Has hydrological alteration driven ecosystem service risks in large floodplain lakes? A novel framework for spatiotemporal assessment and hydrological thresholds identification

Study region Poyang Lake, China’s largest freshwater lake, is a critical ecological hub. Study focus Hydrological alteration strongly affects floodplain ecosystem services (ES), yet their spatiotemporal risks and hydrological controls remain poorly understood. We developed an integrated framework based on ecological deviation to assess ES risks and identify hydrological drivers and thresholds for four leading ES: water supply (WS), nutrient retention (NR), habitat support (HS), and flood regulation (FR). New hydrological insights for the region The framework revealed spatiotemporal differences in ES risks following the Three Gorges Dam operation. WS experienced the most severe degradation, with high-capacity areas declining from 22.76% to 8.62%, and risk increased across 97.37% of the lake area. HS remained relatively stable, although low-suitability areas expanded from 34.38% to 47.15%, mainly in sub-lakes and marginal zones. In contrast, NR and FR risks reduced across 81.07% and 97.39% of the lake, respectively. Temporally, WS risk increased ( P < 0.01), FR risk decreased ( P < 0.05), while HS and NR showed no significant trends. XG-Boost analysis revealed ES-specific and risk-level-dependent hydrological controls. Drivers for WS and HS risks shifted from drought timing (low-risk) to drought duration and water-level extremes (high-risk). NR risk exhibited the largest shift, increasingly controlled by rising and flood-season water levels. The framework provides a tool for quantifying ES risks under hydrological alteration and supporting adaptive management in floodplain lakes.