Mitigating nutrient loss in rice-wheat rotation system: An ecologically engineered solutions with field-ditch-pond systems

The Taihu Lake basin features a typical agricultural landscape where interconnected field-ditch-pond systems serve as transitional zones between rice paddies and adjacent water bodies, though their nutrient regulation mechanisms remain unclear. Through continuous in-situ monitoring across rice-growing seasons and drainage events, this study quantified spatiotemporal patterns of nitrogen and phosphorus migration in a typical field-ditch-pond system. Results demonstrated that paddy surface water nutrient levels peaked one day after basal fertilization. Ammonium concentrations in ditches surged within 60–120 min during rainfall-induced drainage, while total phosphorus peaked at 80 min before stabilizing after five days. The system exhibited distinct seasonal dynamics, with ecological ponds showing 1.13 times higher total nitrogen but and 0.53 times lower total phosphorus during the rainy season (July-September) versus dry periods (October-December). Along the field-ditch-pond continuum, field water peaks preceded ditch responses (total nitrogen at 9 days, total phosphorus at 3 days post-fertilization), while ponds achieved rapid stabilization (1-day peaks). The integrated system delivered average removal efficiencies of 27.81 % total nitrogen and 40.82 % total phosphorus, attenuated peak concentrations (52 % reduction for total nitrogen, 192 % reduction for total phosphorus), and delayed nutrient surges by 24–48 h. These findings highlight the field-ditch-pond systems as effective ecologically engineered solutions for mitigating agricultural nutrient discharge, suggesting that optimized ecological management could enhance their water purification capacity and potentially reduce eutrophication risks in receiving waters across global rice-growing regions with similar hydrological landscapes.