Mercury cycling in the Hells Canyon Complex of the Snake River, Idaho and Oregon

Clark, Gregory M.; Naymik, Jesse; Krabbenhoft, David P.; Eagles‐Smith, Collin A.; Aiken, George R.; Marvin-DiPasquale, Mark C.; Harris, R. O.; Myers, Ralph

doi:10.3133/fs20163051

Cited by 6 publications

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“…Monthly median %MeHg U levels at reservoir outflow locations were as high as 20.1%, and the maximum of discrete samples was 57.2% (Figure 2r−t; SI Table S8), which likely explains the observed increased in fish mercury levels in the reservoir complex. 20 We interpret the increase in %MeHg U (Figure 2q−t) and MeHg F concentration (Figure 2i−l) from inflow to outflow to reflect the seasonal export of MeHg produced within the HCC. Similar observations have been made in Cottage Grove Reservoir (Oregon), where the %MeHg was shown to correlate with higher methylation rates within the reservoir.…”

Section: ■ Discussionmentioning

confidence: 92%

“…This investigation presents an in-depth assessment of concentrations and annual loads of different mercury species through a reservoir complex impaired for mercury. 20 We report inflow and outflow mercury concentrations at high temporal resolution under contrasting hydrologic conditions (i.e., high vs low streamflow years) through the three reservoirs of the Hells Canyon Complex (HCC). In addition, we report calculated inflow and outflow loads for filter-passing and particulate IHg and MeHg fractions.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Seasonal water-column sampling of these reservoirs has shown that MeHg concentrations in the metalimnion and hypolimnion are greater during periods of stratification. 20 The breakdown of thermal stratification in Brownlee Reservoir begins as early as August and is typically complete by late December. 22 The fate of the MeHg accumulated within the stratified reservoirs is unclear during and after destratification.…”

Section: ■ Introductionmentioning

confidence: 99%

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Seasonal Dynamics and Interannual Variability in Mercury Concentrations and Loads through a Three-Reservoir Complex

Baldwin

Poulin

Naymik³

et al. 2020

Environ. Sci. Technol.

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The Hells Canyon Complex (HCC) along the Snake River (Idaho–Oregon border, U.S.A.) encompasses three successive reservoirs that seasonally stratify, creating anoxic conditions in the hypolimnion that promote methylmercury (MeHg) production. This study quantified seasonal dynamics and interannual variability in mercury concentrations (inorganic divalent mercury (IHg) and MeHg) and loads at four reservoir inflow and outflow locations through the HCC (2014–2017). We observed (1) that the HCC is a net sink for both IHg and MeHg, (2) interannual variability in IHg and MeHg loads largely reflecting streamflow conditions, and (3) seasonal variability in particulate IHg loading at the inflow (greatest from February to April) and MeHg export from the outflow (greatest from September to December) of the HCC. Seasonal export of MeHg was evidenced by increases in monthly mean concentrations of unfiltered MeHg (approximately 2-fold) and the percentage of total mercury (THg) as MeHg (≥4-fold) coincident with reservoir destratification. Despite evidence of seasonal export of MeHg from the HCC, annual loads indicate a 42% decrease in unfiltered MeHg from HCC inflow to outflow. Results from this study improve the understanding of seasonal variability in mercury transport through and transformation within a reservoir complex.

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Section: ■ Discussionmentioning

confidence: 92%

Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Seasonal Dynamics and Interannual Variability in Mercury Concentrations and Loads through a Three-Reservoir Complex

Baldwin

Poulin

Naymik³

et al. 2020

Environ. Sci. Technol.

