HR: 08:15h
AN: B51D-02    [Abstracts]
TI: Controls of Submarine Groundwater Discharge on the Redox Conditions in the Outflow Face System of Indian River Lagoon
AU: * Roy, M
EM: moutusi@ufl.edu
AF: Department of Geological Sciences, University of Florida, Gainesville, FL 32611, United States
AU: Martin, J
EM: jbmartin@geology.ufl.edu
AF: Department of Geological Sciences, University of Florida, Gainesville, FL 32611, United States
AU: Cable, J
EM: jcable@lsu.edu
AF: Department of Oceanography and Coastal Sciences/CEI, Louisiana state University, Baton Rouge, LA 70803, United States
AU: Smith, C
EM: csmi125@paws.lsu.edu
AF: Department of Oceanography and Coastal Sciences/CEI, Louisiana state University, Baton Rouge, LA 70803, United States
AU: Cherrier, J
EM: jennifer.cherrier@famu.edu
AF: Environmental Sciences Institute, Florida A and M University, Tallahassee, Fl 32307, United States
AU: Dorsett, A
EM: amanda1.dorsett@famu.edu
AF: Environmental Sciences Institute, Florida A and M University, Tallahassee, Fl 32307, United States
AB: Fresh groundwater discharge to estuaries creates a subsurface zone where oxygenated surface water mixes with reduced pore water, forming redox boundaries in sediment of the outflow face (the subterranean estuary). This mixing has been widely cited to satisfy discrepancies of mass balance calculations for submarine groundwater discharge of terrestrially derived water (terrestrial SGD). Redox boundaries in the subsurface are clearly shown in distributions Fe and Mn in pore waters collected from Indian River Lagoon, Florida. Pore waters were collected from 8 sites in a 30 m transect offshore and at a single site 250 m offshore. Terrestrial SGD decreases offshore to the seaward end of the outflow face at 22.5 m. Both Fe and Mn show maxima in their depth profiles. Manganese maxima are restricted to the upper 40 cmbsf (centimeter below the surface) and always occur above the Fe maxima, which increase in depth offshore. Maximum Fe and Mn concentrations (1.05 and 0.28 μM, respectively) at the shoreline are of the same order of magnitude as maximum Fe and Mn concentrations (0.48 μM and 0.56 μM, respectively), at 250 m offshore. Maximum Fe and Mn concentrations increase to 261 μM, and 2.9 μM respectively, 22.5 and 30m offshore, a few meters seaward of the outflow face. Between 5 and 20 m offshore, the maximum Fe concentrations increase from 3.7 to 22.8 μM, but maximum Mn concentrations show little variability, averaging around 1.05 μM ± 20%. Sediments collected in three vibracores at 0, 20, and 30 m offshore are orange-yellow at the shoreline. A black layer, which occurs above these orange-yellow sediments, increases in thickness from 5 cm to 60 cm from the shoreline to 30 m offshore. The variation in color corresponds to changes in solute concentrations: S^2- maxima occur within the black layer, Fe maxima occur in the orange-yellow layer, and Mn maxima mostly occur in the black layer. Pore water Fe and S^2- are inversely correlated and no correlation exists between Mn and S^2-. These distributions of solutes suggest the source of Fe and Mn are oxyhydroxides coating the orange-yellow sediments. Dissolved Fe accumulates in absence of S^2-, and the depths of the Fe maxima increase as S^2- concentrations increase offshore. The low concentrations of Fe and Mn within the outflow face may reflect discharge of water from the outflow face, while the elevated concentrations seaward of the outflow face reflects a zone of no flow. Farther offshore, Fe concentrations are low because of elevated S2- production there. The distributions of these redox sensitive elements suggest there is little landward flow of marine water that mixes with the terrestrial source of SGD.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0442 Estuarine and nearshore processes (4235)
DE: 4235 Estuarine processes (0442)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting