Eutrophication Evaluation Based on Set Pair Analysis of Baiyangdian Lake, North China

Based on a Set Pair Analysis (SPA), the water eutrophication levels of Caiputai, Shaochedian, Wangjiazhai, Guangdianzhangzhuang, Zaolinzhuang, Duancun and Nanliuzhuang in Baiyangdian Lake were evaluated with five indices, including chemical oxygen demand (COD), total nitrogen (TN), total phosphorus, secchi disk depth (SD) and chlorophyll-a concentration. In the SPA model, the Classification Standard of Lake Eutrophication and evaluation indices of monitoring sites in Baiyangdian Lake were considered as a set pair, and the eutrophication levels of monitoring sites were depicted by a five-element connection degree. Our results demonstrated that the key limiting factors that caused eutrophication were TN, COD and SD. According to the principle of the maximum membership degree and the analysis of the set pair situation, we concluded that Nanliuzhuang experienced hypereutrophy, Zaolinzhuang eutrophy, and the others upper-mesotrophy. Furthermore, the water quality of the seven observation spots was, from better to worse, Caiputai, Duancun, Wangjiazhai, Shaochedian, Guangdianzhangzhuang, Zaolinzhuang and Nanliuzhuang. The SPA adequately deals with the uncertainty problem in the eutrophication evaluation, and our evaluation results can be directly applied to lake restoration and treatment efforts.