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Denitrification-driven transcription and enzyme production at the river–groundwater interface: Insights from reactive-transport modeling
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  • Anna Störiko,
  • Holger Pagel,
  • Adrian Mellage,
  • Philippe Van Cappellen,
  • Olaf A. Cirpka
Anna Störiko
University of Tübingen, University of Tübingen

Corresponding Author:anna.stoeriko@uni-tuebingen.de

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Holger Pagel
University of Hohenheim, University of Hohenheim
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Adrian Mellage
University of Tübingen, University of Tübingen
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Philippe Van Cappellen
University of Waterloo, University of Waterloo
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Olaf A. Cirpka
University of Tübingen, University of Tübingen
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The interface between rivers and groundwater is a key driver for the turnover of reactive nitrogen compounds, that cause eutrophication of rivers and endanger drinking-water production from groundwater. Molecular-biological data and omics tools have been used to characterize microorganisms responsible for the turnover of nitrogen compounds. While transcripts of functional genes and enzymes are used as measures of microbial activity it is not yet clear how they quantitatively relate to actual turnover rates under variable environmental conditions. We developed a reactive-transport model for denitrification that simultaneously predicts the distributions of functional-gene transcripts, enzymes and reaction rates. Applying the model, we evaluate the response of transcripts and enzymes at the river–groundwater interface to stable and dynamic hydrogeochemical regimes. While functional-gene transcripts respond to short-term (diurnal) fluctuations of substrate availability and oxygen concentrations, enzyme concentrations are stable over such time scales. The presence of functional-gene transcripts and enzymes globally coincides with the zones of active denitrification. However, transcript and enzyme concentrations do not directly translate into denitrification rates in a quantitative way because of non-linear effects and hysteresis caused by variable substrate availability and oxygen inhibition. Based on our simulations, we suggest that molecular-biological data should be combined with aqueous chemical data, which can typically be obtained at higher spatial and temporal resolution, to parameterize and calibrate reactive-transport models.
Aug 2022Published in Water Resources Research volume 58 issue 8. 10.1029/2021WR031584