Arsenic Geochemistry of the Great Dismal Swamp, Virginia, USA: Possible Organic Matter Controls

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 lmol/kg) and of low pH (4.2-6.4). Total dissolved As concentrations [i.e., As(III) + As(V)], hereafter As T , 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 As T in inflow waters west of the Suffolk Scarp, and between 54% and 81% of As T 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 PO 4 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.

Organic and inorganic carbon dynamics in a karst aquifer: Santa Fe River Sink‐Rise system, north Florida, USA

“…For example, NDOM can act as a proton donor or acceptor [ Frimmel , ; Jiang and Kappler , ; Ratasuk and Nanny , ], influence mineral precipitation and dissolution, or fuel microbial biogeochemical reactions [ Findlay and Sinsabaugh , ; Schlautman and Morgan , ]. The presence of NDOM also influences the mobilization and fixation of heavy metals such as As [ Haque et al ., ; Lee et al ., ; Petrovic et al ., ] and thus may impact groundwater quality in the course of hydrogeologic projects such as aquifer storage and recovery and aquifer recharge [ Arthur et al ., ; Pavelic et al ., ]. The knowledge of NDOM and its behavior in groundwater remains limited, however due to aquifer heterogeneity.…”

Risk of Metal Mobilization from Redevelopment Activities in Hyperarid Climates: A Laboratory Experiment and Discussion

“…Langmuir et al (2006) reported that scorodite was soluble at a pH [ 4.7. Others have shown that As(V) and Fe(III) tend to increase in tandem at this pH (Haque et al 2007;Robins 1987Robins , 1990. Cai et al (2002) and Langmuir et al (2006) also found that where high concentrations of ferric oxy-hydroxide are detected, As(V) is also present.…”

“…Several studies show that the availability of contaminants is tied to several other processes such as pH, ionic strength, mineralogy, redox, and the availability of moisture (Elkhatib et al 1984;Gustafsson and Jacks 1995;Haque et al 2007;Johannesson and Tang 2009;Manning and Goldberg 1997). Sediment found in many arid climates have a similar pH, as described above, including the Three Kids Mine, which ranges between 7.8 and 8.15.…”

“…Other studies suggest that metalloid species tend not to accumulate at negatively charged surfaces of sand particles or organic matter (Haque et al 2007;Johannesson and Tang 2009;Lombi et al 2000). Since metalloids do not adsorb like trace metals, it is likely that As was initially present in the sediment solution, as there is little organic matter.…”

“…Another possibility as to why As initially increased followed by a decrease is that the sediments at the Three Kids Mine are comprised of crushed igneous rocks containing little organic matter. Studies have shown that metalloid (AsO 4 3-, AsO 3 3-, and Se) mobility is controlled by both nutrient and organic matter availability (Haque et al 2008(Haque et al , 2007Magalhaes 2002;Tye et al 2002). The sediment composition at the Three Kids Mine may have induced metalloid mobility.…”