HR: 16:00h
AN: B44A-03    [Abstracts]
TI: Biogeochemical transport in the Loxahatchee River estuary, FL: The role of submarine groundwater discharge
AU: * Swarzenski, P
EM: pswarzen@usgs.gov
AF: USGS, 600 4th Street S, St Petersburg, FL 33701 United States
AU: Orem, B
EM: borem@usgs.gov
AF: USGS, 12201 Sunrise Valley Drive, Reston, VA 20192 United States
AU: McPherson, B
EM: bmcpherson@usgs.gov
AF: USGS, 10500 University Center Drive, Suite 215, Tampa, FL 33612 United States
AU: Baskaran, M
EM: baskaran@wayne.edu
AF: Wayne State Univ, Geology Dept. 0224 Old Main Building, Detroit, MI 48202 United States
AU: Wan, Y
EM: ywan@sfwmd.gov
AF: SFWMD, P.O. Box 24680, West Palm Beach, FL 33416
AB: The distributions of dissolved organic carbon (DOC), silica, select trace elements (Mn, Fe, Ba, Sr, Co, V,) and a suite of naturally-occurring radionuclides in the U/Th decay series (222Rn, 223,224,226,228Ra, 238U) were studied during high and low discharge conditions in the Loxahatchee River estuary, Florida. The zero-salinity endmember of this still relatively pristine estuary may reflect not only river-borne constituents, but also those advected during active groundwater/surface-water discharge. During low discharge conditions, with the notable exception of Co, trace metals indicate nearly conservative mixing from a salinity of ~12 through the estuary (This statement contracdicts with what is said in p. 7). In contrast, of the trace metals studied, only Sr, Fe, U and V exhibited conservative estuarine mixing during high discharge. Dissolved organic carbon and Si concentrations were highest at zero salinities, and generally decreased with an increase in salinity during both discharge regimes, indicating removal of land-derived dissolved organic matter and silica in the estuary. Suspended particulate matter (SPM) concentrations were generally lowest (< 5 mg L-1) close of zero salinity, and increased several-fold (~18 mg L-1; low discharge) towards the seaward endmember and this attributed dynamic resuspension the estuary. Surface water-column 222Rn activities were most elevated (> 28 dpm L-1) at the freshwater endmember of the estuary, and appear to identify regions of the river most influenced by active submarine groundwater discharge (where is the data that show this?). Activities of four naturally-occurring isotopes of Ra (223,224,226,228Ra) in this estuary and select adjacent shallow groundwater wells indicate mean estuarine water mass residence times of less than 1 day; values in close agreement to those calculated by tidal prism and tidal period. A radium-based model for estimating submarine groundwater discharge to the Loxahatchee River estuary yielded an average of 1.03 V 3.84 x 105 m3 day-1, depending on river discharge stage as well as slight variations in the particular Ra models used. Such calculated flux estimates are in close agreement with results obtained from a 2-day electromagnetic seepage meter (0.9 x 105 m3 d-1) deployment during high discharge at the confluence of Kitching Creek and the Loxahatchee River, as well as with surficial aquifer recharge estimates. Calculated submarine ground-water discharge rates yield NH4+ and PO4-3 flux estimates to the Loxahatchee River estuary that range from 63 - 1060 ŸYmol m-2 d-1 and 69 - 379 ŸYmol m-2 d-1, respectively.
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1832 Groundwater transport
DE: 4805 Biogeochemical cycles (1615)
DE: 4860 Radioactivity and radioisotopes
SC: Biogeosciences [B]
MN: 2005 Joint Assembly