Yatsuka Saijo

Studies on biological metabolism in a meromictic Lake Suigetsu

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.

In situ measurement of oxygen consumption rate in the bottom layer in Mikawa Bay

Direct estimation of the oxygen consumption rate in the bottom layer of Mikawa Bay where eutrophication is in progress was attempted usingin situ continuous measurement of oxygen content and other oceanographic parameters including water movement, and a value 0.65 mgl−1 day−1 was obtained in summer. This value is slightly smaller than previous estimates based on the method of incubation or indirect techniques.

Urea supply from decomposition and excretion of zooplankton

Rates of urea supply from the decomposition and the excretion of zooplankton were determined for samples collected in Suruga Bay. Five species of Zooplankton were incubated in filtered seawater at 20‡C for 276 hrs after being forced to die in a refrigerator. More than 77.6 % of body nitrogen of the Zooplankton was liberated, except forEuphausia similis, which showed a lower decomposition rate of 53.0 %. In the liberated nitrogen. 4.8 to 9.8 % was determined as urea.Incubation experiments of two species of zooplankton at 13‡C during 12 hrs, showed that the organisms excreted 0.86 and 0.73Μg-at. N indi.−1 d−1 as total soluble nitrogen. Urea accounted for 8.3 and 6.8 % of the excreted total soluble nitrogen.

Biogeochemical studies in the sea

My studies on metabolism of organic matter in aquatic environments first involved research on the sedimentation process of organic matter in lacustrine environments. Subsequently, measurements of primary production in lake and sea water were undertaken to know the organic substance supply into the metabolism. After establishing the routine technique of productivity measurement in aquatic environment, the primary production and the photosynthetic characteristics in waters in the northwestern Pacific, the western Indian Ocean and the Antarctic Sea were studied. Following the development of new methods to determine the organic substances in the dissolved and particulate forms and chlorophyll pigment in seawater, their distributions both horizontal and vertical directions were determined. And I have had interest in the mechanism producing a subsurface chlorophyll maximum in the ocean.Recently, my major interest has been directed to the coastal waters. The nitrogen cycle was studied in oyster beds and the research on eutrophication processes in a shallow bay is being carried out from the aspect of production and decomposition of organic matter.