| Summary: | A study on sulfur circulation in sediments wascarried out in dam reservoirs (Sulejów, Siemianówka, Turawa)with different hydrological and age characteristicsas well as with a different level of sediment accumulationand organic matter content.Differences in the isotopic composition of SO2−4 in the watercolumn and small variations in the concentration ofthis ion were observed in the Turawa reservoir. The investigationsdid not show vertical variation in the watercolumnconcentrations and isotopic composition. This isdue to the small depths of the reservoir and mixing of water.A part of sulfate sulfur from the water column is reducedby incorporating it into cell structures, while a partof it is deposited in the sediment. The study revealed asmall exchange of SO2−4 between thewater column and thesediment. Depending on the season of the year and thesediment sampling site, biogeochemical transformationsof sulfur species are observed.A significant variation in the biogeochemical processeswas found between the Siemianówka and Sulejów reservoirs,both in the concentrations and in the isotopic compositionof particular sulfur species. This primarily resultsfrom the different characteristics of either of these reservoirs(flows, sedimentation, and material discharge to thelake). The main source of sulfur supplied to the sedimentsin the Siemianówka reservoir is organic sulfur contained inorganic matter deposited at the bottom. In the sediment,organic sulfur is bacterially oxidized and fixed as SO2−4 .This is manifested in a substantial enrichment of sulfate in34S. The presence of polysulfides was found in both reservoirs,but a distinct depletion of δ34S(S2−) in the light sulfurisotope was observed in the Siemianówka reservoir. Ina part of the Sulejów reservoir, polysulfides are oxidized toSO2−4 ,probably at the sediment/water interface.
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