Studies on biological metabolism in a meromictic Lake Suigetsu

Abstract

Lake Suigetsu is a typical meromictic lake having a deep anoxic layer from 8 m to the bottom at 34 m depth. Large accumulations of sulfide, total CO2, phosphate and ammonium were observed in the deep layer. In August, two photosynthesis maxima, caused by the activity of phytoplankton and photosynthetic sulfur bacteria, were observed at the surface and the boundary between aerobic and anoxic layers respectively. In December, a marked dark carbon fixation was observed at the boundary layer, although there was no indication of bacterial photosynthesis. Sulfate reduction was found only in bottom mud, especially near the surface of sediment. Carbon and sulfur cycles and their interrelation in the anoxic layer are discussed.