes in water table depth. An empirical multiplicative model, using peat temperature and water table depth as independent variables, explained about 81% of the variance in the CO2 flux data. Using the empirical model with measurements of peat temperature and estimates of hollow/hummock microtopographic distribution (relative to water table elevation), daily rates of “site-averaged” CO2 evolution were calculated. For the six-month period (May–October), the total soil CO2 released from this ecosystem was estimated to be about 1340 g CO2 m−2.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-515X
    Keywords: freshwater ; sulfate reduction ; sulfur oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO4 2− reduction rates in the sediment, (2) depletion of SO4 2− in the overlying water column and (3) release of35S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO4 2− in the overlying water. Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core35SO4 2− injection. Rates of SO4 2− consumption in the overlying water were estimated by changes in SO4 2− concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m−2 d−1. Rates of SO4 2− uptake from the enclosed water column varied from −0.5, −0.3 mmol m−2 d−1 (November) to 0.43–1.81 mmol m−2 d−1 (July, August and April). Maximum rates of oxidation to SO4 2− in July 1990 estimated by combination of SO4 2− reduction rates and rates of in situ SO4 2− uptake in the enclosed water column were 10.3 and 10.5 mmol m−2 d−1 at an organic rich and at a sandy site respectively. Experiments with35S2− and35SO4 2− tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO4 2− and (2) the presence of mainly non SO4 2−-S derived from reduced S transported from the sediment into the overlying water. A35S2− tracer experiment showed that about 7% of35S2− injected at 1 cm depth in a sediment core was recovered in the overlying water column. Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.
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  • 4
    ISSN: 1573-515X
    Keywords: denitrification ; nitrification ; nitrous oxide ; rain forest ; riparian ; solute transport ; tropical
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Fluxes of N2O at the soil surface, dissolved N2O in near-surface groundwater, and potential N2O production rates were measured across riparian catenas in two rain forest watersheds in Puerto Rico. In the Icacos watershed, mean N2O fluxes were highest at topographic breaks in the landscape (≃ 40–300 μg N2O­N m−2 h−1). At other locations in the riparian zone and hillslope, fluxes were lower (⩽ 2 μg N2O­N m−2 h−1). This pattern of surface N2O fluxes was persistent. In the Bisley watershed, mean suface N2O fluxes were lower (〈40 μg N2O­N m−2 h−1) and no identifiable spatial or temporal pattern. Although the spatial patterns and intensities of N2O emissions differed between the two watersheds, surface soils from both sites had a high potential to reduce NO3 to N2O (and perhaps N2). This potential declined sharply with depth as did soil %C, %N, and potential N-mineralization. Simple controls on denitrification (i.e. aeration, nitrate, and carbon) explained characteristics of potential N2O production in surface and deep soils from riparian and upslope locations. In the field, spatial patterns in these controlling variables were defined by geomorphological differences between the two watersheds, which then explained the spatial patterns of observed N2O flux
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 19 (1992), S. 195-195 
    ISSN: 1573-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 19 (1992), S. 203-203 
    ISSN: 1573-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 19 (1992), S. 204-204 
    ISSN: 1573-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 19 (1992), S. 149-172 
    ISSN: 1573-515X
    Keywords: anoxic ; decomposition ; hypolimnetic budgets ; lake ; oxygen ; redox reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract During a three year study (1985–1987) we used a mass balance approach to study the oxidation and reduction reactions related to decomposition of organic carbon in Mirror Lake, New Hampshire. The stoichiometry of the reactions allows us to calculate an electron transfer budget for the summer stratification period in the lake, as well as in benthic chambers and sealed jars. The average decomposition rate measured as dissolved inorganic carbon (DIC) production was 5.33 mmol m−2 d−1. The proportions of decomposition accounted for by the various electron acceptors varied both during the summer, as well as from year to year. On average, oxygen accounted for 43% of DIC production, while the processes involving sulfate, nitrate, iron and methane formation together accounted for 20%. Despite conservative assumptions we could not account for 37% of the DIC production. The general pattern, including excess DIC production, was also observed in chamber studies conducted over shallow-water sediments and in sealed-jar experiments. Data on burial rates of reduced iron minerals indicate that such minerals are not sufficient to account for the discrepancy in the electron budget. Our analysis suggests that another electron acceptor such as organic carbon reduction, either via fermentation or selective oxidation, is the most likely explanation of excess DIC production.
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  • 9
    ISSN: 1573-515X
    Keywords: Carbon ; climate ; forests ; landscape ecology ; nitrogen ; productivity ; soil moisture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The interactions between the biotic processes of reproduction, growth, and death and the abiotic processes which regulate temperature and water availability, and the interplay between the biotic and abiotic processes regulating N and light availabilities are important in the dynamics of forest ecosystems. We have developed a computer simulation that assembles a model ecosystem which links these biotic and abiotic interactions through equations that predict decomposition processes, actual evapo-transpiration, soil water balance, nutrient uptake, growth of trees, and light penetration through the canopy. The equations and parameters are derived directly from field studies and observations of forests in eastern North America, resulting in a model that can make accurate quantitative predictions of biomass accumulation, N availability, soil humus development and net primary production.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract An extensive network of bottle/funnel collectors was used to measure hydrologic, SO4 2−, and NO3 − fluxes in rain events and in throughfall beneath the canopies of several high elevation forest stands in the Great Smoky Mountains National Park during 1989–1990. The throughfall fluxes were used as deposition surrogates to quantify trends in atmospheric inputs to sapling trees growing in forest gaps and to the mature forest canopy at the edge surrounding each gap. The paired gap/edge stands were located above (1940 m) and below (1720 m) the base of the clouds typically impacting this mountain. Total hydrologic and ion fluxes beneath the edge trees during the forest growing season exceeded fluxes beneath the adjacent gap saplings by nearly a factor of three (e.g. 230 vs 88 meq m−2 for SO4 2−) at both elevations. Water and SO4 2− fluxes were up to two times greater beneath the forest edge at the cloud-prone 1940 m site than at 1720 m (e.g. 230 vs 110 meq m−2 for SO4 −2). However, throughfall NO3 − fluxes were about 30% higher at 1720 m (17 vs 13 meq m−2), because this lower site receives greater dry deposition of HNO3 due to its ridgetop location and greater wind penetration. Estimates of SO4 2−; deposition from cloud impaction were consistent with the net throughfall flux of SO4 2− (throughfall flux minus rain flux) at the 1940 m forest edge, but greatly exceeded the net throughfall flux at 1940 m gap, suggesting differences in ion concentrations in cloud droplets impacting on mature edge trees and young saplings in forest gaps.
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