Ecosystem-level Response to Complex Disturbances of an Interconnected River–lake System Based on Ecopath Model over the Last 30 Years

Freshwater ecosystems have been severely disturbed in recent years. However, our understanding of the ecosystem-level changes within freshwater food webs under complex disturbances is still limited. To address this knowledge gap, we took Dongting Lake as a case study, which has undergone significant environmental changes. We established Ecopath models for Dongting Lake in 1997, 2013, and 2021, and validated them using stable isotope-determined trophic levels. Our focus was on describing the structure and maturity of the ecosystem, identifying key species, and quantifying energy flows. The verification result showed that the models were acceptable. The model outputs revealed a significant decline in the average energy transfer efficiency of Dongting Lake. The food web maturity of Dongting Lake decreased and subsequently increased in these three representative periods. Simultaneously, the food web structure was successively simplified over time. Moreover, the identification of keystone species revealed the significance of Zooplankton, Other fish, Silurus asotus, and Molluscs within the ecosystem. Overall, our results offer a scientific underpinning for the effective management and conservation of freshwater ecosystems.