Journal
CONTINENTAL SHELF RESEARCH
Volume 53, Issue -, Pages 63-76Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.csr.2012.12.002
Keywords
Groundwater discharge; Seepage meters; Rn-222 and CH4 geochemical tracers; Subseafloor resistivity; Nutrient flux; Sarasota Bay Florida
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Funding
- Florida Sea Grant/EPA Grant
- IFP Ford Foundation PhD Fellowship
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A study was conducted from July 2002 through June 2006 in order to assess the significance of submarine groundwater discharge (SGD) to Sarasota Bay (SB), Florida. The assessment approaches used in this study included manual seepage meters, geochemical tracers (radon, Rn-222 and methane, CH4), and subseafloor resistivity measurements. The estimated SGD advection rates in the SB system were found to range from 0.7 to 24.0 cm/day, except for some isolated hot spot occurrences where higher rates were observed. In general, SGD estimates were relatively higher (5.9-24.0 cm/day) in the middle and south regions of the bay compared to the north region (0.7-5.9 cm/day). Average dissolved inorganic nutrient concentrations within the SB water column ranged: 0.1-111 mu M (NO2 + NO3), 0.1-9.1 mu M (NH4) and 0.2-1.4 mu M (PO4). The average N/P ratio was higher in the north compared to the middle and south regions of the bay. On average, we conservatively estimate that about 27% of the total N in the SB system was derived via SGD. The prevalence of shallow embayed areas in the SB system and the presence of numerous septic tanks in the surrounding settlements enhanced the potential effects of nutrient rich seepages. Statistical comparison of the quantitative approaches revealed a good agreement between SGD estimates from manual seepage meters and those derived from the Rn-222 model (p=0.67: alpha=0.05; n=18). CH4 was found to be useful for qualitative SGD assessments. CH4 and Rn-222 were correlated (r(2)=0.31; alpha=0.05; n=54). Large scale resistivity surveys showed spatial variability that correlates more clearly with lithology than with SGD patterns. (C) 2012 Elsevier Ltd. All rights reserved.
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