Abstract
In this paper, we have examined the cycle of carbon, nitrogen and phosphorus on the basis of the measurement of nutrients and primary production from 1978 to 1983, to elucidate the mechanism of eutrophication in the northern area of Hiroshima Bay.
It became clear that the pollution of water and sediment in this sea area associated with high primary productivity which produced organic matter (270 tC d-1) 15 times as much as the inflow of organic pollutants (as TOC). The contribution rates of inflow to the primary productivity for nitrogen and phosphorus were respectively 21 and 17%, and those of regeneration of nutrients from organic matter in the water column occupied 74 and 75%, respectively. The contribution rates of nutrients benthic fluxes to primary productivity were 5% for nitrogen and 8% for phosphorus. However, in summer, the nutrients release was equivalent to the influent. It was presumed that the turnover times of nitrogen and phosphorus were about 11 and 7 days respectively and the residence times were about 50 days, and that nitrogen and phosphorus were utilized the growth of phytoplankton repeatedly several times until these nutrients flowed out of this sea area.
