Mitigating Reactive Nitrogen Cascade Effects in Deltaic Wetland Systems Through Constructed Riparian Buffer Optimization Under Intensified Agricultural Runoff Regimes

Abstract

Reactive nitrogen (Nr) accumulation in deltaic wetland ecosystems poses a critical threat to biogeochemical cycling, aquatic biodiversity, and downstream coastal eutrophication. This study investigates the efficacy of optimized constructed riparian buffer strips (CRBS) in intercepting Nr flux—specifically nitrate-nitrogen (NO₃⁻-N) and ammonium-nitrogen (NH₄⁺-N)—under intensified agricultural runoff regimes in the Mekong Delta region. Using a combination of stable isotope tracing (δ¹⁵N), in-situ porewater sampling, and HYDRUS-2D vadose zone modelling, we quantified denitrification rates and Nr retention efficiency across five CRBS configurations. Results demonstrate that multi-strata native-species buffers achieving widths ≥35 m reduced total Nr export by 67.4% compared to monoculture grass strips. Microbial community profiling via 16S rRNA amplicon sequencing revealed significant enrichment of Candidatus Accumulibacter and Nitrosomonas lineages correlating with peak denitrification activity. These findings provide actionable design thresholds for wetland buffer policy in Southeast Asian deltaic agroecosystems.