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Organic sulphur fixation in freshwater lake sediments and the implication for US ratios
Author(s) -
Losher A.J.,
Kelts K.R.
Publication year - 1989
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/j.1365-3121.1989.tb00366.x
Subject(s) - sulfur , pyrite , sedimentary rock , anoxic waters , sediment , geology , environmental chemistry , sulfur cycle , organic matter , sulfate , geochemistry , oceanography , chemistry , ecology , paleontology , biology , organic chemistry
A comparative analysis of two sediment cores from perialpine lakes (L. Zürich and L. Geneva) helped to clarify pathways of sulphur fixation in freshwater sediments. Despite greater than three‐fold differences in lake water sulphate concentration equal amounts of sulphur are fixed in the sediments. The maximum sedimentary sulphur concentrations attain 1% (dry weight) which is similar to the sulphur content of modem, near‐shore marine sediments. This is also expressed in low C org /S tot ratios which range from 2.5–8. An analysis of the sulphur pools showed that organic sulphur compounds are the main components of the sedimentary sulphur, accounting for ˜ 80% and ˜ 60% of the total sulphur in Lakes Zürich and Geneva, respectively. The largest single sulphur pool is the sulphate‐esters, which comprise 40–60% of the total sedimentary sulphur. Substantial amounts of the organic sulphur compounds must be formed within the sediment by boundary‐layer microbial communities at the oxic‐anoxic transition zone. This possibly suggests rapid recycling of sulphur in suboxic zones. Because of low concentration of SO 2 4 ‐ ‐ in the watermass, the zone of sulphate reduction is very thin. This coupled with the mobility of some sulphide oxidizing microbial colonies (e.g. Beggiutoa ) potentially results in an almost complete recycling of the sulphur pool near the sediment‐water interface. Reduced sulphur caught in this cycling process is unavailable for sedimentary pyrite formation. The C org /S pyrite ratios for these sediments are thus high. If organically bound sulphur is not completely transformed into pyrite during late diagenesis, the C org / S pyrite ratio can serve as a sensitive indicator for the salinities of anaent depositional environments.