Sulfate reduction processes in sediments at different sites in Lake Kinneret, Israel.

Lake Kinneret, Israel, is a warm (13-30°C) monomictic lake that stratifies in April and turns over in December. Between January and June each year, a heavy bloom (up to 250 g wet weight n(-2) 2) of the dinoflagellate Peridinium gatunense dominates the phytoplankton biomass. In early summer, the bloom collapses, and the sinking Peridinium biomass serves as a trigger for intense sulfate-reduction activity throughout the hypolimnion and within the sediments. The availability of organic matter and sulfate was high shortly after the bloom crash and the beginning of stratification and was lowest in December before overturn. Sulfate-reduction rates at three different sites in the lake were studied. In the sediments, the rates varied seasonally and among stations from 5 to 1600 nmol SO4 (-2) reduced cm(-3) day(-1), with respect to the distance from the Jordan River, depth, organic content, and stratification period. During years of low lake water levels, intense sulfate reduction occurred in the hypolimnion, resulting in anoxia and high concentrations of H2S (>400 μM). In years with high water levels, early bloom, and delayed stratification, higher rates of sulfate reduction were recorded in the sediments, probably as a result of a greater fraction of the primary production (organic matter) reaching the bottom.