On the water environmental capacity of Lake Songhua based on eutrophication threshold

通过对松花湖水体中浮游植物的绝对优势种——铜绿微囊藻(Microcystis aeruginosa)单藻株生长与磷、氮定量关系的室内模拟研究,得出松花湖富营养化发生的阈值为:总磷浓度0.065 mg/L,总氮浓度0.843 mg/L.利用风险分析理论和蒙特卡罗随机模拟方法,在分析2002-2004年松花湖水体中总磷和总氮浓度实际分布规律的基础上,提出了计算湖、库总磷和总氮水环境容量的不确定性方法.通过对松花湖磷、氮水环境容量的计算,得出松花湖流域总磷和总氮的最大允许排放量为2123.78 t/a和7018.82 t/a,为了使松花湖富营养化发生的概率在0.001以下,总磷和总氮需要分别削减3208.34 t/a和18648.91 t/a.;The water environmental capacity of phosphorus and nitrogen is an important factor to control water eutrophication in lakes/reservoirs. The quantitative connection between the growth of predominant species i. e. uniol-gat strain of Microcystis aeruginosa and the concentration of TP and TN in Lake Songhua was studied in the laboratory using simulation method. Results indicated that TP threshold is 0.065 mg/L, TN threshold is 0.843 mg/L in the Lake Songhua. Risk assessment theory and Monte Carlo method were employed to analyze the concentration distribution regulation of TP and TN in the lake based on the data from 2002 to 2004. The paper developed an uncertainty method to calculate water environmental capacity of TP and TN in lakes/reservoirs. Because the uncertainty method was based on water self-purification law, and it isn * t needed to calculate some parameters difficult to identify, such as the degradation coefficient of the pollutants. It is useful to calculate the water environmental capacity of TP and TN in the Lake Songhua with the uncertainty methods. The result indicated that the maximum permissible discharge amounts of TP and TN in the Lake Songhua watershed were 2123. 78 t/a and 7018. 82 t/a. In order to control that eutrophication probability in the Lake Songhua was below 0.001, amounts of TP and TN were need to decrease 3208.34 t/a and 18648.91 t/a, respectively.