Climate change has intensified hydrological extremes in many deltaic coastal zones, amplifying both flood hazards and agricultural non-point source (NPS) pollution. The newly reclaimed deltaic farmland in coastal Shanghai represents a typical climate-sensitive agroecosystem where irrigation and rainfall jointly drive nutrient losses. This study employs a high-frequency, flow-triggered hydrological and water-quality monitoring system capable of distinguishing irrigation-driven versus rainfall-driven runoff to evaluate the performance of a constructed ditch–pond system (DPS). It provides the first field-based assessment of DPS functioning in such reclaimed coastal farmland, where irrigation dominates early-stage nutrient export. By integrating water-level, Doppler flow, and event-scale nutrient measurements, we further examine DPS regulation of flood peaks and nutrient retention. The results indicate that: (1) Irrigation-driven runoff accounted for more than 80% of total nitrogen and ammonium losses, particularly within 10 days after fertilization, highlighting a critical early-loss window. (2) The DPS demonstrated strong nutrient retention capacity, with removal efficiencies of 56.2–91.2% for TN, 17.2–96.2% for AN, and 30.1–91.4% for TP, driven by enhanced residence time and internal biogeochemical processing. (3) Hydrological regulation was substantial, as the DPS attenuated typhoon-induced flood peaks by up to 37.8% and delayed runoff propagation across the field–ditch–pond continuum. Event-triggered reuse of pond water during fertilization reduced nutrient discharge and improved fertilizer use efficiency. Overall, this study provides an integrated hydrological–biogeochemical evaluation of DPS performance and demonstrates that such systems offer a practical, low-cost nature-based solution for mitigating NPS pollution and flood risks in vulnerable deltaic agricultural landscapes under intensifying climate pressures.
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Funding
Shanghai Agriculture Commission Science and Technology Innovation Project(SH-AST(A2025010))
Shanghai Municipal Bureau of Ecology and Environment Research Project(SH-ESE [2024] No. 3)
Science and Technology Innovation Action Plan Social Development Key Science and Technology Project of Shanghai(21DZ1202400)
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The Author(s)
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