Advection Within Shallow Pore Waters of a Coastal Lagoon, Florida

Abstract

Ground water sources can be a significant portion of a local water budget in estuarine environments, particularly in areas with high recharge rates, transmissive aquifers, and permeable marine sediments. However, field measurements of ground water discharge are often incongruent with ground water flow modeling results, leaving many scientists unsure which estimates are accurate. In this study, we find that both measurements and model results are reasonable. The difference between estimates apparently results from the sources of water being measured and not the techniques themselves. In two locations in the Indian River Lagoon estuarine system, we found seepage meter rates similar to rates calculated from the geochemical tracers 222Rn and 226Ra. Ground water discharge rates ranged from 4 to 9 cm/d using seepage meters and 3 to 20 cm/d using 222Rn and 226Ra. In contrast, in comparisons to other studies where finite element ground water flow modeling was used, much lower ground water discharge rates of ∼0.05 to 0.15 cm/d were estimated. These low rates probably represent discharge of meteoric ground water from land‐recharged aquifers, while the much higher rates measured with seepage meters, 222Rn, and 226Ra likely include an additional source of surface waters that regularly flush shallow (< 1 m depth) sediments. This resultant total flow of mixed land‐recharged water and recirculated surface waters contributes to the total biogeochemical loading in this shallow estuarine environment.

Flow and geochemistry of groundwater beneath a back-barrier lagoon: The subterranean estuary at Chincoteague Bay, Maryland, USA

“…The importance of bioirrigation in exchange of pore fluids in lagoon settings was highlighted by recent work in Florida (Martin et al, 2006). This is likely an important process in Chincoteague Bay as well, and may explain some of the rapid penetration of young saline water into groundwater beneath this estuary and similar settings Cable et al, 2004). The approach used in this investigation, particularly the greater depth and time components obtained by drilling and age dating, could be productively applied to experiments like the intercomparison studies of submarine groundwater discharge that have been done at geologically distinct sites in Florida, New York, Italy, Australia, Brazil, and Mauritius (Burnett et al, 2003(Burnett et al, , 2006.…”

Submarine groundwater discharge is an important net source of light and middle REEs to coastal waters of the Indian River Lagoon, Florida, USA

“…Freshwater is delivered to the studied portion of the Indian River Lagoon via direct precipitation, urban runoff, discharge of the Eau Gallie River and Crane Creek, and terrestrial SGD . Fluxes of SGD were previously determined at the study site using a combination of methods that included seepage meters, chemical and thermal tracers, and models of chemical profiles (excess 222 Rn, Ra isotope decay, Cl concentrations; Cable et al, 2004Cable et al, , 2006Martin et al, 2004Martin et al, , 2006Martin et al, , 2007Smith et al, 2008a,b;Roy et al, 2010). The flux of terrestrial SGD decreases with distance offshore becoming negligible near the freshwater-saltwater seepage face within the subterranean estuary (Fig.…”

Isotopic, geophysical and biogeochemical investigation of submarine groundwater discharge: IAEA-UNESCO intercomparison exercise at Mauritius Island

“…springs) or dispersed seepage. Since these isotope tracers integrate SGD fluxes over the scale of sampling, they have contributed to a better understanding of SGD dynamics, opposed to physical seepage measurements, which only constrain SGD fluxes on small, local scales Moore, 2006;Povinec et al, 2006aPovinec et al, ,b, 2008aSwarzenski et al, 2006;Cable et al, 2004;Weinstein et al, 2006;Stieglitz et al, 2008). …”