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 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 U, vegetation 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 vegetation-induced hyporheic
exchange at the sediment-water interface can be characterized by an
effective hyporheic exchange velocity, VH. We
further demonstrate that VH could correlate with
the total near-bed turbulent kinetic energy kt
rather than U. A kt-based model was
developed to characterize the impacts of vegetation on hyporheic
exchange.