Integrated watershed management through multi-level and stepwise optimization for allocation of total load of water pollutants at large scales

The contradictory problem between water quality-induced water shortage and shortage of water quantity has been increasingly emerging. This research aims to control the total pollutant discharge in a transboundary river basin, to improve the water environment, and enhance the capabilities of water resources management and decision-making. The organic connection between the control of total discharge quantity, the reduction of pollutant discharge, and the improvement of water environmental quality is established at large-scale from the perspective of comprehensive decision-making and management. In addition, this paper innovatively proposes a comprehensive watershed management model of multi-level and stepwise optimization for allocation of total load of water pollutants, which is integrated through the Gini coefficients method, the comprehensive weights method, and the minimal optimization model of environmental Gini coefficient. It is capable of optimizing distributions of total amount control of water pollutants in the whole basin and controlling units both spatially and temporally. The model is applied to the Songhua River basin to address the conflicts among regions’ environmental fairness and environmental sustainability. According to the optimization results based on the proposed model, the scheme for the total load allocation of water pollutants developed through optimization is consistent with the actual present situation of Heilongjiang section. Major dischargers like Harbin, Suihua, Qiqihar, and Daqing are mainly controlled, and the control units with a low discharge load were rationally controlled. The study has shown that the model was useful in providing decision-making support for water pollution total amount control of the Songhua River basin.