Volatile organic sulfur compounds in a meromictic Alpine lake

The full spectrum of volatile sulfur compounds was detected in the water co lumn of the permanently stratified meromictic Lake Cadagno. Besides hydroge n sulfide it included methanethiol, carbonyl sulfide, dimethyl sulfide, car bon disulfide, and dimethyl disulfide. Their distribution in the water colu mn suggests that these compounds are of biogenic origin. Except for carbon disulfide which is present in all layers of Lake Cadagno, these volatile or ganic sulfur compounds are restricted to the anoxic part of the lake. For m ethanethiol, dimethyl sulfide, and carbon disulfide maximum concentrations were observed in the redox transition zone and in the sediment porewater. C arbon disulfide is the most abundant volatile organic sulfur compound with concentrations of up to 60 mu mol L-1. The concentrations of the methylated sulfides are in the nmolar range. Although their concentrations varied dur ing the summer months, seasonal trends of the concentrations of volatile or ganic sulfur compounds did not follow a consistent pattern. The restriction of most sulfur species to the anoxic layers of the lake indicates that the ir production originates from anaerobic microbial degradation of biomass an d not from its release from a specific precursor like dimethylsulfoniumprop ionate as in marine environments.