Modeling Nitrate Export From a Mesoscale Catchment Using StorAge Selection Functions

StorAge Selection (SAS) functions describe how catchments selectively remove water of different ages in storage via discharge, thus controlling the transit time distribution (TTD) and solute composition discharge. SAS-based models have been emerging as promising tools for quantifying catchment-scale export, providing a coherent framework describing both velocity-driven celerity-driven transport. Due to their application headwaters only, spatial heterogeneity catchment physiographic characteristics, land use management practices, large-scale validation not adequately addressed with models. Here, we integrated SAS into grid-based mHM-Nitrate model (mesoscale Hydrological Model) at grid scale (distributed model) (lumped model). The proposed provides spatially distributed representation nitrogen dynamics within soil zone unified approach representing subsurface transport below zone. was tested heterogeneous mesoscale catchment. Simulated results show strong zone, highlighting necessity explicit near-surface processing. lumped could well capture instream nitrate concentration concentration–discharge relationship outlet. In addition, provide insights relations between storage, mixing scheme, TTDs shows that are comparable model. Overall, reveal potential applications models, contributing understanding quality-related issues agricultural landscapes.