Using eutrophication and ecological indicators to assess ecosystem condition in Poyang Lake, a Yangtze-connected lake

Poyang Lake, the largest freshwater lake in China, has been facing shrinkage and environmental problems in recent years, making it imperative to assess the status of its ecosystem. In this study, such an assessment was conducted based on the trophic status index, phytoplankton biomass, the ratio of zooplankton biomass to phytoplankton biomass, eco-exergy, structural eco-exergy, and ecological buffer capacity to total phosphorus for phytoplankton. First, the spatial and temporal variations of the ecosystem status in Poyang Lake were assessed based on these six indicators. Then, cluster analysis was utilized to classify the 15 sites based on the various indicators and to identify the most influential indicators. The results showed that the ecological status of Poyang Lake was affected not only by eutrophication but also by hydrological characteristics. All of the 15 sites had deteriorated to a certain degree. An analysis of the relative spatial ecological status showed that the status of the water in the rivers was superior to the status of water in the central lake. Furthermore, the relative ecological status was found to be best in summer and second best in autumn with ecological status deteriorating in winter. There was no significant correlation between eco-exergy and trophic status index, but a very strong relationship was found between eco-exergy and macrozoobenthos biomass with an R2 of 0.92, indicating that macrozoobenthos contributed greatly to the eco-exergy.