Abstract:

Nitrogen pollution poses a fundamental challenge to sustainable coastal development, requiring coordinated governance across terrestrial, riverine, and coastal systems. Yet economic drivers, riverine transport and coastal responses are commonly examined in isolation, limiting attribution of coastal impacts to their inland and socioeconomic sources. This study proposes a process-based economy-land-river-ocean framework for source attribution of coastal eutrophication and hypoxia, using the Pearl River Basin-Estuary system as a representative case. A city-level nitrogen discharge inventory is integrated with a multi-regional input-output (MRIO) model to characterize nitrogen discharge from production-based and consumption-based perspectives. Nitrogen loads are then routed through the river network using the Soil and Water Assessment Tool (SWAT) to resolve riverine transport, retention and delivery to estuarine outlets. The delivered nitrogen subsequently enters the estuarine and coastal ocean, where the China Sea Multiple-scale Ocean Modelling System (CMOMS) simulates its transport and biogeochemical transformation to assess nutrient-driven surface eutrophication and benthic hypoxia. This study pursues five objectives: (O1) quantify anthropogenic nitrogen discharge across cities and sectors and trace production-linked nitrogen to associated consumption through supply chains; (O2) quantify the downstream transport, retention and accumulation of land-based nitrogen through river networks and its delivery to estuarine outlets; (O3) evaluate how outlet-specific nitrogen delivery contributes to surface eutrophication and benthic hypoxia in the coastal ocean; (O4) attribute these coastal ecological impacts to their physical nitrogen sources and associated consumption under nitrogen chain-based and supply chain-based perspectives; and (O5) explore how future climate and socioeconomic pathways may reshape anthropogenic nitrogen discharge, riverine delivery and coastal ecological responses. The novelty of this study lies in three aspects: (N1) It reframes nitrogen-driven marine eutrophication and hypoxia as a source-to-impact process across the land-river-ocean continuum under joint human and natural controls. (N2) It operationalizes process-based source attribution by coupling MRIO, SWAT and CMOMS into economy-land-river-ocean modelling. (N3) It traces coastal eutrophication and hypoxia to city- and sector-level nitrogen sources and associated consumption across the Pearl River Basin under both nitrogen chain-based and supply chain-based perspectives. This research provides a process-based basis for understanding nitrogen source-to-impact pathways and informing coordinated land-sea nutrient governance.