Traditional research on lake eutrophication has failed to consider the effect of the south-to-north water transfer project (SNWTP) policy; thus, the difference-in-differences (DID) model, which is usually applied to economic factors, was innovatively introduced to evaluate the effect of such policies on lake eutrophication. Nansi Lake and Dongping Lake in the Shandong Peninsula were selected as the experimental group, and Daming Lake and Mata Lake were selected as the control group. The eutrophication indices of the experimental group and the control group were calculated by the measured chlorophyll-a, total phosphorus, total nitrogen, water transparency and chemical oxygen demand data and used as the explanatory variables of the DID model. Nine environmental and socio-economic factors, such as dissolved oxygen and rural population, were selected as the control variables of the DID model to analyze the impact of the SNWTP policy on lake eutrophication. A joint consideration of environmental and socio-economic factors showed that the eutrophication degree of the experimental lakes deteriorated by 7.10% compared with the control under the influence of the implemented policy. Dissolved oxygen is the main factor affecting the eutrophication of the Shandong Peninsula. This study verifies that the DID model has the potential for use in quantitative analyses of the effect of the SNWTP policy on lake eutrophication.

中文翻译：

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调水政策实施对山东半岛湖泊富营养化的潜在影响：差异中的方法

传统的湖泊富营养化研究未能考虑南水北调（SNWTP）政策的影响；因此，创新性地引入了通常应用于经济因素的差异（DID）模型来评估此类政策对湖泊富营养化的影响。以山东半岛的南四湖和东平湖为实验组，以大明湖和马塔湖为对照组。通过实测叶绿素a、总磷、总氮、水体透明度和化学需氧量数据计算实验组和对照组的富营养化指数，并作为DID模型的解释变量。九个环境和社会经济因素，如溶解氧和农村人口，被选为 DID 模型的控制变量来分析 SNWTP 政策对湖泊富营养化的影响。综合考虑环境和社会经济因素，实验湖泊富营养化程度在政策实施的影响下比对照恶化了7.10%。溶解氧是影响山东半岛富营养化的主要因素。本研究验证了 DID 模型具有用于定量分析 SNWTP 政策对湖泊富营养化影响的潜力。与执行政策影响下的控制相比10%。溶解氧是影响山东半岛富营养化的主要因素。本研究验证了 DID 模型具有用于定量分析 SNWTP 政策对湖泊富营养化影响的潜力。与执行政策影响下的控制相比10%。溶解氧是影响山东半岛富营养化的主要因素。本研究验证了 DID 模型具有用于定量分析 SNWTP 政策对湖泊富营养化影响的潜力。