Reduction of Point Source Pollutant Load: An Allocation Model for the Watershed TMDL Program

An allocation scheme of water pollutant reduction is the key procedure to implement a watershed total maximum daily load (TMDL) program. In order to improve the equity for the allocation scheme of water pollutant load reduction, five indexes involved in allocation processes were selected from fields associated with society, environment, economics, and resources. The weights of these indexes were determined by using fuzzy optimization and entropy weight methods, and a multi-dimensional Gini coefficient-based allocation model for watershed point source pollutant load reduction was established. Corresponding constraint conditions were set to optimize the allocation scheme of point source pollutant load reduction. This model embodies the variability in importance of various indexes in the allocation process, and improves the equity and scientific basis of the allocation scheme. It is a reasonably ideal allocation model, and was used to allocate amino nitrogen load reductions in the Zhangweinan River basin. As validated by the soil and water assessment tool (SWAT) model, the optimized reduction scheme meets the water quality criteria for the relevant water functional area in the watershed in various target years. Authors in this paper made great efforts for the reduction allocation of watershed point source pollutant load in the watershed with intensive anthropogenic activities. The results provide a scientific basis and technical support for water environmental protection and sustainable uses of water resources in the Zhangweinan River basin.