Evaluation of the effectiveness and effects of long-term ecological restoration on watershed water quality dynamics in two eutrophic river catchments in Lake Chaohu Basin, China

The ecological restoration projects are important in alleviating the ecological degradation conditions. The evaluation of the long-term effects and effectiveness of ecological restoration projects could provide an empirical foundation for future projects and assessment of watershed water environment restoration. However, empirical research, based upon long-term monitoring data on this topic is relatively lacking. In this study, the effectiveness of restoration projects on water quality improvement of two eutrophic rivers in Lake Chaohu Basin (LCB) was investigated. The spatiotemporal dynamics of water quality from 2000 to 2021 were studied and a delayed water quality response to restoration projects was revealed. In the past two decades, especially since 2014, the water quality in the LCB improved significantly whereas restoration projects have been implemented since late 2012. Additionally, a sharp regression discontinuity (RD) design was constructed to confirm the effectiveness of restoration projects on water quality improvement successfully. Moreover, the positive effects of restoration projects on water quality dynamics were quantified and distinguished from the effects of negative human ac-tivities and climate change using the residual trend method. During 2014-2020, ecological restoration projects contributed more than half (64.3 % SWL1 and 58.2 % HB2) of water quality variation in two eutrophic river catchments. Finally, a framework from the perspective of lake eutrophication management with effective measures is proposed for maintaining the sustainable development of ecological restoration projects in water-sheds. The empirical study here provides scientific support for achieving better effectiveness of ecological restoration projects in watersheds with water pollution problems worldwide.