Study on establishing lake reference condition for nutrient

Lake nutrient reference condition Establishment in an ecoregion is a critical part in nutrient criteria development.Several methods of reference condition establishment have been reviewed as statistical methods,including reference lake approach,lake population distribution approach,trisection approach,regression approach,and model extrapolation and paleolimnological reconstruction.In this paper,based on the historical monitoring data of total phosphorus,total nitrogen,chlorophyll a and Secci depth,statistical method was applied to establish the nutrient reference condition of Chaohu Lake.Through comparative analysis and the validation of paleolimnological reconstruction data about the middle and lower reaches of Changjiang River,5th percentile of lake population distribution was recommended as reference conditions.Thus,the threshold rang of Chaohu Lake showed that total phosphorus is 0.023～0.27 mg·L-1,total nitrogen is 0.62～0.63 mg·L-1,chlorophyll a is 0.65～0.67 mg·m-3,Secci depth is 0.65～0.72 m.