Optimizing phosphorus retention in agricultural ditch and pond systems: ecological engineering and dynamic water management

Abstract Agricultural non-point source phosphorus pollution is a major contributor to eutrophication in freshwater ecosystems. Recent studies have highlighted the potential of small water bodies, such as ditches and ponds, for phosphorus retention. However, due to limitations in remote sensing resolution and accuracy for small water bodies, their monitoring and management remain challenging; most have focused on static hydrological conditions or single ecological measures, leaving the combined effects of multiple management strategies largely unexplored. Here, we conducted a controlled field experiment and applied a first-order kinetic model to evaluate the effects of ecological enhancement and water-level regulation on phosphorus retention performance. Our results indicate that the concentrations of total phosphorus (TP) and soluble reactive phosphorus (SRP) gradually decreased over time, with the rate of decrease showing a clear marginal effect. In sediment-rich ponds, the average removal rate of TP ranged from 59% to 92%, whereas in ponds without sediment, it ranged from 33% to 71%. The first-order rate constants ( k ) for TP retention ranged from 0.04 to 0.25 d −1 . Our findings provide a low-cost and scalable approach for mitigating agricultural non-point source phosphorus pollution and enhancing nutrient management in agroecosystems.