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Mercury (Hg) from a former Chlor-Alkali Facility (active from the late 1890s until the 1960s) continues to leach into the Androscoggin River from glacial till and bedrock, contaminating the downstream floodplain. Previous work has shown that downstream gradients in stream power affect the erosion and deposition of the floodplain. This study sought to determine if the spatial distribution of Hg downstream of the point source can be predicted from gradients in stream power along a 5 km reach starting 4 km downstream from the point source. Floodplain soil samples were collected at five transects, across three flood recurrence intervals (2-, 5-, 10- year), and up to 30 cm depths. Stream power gradients were determined from channel width, flow accumulation, and elevations extracted from digital elevation model data. Soil samples were analyzed using a Milestone Direct Mercury Analyzer (DMA- 80) and were weighed pre- and post- combustion to estimate percent soil organic carbon (SOC). Multiple regression analyses showed that, in order of significance, SOC, distance from the source, and flood recurrence interval had the most effect on Hg concentration, but stream power gradient was not significantly correlated with Hg inventory. However, once the possible additional input of Hg from atmospheric deposition was considered, normalized Hg inventories are broadly consistent with variations in stream power. Applications of this work could support environmental remediation practices in fluvial environments affected by Chlor-Alkali Facilities.
Sulca, Debbie F., "Understanding the Spatial Distribution of Mercury- Contaminated Sediment Along the Androscoggin River" (2023). Dartmouth College Master’s Theses. 94.
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