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Agricultural drainage ditches are subjected to high anthropogenic nitrogen input, leading to eutrophication and greenhouse gas emissions. Nitrate-dependent anaerobic methane oxidation (N-DAMO) could be a promising remediation strategy to remove methane (CH₄) and nitrate (NO₃⁻) simultaneously. Therefore, we aimed to evaluate the potential of N-DAMO to remove excess NO₃⁻ and decrease CH₄ release from agricultural drainage ditches. Microcosm experiments were conducted using sediment and surface water collected from three different sites: a sandy-clay ditch (SCD), a freshwater-fed peatland ditch (FPD), and a brackish peatland ditch (BPD). The microcosms were inoculated with an N-DAMO enrichment culture dominated by Candidatus Methanoperedens and Candidatus Methylomirabilis and supplemented with ¹³CH₄ and ¹⁵NO₃⁻. A significant decrease in CH₄ and NO₃⁻ concentration was …