[Response Characteristics of Algal Chlorophyll-a to Nitrogen, Phosphorus and Water Temperature in Lake Erhai Based on...

Based on water quality monitoring data of Lake Erhai from 1990 to 2013,the yearly and seasonally response characteristics of algal chlorophyll-a to total nitrogen (TN),total phosphorus (TP) and water temperature was investigated using quantile regression method.It indicated that water temperature was always the primary limiting factor of algal biomass indicated by chlorophyll a (Chl-a) across recent 24 years,but its limiting effect on algal Chl-a content was kept descending sharply and replaced much by nutrients (e.g.P,N) with the increasing eutrophic level.Especially the slope values of TP on Chl-a were kept ascending from -0.3 to 0.8.Since 2002,the positive effect of TN on Chl-a presented slow descending tendency,and P became the most important limiting nutrient factor of algal growth.According to the seasonal variation analysis,water temperature and N had dominant effects on algal Chl-a in spring and autumn,but they were replaced by P in the case of Chl-a>8 mg·m^-3 in spring.In summer,N and P had strong interactive impacts on the algal growth,and the positive effect of P was stronger than that of N in the case of Chl-a>3 mg·m^-3.In winter,algal biomass was co-limited by temperature and P.It suggested that P reduction is the prior choice of eutrophication control of Lake Erhai,and simultaneously reducing N load is necessary in the background of global warming.In addition,so far a emergency controlling measure should be taken to monitor algal blooming due to sharp ascending of water temperature within a few days in spring and autumn.