基于分位数回归的洱海藻类对氮、磷及水温的响应特征

基于云南洱海长时间尺度水质观测数据,运用分位数回归方法分析浮游藻类叶绿素a(Chl-a)对氮(N)、磷(P)、水温的定量响应关系.结果表明过去20余年洱海藻类生物量受水温、N、P共同影响,随着洱海富营养化程度的加剧,水温对藻类生物量的相对重要度在持续下降,斜率平均值从2.70下降至0.44.而营养物对藻类的促进效应明显在提升,尤其是TP对藻类的相对重要度持续在攀升,斜率平均值从-0.3增长至0.8.TN对藻类生物量整体表现为较稳定的正效应,但近些年(2008~2013年)TN对藻类正效应达到最低.2002之后,P已逐渐取代N成为最重要的营养物限制因子.在季节方面,春季和秋季以水温和N的共同限制为主导,但春季当Chl-a8 mg·m-3时,N和水温对藻类的正效应逐渐被P取代.夏季完全以N、P共同限制效应占主导,当Chl-a3 mg·m-3时,TP的正效应逐渐超过TN,冬季则以P和水温的共同限制效应为主导.在气候变暖的大背景下,洱海富营养化控制应以"控P"为主和N、P协同削减的策略.当前富营养化控制过程中,应着重监控春、秋两季温度短期快速上升可能引发的全湖藻华风险.

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

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.