Characteristics and mechanismes of water environmental changes in the lakes along the middle and lower reaches of Yangtze River

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 chlorophyⅡ 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 dif erent nutrient levels.The seasonal variations of Chla,ammonia nitrogen(NH₄-N),DIP,TP,and TN,especialy 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.