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Modeling Nitrate Export from a Mesoscale Catchment Using StorAge Selection Functions
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  • Tam Van Nguyen,
  • Rohini Kumar,
  • Stefanie Rayana Lutz,
  • Andreas Musolff,
  • Jie Yang,
  • Jan Fleckenstein
Tam Van Nguyen
Helmholtz Centre for Environmental Research

Corresponding Author:[email protected]

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Rohini Kumar
UFZ-Helmholtz Centre for Environmental Research
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Stefanie Rayana Lutz
UFZ Helmholtz Centre for Environmental Research
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Andreas Musolff
UFZ - Helmholtz-Centre for Environmental Research
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Jie Yang
Helmholtz-Center for Environmental Research - UFZ
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Jan Fleckenstein
Helmholtz Center for Environmental Research - UFZ
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Abstract

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 of discharge. SAS-based models have been emerging as promising tools for quantifying catchment-scale solute export, providing a coherent framework for describing both velocity and celerity driven transport. However, due to their application in headwaters only, the spatial heterogeneity of catchment physiographic characteristics, land-use management practices, and large-scale validation have not been adequately addressed with SAS-based models. In this study, we integrated SAS functions into the grid-based mHM-Nitrate model (mesoscale Hydrological Model) at both grid scale (distributed model) and catchment scale (lumped model). The proposed model provides a spatially distributed representation of nitrogen dynamics within the soil zone and a unified approach for representing both velocity and celerity driven subsurface transport below the soil zone. The model was tested in a heterogeneous mesoscale catchment. Simulated results show a strong spatial heterogeneity in nitrogen dynamics within the soil zone, highlighting the necessity of a spatially explicit approach for describing near-surface nitrogen processing. The lumped model could well capture instream nitrate concentration dynamics and the concentration-discharge relationship at the catchment outlet. In addition, the model could satisfactorily represent the relations between subsurface storage, mixing scheme, solute export, and the TTDs of discharge. The distributed model shows comparable results with the lumped model. Overall, the results reveal the potential for large-scale applications of SAS-based transport models, contributing to the understanding of water quality-related issues in agricultural landscapes.
Feb 2021Published in Water Resources Research volume 57 issue 2. 10.1029/2020WR028490