Abstract
PurposeIn contaminated streams, understanding the role of streambank and streambed source contributions is essential to developing robust remedial solutions. However, identifying relationships can be difficult because of the lack of identifying signatures in source and receptor pools. East Fork Poplar Creek (EFPC) in Oak Ridge, TN, USA received historical industrial releases of mercury that contaminated streambank soils and sediments. Here, we determined relationships between the contaminated streambank soils and sand-sized streambed sediments.Materials and methodsField surveys revealed the spatial trends of the concentrations of inorganic total mercury (Hg) and methyl mercury (MeHg), Hg lability as inferred by sequential extraction, particle size distribution, and total organic carbon. Statistical tests were applied to determine relationships between streambank soil and streambed sediment properties.Results and discussionConcentrations of Hg in streambank soils in the upper reaches averaged 206 mg kg−1 (all as dry weight) (n = 457), and 13 mg kg−1 in lower reaches (n = 321), while sand-sized streambed sediments were approximately 16 mg kg−1 (n = 57). Two areas of much higher Hg and MeHg concentrations in streambank soils were identified and related to localized higher Hg concentrations in the streambed sediments; however, most of the streambank soils have similar Hg concentrations to the streambed sediments. The molar ratio of Hg to organic carbon, correlation between MeHg and Hg, and particle size distributions suggested similarity between the streambank soils and the fine sand-sized fraction (125–250 μm) collected from the streambed sediments. Mercury in the fine sand-sized streambed sediments, however, was more labile than Hg in the streambank soils, suggesting an in-stream environment that altered the geochemistry of sediment-bound Hg.ConclusionsThis study revealed major source areas of Hg in streambank soils, identified possible depositional locations in streambed sediments, and highlighted potential differences in the stability of Hg bound to streambank soils and sediments. This work will guide future remedial decision making in EFPC and will aid other researchers in identifying source–sink linkages in contaminated fluvial systems.
Highlights
Known for its neurotoxicity and persistence in the environment, mercury (Hg) is a contaminant of concern with over 3000 contaminated sites identified globally (Kocman et al 2013)
This study revealed major source areas of Hg in streambank soils, identified possible depositional locations in streambed sediments, and highlighted potential differences in the stability of Hg bound to streambank soils and sediments
There is a critical need to identify and better understand how contaminated soils contribute to net mass fluxes of contaminants in freshwater aquatic systems; this study was conducted in the East Fork Poplar Creek (EFPC), a low gradient freshwater stream in Oak Ridge, Tennessee (USA)
Summary
Known for its neurotoxicity and persistence in the environment, mercury (Hg) is a contaminant of concern with over 3000 contaminated sites identified globally (Kocman et al 2013). There is a critical need to identify and better understand how contaminated soils contribute to net mass fluxes of contaminants in freshwater aquatic systems; this study was conducted in the East Fork Poplar Creek (EFPC), a low gradient freshwater stream in Oak Ridge, Tennessee (USA). The downstream environment has elevated Hg concentrations in streambank and floodplain soils, streambed sediments, surface waters, and biota. Fluxes from bank erosion were estimated at 38.6 kg year−1 for Hg and as 5.6 g year−1 for MeHg (Watson et al 2017). An improved understanding of the legacy Hg sources in streambank soils and sediments downstream of the Y-12 facility would aid in achieving these goals
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