Abstract
Hyporheic exchange, or the exchange of water and solutes between surface
and subsurface water at the sediment-water interface, regulates water
quality and biogeochemical cycles in aquatic ecosystems. Vegetation,
which is ubiquitous in aquatic ecosystems, 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 U, vegetation-generated turbulence
increases the rate of hyporheic exchange by a factor of four. By
tracking the movement of fluorescent dye in a flume with index-matched
sediment and translucent vegetation dowels, we demonstrate that
turbulence-induced hyporheic exchange at the sediment-water interface
can be characterized by a one-dimensional diffusion coefficient,
DSWI. We further demonstrate that
DSWI correlates with the total near-bed turbulent
kinetic energy kt rather than mean flow velocity
U. A kt-based model was developed to
characterize the impacts of vegetation-generated turbulence on hyporheic
exchange.