Hyporheic exchange, or the exchange of water and solutes between surface and subsurface water at the sediment-water interface, regulates water quality and biogeochemical cycle in aquatic ecosystems. Vegetation, which is ubiquitous in nature, is known to impact hyporheic exchange; yet how vegetation impacts hyporheic exchange remains to be characterized. Here, we show that at the same spatially and temporally-averaged flow velocity (Formula presented.), vegetation increases the rate of hyporheic exchange by a factor of four. By tracking the movement of fluorescent dye in a flume with the refractive-index-matched sediment and translucent vegetation dowels, we demonstrate that the vegetation-induced hyporheic exchange can be characterized by an effective hyporheic exchange velocity, (Formula presented.). We further demonstrate that (Formula presented.) correlates with the total near-bed turbulent kinetic energy (Formula presented.) rather than (Formula presented.), when (Formula presented.), indicating that turbulent kinetic energy is a better metric than flow velocity for predicting hyporheic exchange in regions with vegetation.
Bibliographical noteFunding Information:
Partial support was provided by the University of Minnesota through JQY's startup funds and the Minnesota Water Research Fund. The authors would like to thank Sam Nguyen for his assistance with the experiments and Benjamin Erickson, Erik Steen, Matthew Lueker, Jim Tucker, and Jeffrey Marr for help with the flume.
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- hyporheic flow
- spatial heterogeneity
- turbulent kinetic energy