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Model choice impacts the quantification of seasonal hyporheic exchange depths and fluxes
  • Lara-Maria Schmitgen,
  • Reinhard Bierl,
  • Tobias Schuetz
Lara-Maria Schmitgen
University of Trier, University of Trier

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Reinhard Bierl
University of Trier, University of Trier
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Tobias Schuetz
University of Trier, University of Trier
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Abstract

Direction and depths of hyporheic exchange fluxes at the groundwater - surface water interface are drivers of biogeochemical processes influencing nutrient cycling and water quality. Model concepts on the dynamic relationship between hyporheic exchange fluxes and exchange depth are typically based on the assumption of a linear relationship between both measures. Here, we quantify seasonal and episodic variations of hyporheic exchange fluxes and hyporheic exchange depths with methods of heat tracing. Numerically (FLUX-BOT) and analytically (VFLUX; method based on temperature amplitude dampening developed by Hatch et al., 2006) working program scripts were used to solve the one-dimensional conduction-advection-dispersion equation and compute hyporheic flux rates from three vertical sediment water temperature profiles recorded continuously in a small low mountain creek between 2011 and 2017. By comparing the behavior of two differing water temperature-based modelling approaches, dissimilarities in the sensitivity to sediment thermal properties were identified. These differences in parameter responsivity explain deviating behavior of the models regarding exchange flux and depth calculations. We show that the vertical extension of hyporheic exchange depth has a distinctive seasonal pattern over seven years, which differs between the chosen models. Surface water levels, groundwater levels and stream discharges show significant correlations with both flux direction and hyporheic zone extension. In contrast to the numerical modelling approach, analytically derived flux data allowed for establishing a significant relationship between the hydraulic gradient observed at a nearby groundwater well and simulated hyporheic exchange depths.
Dec 2021Published in Water Resources Research volume 57 issue 12. 10.1029/2021WR030298