Exploring the impacts of spatial regulation on environmentally sustainable development: A new perspective of quasi-experimental evaluation based on the National Key Ecological Function Zones in China

With increasing ecological damage caused by regional development, many countries seek to promote sustainable development through spatial regulation. This study treated China's development of National Key Ecological Functional Zones (NKEFZ) as a quasi-natural experiment, applying a time-varying difference-in-differences model to data from 148 water quality monitoring cross-section points of major river systems in China from 2004 to 2018. The results revealed that NKEFZ improved the mean of comprehensive water quality (CWQ) and individual water quality indicators of dissolved oxygen and ammonia nitrogen content index by restricting urbanization and increasing government investment. The mean value of CWQ was improved by about 0.22 grades, and the optimization effect of spatial regulation on average water quality was more prominent in coastal cities, cities with high-pollution levels, and large-sized cities. Nevertheless, the impact of NKEFZ on water quality exhibited a "Matthew effect", in which NKEFZ were not effective in improving the bottom line standard of water quality in the pilot zones, as NKEFZ did not significantly improve the peak values of CWQ or individual pollutant indicator. In addition, an economic effect estimation indicated that NKEFZ significantly facilitated local economic growth and primary industry development and had a significantly negative impact on secondary industry growth and foreign investment. This study contributes new evidence for measuring the effect of the trans-regional spatial regulation, eliciting policy implications for improving ecological spatial regulation and incentive mechanisms, and promoting the sustainable development of the regional environment and economy.