长江中下游水生态系统物理完整性对人类活动强度的阈值响应研究OA

Current assessments of aquatic ecosystem health in the middle and lower Yangtze River largely focus on single-factor indicators,limiting their ability to capture cumulative disturbance effects.To address this gap,this study develops a basin-scale framework for evaluating physical integrity.Five core functions—hydrological connectivity,flood regulation,physical habitat structure,water-quality purification,and ecological continuity—were identified.Seven categories of anthropogenic stressors were spatially mapped and weighted to construct an Index of Physical Integrity(IPI),accompanied by high-resolution mapping.A Human Activity Index(HAI)was also calculated to quantify disturbance intensity,enabling a quantitative analysis of IPI sensitivity to human pressures and offering a new tool for large-scale integrity assessment.Results show a persistent spatial gradient of"low in urban areas,moderate in plains,and high in hills."From 2015 to 2020,the area of extremely low IPI patches expanded by nearly 70%.The IPI-HAI relationship follows a four-phase nonlinear pattern:(i)a collapse threshold at HAI=0.35;(ii)a recovery zone in the range of 0.35<HAI≤0.50;(iii)a high-resilience window at 0.50<HAI≤0.70;and(iv)marginal decline when HAI>0.75.Seasonal differences were evident:wet-season IPI values exceeded dry-season levels by 0.10～0.30 on average,with differences around lake clusters reaching 0.20.About 93%of the region exhibited declining seasonal integrity,primarily driven by flood-vegetation interactions.Based on these findings,a zoned regulation strategy is proposed:"push beyond 0.35—cross 0.50—hold 0.75."This framework provides an operational,quantitative reference for water-ecological management and restoration,while offering a transferable pathway for assessing physical integrity in other large river systems.