How to allocate discharge permits more fairly in China?-A new perspective from watershed and regional allocation comparison on socio-natural equality.

Equitable and efficient allocation of pollutant discharge permits is vital for controlling total pollutant amounts. However, the conventional water pollutant discharge permit allocation method is criticized for dividing the environmental attributes of water bodies, which is mainly based on administrative units. China is establishing a water ecological environment zoning management system to manage the water environment more scientifically, which may have a great impact on for controlling total pollutant amounts. Whether the ecological environment zoning management system can promote more equitable and efficient permit allocation remains unknown. In this paper, an environmental zoning system and "basin-region" correlation are established to take both regional and watershed allocation processes into consideration. Then, a multi-index Gini coefficient method is established to evaluate the equality of different allocating methods. The Gini coefficient is then combined with a linear interactive and general optimizer method to achieve an equitable allocation of ammonia nitrogen discharge permits in the Songhua River Basin from both watershed and regional perspectives. Forty-five water pollutant discharge allocation scenarios are considered to represent different manager tendencies. The results show that allocation based on watershed functional units is more equitable than that based on administrative units. The index weighting settings also have a large impact on regional and total equality and environmental efficiency. Midstream and downstream areas show large allocation differences, although no scenario can satisfy all watershed regions in terms of equality and environmental efficiency at the same time. Thus, more trade-offs are needed during decision making. By considering the coordination of social, environmental and economic development at the basin level, this study provides new insight into equitable and efficient allocation. Moreover, the findings suggest that an environmental zoning system should be considered for discharge permit allocation in water resource management.