EVOLUTION OF THE WATER ECOLOGICAL ENVIRONMENT OF LIANGZI LAKE IN THE PAST 70 YEARS

This work combines literature findings with recent monitoring data of the author's group to elucidate the evolutionary process of the aquatic environment and ecosystem in Liangzi Lake. Analysis shows that disconnecting of the rivers and lakes, as well as the artificial water level regulation by gates and dams, have changed the original hydrological rhythm of Liangzi Lake. Since 2005, a pronounced trend towards eutrophication has been observed, with Liangzi Lake transitioning from an oligotrophic state to a mesotrophic-mild eutrophic state. While external pollution has been partially controlled, internal pollution release appears to be a significant contributor to water quality deterioration. The degradation of aquatic ecosystems is observed, characterized by a shift in dominant planktons and zoobenthos species towards those tolerant to pollution. In summer, the risk of cyanobacterial bloom increases. Mollusks nearly disappear, the decline of submerged plants is severe, and the number of fish species decreases and showed a trend of miniaturization. The accumulation of pollutants input from the watershed, disruption of hydrological rhythms, fishing production activities, and continuous high-water levels caused by floods are key factors driving the evolution of the aquatic ecological environment in Liangzi Lake. Effective remediation of Liangzi Lake requires comprehensive consideration and long-term planning from several aspects including pollutant control, habitat improvement, and optimization of fish community structure, ultimately restoring Liangzi Lake to its original clear water and submerged macrophyte dominated state.