Hg isotopes reveal in-stream processing and legacy inputs in East Fork Poplar Creek, Oak Ridge, Tennessee, USA. Issue 4 (9th March 2018)

• Record Type: Journal Article
• Authors: Demers, Jason D.; Blum, Joel D.; Brooks, Scott C.; Donovan, Patrick M.; Riscassi, Ami L.; Miller, Carrie L.; Zheng, Wang; Gu, Baohua
• Is Part Of: Environmental science. Volume 20:Issue 4(2018)
• Page Start: 686
• Page End: 707
• Publication Date: 2018-03-09
• Subjects: Environmental monitoring -- Periodicals; Biological monitoring -- Periodicals; Environmental chemistry -- Periodicals; 363.7363
• DOI: 10.1039/c7em00538e
• Languages: English
• ISSNs: 2050-7887

Abstract

Abstract : Reduction processes and inputs of hyporheic pore water influence Hg cycling and flux in Hg-contaminated headwater stream. Abstract : Natural abundance stable Hg isotope measurements were used to place new constraints on sources, transport, and transformations of Hg along the flow path of East Fork Poplar Creek (EFPC), a point-source contaminated headwater stream in Oak Ridge, Tennessee. Particulate-bound Hg in the water column of EFPC within the Y-12 National Security Complex, was isotopically similar to average metallic Hg(0) used in industry, having a mean δ 202 Hg value of −0.42 ± 0.09‰ (1SD) and near-zero Δ 199 Hg. On average, particulate fraction δ 202 Hg values increased downstream by 0.53‰, while Δ 199 Hg decreased by −0.10‰, converging with the Hg isotopic composition of the fine fraction of streambed sediment along the 26 km flow path. The dissolved fraction behaved differently. Although initial Δ 199 Hg values of the dissolved fraction were also near-zero, these values increased transiently along the flow path. Initial δ 202 Hg values of the dissolved fraction were more variable than in the particulate fraction, ranging from −0.44 to 0.18‰ among three seasonal sampling campaigns, but converged to an average δ 202 Hg value of 0.01 ± 0.10‰ (1SD) downstream. Dissolved Hg in the hyporheic and riparian pore water had higher and lower δ 202 Hg values, respectively, compared to dissolved Hg in stream water. Variations in Hg isotopic composition of the dissolved and suspended fractions along the flow path suggest that: (1) physical processes such as dilution and sedimentation do not fully explain decreases in total mercury concentrations along the flow path; (2) in-stream processes include photochemical reduction, but microbial reduction is likely more dominant; and (3) additional sources of dissolved mercury inputs to EFPC at baseflow during this study predominantly arise from the hyporheic zone.