Limnological of the Mikata Lake Group.

Abstract

Some limnological features are studied of the Mikata Lake Group consisting of four lakes, Mikata, Suigetsu, Hiruga and Kugushi, and of the influence of the neighboring three out of them on the biological metabolism in a meromictic Lake Suigetsu. Both lakes, Hiruga and Kugushi, which open to the sea, contain a large amount of salt water, while Lake Mikata, situated in the innermost part of the group, is fresh water. Meromixis of Lake Suigetsu, situated in the center, results from the entry of two different waters, fresh water through Lake Mikata and salt water through the lakes of Hiruga and Kugushi. The deeper salt water of Lake Suigetsu stagnates. The mean resident time of salt water is estimated as 20-40 years. On the lake bottom, sulfate oxygen is used for bacterial decomposition of organic matter, because the circulatory supply of upper oxygen-containing water is quite limited, and as a result high concentrations of sulfide, total carbon dioxide and ammonium accumulate in the deeper water. In the boundary layer between the upper fresh and the deeper anoxic salt water, a marked photo- and chemosynthetic carbon assimilation takes place by sulfur bacteria using the sulfide and other decomposition products supplied from the bottom. The supply of organic matter from Lake Mikata and the inflow of sulfate-containing salt water through the lakes of Hiruga and Kugushi are indispensable for biological metabolism in Lake Suigetsu.