Abstract
Abstract 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.
Highlights
The pumped water will be diverted from the south to the north, primarily through the existing Grand Canal, and impound in a chain of natural lakes, as regulating reservoirs, namely Gao-Bao-Shaobo Lake (GBSL), Hongze Lake (HZL), Luoma Lake (LML), Nansi Lake (NSL) and Dongping Lake (DPL) (Wang et al ; Zhang ; Wu et al ; Guo et al, a)
To analyze the spatial and temporal variation trend of eutrophication in Nansi Lake, Dongping Lake, Daming Lake and Mata Lake affected by the implementation of the SNWTPER policy, the trophic level indices (TLIs) of each section in four lakes from 2009 to 2017 were calculated using the chemical oxygen demand (CODMN), total phosphorus (TP), total nitrogen (TN), Chl-a and SD (Figure 2)
After the official water transfer began in 2015, an obvious slight upward trend is suggested throughout Dongping Lake as shown in the lower left of Figure 2
Summary
A total of more than 3 × 1010 m3 of water has been transferred from the lower Yangtze River in Yangzhou city, Jiangsu Province, and crossed the Huai River to the water shortage areas in the Yellow River basin (Guo et al a, b). The SNWTP-ER will consist of 1,156 km of canals and 54 pumping stations designed to lift water up to 65 m over the Yellow River (Wang et al ). The pumped water will be diverted from the south to the north, primarily through the existing Grand Canal, and impound in a chain of natural lakes, as regulating reservoirs, namely Gao-Bao-Shaobo Lake (GBSL), Hongze Lake (HZL), Luoma Lake (LML), Nansi Lake (NSL) and Dongping Lake (DPL) (Wang et al ; Zhang ; Wu et al ; Guo et al , a)
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