Evaluation of the Water Environment Improvement Effect of the Niulanjiang-Dianchi Water Diversion Project on the Outer Lake of Dianchi Lake

The Niulanjiang-Dianchi Water Diversion Project is one of the key measures for the comprehensive treatment of the water environment of Dianchi Lake. Assessing its actual effect on improving the water environment of Dianchi Lake during operation is of great importance for the quantitative evaluation of project benefits. Taking the outer lake of Dianchi Lake as the study area, this research was based on measured water quality data. By comparing the changes in major pollutant indicators, trophic state index, and aquatic biological indicators before and after project operation, and investigating their correlation relationships with driving factors, the improvement effect of the project on the water environment of the outer lake of Dianchi Lake was analyzed. The results show that the water quality of the outer Dianchi Lake shows a significantly negative correlation with the total inflow discharge into the lake, after the implementation of the Niulanjiang-Dianchi Water Diversion Project, the concentrations of four major pollutants in the outer lake of Dianchi Lake, namely NH3-N, TP, CODMn, and TN, decreased significantly. The eutrophication level improved markedly, and algal cell density declined substantially. The project has achieved a clear improvement effect on the water environment of the outer lake of Dianchi Lake. The findings can provide a reference for inter-basin water diversion projects aimed at controlling lake water pollution.