Ecological health assessment of lakes based on the coordination of "three waters": a case study of Lihu of Taihu Lake

Various methods, such as system integration frequency analysis, principal component analysis, entropy weight method, etc., were used to preliminarily sort, screen, and streamline key indicators of lake ecological health. Based on the concept of coordinating water resources, water environment, and water ecology ("three waters"), a lake ecological health assessment index system was proposed. Taking Lihu Lake, a city lake of Taihu Lake, as a case study, the proposed assessment method was used for ecological health assessment, and the assessment results were analyzed in combination with the governance status of Lihu Lake. A total of 36 indicators related to lake ecological health were preliminarily sorted out. Through screening and streamlining, seven indicators were finally determined to construct a lake ecological health assessment index system, including the proportion of natural lake shoreline, water exchange cycle, water resource development and utilization rate, comprehensive nutritional status index, floating plant diversity index, planktonic animal diversity index, and benthic animal diversity index. At the same time, the comprehensive index method was proposed to calculate the lake ecological health score and evaluate the health level. Using the constructed assessment method to assess Lihu Lake, it was shown that in 2023, Lihu Lake remained in a healthy state throughout all seasons, with lower overall scores in spring and summer. The total score of ecological health for the whole year was 68.88, and the evaluation result was healthy. The environmental condition of Lihu Lake had been improved, but it had not yet returned to its pre destruction state, and there was still a certain gap from reaching a very healthy state (80~100). Overall, it had entered the ecological restoration stage from the pollution control stage. The evaluation results of Lihu Lake indicate that the lake ecosystem health assessment index system based on the coordination of water resources, environment and ecology has good logical and systematic characteristics, and can provide methodological support for the ecological health assessment of urban landscape lakes in China.