Allocation of total load reduction considering the social-economic benefits and water quality impacts of subregions

Reducing nutrient inputs from land-based anthropogenic pollutions is a crucial task to enhance the water quality and maintain the ecological functionality. This study aims to develop a novel method for allocating the total load reduction task to different administrative zones considering the economic and social benefits and water quality effects of each zone, taking the Mainstream of Liao River Watershed (MLRW) in China as an example. The soil and water assessment tool (SWAT) was employed as a water quality model to quantify nutrient load contributions from each pollution source and predict the water quality responses to various allocation schemes. Four load allocation schemes were developed based on environmental efficiencies calculated by Data Envelopment Analysis (DEA) and load contributions of different zones. The impacts on environmental (nutrient load), economic (GDP) and social (crop yield) benefits of the watershed were evaluated. To ensure the equality of allocation results, the environmental Gini coefficient was used to examine the equality level. The results indicated that crop planting was the largest pollution source to total nitrogen (TN), accounting for 48.7%, while animal breeding was the largest pollution source to total phosphorus (TP), accounting for 46.0%. The allocation schemes involving the environmental efficiencies were found to enhance economic and social benefits compared to those solely considered the load contributions of zones. For maximizing economic benefits, the most suitable pollution load reduction scheme involves using economic-environmental efficiency as the adjustment factor for allocation proportion. Likewise, for maximizing social benefits, the preferred scheme is to incorporate the social-environmental efficiency. The pollution load reduction scheme incorporating economic-social-environmental efficiency serves as a balanced compromise, addressing both economic and social benefits. The Gini coefficients of the four schemes were below 0.4, affirming adherence to the equality principle. The analysis framework used in this study provides decision-makers with the flexibility to select allocation schemes tailored to their specific needs when formulating water quality management strategies.