Research On The Statistical Method In Lake Nutrient Criteria Establishment In China

Lake eutrophication has been one of the most important global water environmental problems. As the base of eutrophication control standard, lake nutrient criteria development is a priority in China. There are thousands of lakes over the country, the nutrient levels and the effect of eutrophication vary significantly. Thus, criteria should be established in each region to develop nutrient criteria scientifically.Nutrient criteria variables could be used to measure water quality, evaluate trophic status or predict eutrophication and were the basis of lake nutrient criteria in regions. In this study, a series of variables and the situation in U.S.A were reviewed, and some principles and suggestions about variable selection were proposed.Lake nutrient reference condition Establishment in an ecoregion is a critical part in nutrient criteria development. In this study, several methods of reference condition establishment have been reviewed as statistical methods, including statistical method, model extrapolation, paleolimnological reconstruction and expert judgement; reference lake approach, lake population distribution approach, trisection approach and regression approach were analyzed.In this paper, based on the historical monitoring data of water quality in three regions, total phosphorus, total nitrogen, chlorophyll a and Secci depth were selected as nutrient indicators. Based on the analysis of regional variety, relationships between the variables were studied and regression equations were set up; typical nutrient concentrations, trophic state indices and N/P ratio were analyzed; reference conditions set by different approaches were compared. Statistical method (lake population distribution approach) was applied to establish the nutrient reference conditions for each region, and the trophic status of each reference condition was evaluated.Results showed that variable relationships in different region differed, eg. organic concentration, turbidity and total dissolved solids could affect trophic status. Through comparative analysis, reference condition values of total phosphorus, total nitrogen were 0.025mg·L-1, 0.005mg·L-1, 0.008mg·L-1 and 0.622mg·L-1, 0.633mg·L-1, 0.173mg·L-1; reference condition values of chlorophyll a and Secci depth were 0.65mg·m-3,0.798mg·m-3,2.24mg·m-3 and 0.60m,2.68m,4.97m. Region1 was in mesotrophic status and the others were both in eutrophic status without human disturbance.