Establishment of the evaluation method of trade-off among various environmental aspects in the improving countermeasures of water environment

通过条件价值法，对改善水环境的收益进行了评估，结果为每年7.3亿日元。另一方面，产生的CO2等二次环境负荷的损失为2300万日元。这一对比证明了该湖水质改善的合理性。选择性实验表明，人们对野生动物保护的重视程度较低，对水环境改善的重视程度高于对死亡风险的降低。人类活动的分析表明，近30年来，进入琵琶湖的氮负荷减少了一半。经常的水质调查显示，非点源，如农田产生高负荷的降雨。这说明防止水土流失是减少营养盐入湖的有效途径。分析了路边空气中多环芳烃浓度与交通量的相关性。对广岛湾生态系统和饮用水中化学物质的风险进行了评价。分析了多环芳烃和丁基锡的入湖量与入湖量的关系。这两个人的意见比较一致。近几年来，在Suwa湖，藻类水华的爆发减少，蚊子的生存量也明显下降。此外，事实证明，随着20世纪70年代污染最严重的高峰，鱼类捕捞量的减少正在加强。虽然水质改善进展的下水道建设在Suwa湖，非点源负荷的贡献的百分比增加。

Benefit of water environmental improvement of Lake Suwa was evaluated to be 730 million Yen per year by Contingent Valuation Method. On the other hand, the damage of secondary environmental loads, such as CO2 generated was 23 million Yen. This comparison justifies the water improvement of this lake. Choice experiments showed that people give low value to protection of wildlife, and the water environmental improvement was esteemed be higher than mortal risk reduction. The analysis or human activities showed that the nitrogen load to Lake Suwa was reduced by half in the past 30 years. Frequent survey of water quality revealed that non-point source like the cropland generates high loading with rainfall. This shows that prevention of soil erosion is effective method to reduce nutrient loading to this lake. The correlation between concentration of PAHs in roadside and amount of traffic was analyzed. The risk of chemical substances in the ecosystem and drinking water in Hiroshima Bay was evaluated. The relation between the amount of loading from the basin, and the amount of deposition in the lake was analyzed for poly aromatic hydrocarbon and butyl tin. These two were comparatively well in agreement. In Lake Suwa, outbreak of algal bloom decreased in recent years and the amount of existing of mosquito fell remarkably. Moreover, it turns out that reduction of a fish catch is being enhanced with a peak of the 1970s which were the severest as for contamination. Although water quality improvement progressed by construction of a sewer in Lake Suwa, the percentage of contribution of the load from non-point source increased.