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Rapid depletion of dissolved organic sulphur (DOS) in freshwaters

Rapid depletion of dissolved organic sulphur (DOS) in freshwaters Thumbnail


Abstract

Sulphur (S) is a key macronutrient for all organisms, with similar cellular requirements to that of phosphorus (P). Studies of S cycling have often focused on the inorganic fraction, however, there is strong evidence to suggest that freshwater microorganisms may also access dissolved organic S (DOS) compounds (e.g. S-containing amino acids). The aim of this study was to compare the relative concentration and depletion rates of organic 35S-labelled amino acids (cysteine, methionine) with inorganic S (Na235SO4) in oligotrophic versus mesotrophic river waters draining from low nutrient input and moderate nutrient input land uses respectively. Our results showed that inorganic SO42- was present in the water column at much higher concentrations than free amino acids. In contrast to SO42-, however, cysteine and methionine were both rapidly depleted from the mesotrophic and oligotrophic waters with a halving time < 1 h. Only a small proportion of the DOS removed from solution was mineralized and excreted as SO42- (< 16% of the total taken up) suggesting that the DOS could be satisfying a demand for carbon (C) and S. In conclusion, even though inorganic S was abundant in freshwater, it appears that the aquatic communities retained the capacity to take up and assimilate DOS.

Acceptance Date Apr 26, 2020
Publication Date May 2, 2020
Publicly Available Date Mar 29, 2024
Journal Biogeochemistry
Print ISSN 0168-2563
Publisher Springer Verlag
Pages 105 - 113
DOI https://doi.org/10.1007/s10533-020-00669-4
Keywords Dissolved organic matter
DOS processing
Nutrient cycling
Radioisotopes
Sulphate
Publisher URL https://link.springer.com/article/10.1007%2Fs10533-020-00669-4

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