Rice Cultivation and Nitrogen Transport Across Connected Catchment–Coastal Systems: A Systematic Review (2016–2025)

Rice-growing landscapes connect nitrogen management with coastal water quality, but mixed sources and transformations complicate attribution. This systematic review examines transport, management, attribution and monitoring across connected catchment–coastal systems. Scopus was searched on 1 September 2026 for articles published during 2016–2025. Archived exports identify 89 initial records and 26 retained articles, including rice studies and contextual agricultural and coastal evidence. All six authors participated in selection and extraction. Study-specific design, measurement and transferability domains informed a narrative synthesis; heterogeneous endpoints precluded meta-analysis. In the Albufera network, nitrate-N averaged 1.947 ± 0.188 mg N L−1 (SE; range 0.013–4.705). At one lagoon site, reported nitrate rose from 2.26 to 7.94 mg L−1 across the October 2024 flood; its unspecified mass basis prevents conversion to nitrate-N. These observations describe mixed-source exposure rather than rice-derived coastal loads. Red River isotope evidence identifies substantial domestic and manure contributions, while Po Delta incubations support season-specific denitrification. Rice experiments inform fertiliser management but do not establish marine effects; non-rice modelling provides conditional management comparisons. Single-database and open-access search restrictions, incompletely assigned exclusion reasons and partial full-text verification limit reproducibility and appraisal. The synthesis supports coordinated fertiliser and drainage management, source apportionment and flow-weighted monitoring. A universal rice-specific effect on marine eutrophication remains unestablished. The review received no external funding; no verifiable registration identifier was available.