Characteristics and source analysis of water pollution in dry season (November to March) of Dongping Lake (China)

In this study, factor analysis, principal component analysis (PCA) and correlation analysis were used to analyze the water quality in dry season of Dongping Lake, which is the only natural lake in the lower Yellow River and an important hub of South-North Water Diversion Project (SNWDP) of China. The nutritional status of the lake was evaluated by trophic level index, and the spatial heterogeneity and aggregation status of the eutrophication level were studied by spatial autocorrelation analysis. Moreover, the pollution-discharge-coefficient method was carried out to clarify the potential pollutant sources. Results showed that the lake was in the light eutropher state with the water quality of V and poor V. Nitrogen pollutants were the primary driving factor of water quality, and water depth was the main environmental factor affecting the spatial distribution of nitrogen pollutants. The eutrophication level of the entire lake showed significant positive spatial autocorrelation. Due to the influence of regional eutrophication levels, the spatial heterogeneity of eutrophication level was low. Two hotspots (High-High concentration) of eutrophication were present in the southeast (P < 0.01) and the north (P < 0.05) of the lake. However, causes for the formation of these two hotspots were different, which mainly resulted from the non-point source discharge of surrounding towns along the southeastern lake and the weak hydrodynamic conditions in the northern lake, respectively. Therefore, it is necessary to pay more attention to control the non-point source discharge into Dongping Lake, especially for regions around the southeast of the lake, in the future management.