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Winter post-droughts amplify extreme nitrate concentrations in German rivers

Saavedra, Felipe, Musolff, Andreas, Von Freyberg, Jana, Merz, Ralf, Knöller, Kay, Müller, Christin, Brunner, Manuela, Tarasova, Larisa·2024·Environmental Research Letters
DOI 10.1088/1748-9326/ad19ed
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Abstract

Hydrological extremes can affect nutrient export from catchments to streams, posing a threat to aquatic ecosystems. In this study, we investigated the effects of hydrological drought on nitrate concentrations in the streamflow of 182 German catchments from 1980 to 2020. We found that across all seasons, 40% and 25% of the catchments showed significantly lower nitrate concentrations during drought and post-droughts, respectively, when compared to non-drought conditions. However, we observed pronounced spatial variability in the responses, particularly during winter droughts and post-droughts, with more catchments exhibiting higher nitrate concentrations. Specifically, nitrate concentrations were significantly higher in 25% of the study catchments during winter droughts, particularly in wetter catchments with low nitrogen retention. During winter post-droughts, nitrate concentrations are significantly higher in 19% of the catchments, especially in wetter catchments with more nitrogen surplus. Moreover, the likelihood of nitrate seasonal extremes increased by 6% during winter post-drought in our study catchments. Considering the projected increase in the frequency of droughts in Germany, the increase in nitrate concentrations during the corresponding post-drought periods poses a potential threat to aquatic ecosystem health.

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  • The spring peak in NO3 concentrations is likely due to agricultural runoff.

    “likely due to agricultural runoff”

    From A study of surface water quality using organic pollution indices: Comparative characteristics and educational opportunities (2025) · cites this paper as Saavedra et al. 2024

    The Introduction says agricultural nitrate can reach streams through runoff-related pathways, supporting the proposed mechanism. It describes high concentrations in winter and low concentrations in summer, but does not identify a spring peak or attribute one to agricultural runoff. The Results (section 3.1) instead report lower spring concentrations during drought and post-drought periods than under non-drought conditions. (LLM, conf=0.82)

    Experimental — accuracy not yet measured

  • The autumn and winter phosphate peaks are possibly due to runoff and reduced uptake by aquatic plants.

    “possibly due to runoff and reduced uptake by aquatic plants (Saavedra et al. 2024).”

    From A study of surface water quality using organic pollution indices: Comparative characteristics and educational opportunities (2025) · cites this paper as Saavedra et al. 2024

    The Introduction and section 4.2 discuss runoff-driven transport of nitrate, while the Introduction describes reduced nitrogen uptake by water-stressed vegetation. Neither the supplied passages nor searches for phosphate peaks and aquatic-plant uptake address the proposed explanation for autumn and winter phosphate peaks. (LLM, conf=0.76)

    Experimental — accuracy not yet measured

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Cited by

Sorted by citations

Authors
Saavedra, F., Musolff, A., Von Freyberg, J., Merz, R., Knöller, K., Müller, C., Brunner, M., & Tarasova, L.
ORCID
Venue
Environmental Research Letters
Publisher
IOP Publishing
Published
2024-01-18
Volume
19
Issue
2
Pages
024007
ISSN
1748-9326
DOI
10.1088/1748-9326/ad19ed
Cited by
13
References
0
Licence
Funders
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (PR00P2_185931)

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