THE MAIN SOURCES OF NITROGEN AND PHOSPHORUS IN LAKE DONGHU, WUHAN
Zhang Shuiyuan, Liu Quxia and Huang Yaotong(Institute of Hydrobiology, Academia Sinica, Wuchang)
The annual input of the total dissolved nitrogen (N) was 536.3 t, corresponding to an average loading per unit area of 19.22 g/m2.a. The annual input of total dissolved phosphate (PO43-) was 87.8 t, corresponding to an average loading per unit area of 3.15 g/m2. a. Of the nitrogen loading, 59.2% was derived from domestic sewage and industrial wastewa-ter, 34.0% from terrestrial run-off and 6.8% from precipitation. Of the phosphorus loading, 74.7% come from domestic sewage and industrial wastewater, 24.2% from terrestrial run-off and only 1.1% from precipitation.The total outputs of nitrogen and phosphorus were 213.1 and 20.1 t/a respectively. 90.8% of the nitrogen and 51.7% of the phosphorus were removed through water supply, while 9.2% of the nitrogen and 48.3% of the phosphorus were removed through fish yielding and macrophyte harvesting.The differences between the influx and efflux of the nutrients were 323.2 t N/a and 67.7 t P/a, so that 60.3% N and 77,1% P of the total annual inputs were presumed to have been accumulated in the Jake.Based on the results, important factors causing eutrophication in Lake Donghu is given. Suggestions of measures to control lake eutrophication are presented as well.