Heat-based hyporheic flux calculations in heterogeneous salmon spawning gravels

Christian Birkel*, Chris Soulsby, Dylan J. Irvine, Iain Malcolm, Laura K. Lautz, Doerthe Tetzlaff

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)

Abstract

Groundwater-surface water interactions in rivers are a critically important factor for fish spawning, as streamwater downwelling or upwelling of low-oxygen groundwater can affect egg survival. Assessing such dynamics at the reach scale using distributed temperature measurements as a tracer proved reliable in determining flux rates and directions in the hyporheic zone in a number of studies. Here, we report heat-based vertical flux rates from a heterogeneous gravel-bed stream reach used by spawning Atlantic salmon in the Scottish Highlands. Results showed mostly small downwelling fluxes (~0.3 m d<sup>−1</sup>), which were largely independent of discharge. Contrasting, and at times unusual flux-depth profiles (e.g., increasing flux with depth) were detected, consistent with the heterogeneous streambed material causing diverse hyporheic flow paths. This was tested in a numerical 2-D model setup attempting to reproduce such behavior with variable random hydraulic conductivity (K) fields. The 2-D model clearly demonstrated that strong deviations from the expected decrease of fluxes with depth can be explained by high heterogeneity coupled with relatively low K fields. This showed that using simple 1-D heat-based flux estimates in combination with 2-D models is a useful approach to testing hypotheses about the influence of variable streambed materials on groundwater–surface water exchange in an ecological context.

Original languageEnglish
Pages (from-to)203-213
Number of pages11
JournalAquatic Sciences
Volume78
Issue number2
Early online date19 Aug 2015
DOIs
Publication statusPublished - 1 Apr 2016

Bibliographical note

Acknowledgments We thank J. Grant for her efforts in the field collecting the data used in this study. Auxiliary data provided by Marine Sciences Scotland, Freshwater Laboratory and the Scottish Environmental Protection Agency. Dylan Irvine and Laura Lautz were supported by the National Science Foundation under Grant No. EAR–0901480.

Keywords

  • ground water-surface water interaction
  • heat tracer
  • hyporheic zone
  • numerical 2-D model
  • Vflux

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