The evaluation of influent pollutants load to the Southern basin of Lake Biwa

Abstract

The influent pollutants load have been estimated using the material balance model, based on the data for the Southern basin of Lake Biwa which have been collected at 10 to 30 days intervals from April 1976 to February 1980. The material balance model was used because the short term variation in thewater quarity of the lake appears to be small in comparison with the large and short term variationsobserved in the influent and to show the result of the load discharged over a long period.The lake is regarded as a complete mixing pond, where 6 conditions and 2 parameters are given. (Conditions; influent from the northern basin, rain load, decomposition, sedimentation, effluent to the Seta River and effluent to the Biwako artificial canal, Parameters; sedimentation and decomposition rate) As a result of the estimation under the constituent ratio of COD: N: P on the sediments, it is clear that the large amount of the total COD is supplied from the northern basin and the internal organic production (by phytoplankton etc.), and also the total quantity of Nitrogen almost equally from the rivers and the northern basin, and more than 50% of Phosphorus from the rives.