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

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2011-09Author
Povinec, Pavel P.
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Burnett, William C.
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Beck, A.
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Bokuniewicz, Henry J.
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Charette, Matthew A.
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Gonneea, Meagan E.
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Groening, M.
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Ishitobi, T.
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Kontar, E.
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Kwong, L. Liong Wee
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Marie, D. E. P.
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Moore, Willard S.
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Oberdorfer, J. A.
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Peterson, R.
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Ramessur, R.
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Rapaglia, J.
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Stieglitz, T.
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Top, Zafer
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https://hdl.handle.net/1912/4926As published
https://doi.org/10.1016/j.jenvrad.2011.09.009Keyword
Submarine groundwater discharge; Groundwater; Seawater; Seepage meters; Stable isotopes; δD; δ18O; Tritium; Radium isotopes; Radon; Nutrients; Coastal zone; Volcanic island; Mauritius IslandAbstract
Submarine groundwater discharge (SGD) into a shallow lagoon on the west coast of Mauritius Island (Flic-en-Flac) was
investigated using radioactive (3H, 222Rn, 223Ra, 224Ra, 226Ra, 228Ra) and stable (2H, 18O) isotopes and nutrients. SGD
intercomparison exercises were carried out to validate the various approaches used to measure SGD including radium and radon
measurements, seepage-rate measurements using manual and automated meters, sediment bulk conductivity and salinity surveys.
SGD measurements using benthic chambers placed on the floor of the Flic-en-Flac Lagoon showed discharge rates up to 500
cm/day. Large variability in SGD was observed over distances of a few meters, which were attributed to different
geomorphological features. Deployments of automated seepage meters captured the spatial and temporal variability of SGD with
a mean seepage rate of 10 cm/day. The stable isotopic composition of submarine waters was characterized by significant
variability and heavy isotope enrichment and was used to predict the contribution of fresh terrestrially derived groundwater to
SGD (range from a few % to almost 100 %). The integrated SGD flux, estimated from seepage meters placed parallel to the
shoreline, was 35 m3/m day, which was in a reasonable agreement with results obtained from hydrologic water balance
calculation (26 m3/m day). SGD calculated from the radon inventory method using in situ radon measurements were between 5
and 56 m3/m per day. Low concentrations of radium isotopes observed in the lagoon water reflected the low abundance of U and
Th in the basalt that makes up the island. High SGD rates contribute to high nutrients loading to the lagoon, potentially leading to
eutrophication. Each of the applied methods yielded unique information about the character and magnitude of SGD. The results
of the intercomparison studies have resulted a better understanding of groundwater-seawater interactions in coastal regions. Such
information is an important pre-requisite for the protection management of coastal freshwater resources.
Description
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Environmental Radioactivity 104 (2012): 24-45, doi:10.1016/j.jenvrad.2011.09.009.
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Preprint: Povinec, Pavel P., Burnett, William C., Beck, A., Bokuniewicz, Henry J., Charette, Matthew A., Gonneea, Meagan E., Groening, M., Ishitobi, T., Kontar, E., Kwong, L. Liong Wee, Marie, D. E. P., Moore, Willard S., Oberdorfer, J. A., Peterson, R., Ramessur, R., Rapaglia, J., Stieglitz, T., Top, Zafer, "Isotopic, geophysical and biogeochemical investigation of submarine groundwater discharge : IAEA-UNESCO intercomparison exercise at Mauritius Island", 2011-09, https://doi.org/10.1016/j.jenvrad.2011.09.009, https://hdl.handle.net/1912/4926Related items
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