Integrated modeling framework to evaluate the impacts of multi-source water replenishment on lacustrine phytoplankton communities

An extensive artificial water diversion project aimed at alleviating the shortage of ecological water in lakes can change the original hydrological and physicochemical states and further affect the structure and distribution of phytoplankton communities. Therefore, it is important to fully evaluate the ecological restoration effect of the water diversion project on the water-receiving area before implementing water replenishment. For this purpose, we developed an integrated model framework based on the Environmental Fluid Dynamics Code (EFDC) and Random Forest (RF). We adopted a probability distribution method to address the uncertainty during model coupling. This framework was implemented to simulate and predict the evolution of phytoplankton diversity in Baiyangdian Lake (BL) in China. To solve the problem that the phytoplankton biodiversity in BL decreased especially in summer due to human activity, the Yellow River into BL, the south-to-north water diversion project, and joint replenishment of upstream reservoirs have been implemented in recent years. Our framework was used to analyze the biodiversity restoration effects of multi-source water replenishment through different routings. The results show that spatiotemporal coverage should be considered to reduce uncertainty during model coupling. Water replenishment has a positive impact on the biodiversity of BL; however, there are effective areas for phytoplankton diversity restoration, which are related to water quality and quantity, water replenishment routing and internal hydrological connectivity. The Xiaobai River has the most significant water ecological restoration potential among the routings, compared with that of the Baigou and Fu Rivers. Appropriate water replenishment in spring will play a vital role in alleviating the decrease in phytoplankton biodiversity in summer owing to flood control.