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  • 1
    Electronic Resource
    Electronic Resource
    Interpretation of sulfur cycling in two catchments in the Black Forest (Germany) using stable sulfur and oxygen isotope data (1995)
    Springer
    Biogeochemistry 30 (1995), S. 31-58 
    Details
    ISSN: 1573-515X
    Keywords: Catchment ; isotope fractionation ; sulfur cycling ; stable isotopes ; δ34S ; δ18Osulfate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The isotopic composition of SO 4 2- in bulk precipitation, canopy throughfall, seepage water at three different soil depths, stream water, and groundwater was monitored in two forested catchments in the Black Forest (Germany) between November 1989 and February 1992. Isotope measurements on aqueous sulfate were complemented by δ34S-analyses on SO2 in the air, total sulfur and inorganic sulfate in the soil, and bedrock sulfur, in order to identify sources and biogeochemical processes affecting S cycling in catchments with base poor, siliceous bedrock. Stable S isotope data indicated that atmospheric deposition and not mineral weathering is the major source of S in both catchments since δ34S-values for sulfate in the soil, in seepage water, and in stream water were generally found to be similar to the mean δ34S-values of precipitation SO 4 2- (+2.1. However, δ18O-values of seepage water SO 4 2- at 30 cm and especially at 80 cm depth were depleted by several per mil with respect to those of the atmospheric deposition (+7.5 to +13.5. This indicates that in both catchments a considerable proportion of the seepage water SO 4 2- is derived from mineralization of carbon-bonded soil S and must therefore have cycled through the organic soil S pool. δ34S-values for different S compounds in the solid soil were found to differ markedly depending on S fraction and soil depth. Since atmospheric S deposition with rather constant δ34S-values was identified as the dominant S source in both catchments, this is interpreted as a result ofin situ isotope fractionation rather than admixture of isotopically different S. The differences between the δ34S-values of seepage water and soil sulfate and those of organic soil S compounds are consistent with a model in which SO 4 2- uptake by vegetation and soil microorganisms favours34SO 4 2- slightly, whereas during mineralization of organic soil S to aqueous SOSO 4 2- ,32S reacts preferentially. However, the data provide evidence for negligible isotope fractionation during physico-chemical S transformations such as adsorption/desorption in aerated forest soils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02181039
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  • 2
    Electronic Resource
    Electronic Resource
    Isotope ratios and concentrations of sulfur and nitrogen in needles and soils of Picea abies stands as influenced by atmospheric deposition of sulfur and nitrogen compounds (1994)
    Springer
    Plant and soil 164 (1994), S. 267-281 
    Details
    ISSN: 1573-5036
    Keywords: atmospheric deposition ; δ15N ; δ34S ; forest decline ; nitrogen ; Picea abies ; stable isotopes ; sulfur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Concentrations and natural isotope abundance of total sulfur and nitrogen as well as sulfate and nitrate concentrations were measured in needles of different age classes and in soil samples of different horizons from a healthy and a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), in order to study the fate of atmospheric depositions of sulfur and nitrogen compounds. The mean δ15N of the needles ranged between −3.7 and −2.1 ‰ and for δ34S a range between −0.4 and +0.9 ‰ was observed. δ34S and sulfur concentrations in the needles of both stands increased continuously with needle age and thus, were closely correlated. The δ15N values of the needles showed an initial decrease followed by an increase with needle age. The healthy stand showed more negative δ15N values in old needles than the declining stand. Nitrogen concentrations decreased with needle age. For soil samples at both sites the mean δ15N and δ34S values increased from −3 ‰ (δ15N) or +0.9 ‰ (δ34S) in the uppermost organic layer to about +4 ‰ (δ15N) or +4.5 ‰ (δ34S) in the mineral soil. This depth-dependent increase in abundance of 15N and 34S was accompanied by a decrease in total nitrogen and sulfur concentrations in the soil. δ15N values and nitrogen concentrations were closely correlated (slope −0.0061 ‰ δ15N per μmol eq N gdw −1), and δ34S values were linearly correlated with sulfur concentrations (slope −0.0576 ‰ δ34S per μmol eq S gdw −1). It follows that in the same soil samples sulfur concentrations were linearly correlated with the nitrogen concentrations (slope 0.0527), and δ34S values were linearly correlated with δ15N values (slope 0.459). A correlation of the sulfur and nitrogen isotope abundances on a Δ basis (which considers the different relative frequencies of 15N and 34S), however, revealed an isotope fractionation that was higher by a factor of 5 for sulfur than for nitrogen (slope 5.292). These correlations indicate a long term synchronous mineralization of organic nitrogen and sulfur compounds in the soil accompanied by element-specific isotope fractionations. Based on different sulfur isotope abundance of the soil (δ34S=0.9 ‰ for total sulfur of the organic layer was assumed to be equivalent to about −1.0 ‰ for soil sulfate) and of the atmospheric SO2 deposition (δ34S=2.0 ‰ at the healthy site and 2.3 ‰ at the declining site) the contribution of atmospheric SO2 to total sulfur of the needles was estimated. This contribution increased from about 20 % in current-year needles to more than 50 % in 3-year-old needles. The proportion of sulfur from atmospheric deposition was equivalent to the age dependent sulfate accumulation in the needles. In contrast to the accumulation of atmospheric sulfur compounds nitrogen compounds from atmospheric deposition were metabolized and were used for growth. The implications of both responses to atmospheric deposition are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010079
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