[Cost-benefit Analysis of Synergistic Pollutant and Carbon Reduction Through Watershed Interventions]

Quantitative analysis of the environmental benefits， carbon emissions， and economic costs of watershed management interventions is crucial for meeting pollution and carbon reduction targets. However， existing watershed studies mainly focus on assessing the environmental benefits and financial costs of pollution control facilities. Few evaluate their carbon emissions， and those that do typically focus on single facility types， missing a comprehensive and systematic analysis of emissions across entire watershed pollution control systems. This study creates a watershed cost-benefit assessment framework for water interventions， demonstrated in the Dianchi watershed. By comparing the characteristics of interventions and their effects on water quality and quantity， along with carbon emission and economic cost data from facility construction and operation， this analysis examines the cost-benefit performance under various scenarios. The results revealed notable synergistic effects between urban low impact development （LID） implementation and other watershed facilities. Urban LID and rural best management practices （BMP） measures showed lower marginal carbon abatement costs per unit pollutant reduction， while the inter-basin ecological water diversion involved higher costs. Conversely， water diversion and combined sewer storage capacity expansion （SCE） exhibited lower marginal economic costs， whereas urban LID implementation incurred higher costs. This framework uncovers synergistic interactions among water environment control measures， providing a methodological foundation for systematic cost-benefit assessment of watershed intervention systems.