Abstract
The present study attempts to determine the effects and limits of current water-quality preservation measures. The target region was the watershed of Lake Biwa. We also suggest future directions for watershed management.
The carrying capacity of COD, TN, TP of Lake Biwa estimated by multiplying the allowable concentration of pollutant loads by the volume of inflow. The allowable TN, TP concentration of inflow was determined using Vollenweider's model. Separately, the allowable COD concentration of inflow was determined by subtracting “produced COD concentration in the lake” from environment standard concentration.
The carrying capacity of Lake Biwa was estimated to be 1.4, 2.7, and 0.59kton·y-1 of COD, TN, and TP, respectively.
Under a scenario of an increasing number of pollution abatement measures, even under the strictest of scenarios, COD and TN loads would still surpass the carrying capacity by 4.6 and 1.8 times, respectively.
The results of the present study demonstrate that there is a limit to the degree to which the water quality at Lake Biwa can be controlled via the implementation of tichnological measures. Therefore, the concept of growth management, which rationalizes social economic activity itself within the watershed, is indispensable for future watershed management.
