中文摘要：

选择长江中下游49个湖泊进行不同季节的水体溶解无机氮（DIN）、总氮（TN）、总磷（TP），溶解性无机磷（DIP）以及叶绿素a（Chla）等环境参数分析，开展不同营养水平湖泊水体环境变化特征及生物响应机制研究。结果表明：DIN、TN／TP随TP的变化规律反映了不同营养水平和季节下地球化学作用的影响；氨氮（NH4-N）、TP、DIP、Chla尤其是NH4-N的季节性变化规律与营养水平关系密切TP〈0．05mg／L时，NH4-N随总磷升高的趋势夏季大于其他季节，TN／TP与硝态氮（NO3-N）、TN相关性好，营养源组成和氨化作用是主要影响因素；0．05mg／L〈TP〈0．1mg／L时，各季节NH4-N随总磷升高的趋势基本相同，TN／TP与亚硝态氮（NO2-N）、NO3-N、TN相关好，水生植物利用、氨化和反硝化作用是主要影响因素。TP〉0．1mg／L，冬季NH4-N随总磷升高的趋势明显大于其他季节，TN／TP在冬季和春季与TN、NO3-N相关性好，夏季和秋季与TP相关性好，其主要原因在于夏季和秋季水生植物对DIN的利用量、反硝化作用和湖泊内源释放的显著增强。

英文摘要：

In this paper, forty-nine lakes along the middle and lower reaches of Yangtze River are chosen. Based on the analysis of the seasonal changes of environmental parameters, including dissolved inorganic nitrogen （DIN）, total nitrogen （TN）, total phosphorus （TP）, dissolved inorganic phosphorus （DIP） and chlorophyll a （ Chla）, etc, the characteristics of water environmental change and the mechanisms of biological response in lakes of different nutrient levels are studied. The results show that the impacts of geochemical processes are reflected by the variational laws of lakes in different nutrient levels. The seasonal variations of Chla, ammonia nitrogen（NH4-N）, DIP, TP, and TN, especially NH4-N are closely related to nutrient levels. When TP 〈 0.05 mg/L, because NH4-N increases more quickly in winter than other seasons with TP increasing and TN/TP is closely related to nitrate nitrogen （NO3-N） and TN, the composition of nutrient sources and ammonification might be the main determinant. When 0.5 mg/L 〈 TP 〈 0.10 mg/L, NH4-N increases equally in each season with TP increasing and TN/TP is closely related to NO3-N, nitrite nitrogen （NO2-N） and TN, which suggests that the composition of nutrient sources, ammonification and denitrification might be the main determinant. When TP 〉 0.1 mg/L, NH4-N increases more quickly in winter than other seasons with TP increasing and TN/TP are closely related to TN and NO3-N in spring and winter, but to TP in summer and autumn. The main reasons are that the effects of hydrophyte and denitrification and the internal release of phosphorus from sediment increase significantly.