Impacts of Emergent Vegetation on Hyporheic Exchange

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.