Rapid response of aquatic ecosystems and environment in shallow macrophytic lakes to large-scale cofferdam removal

The high-density and scattered distribution of cofferdams in shallow lakes severely disrupts hydrological connectivity, weakens hydrodynamic conditions, and undermines the stability of aquatic ecosystems. As a typical shallow macrophytic lake in northern China, Baiyangdian initiated a large-scale cofferdam removal project in 2020. Over a three-year period, approximately 40 km of cofferdams — accounting for 80% of the original total area — were removed, profoundly reshaping the lake’s spatial structure. This study, for the first time, systematically investigates the status and impact of cofferdam removal in Baiyangdian’s major sub-lakes at a macro scale, focusing on 143 sub-lake units. A Sentinel-2 time series dataset with nominal five-day intervals throughout the year was constructed, and, in combination with an improved Pixel Binary Method and the FUI-TSI model, key ecological and environmental parameters — including submerged aquatic vegetation (SAV) coverage, water transparency, and trophic state — were extracted to comprehensively assess the effects of cofferdam removal on the lake’s aquatic ecosystem and environment. Results show that SAV spatial patterns were closely linked to cofferdam density. During the early phase of removal, the SAV area declined sharply from 28.1 km 2 to 12.5 km 2 but gradually recovered in the following years and eventually stabilized. Concurrently, water transparency fluctuated between 0.4 and 0.8 m, with an average of 0.6 m and an overall increasing trend. The trophic status remained within the mesotrophic range, with a continuous decline in eutrophication levels, indicating sustained improvements in water quality. The findings suggest that cofferdam removal significantly enhanced hydrological connectivity and restoration potential in Baiyangdian, improved hydrodynamic and light conditions, and promoted SAV regeneration and colonization, thereby driving the aquatic ecosystem toward a more favorable successional trajectory. By integrating multi-temporal satellite remote sensing with improved ecological modeling, this study achieved the first large-scale coordinated monitoring of both aquatic vegetation and water quality in Baiyangdian, providing data support and methodological insights for the ecological restoration of shallow macrophytic lakes and the recovery of submerged vegetation. • Develops an FUI-TSI model for assessing water status in shallow macrophytic lakes. • Reveals how cofferdam removal affects vegetation and water quality recovery. • Combines multi-source data and spatial tools to assess vegetation–water interactions. • Provides technical support for ecosystem management in shallow macrophytic lakes.