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Biogeochemical and hydrologic synergy control mercury fate in an arid land river-reservoir system

April 26, 2023

Reservoirs in arid landscapes provide critical water storage and hydroelectric power but influence the transport and biogeochemical cycling of mercury (Hg). Improved management of reservoirs to mitigate the supply and uptake of bioavailable methylmercury (MeHg) in aquatic food webs will benefit from a mechanistic understanding of inorganic divalent Hg (Hg(II)) and MeHg fate within and downstream of reservoirs. Here, we quantified Hg(II), MeHg, and other pertinent biogeochemical constituents in water (filtered and associated with particles) at high temporal resolution from 2016–2020. This was done (1) at inflow and outflow locations of three successive hydroelectric reservoirs (Snake River, Idaho, Oregon) and (2) vertically and longitudinally within the first reservoir (Brownlee Reservoir). Under spring high flow, upstream inputs of particulate Hg (Hg(II) and MeHg) and filter-passing Hg(II) to Brownlee Reservoir were governed by total suspended solids and dissolved organic matter, respectively. Under redox stratified conditions in summer, net MeHg formation in the meta- and hypolimnion of Brownlee reservoir yielded elevated filter-passing and particulate MeHg concentrations, the latter exceeding 500 ng g−1 on particles. Simultaneously, the organic matter content of particulates increased longitudinally in the reservoir (from 9–29%) and temporally with stratified duration. In late summer and fall, destratification mobilized MeHg from the upgradient metalimnion and the downgradient hypolimnion of Brownlee Reservoir, respectively, resulting in downstream export of elevated filter-passing MeHg and organic-rich particles enriched in MeHg (up to 43% MeHg). We document coupled biogeochemical and hydrologic processes that yield in-reservoir MeHg accumulation and MeHg export in water and particles, which impacts MeHg uptake in aquatic food webs within and downstream of reservoirs.

Publication Year 2023
Title Biogeochemical and hydrologic synergy control mercury fate in an arid land river-reservoir system
DOI 10.1039/D3EM00032J
Authors Brett Poulin, Michael T. Tate, Jacob M. Ogorek, Sara E. Breitmeyer, Austin K. Baldwin, Alysa Muir Yoder, Reed C. Harris, Jesse Naymik, Nick Gastelecutto, Charles Hoovestol, Christopher F. Larsen, Ralph Myers, George R. Aiken, David P. Krabbenhoft
Publication Type Article
Publication Subtype Journal Article
Series Title Environmental Science: Processes & Impacts
Index ID 70243151
Record Source USGS Publications Warehouse
USGS Organization Idaho Water Science Center; Wisconsin Water Science Center; Upper Midwest Water Science Center