Effects of ecological protection and restoration on phytoplankton diversity in impounded lakes along the eastern route of China's South-to-North Water Diversion Project.

Traditional lake phytoplankton diversity studies do not take into account the impact of ecological protection and restoration project policies. Here, a difference-in-differences (DID) model, which is commonly used to analyze the relative importance of economic factors, was used to evaluate the impact of such policies on phytoplankton diversity in lakes. Dongping Lake was used as the experimental group, and the upstream Nansi Lake was used as the control group. The phytoplankton diversity index of the experimental group and the control group was used as the explanatory variable of the DID model. Six environmental and socioeconomic factors, temperature and precipitation, were used as control variables in the DID model. The effects of ecological protection and restoration project policy on phytoplankton diversity in lakes were analyzed. Under the influence of policy implementation, the phytoplankton diversity in the experimental lake was improved by 2.79% compared with that in the control lake. Temperature and precipitation were the main factors affecting phytoplankton diversity in the two connected shallow lakes in the Shandong Peninsula. This study verified that DID models can be used to quantitatively analyze the impact of ecological protection and restoration project policies on phytoplankton diversity in lakes.