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Droughts can reduce the nitrogen retention capacity of catchments
  • +4
  • Carolin Winter,
  • Van Tam Nguyen,
  • Andreas Musolff,
  • Stefanie Lutz,
  • Michael Rode,
  • Rohini Kumar,
  • Jan H. Fleckenstein
Carolin Winter
Helmholtz Centre for Environmental Research - UFZ, Helmholtz Centre for Environmental Research - UFZ

Corresponding Author:[email protected]

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Van Tam Nguyen
Helmholtz Centre for Environmental Research - UFZ, Helmholtz Centre for Environmental Research - UFZ
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Andreas Musolff
UFZ - Helmholtz-Centre for Environmental Research, UFZ - Helmholtz-Centre for Environmental Research
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Stefanie Lutz
Universiteit Utrecht, Universiteit Utrecht
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Michael Rode
Department Aquatic Ecosystem Analysis and Management, Helmholtz Centre for Environmental Research - UFZ, Germany, Department Aquatic Ecosystem Analysis and Management, Helmholtz Centre for Environmental Research - UFZ, Germany
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Rohini Kumar
Helmholtz Centre for Environmental Research - UFZ, Helmholtz Centre for Environmental Research - UFZ
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Jan H. Fleckenstein
Universität Bayreuth,Helmholtz-Zentrum für Umweltforschung UFZ, Universität Bayreuth,Helmholtz-Zentrum für Umweltforschung UFZ
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Abstract

In 2018–2019, Central Europe experienced an unprecedented multi-year drought with severe impacts on society and ecosystems. In this study, we analyzed the impact of this drought on water quality by comparing long-term (1997-2017) nitrate export with 2018–2019 export in a heterogeneous mesoscale catchment. We combined data-driven analysis with process-based modelling to analyze nitrogen retention and the underlying mechanisms in the soils and during subsurface transport. We found a drought-induced shift in concentration-discharge relationships, reflecting exceptionally low riverine nitrate concentrations during dry periods and exceptionally high concentrations during subsequent wet periods. Nitrate loads were up to 70% higher compared to the long-term load-discharge relationship. Model simulations confirmed that this increase was driven by decreased denitrification and plant uptake and subsequent flushing of accumulated nitrogen during rewetting. Fast transit times (<2 months) during wet periods in the upstream sub-catchments enabled a fast water quality response to drought. In contrast, longer transit times downstream (>20 years) inhibited a fast response but potentially contribute to a long-term drought legacy. Overall, our study reveals that severe multi-year droughts, which are predicted to become more frequent across Europe, can reduce the nitrogen retention capacity of catchments, thereby intensifying nitrate pollution and threatening water quality.