Evaluating the effects of ecological water replenishment on lake water exchange in semi-arid regions insights from an 11-year modeling study.

Under the combined impacts of climate change and human activities, lakes in arid and semi-arid regions are universally confronting critical challenges including water scarcity, surface area shrinkage, and water quality deterioration. As one of the principal measures for ecological restoration of irrigation-district lakes, ecological water replenishment projects have been widely implemented. However, given the inherent complexity of lacustrine systems, the efficacy of ecological water replenishment in enhancing water quality and hydrological exchange capacity remains scientifically contentious. This study utilizes the MIKE 21 model to develop a 2D hydrodynamic model based on measured data (2011-2021), evaluating both the water exchange capacity and its influencing factors for a large semi-arid irrigation district lake under ecological water replenishment conditions. Furthermore, a modified Comprehensive Water Quality Identification Index (WQI) was employed to evaluate the characteristics of water quality changes. The results indicate that: (1) Over the 11-year period, the water renewal cycle shortened from 28-185 days to 25-115 days with increasing inflow to the lake. The water exchange capacity exhibited significant spatial heterogeneity. This was influenced by factors such as the location of the water replenishment inlet, lake topography, and aquatic vegetation. (2) As a typical artificially controlled lake in a semi-arid region, the continuous water replenishment rate over a specific time period determined the seasonal differences in water exchange rate. The variable inputs from multiple water sources led to varying water exchange rates among different years. (3) During the implementation of ecological water replenishment, the lake water quality improved significantly. Further integration of ecological water replenishment with point-source、non-point-source、and internal pollution control is necessary for the sustainable development of irrigation district lakes. Our study dynamically demonstrates the effects of external disturbances, such as ecological water replenishment projects, on the restoration and management of irrigation district lakes and provides theoretical and data support for sustainable management decision-making of artificially controlled lakes in irrigation districts.