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Hydrologic and Geochemical Variables and their Effect on Groundwater Quality at Jamestown Fort, Virginia
Rowland, R. Douglas
Rowland, R. Douglas
Abstract
This study aims to quantify the hydrologic and geochemical nature of the aquifer at Jamestown Island in Virginia, focusing on controls on groundwater dynamics, salinity, and variations in aqueous arsenic and associated iron concentrations. Arsenic and iron here are derived from the sediments composing the unconfined aquifer under the Pitch and Tar Swamp and is released by reductive processes mediated by the metabolic activity of facultative anaerobic microbes. Extreme mortality rates amongst colonists in the 1607 Jamestown settlement were likely affected by the poor quality of the groundwater they drank with arsenic and salinity being plausible culprits. Reducing conditions are present below wetlands in many shallow coastal plain aquifers and can decrease the valence state of metal ions in sediments with an associated increase in solubility. Potential controls on arsenic release and mobility on the aquifer include oxidation and altered flow patterns caused by precipitation and tidal cycles communicated from the James River in addition to seasonal trends associated with evapotranspiration. Major implications of this study include postulation on the arsenic and salinity levels during drought conditions in colonial times and furthered understanding of arsenic mobility in regions such as Southeast Asia where is poses a major threat to public health. Results indicate that arsenic, iron, and salinity all display strong downward gradients away from the swamp and suggest that physical patterns in groundwater flow and stratigraphy may dominate metals’ concentrations in the aquifer more than interchemical processes.
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2012-01-01
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Geology