Integration of Process Mechanisms and Policy Measures for Pollution Reduction and Carbon Mitigation: Employing Water and Environmental Institutions in the Yellow River Basin, China

Water environment governance (WEG) plays an important role in absorbing pollutants and reducing carbon emissions. This study focuses on the synergistic pollution reduction and carbon mitigation effect achieved by implementing WEG through process mechanisms and policy measures, and explores the focus point aimed at achieving the co-benefits of pollution reduction and carbon mitigation effectively at a local level within the basin. After selecting synergy indicators of comprehensive environmental pollution and carbon emissions and conducting modeling tests, the synergistic pollution reduction and carbon mitigation effect of WEG in the Yellow River Basin is examined. The analysis results show that WEG is characterized by the “Matthew effect” (i.e., the phenomenon of “the stronger get stronger”), and it can generate a synergistic pollution reduction and carbon mitigation effect with a lag, though the extent of reduction differs between pollutants and carbon emissions. The process mechanisms of source decarbonization (i.e., industrial structure transformation) and process emission reduction (i.e., green technology innovation) can achieve overall co-benefits, while end sink enhancement (i.e., environmental regulation) is only effective in reducing the pollution. The mixed nature of policy measures influences the overall co-benefits: homogeneous policy measures (e.g., river chief system policy and water ecological civilization construction pilot) contribute positively, while the opposite is true for heterogeneous policy measures (e.g., integrating WEG and energy utilization policies). These findings provide useful operational recommendations for decision-makers to efficiently reduce pollutants and carbon emissions and promote low-carbon sustainability in China’s watersheds.