TY - JOUR
T1 - Exchange across the sediment-water interface quantified from porewater radon profiles
AU - Cook, Peter G.
AU - Rodellas, Valentí
AU - Andrisoa, Aladin
AU - Stieglitz, Thomas C.
PY - 2018/4
Y1 - 2018/4
N2 - Water recirculation through permeable sediments induced by wave action, tidal pumping and currents enhances the exchange of solutes and fine particles between sediments and overlying waters, and can be an important hydro-biogeochemical process. In shallow water, most of the recirculation is likely to be driven by the interaction of wave-driven oscillatory flows with bottom topography which can induce pressure fluctuations at the sediment-water interface on very short timescales. Tracer-based methods provide the most reliable means for characterizing this short-timescale exchange. However, the commonly applied approaches only provide a direct measure of the tracer flux. Estimating water fluxes requires characterizing the tracer concentration in discharging porewater; this implies collecting porewater samples at shallow depths (usually a few mm, depending on the hydrodynamic dispersivity), which is very difficult with commonly used techniques. In this study, we simulate observed vertical profiles of radon concentration beneath shallow coastal lagoons using a simple water recirculation model that allows us to estimate water exchange fluxes as a function of depth below the sediment-water interface. Estimated water fluxes at the sediment water interface at our site were 0.18–0.25 m/day, with fluxes decreasing exponentially with depth. Uncertainty in dispersivity is the greatest source of error in exchange flux, and results in an uncertainty of approximately a factor-of-five.
AB - Water recirculation through permeable sediments induced by wave action, tidal pumping and currents enhances the exchange of solutes and fine particles between sediments and overlying waters, and can be an important hydro-biogeochemical process. In shallow water, most of the recirculation is likely to be driven by the interaction of wave-driven oscillatory flows with bottom topography which can induce pressure fluctuations at the sediment-water interface on very short timescales. Tracer-based methods provide the most reliable means for characterizing this short-timescale exchange. However, the commonly applied approaches only provide a direct measure of the tracer flux. Estimating water fluxes requires characterizing the tracer concentration in discharging porewater; this implies collecting porewater samples at shallow depths (usually a few mm, depending on the hydrodynamic dispersivity), which is very difficult with commonly used techniques. In this study, we simulate observed vertical profiles of radon concentration beneath shallow coastal lagoons using a simple water recirculation model that allows us to estimate water exchange fluxes as a function of depth below the sediment-water interface. Estimated water fluxes at the sediment water interface at our site were 0.18–0.25 m/day, with fluxes decreasing exponentially with depth. Uncertainty in dispersivity is the greatest source of error in exchange flux, and results in an uncertainty of approximately a factor-of-five.
KW - Benthic flux
KW - Lake
KW - Porewater exchange
KW - Radon
KW - Recirculated seawater
KW - Tracers
UR - http://www.scopus.com/inward/record.url?scp=85043359553&partnerID=8YFLogxK
U2 - 10.1016/j.jhydrol.2018.02.070
DO - 10.1016/j.jhydrol.2018.02.070
M3 - Article
AN - SCOPUS:85043359553
VL - 559
SP - 873
EP - 883
JO - Journal of Hydrology
JF - Journal of Hydrology
SN - 0022-1694
ER -