Some physicochemical features of a meromictic Lake Suigetsu

Physicochemical features of a typically meromictic lake, Lake Suigetsu, are studied. Vertical distributions of temperature and chlorinity show that the lake is well stratified, and no marked mixing occurs between the upper fresh water and lower salt water. In the chemocline, the vertical gradient of density is large, and the vertical eddy diffusion coefficient is as low as 1.5 × 10 −2 cm 2 sec. −1 Dissolved oxygen is saturated in the surface portion of the upper water, and then rapidly decreases with depth towards the chemocline, where sulfide first appears and increases towards the bottom. In the chemocline oxygen consumption is prominent process reaching 290 mg 0 2 /m 2 /day. The oxidation of sulfide, supplied from the underlying water layer, is the main factor causing the oxygen consumption in the chemocline.