東京湾における窒素の分布,代謝と収支

抄録

Data on distributions of various forms of nitrogen in the Tokyo Bay waters during a 3-year period (1979-1981) are summarized. Ammonium and nitrate concentrations range from 0 to 50 μM, and show substantial seasonal or sporadic variation. Temporal change in river runoff is primarily responsible for the latter. On the other hand, urea concentrations fall within a narrow range of 0.1 to 1 μM, and do not show any seasonal trend. In summer, particulate organic nitrogen (PON) accounts for more than 70% of total nitrogen in the surface layer, and it decreases with depth. In winter, PON is minor (ca. 10%), and all forms of nitrogen exhibit vertically uniform distributions. Nitrogen- 15 tracer experiments disclose that, on an average, ammonium supports 69% of phyto-plankton growth, nitrate 28% and urea 3%. The nitrogen once taken up by phyto-plankton is rapidly regenerated within the water column. Only a small fraction of PON produced in the surface layer reaches the sea floor. These findings are consistent with the estimate of nitrogen budget presented by Matsumoto (1979).