Abstract:

Based on the systematic determination of nitrogen (N) and phosphorus (P) concentrations in Poyang Lake water，the main river water，Yangtze River water，and some agricultural drainage，groundwater and urban sewage at August 2005(high water period)，the concentration variations of nitrogen and phosphorus and their sources were investigated.The results showed that NO-3N dominated in the forms of nitrogen in Poyang Lake，most of those came from Ganjiang River.The mean concentration of NO-3N was 090 mg/L and the mean content of total nitrogen (TN) was 104 mg/L in Poyang Lake.Among the main five river，the highest concentration of NO-3N was found in Ganjiang River，the highest concentrations of NH+4N and TN were found in Raohe River and the concentrations of TP is highest in Xinjiang River.The nitrogen and phosphorus concentrations of agricultural drainage，groundwater and urban sewage were very high，which were the main sources of Poyang Lake catchments.The mean concentration of TN and total phosphorus (TP) was 1347 and 2863 mg/L respectively in agricultural drainage.The mean content of NO-3N was 735 mg/L in groundwater and the mean concentration of NH+4N was 548 mg/L in urban sewage.The loads of nitrogen were very high in Poyang Lake water，and the ratio of N/P more than 7.The content of nitrogen was increasing along the water flow direction in the main riverway of Poyang Lake，which is due to the recharge from the stagnant area and the inflow of Ganjiang River and Xiushui River.The highest nitrogen concentration was in the downflow water，followed by in the stagnant area，and the lowest was in the main upstream riverway.But the content of phosphorus showed an adverse trend，the lowest was in the downflow water.The concentrations of NO-3N，NH+4N，TN and TP were higher in surface water than in bottom water due to the degradation of sedimentary organic matters and disturbance.

Key words: nitrogen, phosphorus, eutrophication, high water period, Poyang Lake