Effect of topographic slope on the export of nitrate in humid catchments: a 3D model study

Abstract. Excess export of nitrate to streams affects ecosystem structure and functions has been an environmental issue attracting worldwide attention. The dynamics catchment-scale solute from diffuse nitrogen sources can be explained by the changes dominant flow paths, as attenuation (including degradation nitrate) is linked age composition outflow. Previous data-driven studies suggested that catchment topographic slope strong impacts on streamflow consequently in-stream concentrations. However, have not systematically assessed in terms mass fluxes concentration levels, particularly humid catchments with seasonality meteorological forcing. To fill this gap, we modeled groundwater transport for a small agricultural Central Germany. We used fully coupled surface subsurface numerical simulator HydroGeoSphere (HGS) model overland transport. computed water ages using tracer experiments. represent various slopes, additionally simulated 10 synthetic generated modifying real-world scenario. Results suggest negative correlation between young fraction slope. This more pronounced flat landscapes slopes <1:60. Flatter tend retain N soil degraded soil) less stream, due reduced leaching increased degradation. mean shows decreasing trend response slope, suggesting large sufficient high Our results improve understanding temperate climate, important implications management stream quality.