Dynamics of particulate matter near the mouth of influx river in Takahamairi Bay of Lake Kasumigaura, with special reference to nitrogen and phosphorus.

Abstract

To understand the dynamic changes in water quality near the mouth of influx rivers (lake estuary), two kinds of surveys were performed in Takahamairi Bay of Lake Kasumigaura. The first survey was the regular water sampling mainly to measure carbon, nitrogen, phosphorus, and metal compositions of particulate matter, and then to analyze the mutual relationships. Three-component model (comprised of soil particles, allochthonous organic matter, and autochthonous matter) on the basis of Ti and chlorophyll-a compositions was successfully applied for the explanations of the longitudinal distribution of phosphorus content, which had relatively different characteristics from those of organic carbon, organic nitrogen. Besides, the varia-tions in some compositions could be accounted for by the meteorological, hydraulic conditions. As for the second survey, the dynamics of nitrogen, phosphorus, and other water qualities were described for the direct runoff period due to a rainfall of 23 mm. Through budgetary calculation, it was elucidated that 40% of the total load for a stormy period and 55% on a dry weather day were trapped in the lake estuary. Hence, these surveys indicate that the behavior of particulate matter in lake estuary affects greatly the fate of influent nitrogen and phosphorus in whole lake.