Cable, Jaye, Martin, Jonathan, and Stieglitz, Thomas (2005) In situ evaluation of nearshore porewater exchange rates in Flamengo Bay, Brazil. In: Interactions of Groundwater and Surface Water at the Land-Sea Margin. 191-4. From: 2005 Salt Lake City Annual Meeting , 16-19 October 2005, Salt Lake City, USA.

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Abstract

As part of a larger IAEA/UNESCO intercomparison study of submarine groundwater discharge measurement techniques in southeastern Brazil, we sampled porewaters from four multilevel piezometers installed along a 45-m long transect normal to shore. In addition, water level recovery rates were estimated using pump tests along a parallel onshore-to-offshore well transect. This coastline is characterized by the Serra do Mar Mountain range, which abuts Flamengo Bay leaving a thin strip of sandy beaches along this rugged Atlantic coast. Tidal ranges measured in the coastal community of Ubatuba adjacent to the bay were about 1 to 1.5 m. The shoreline is steep (~ 0.044) and wave run-up is about 0.3 to 0.6 m above sea level, especially on flood tide. Rn-222 and Cl-, along with conductivity and temperature, were measured at discrete depth intervals from the piezometers down to 1.5 to 2 m below the sediment-water interface to evaluate the contribution of groundwater to the bay. Additionally, a fluorescien dye solution saturated with SF₆ was injected into one discrete depth interval in each piezometer to evaluate the exchange rate between the upper sediments and the surface waters. Using the SF₆, exchange rates were rapid, on the order of 28 to 184 cm/day, in the upper 1 to 2 m of sediments. Rn-222 and Cl- in porewaters support a high turnover rate in these sediments. In this well-mixed sediment-porewater regime, terrestrial groundwater inputs were difficult to quantify. Nonetheless, below about 50 cmbsf, porewater salinities were less than 5 ppt in the nearest piezometers to shore, indicating terrestrial groundwater was discharging to the bay.

Item ID:	27661
Item Type:	Conference Item (Non-Refereed Research Paper)
Date Deposited:	05 Jul 2013 05:04
FoR Codes:	04 EARTH SCIENCES > 0402 Geochemistry > 040299 Geochemistry not elsewhere classified @ 40% 04 EARTH SCIENCES > 0405 Oceanography > 040502 Chemical Oceanography @ 40% 04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040603 Hydrogeology @ 20%
SEO Codes:	96 ENVIRONMENT > 9611 Physical and Chemical Conditions of Water > 961102 Physical and Chemical Conditions of Water in Coastal and Estuarine Environments @ 100%
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