23 Jun 2022
23 Jun 2022
Status: this preprint is open for discussion.

Droughts can reduce the nitrogen retention capacity of catchments

Carolin Winter1, Tam V. Nguyen1, Andreas Musolff1, Stefanie R. Lutz2, Michael Rode3,4, Rohini Kumar5, and Jan H. Fleckenstein1,6 Carolin Winter et al.
  • 1Department for Hydrogeology, Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany
  • 2Copernicus Institute of Sustainable Development, Utrecht University, Utrecht, Netherlands
  • 3Department Aquatic Ecosystem Analysis and Management, Helmholtz Centre for Environmental Research - UFZ, Magdeburg, Germany
  • 4Institute of Environmental Science and Geography, University of Potsdam, Potsdam-Golm, Germany
  • 5Department of Computational Hydrosystems, Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany
  • 6Hydrologic Modelling Unit, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, Germany

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.

Carolin Winter et al.

Status: open (until 18 Aug 2022)

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Carolin Winter et al.


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Short summary
We investigated the impact of the severe 2018–2019 Central European drought on riverine nitrate pollution. We found that under severe drought, catchments can lose part of their nitrogen retention capacity due to decreased denitrification and plant uptake, but the time scale of riverine nitrate export responses to drought can be catchment specific. These results imply that severe and prolonged droughts can intensify nitrate pollution and threaten water quality.