VERTICAL DISTRIBUTION AND ORGANIC MATTER PRODUCTION OF PHOTOSYNTHETIC SULFUR BACTERIA IN JAPANESE LAKES

Abstract

The role of photosynthetic sulfur bacteria as primary producers in stagnant lakes having hydrogen sulfide is described. Photosynthetic bacteria normally appear at the boundary layer of the oxidative and reductive zones, where H 2 S is present and the light intensity is lower than 10% of the surface value. The water of this layer was milky green or pink due to dense populations of Thiorhodaceae or Chlorobacteriaceae. The amount of photosynthetic bacterial biomass measured on a chlorophyll basis ranged from 100 to 828 mg/m 3 for Chl‐650, 60.7 to 79.5 mg/m 3 for Chl‐660, and 19.8 to 186 mg/m 3 for BChl in the growing period from July to October. In the lakes studied, organic matter was produced by phytoplankton in the epilimnion and mainly by photosynthetic sulfur bacteria in the reducing zone. The organic matter synthesized by these bacteria ranged from 9 to 25% of the total annual production in lakes rich in H 2 S and from about 3 to 5% in lakes poor in it.