Arsenic Geochemistry of the Great Dismal Swamp,Virginia, USA: Possible Organic Matter Controls |
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Authors: | Shama E Haque Jianwu Tang William J Bounds David J Burdige Karen H Johannesson |
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Institution: | (1) Department of Earth and Environmental Sciences, The University of Texas at Arlington, Arlington, TX 76019-0049, USA;(2) Institute of Applied Geosciences, Graz University of Technology, Rechbauerstrasse 12, Graz, 8010, Austria;(3) Department of Ocean, Earth, and Atmospheric Sciences, Old Dominion University, Norfolk, VA 23529-0276, USA;(4) Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA 70118-5698, USA |
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Abstract: | Surface water samples for arsenic (As) concentration and speciation analysis were collected from organic matter-rich blackwaters
of the Lake Drummond portion of the Great Dismal Swamp in southeastern Virginia, USA. Arsenic concentrations and speciation
were determined by selective hydride generation, gas chromatography with photoionization detection. Surface waters from the
Great Dismal Swamp are high in dissolved organic carbon (DOC) concentrations (445–9,600 μmol/kg) and of low pH (4.2–6.4).
Total dissolved As concentrations i.e., As(III) + As(V)], hereafter AsT, range from 2.2 nmol/kg to 21.4 nmol/kg. Arsenite, As(III), concentrations range from ∼1 nmol/kg to 17.7 nmol/kg, and As(V)
ranges from ∼1 nmol/kg to 14.1 nmol/kg. Arsenate, As(V), is the predominant form of dissolved As in the inflow waters to the
Great Dismal Swamp, whereas within the swamp proper arsenite, As(III), dominates. Arsenite accounts for 8–37% of AsT in inflow waters west of the Suffolk Scarp, and between 54% and 81% of AsT in Lake Drummond and Great Dismal Swamp waters east of the scarp. Arsenite is strongly correlated to DOC (r = 0.94) and inversely related to pH (r = −0.9), both at greater than the 99% confidence level. Arsenate is weakly related to pH and DOC (r = 0.4 and −0.37, respectively), and neither relationship is statistically significant. No statistical relationships exist
between As(V) or As(III) and PO4 concentrations. The predominance of As(III) and its strong correlation with DOC in Great Dismal Swamp waters suggest that
DOC may inhibit As(III) adsorption or form stable aqueous complexes with As(III) in these waters. Alternatively, phytoplankton
and/or bacterially mediated reduction of As(V) may be important processes in the organic-rich blackwaters and/or sediment
porewaters of the swamp, leading to the prevalence of As(III) in the water column. |
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Keywords: | Arsenic Chemical speciation Organic matter Great Dismal Swamp Northwest River |
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