中文摘要：

在确立湖泊营养物基准的过程中,湖泊水体参照状态的确定是十分重要的一个步骤.本文基于广义极值分布理论,发展提出了一种确定湖泊参照状态浓度的新方法.该方法克服了频率分析法等描述性统计方法存在的数据分组可能造成人为误差和不便于统计推断,难以进行可信度评价的缺陷,能有效地推断给出参数和物质浓度置信区间.将该方法应用到太湖的水质基准参照状态中,通过对太湖湖心两个站点1995～2006年总氮（total nitrogen,TN）,总磷（total phosphorus,TP）和叶绿素a（chlorophyll a,Chl-a）的数据进行分析,其年最小值的相反数符合广义极值分布,验证了方法的可行性.推荐采用25%分位点的值作为太湖总氮,总磷和叶绿素a的参照状态,即太湖的参照状态是：总氮0.71 mg·L-1,总磷0.025 mg·L-1,叶绿素a为1.81μg·L-1,并分别得出了它们各自的95%置信区间.

英文摘要：

It＇s a key step to estimate the nutrient reference condition of lakes for their nutrient criteria development.A new method was established to calculate the lake nutrient reference condition based the generally extreme statistical theory in the paper.The deficiencies,which lead to artificial error by grouping observed values and difficulty to do statistical inference and reliability evaluation in descriptive statistical methods,taking the frequency analysis as an example,can be overcome.The confidence intervals of parameters and substance concentrations can be obtained by this new method.This method was applied to estimate the reference conditions of Taihu Lake.The calculated results on total nitrogen（TN）,total phosphorus（TP） and chlorophyll a（Chl-a） observed by two sites located in the central of Taihu Lake show that the negative minima data of every year fit the generally extreme statistical model well and the feasibility of the approach has been verified.The 25th percentile was recommended as reference conditions.Thus,values of reference conditions show that TN is 0.71 mg·L-1,TP is 0.025 mg·L-1 and Chl-a is 1.81 μg.L-1.The 95% confidence intervals of each measurement was also obtained.