中文摘要：

阳澄湖丰水期和枯水期水质调查结果显示：TN、叶绿素、TP和CODMn丰枯期都呈从西湖区向东湖区递减趋势，且一般枯水期大于丰水期，TP反之；丰枯期水质均较差，为Ⅳ类或劣V类，污染物主要为TN和TP；富营养化加重趋势有所缓解，但水体仍呈富营养化状态。氮磷来源分析表明：丰枯期NO3^-N、NO2--N与TN以及丰水期PO4^3-P与TP有显著正相关关系。叶绿素浓度与TN在枯水期有显著相关性，其他时期叶绿素浓度与TN、TP的相关性均不显著。阳澄湖养殖活动和底泥营养盐释放可能是导致上述变化的主要原因。

英文摘要：

Based on the water quality investigation in May （dry period） and October （wet period） 2009, the spatio-temporal variations of water quality and nutritional status in the large, shallow and subtropical Yangcheng Lake were analyzed, and the reasons for the differences in water quality and the emergency of eutrophication were discussed. The results are as following： the concentrations of main water quality parameters including TN＇, chlo- rophyll, TP and CODMn decrease gradually from the western part to the eastern part of the lake consistently, and TP in wet period is higher than in dry period while the others are opposite. The water quality are all classified as inferior Class V except of the central area of eastern part which is in Class IV with TN and TP acting as the primary pollutants though the whole lake in both periods. Although the trend of eutrophication increase has been eased, however, the water body is still in eutrophic state. The major source of pollution nitrogen and phosphorus analysis suggests that the concentrations of NO3 -- N and NO2 - N are significantly positive correlated with TN in both periods, and PO43-- P and TP concentrations also shows significantly positive correlation in wet period. Additionally, there are significantly positive linear relationships between the content of Chl-a and TN only in dry period, while the correlation between Chl-a and TN and TP concentrations is not significant in both periods. Farming activities and sediments releasing may contribute to the above characteristics in Yangcheng Lake.