How top‐down and bottom‐up processes influence food web stability in the river‐connected lake

Lakes in densely populated regions face pressures from watersheds (e.g. nutrient inputs) and internal activities (e.g. fishing), which alter trophic state and biological communities, ultimately threatening food web stability. While both bottom‐up (resource‐driven) and top‐down (fishing‐driven) processes jointly regulate food web structure and function, their interactive effects are rarely evaluated over decadal scales across multi‐pathway food web.

This study constructed a linear inverse model integrated with Monte Carlo Markov chain methods, reconstructing a comprehensive, multitrophic food web with quantified energy fluxes of a representative river‐connected lake (Dongting Lake) over a 33‐year period (1990–2022). Based on ecological network analysis and Jacobian matrices, we quantified the response patterns of trophic interactions, energy flow and food web stability to the effects of bottom‐up and top‐down controls, to mechanistically quantify how coupled food web pathways respond to prolonged macro‐management and environmental evolution.

The results showed that an imbalance between the pelagic and benthic energy pathways drives primarily the degradation of the efficiency and stability of the ecosystem. Nutrient enrichment led to a less organized ecosystem with a relatively low dependence on detrital carbon sources and a decreased material cycling capacity (an 8.2% decrease in average path length). This reflects a high systemic stress that ultimately destabilizes the food web. Such stability declines, caused by resource disturbances, are difficult to mitigate via top‐down controls, despite their dominant role in shaping the trophic structure. Interestingly, moderate fishing promoted a food web with more specialized predators and high system efficiency. While fishing bans restored ecosystem activity, an algal surplus increased the heaviest loop weight, further destabilizing the food web.

Synthesis and applications . Our temporal analysis of the lake food web offers a cautionary insight. The control of nutrient loading should be prioritized to maintain food web stability, even in mesotrophic lakes. Implementing moderate fishing to regulate the top predator population is beneficial for improving energy efficiency and material cycling capacity within the food web, maintaining the stability of the ecosystem. This study recommended that the management of river‐connected lakes integrates nutrient control with moderate, regulated fishing practices as complementary strategies to sustain long‐term food web resilience.