抄録
Nitrogen and phosphorus concentrations, phytoplankton, primary production, total community respiration, and sediment were studied during 1977-1931 in Mikawa Pay, one of the representative bays which have been highly eutrophic for the last ten years in central Japan.
Oxygen and carbon balances were presented on the interrelations during stagnation period, June-August 1931 as follows : The range of gross production varied from 7.1 to 41.9 gO2/m2/day with an average rate of 17.7 gO2/m2/day (6.6 gC/m2/day), and less than one half of the total fixation was consumed by phytoplankton itself. Mean daily net production, therefore, was estimated to be about 9.4 gO2/m2/day (3.5 gC/m2/day). Community respiration, being due to heterotrophic organisms, ranged from 3.2 to 20.9 gO2/m2/day with an average rate of 3.6 gO2/m2/day (3.2 gC/m2/day) in the euphotic zone, which contributed about 90 % of the nutrient sources required for the mean net production. Mean daily sedimentaion rates in terms of COD and organic carbon were 0.52 gO2/m2/day and 0.54 gC/m2/day, respectively. The flux of sedimentation was only 5-6 % and about 15 % of the mean net production, in terms of oxygen and carbon, respectively. From these results, it was suggested that regeneration of nutrients by heterotrophic organisms is of the greatest importance in maintaining the primary production.
Nitrogen and phosphorus concentrations, requiring to increase COD by 1 mg/l, were equivalent to 0.166 and 0.026 mg/l, respectively. On the basis of the assessment, total nitrogen levels, regulating the environmental quality standard in a shallow bay, were also discussed.
