Microbial Geochemistry Of Sulfur Transformations In Typical Lake Sediments At Fildes Peninsula,Antarctic

Sulfur is an important nutrient element,and its biogeochemical transformation and recycling play an important role in maintaining the function of aquatic ecosystems.Sulfur biogeochemistry is coupled closely with a series of important ecological and environmental processes,such as the remineralization of organic matter,acidification of water bodies,formation of biogenic pyrite and control of trace metal bioavailability in aquatic environments.It is of great scientific value and significance to study the biogeochemical transformation and cycle of sulfur for understanding the coupling cycle of nutrient in the circle layer,the function transformation of source and sink,and the driving mechanism of global cycle of elements.In our previous studies,we analyzed the various sulfur species and ratio(RIS/SO₄^2-)in an ornithogenic sediment（Y2）from Ardley Island and a pristine lake sediment（YO）from Fildes Peninsula,Antarctic and discussed the sulfate reduction and its restriction on the bioavailability of trace metals.The specific transformations of sulfur in such aquatic ecosystems,however,remain unclear.In the present study,we analyzed the sulfur cycle-related bacterial genus,sulfur isotope of sulfides(δ³⁴S_AVSandδ³⁴S_CRS),sulfur and oxygen isotopes of sulfate(δ³⁴S_SO4andδ¹⁸O_SO4),sulfur isotope of organic sulfur(δ³⁴S_org),degree of pyritization（DOP）and degree of sulfurization（DOS）in sediments,in order to study the diverse transformations of sulfur and their relationships with iron sulfides.We obtain the following results and conclusions.（1）Microbial communities,sulfur isotope of sulfides(δ³⁴S_AVSandδ³⁴S_CRS)and sulfur and oxygen isotopes of sulfate(δ³⁴S_SO4andδ¹⁸O_SO4)in sediments were analyzed to study and reveal the biogeochemical transformations of sulfur in a penguin-affected lake Y2 and a pristine YO from Fildes Peninsula,Antarctic Peninsula.The microbial communities in Y2 were mainly associated with penguin activities,while those in YO were limited by nutrients.The much enrichedδ³⁴S_SO4recorded at depth of 30,41 and 52 cm in Y2 indicates very strong sulfate reduction therein.The sulfur-degrading bacteria Pseudomonas in 0–23 cm of Y2 was 3.5 times as abundant as that of sulfur oxidizing bacteria（SOB）,indicating remarkable remineralization of organic sulfur.While abundant SOB and 34S-depleted sulfate indicate considerable sulfur oxidation in 34–56 cm layer in Y2.In YO sediments,the highest abundance of Desulfotalea and the most enrichedδ³⁴S_SO4（35.2‰）andδ³⁴S_CRS（2.5‰）indicate strongest sulfate reduction in 28 cm layer.High abundance of Pseudomonas indicates active remineralization of organic sulfur in 3–5 cm layer in YO.While the mediumδ³⁴S_SO4and considerable abundance of SOB and SRB indicate concurrence of sulfur oxidation and sulfate reduction in other layers in YO.Our results show that high level of organic matter inputs from penguin populations support the diverse microbial community and transformations of sulfur in freshwater ecosystems in Antarctica.（2）The depleted ³⁴S_orgvalues in Y2 sediments of 1–15 cm indicated a high proportion of ³⁴S-depleted diagenetic organic sulfur(S_diag)in total sulfur.Meanwhile,the high DOS in Y2 sediments of 8–15 cm indicated a concurrent sulfurization of iron and the organic matter,likely due to the high available of active iron in this layer.The observed much enrichedδ³⁴S_orgin Y2 sediments of 48–56 cm corresponding to the period of high penguin populations,which indicated that large external inputs of penguin guanos result a rapid increase in 34S-enriched biological organic sulfur(S_bio)in the sediments,and exceeds the S_diagthat from the internal sulfur transformations.The depletedδ³⁴S_orgin YO sediment of 28 cm indicates a high proportion（95.4%）of34S-depleted S_diagwhich was from strong sulfurization of organic matter,corresponding to the strongest sulfate reduction in this layer.Meanwhile,the high DOP in YO sediment of 28 cm indicated a concurrent formation of CRS and the sulfurization of organic matter in this layer,due to the high available precursors of hydrogen sulfide and/or intermediate species of sulfur from the sulfate reduction.