Source Identification of Florida Bay's Methylmercury Problem: Mainland Runoff Versus Atmospheric Deposition and <Emphasis Type="Italic">In situ</Emphasis> Production |
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Authors: | Darren G Rumbold David W Evans Sharon Niemczyk Larry E Fink Krysten A Laine Nicole Howard David P Krabbenhoft Mark Zucker |
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Institution: | (1) South Florida Water Management District, West Palm Beach, FL, USA;(2) Florida Gulf Coast University, 10501 FGCU Blvd. South, Ft. Myers, FL 33965, USA;(3) National Oceanic and Atmospheric Administration, Beaufort, NC, USA;(4) The Abaco Group, LLC, Boynton Beach, FL, USA;(5) East Bay Municipal Utility District, Oakland, CA, USA;(6) U.S. Geological Survey, Middleton, WI, USA;(7) U.S. Geological Survey, Ft. Lauderdale, FL, USA |
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Abstract: | The first advisory to limit consumption of Florida Bay fish due to mercury was issued in 1995. Studies done by others in the
late 1990s found elevated water column concentrations of both total Hg (THg) and methylmercury (MeHg) in creeks discharging
from the Everglades, which had its own recognized mercury problem. To investigate the significance of allochthonous MeHg discharging
from the upstream freshwater Everglades, we collected surface water and sediment along two transects from 2000 to 2002. Concentrations
of THg and MeHg, ranging from 0.36 ng THg/L to 5.98 ng THg/L and from <0.02 ng MeHg/L to 1.79 ng MeHg/L, were elevated in
the mangrove transition zone when compared both to upstream canals and the open waters of Florida Bay. Sediment concentrations
ranged from 5.8 ng THg/g to 145.6 ng THg/g and from 0.05 ng MeHg/g to 5.4 ng MeHg/g, with MeHg as a percentage of THg occasionally
elevated in the open bay. Methylation assays indicated that sediments from Florida Bay have the potential to methylate Hg.
Assessment of mass loading suggests that canals delivering stormwater from the northern Everglades are not as large a source
as direct atmospheric deposition and in situ methylation, especially within the mangrove transition zone. |
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