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“…Previous studies in Brownlee Reservoir have identified that upstream nutrient loading from agricultural lands has contributed to high primary productivity in surface waters, which can result in large amounts of settling organic material raining down through the water column (Clark et al 2016). Because this organic matter is utilized as a carbon source, it is hypothesized that microzones of anoxic conditions develop—especially in deep‐water systems like Brownlee (up to 80 m deep), where particle‐settling times would be long enough to support the development of anoxic conditions.…”

Section: Resultsmentioning

confidence: 99%

“…Brownlee is the largest of the 3 reservoirs (93 km long and up to 91 m deep); it is located upriver from the other 2 and therefore receives the largest inputs of nutrients, DOM, and Hg from the upstream watershed, which includes large agricultural areas (Baldwin et al 2020). Fish consumption advisories for elevated MeHg concentrations have been in place over the last 2 decades in the Hells Canyon complex (Clark et al 2016).…”

Section: Methodsmentioning

confidence: 99%

Methylmercury Production and Degradation under Light and Dark Conditions in the Water Column of the Hells Canyon Reservoirs, USA

Eckley

Luxton

Knightes

et al. 2021

Enviro Toxic and Chemistry

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Methylmercury (MeHg) is a highly toxic form of mercury that can bioaccumulate in fish tissue. Methylmercury is produced by anaerobic bacteria, many of which are also capable of MeHg degradation. In addition, demethylation in surface waters can occur via abiotic sunlight-mediated processes. The goal of the present study was to understand the relative importance of microbial Hg methylation/demethylation and abiotic photodemethylation that govern the mass of MeHg within an aquatic system. The study location was the Hells Canyon complex of 3 reservoirs on the Idaho-Oregon border, USA, that has fish consumption advisories as a result of elevated MeHg concentrations. Our study utilized stable isotope addition experiments to trace MeHg formation and degradation within the water column of the reservoirs to understand the relative importance of these processes on the mass of MeHg using the Water Quality Analysis Simulation Program. The results showed that rates of MeHg production and degradation within the water column were relatively low (<0.07 d -1 ) but sufficient to account for most of the MeHg observed with the system. Most MeHg production within the water column appeared to occur in the spring when much of the water column was in the processes of becoming anoxic. In the surface waters, rates of photodemethylation were relatively large (up to -0.25 d -1 ) but quickly decreased at depths >0.5 m below the surface. These results can be used to identify the relative importance of MeHg processes that can help guide reservoir management decisions.

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In-Reservoir Physical Processes Modulate Aqueous and Biological Methylmercury Export from a Seasonally Anoxic Reservoir

Baldwin

Eagles‐Smith

Willacker

et al. 2022

Environ. Sci. Technol.

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Anoxic conditions within reservoirs related to thermal stratification and oxygen depletion lead to methylmercury (MeHg) production, a key process governing the uptake of mercury in aquatic food webs. Once formed within a reservoir, the timing and magnitude of the biological uptake of MeHg and the relative importance of MeHg export in water versus biological compartments remain poorly understood. We examined the relations between the reservoir stratification state, anoxia, and the concentrations and export loads of MeHg in aqueous and biological compartments at the outflow locations of two reservoirs of the Hells Canyon Complex (Snake River, Idaho-Oregon). Results show that (1) MeHg concentrations in filter-passing water, zooplankton, suspended particles, and detritus increased in response to reservoir destratification; (2) zooplankton MeHg strongly correlated with MeHg in filter-passing water during destratification; (3) reservoir anoxia appeared to be a key control on MeHg export; and (4) biological MeHg, primarily in zooplankton, accounted for only 5% of total MeHg export from the reservoirs (the remainder being aqueous compartments). These results improve our understanding of the role of biological incorporation of MeHg and the subsequent downstream release from seasonally stratified reservoirs and demonstrate that in-reservoir physical processes strongly influence MeHg incorporation at the base of the aquatic food web.

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Mercury cycling in the Hells Canyon Complex of the Snake River, Idaho and Oregon

Cited by 6 publications

References 0 publications

Seasonal Dynamics and Interannual Variability in Mercury Concentrations and Loads through a Three-Reservoir Complex

Seasonal Dynamics and Interannual Variability in Mercury Concentrations and Loads through a Three-Reservoir Complex

Methylmercury Production and Degradation under Light and Dark Conditions in the Water Column of the Hells Canyon Reservoirs, USA

In-Reservoir Physical Processes Modulate Aqueous and Biological Methylmercury Export from a Seasonally Anoxic Reservoir

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