Hydrological amplification effect of pollutant flux in rivers discharging to the sea under climate change

Study region The Luanhe River Basin (LRB) in northern China. Study focus Climate change has intensified hydrological variability, yet the specific effects of pronounced hydrological changes on the transport and seaward fluxes of river pollutants remain unclear. To address this, this study utilized remote sensing hydrological station (RSHS) technology to obtain monthly runoff in the LRB. Combined with water quality monitoring data, the annual fluxes of total nitrogen (TN) and total phosphorus (TP) were calculated. Through correlation analysis, flux contribution decomposition, and ridge regression analysis, the relationships among changes in runoff, pollutant concentration, and pollutant flux were investigated, along with the influence of fluxes on estuarine chlorophyll-a (Chl-a) concentrations. New hydrological insights for the region This study first quantifies the "hydrological amplification effect" in the LRB. Climate-driven runoff significantly increased across all sub-basins (Mann–Kendall test Z > 1.96), driving sustained rises in seaward TN and TP fluxes. Runoff contributed 92–94% of flux changes, completely overwhelming emission reductions from decreasing local concentrations. This mechanism reveals that even with improved basin water quality, persistent runoff growth exacerbates estuarine eutrophication through enhanced scouring—31% and 27% of the Chl-a increase are attributable to TP and TN fluxes, respectively. Therefore, future environmental strategies must shift from concentration-based control to flux management and embed climate adaptation planning into integrated basin–estuary governance.