Seasonal Changes in Sulfate Reduction in Sediments in the Inner Part of Tokyo Bay.

Abstract

In highly eutrophicated Tokyo Bay, anoxic, sulfide-containing bottom water is formed in warm stagnant seasons. It seems to develop especially in the northeast area where there are many large holes made by dredging to collect sand in addition to navigation channels. At such dredged sites, the seasonal variation in the rate of sulfate reduction in sediment was examined by a radiotracer method together with various environmental factors for two years and the results were compared with those obtained at a site on the natural sea floor. The rate of sulfate reduction was much higher at the dredged sites than on the natural sea floor. The dissolved oxygen concentration in bottom water and sulfate concentration in the sediment layer were lower, and the density of sulfate-reducing bacteria and acid-volatile sulfides were higher at the dredged sites than the natural floor site. However, there was no significant correlation between the sulfate reduction rate and any of the environmental factors examined (temperature, ignition loss, DO in bottom water and density of sulfate-reducing bacteria). The rate on an area basis seemed to fluctuate in a similar pattern to the change of chlorophyll a in the water column. The addition of seston mainly composed of diatoms to the sediment sample greatly stimulated sulfate reduction in contrast to the addition of lactate. Sulfate reduction at these sites might be controlled by the supply of organic substrates especially those of algal origin.