[Spatial Differences in Water Quality and Spatial Autocorrelation Analysis of Eutrophication in Songhua Lake]

To identify the spatial differences in the water quality and eutrophication characteristics of Songhua Lake, the largest artificial lake in northeast China, analysis of variance (ANOVA) and factor analysis were used to analyze the water quality sampling and testing results in 2017 in three regions, namely the main reservoir area of the Fengman Reservoir (MRAFR), the experimental area of the Songhua River Three Lakes Protection Zone (EASRTLPZ), and the Jiaohe River backwater area (JRBA). The nutrient status of the lake was evaluated by the trophic state index method, and the spatial correlation and aggregation status of the eutrophication level in Songhua Lake were studied using spatial autocorrelation analysis. The main results were as follows: ① the ANOVA showed that, except for dissolved oxygen and chlorophyll-a (Chl-a), there were significant differences (P<0.05) in the total nitrogen (TN), total phosphorus (TP), water temperature (WT), and pH in the three areas of Songhua Lake, with the clearest difference between TN and TP. ② The factor analysis showed that the changes in the climatic condition factor (WT), nutrient salt factors (TN and TP), and algal biomass factor (Chl-a) dominated the water quality in the lake. ③ The results of the trophic state index showed that the nutrient status of Songhua Lake as a whole is mildly eutrophic, and the eutrophication levels of the three regions from strong to weak are JRBA > MRAFR > EASRTLPZ. ④ The global spatial autocorrelation showed that the eutrophication level of the lake as a whole has significant positive spatial autocorrelation owing to the influence of regional eutrophication levels. The spatial heterogeneity of the eutrophication level of Songhua Lake is low. ⑤ The results of the local spatial autocorrelation showed that the central and northern areas of JRBA are the hot spots (high/high concentration) of eutrophication in the lake (P<0.01), and the central part of EASRTLPZ is the cold spot (low/low concentration) of eutrophication in the lake (P<0.05). Therefore, when conducting water environmental management of Songhua Lake, the key areas for eutrophication control should be the JRBA and MRAFR.