Identification of key water environmental factor contributions and spatiotemporal differential characteristics for eutrophication in Dianchi Lake

The main influencing factors of water environment and the spatiotemporal differences of eutrophication were identified in the Dianchi Lake, the results indicated a comparatively poor and fluctuating the water environmental condition in the Caohai compared to the Waihai, and differences in the correlation between water environment indicators were observed in Caohai and Waihai. The absolute contribution rates of the inner sources to water temperature, pH, electrical conductance, total nitrogen, chlorophyll a and algal density were the largest in Caohai, while offshore sources are pH, electrical conductance, permanganate index, total phosphorus and chlorophyll a in Waihai. The eutrophication level is relatively high near the Xiyuan Suidao section, and the comprehensive trophic level indexes are 61.14, 64.45 and 64.45 in spring, summer and autumn, respectively, which all reach the state of moderate eutrophication; the comprehensive trophic level index is 55.72 in winter, which reaches the state of light eutrophication. The algal density near the Xiyuan Suidao and Luojiaying sections exhibited high levels, reaching a state of moderate algal bloom in summer. Spatial autocorrelation analyses highlighted significant positive and negative spatial autocorrelation for comprehensive Trophic Level Index and algal density, respectively, in Dianchi Lake. The High-High aggregation of the comprehensive Trophic Level Index and algal density was mainly concentrated in the Caohai, while the Low-Low aggregation of the comprehensive Trophic Level Index was primarily observed in the Waihai. Consequently, the risk of eutrophication and algal bloom outbreak in Caohai surpassed that in Waihai. Therefore, it is imperative to propose appropriate treatment measures based on the varying eutrophication level and algal bloom outbreak during different time periods and in distinct regions of the aquatic ecological environment in Dianchi Lake.