On the relation between vicissitude process of nutrition and the non-pointpollution load in a mountainous lake under restricted phosphorus nutrition

基于流域非点源污染物负荷量与湖泊营养状况的关系，研究了山区湖泊营养平衡的变迁过程。研究在小野川山区湖泊进行，该湖泊具有典型的中营养化和分层条件。首先对小野川湖流域的污染负荷进行了估算。流域自然负荷和湖泊内部负荷估计大于流域的人工污染。夏季低氯离子的内负荷显著，特别是一次降雨的密度流带来的氨氮和硝态氮。因此，认识到该湖泊的非点源污染主要由硝酸盐组成。其次，用一维扩散微分方程近似了湖泊中氨的垂直分布。最后，对夏季湖泊热平衡进行了分析。因此，河流带来了负热通量，而上游湖泊的水流为正热通量，这种正热通量加速了分层的恢复。

This study focuses on the vicissitude process of nutritive balance in a mountainous lake based on the relation between amount of non-point pollutant load in the basin and nutritive condition of the lake. The study conducted in mountainous Lake Onogawa which have typical characteristics in condition with mesotrophic and stratification.At first, pollution load in the catchment-area of the lake Onogawa was estimated. Natural load of the basin and the inner load in hypoliminon of the lake estimated larger than the artificial pollution in the basin. Inner load of hypoli-minon in summer season, especially, ammonia and nitrate that brought by the density current of a rain was notable. So, it was recognized that the non-point pollution in this lake is mainly consisted of the nitrate.And next, the vertical distribution of ammonia in hypoliminon of the lake was approximated by the one-dimensional differential equation of diffusion.Finally, the heat balance of the lake in summer season was analyzed. So, the negative heat flux were brought by the river and the flow from the upper lake was given positive heat flux, it was recognized that the restoration of the stratification was accelerated by this positive heat flux.