Integration of SWAT-DPS and optimization algorithm for spatial design of ditch-pond systems in small agricultural catchments

Abstract

Ditches and ponds are widely used in rural landscapes, forming integrated adaptation systems that play a pivotal role in reducing non-point source (NPS) pollution. However, existing semi-distributed models are not capable of accurately simulating pollution removals of ditches and ponds, resulting in a critical gap in integrating simulation, optimization, and spatial configuration for effective pollution control. To address this issue, the newly developed SWAT-DPS model was integrated with multi-objective optimization to construct an integrated framework for optimizing the layouts of ditches and ponds while effectively balancing environmental and economic benefits. This framework enables more accurate grid-scale simulation of pollution reduction of measures, offering more practical layout solutions. Results showed that implementing vegetated ditches, multiple ponds, and vegetation filter strips could reduce NPS pollutants by 20–60 %. Comparative analysis revealed the costs ranging from 0 to 6.28 × 10⁶ yuan, with all cost levels achieving required reductions in total nitrogen (TN) and total phosphorus (TP). Specifically, TN reductions exceeded 60 % in the medium-cost scheme, while TP reductions reached 60 % similarly in the high-cost scheme. This study provides a flexible framework for evaluating the removal efficiencies of NPS pollution, with fully consideration of the spatial configuration of ditch-pond system.