Biogeochemistry of dimethylsulfide in a seasonally stratified coastal salt pond

Dimethylsulfide (DMS) is the major volatile reduced organic sulfur compound in the water column of coastal Salt Pond, Cape Cod, MA. DMS concentration and vertical distributions vary seasonally in response to changing biogeochemical processes in the pond. When the pond is thermally stratified in summer, maximum DMS concentrations of up to 60 nmol/l were found in the oxygen-deficient metalimnion. DMS concentrations in the epilimnion (typically 5-10 nmol/l) were always an order of magnitude higher than in the hypolimnion (less than 0.2 nmol/l). The most likely precursor for DMS is algal dimethylsulfoniopropionate (DMSP), which showed vertical profiles similar to those of DMS. Laboratory experiments show that microorganisms in the pond, especially in the metalimnion, are capable of decomposing DMSP to DMS, while photosynthetic sulfur bacteria in the hypolimnion can consume DMS. Estimates of DMS production and consumption in Salt Pond have been made, considering production of DMS in the epilimnion and metalimnion and removal of DMS via gas exchange to the atmosphere, tidal exchange, and microbial consumption in the hypolimnion.