Non-point source pollution in a heterogeneous metropolitan region: land use and environmental drivers across urban and non-urban areas

Non-point source (NPS) pollution remains a persistent challenge in metropolitan areas with complex land use patterns and increasing environmental variability. Management strategies often rely on broad land use categories that may not fully capture this heterogeneity. We examine how detailed land use and environmental factors jointly shape NPS pollution across urban and non-urban areas in the Seoul Metropolitan Area. By considering detailed land use categories with slope and flooding conditions, the analysis identifies consistent and context-dependent land use – pollution relationships beyond a simple urban – non-urban distinction. The results show that commercial and industrial areas were associated with higher NO3-N concentrations across urban and non-urban contexts, while agricultural areas showed greater variation across years and contexts. Mixed forests and natural grasslands were associated with lower pollutant concentrations, although these relationships changed under flooding conditions. These findings highlight the need for more targeted, context-sensitive approaches that account for spatial heterogeneity and environmental variability.