Sulfur species in Rogoznica Lake

Reduced sulfur compounds were analyzed in the water column of a small sea lake, Rogoznica Lake, in dependence on the concentration of oxygen and organic matter, and temperature and salinity of the lake water. Cathodic stripping a.c. voltammetry was used to detect and quantify sulfur species. This is a direct method requiring no sample preparation. Rogoznica Lake was found rich with sulfur (up to 900 mu M), especially in the forms of sulfide and elemental sulfur. Anoxic water contained mainly sulfide (760 mu M) while in the oxic layer only trace amounts of elemental sulfur were found (4-30 nM). Relatively high concentrations (140 mu M) of elemental sulfur were found in the anoxic water too, which can be ascribed to the presence of polysulfide. It is known that due to biotic and abiotic processes the content and speciation of sulfur compounds in the samples change with time. Therefore, all samples were measured fresh, immediately after sampling. Additionally, we have investigated the influence of different preserving agents (formaldehyde, hydroxylamine and ascorbic acid) on electrochemical measurements and the concentration of sulfur. The best results were obtained with formaldehyde; the total concentration of sulfur was not changed in the sample within 7 days, while the ratio between elemental sulfur and sulfide was changed.