With reference to the number of grades and threshold for each grade in a certain standard for water quality eval⁃uation, a water quality evaluation method was established combining multivariate analysis with multi⁃factor evaluation. Through the regression analysis a corresponding function equation was established, and then by substituting sample data in⁃to corresponding relational expressions to build up a table of water quality evaluation indices. At the same time factor analy⁃sis was performed to allocate weight to each type of numeric data. Finally, by combining the use of the table of water quali⁃ty evaluation indices with the weight for each type of numeric data, water quality evaluation indices were worked out for the sampling sites, and then the evaluation was done. With reference to the thresholds in the standard specific to lakes and res⁃ervoirs in the “Standard for Surface Water Environment Quality” ( GB 3838-2002) , case studies were done of the Dians⁃han Lake and the Yuandang Lake. TN, TP, Chl⁃a and SD were monitored for four seasons consecutively through sampling at 29 sampling points in the studied area. Based on the monitoring data and the analysis with the established model, evalu⁃ation was done. Results show that the annual overall evaluation index of the Dianshan Lake is 5�727 and the Yuandang Lake is 5�418, both falling into Category Ⅴ in water quality. The latter is a little better than the former. Among the four seasons, spring is the best with water quality generally in CategoryⅣ, and summer the worst with water quality in Catego⁃ry Ⅴ minus.%构建了多元分析与多因子评价相结合的水质评价方法，参照某一水质评价标准中的各级阈值和级数，通过回归分析建立对应的函数关系式，再将样本数据代入对应关系式中构建水质评价指数表；同时运用因子分析法对数据类型分配权值，最终结合水质评价指数表和数据类型的权值，计算出样点的水质评价指数，得出评价结果。以淀山湖及元荡为例，依据GB 3838—2002《地表水环境质量标准》中湖泊水库特定项目标准限值，对研究区域内29个样点的总氮（TN）、总磷（TP）、叶绿素a（Chl⁃a）和透明度（SD）分别进行4个季度的连续测定。在水质采样分析测定的基础上，利用所构建的模型得出评价结果。结果表明，淀山湖全年综合水质评价指数为5�727，元荡为5�418，均属于Ⅴ类水质，但元荡水质稍好于淀山湖水质；4个季度中，春季水质最好，总体呈Ⅳ类，夏季水质最差，总体呈劣Ⅴ类。
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