The long-term changes in food web structure and ecosystem functioning of a shallow lake: Implications for the lake management

The food web structure (FWS) and ecosystem functioning (EF) of lakes worldwide are impacted by multiple disturbances. The historical evolution of the FWS and EF are not well understood due to the lack of sufficient long-term records of biotic variations. This study reconstructed the food web models in the 1950s, 1980s, 1990s, 2000s, and 2010s for Baiyangdian Lake (BYDL), the largest shallow lake in northern China, using the Linear Inverse Modeling (LIM) and investigated EF in different periods. Our results confirmed that the FWS and EF of BYDL have undergone significant changes. The biomass of phytoplankton continuously increased, and the primary productivity of phytoplankton began to replace the primary productivity of submerged macrophytes in the 2000s and became the largest energy flow in the food web. Changes in the energy flow of primary producers are transmitted to high-trophic functional groups, which affects the diet composition of fish. Based on the ecological network analysis indices and food web stability indicators, it was concluded that after a turning point in the 1990s, the ecosystem showed initial stability and then gradually became unstable. Water level fluctuations and nutrient enrichment may be the key driving factors for changes in ecosystem state. Therefore, to maintain a good state of the ecosystem, we recommend implementing comprehensive management measures of hydrological management, nutrient-loading reduction, and biomanipulation. Furthermore, this study extended LIM to lake ecosystems, which may provide a new method for lake ecological environment management.