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. 2022 Oct 4;56(19):13751-13760.
doi: 10.1021/acs.est.2c03958. Epub 2022 Sep 15.

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

Austin K Baldwin  1 , Collin A Eagles-Smith  2 , James J Willacker  2 , Brett A Poulin  3 , David P Krabbenhoft  4 , Jesse Naymik  5 , Michael T Tate  4 , Dain Bates  5 , Nick Gastelecutto  5 , Charles Hoovestol  5 , Chris Larsen  5 , Alysa M Yoder  1 , James Chandler  5 , Ralph Myers  5
Affiliations

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

Austin K Baldwin et al. Environ Sci Technol. .

Abstract

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.

Keywords: anoxia; aquatic food web; bioaccumulation; biological uptake; destratification; methylation; suspended sediment; zooplankton.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Longitudinal cross sections of Brownlee Reservoir (A) water temperature and (B) DO concentrations on different dates during the 2018 destratification period. River flow is from left to right. Gray triangles indicate penstock centerline elevation. A companion set of plots for the 2019 destratification period is provided in Figure S3. (C) Volume of hypoxic and anoxic water in Brownlee Reservoir during late May 2018 to November 2019, with the study period indicated along the x-axis [°C, degrees Celsius; m3, cubic meters; mg/L, milligrams per liter].
Figure 2
Figure 2
(A) Biomass density and SPM in water and (B) MeHg concentration in biological material and SPM in samples from Brownlee Outflow and Oxbow Outflow, June 2018 to September 2019. Boxplots present median and quartile ranges, and whiskers extend 1.5× the interquartile ranges. Lower case letters (a–e) indicate statistical differences between groups based on the Kruskal–Wallis multiple comparison test, with p value of 0.05 [SPM, suspended particulate material; ng/g, nanograms per gram; mg/m3, milligrams per cubic meter].
Figure 3
Figure 3
Aqueous and biological methylmercury (MeHg) at Brownlee Inflow, Brownlee Outflow, and Oxbow Outflow, June 2018 to September 2019. Data gaps in fish and other invertebrates indicate dates when the biomass was below detection. August through December of each year are highlighted in yellow to indicate the approximate destratification periods of Brownlee Reservoir. Data for the Brownlee Inflow location were only available for plots A–E [THg, total mercury; ng/L, nanograms per liter; ng/g, nanograms per gram dry weight].
Figure 4
Figure 4
Relationship between the annual maximum volume of Brownlee Reservoir hypoxic and anoxic water and concentrations of filter-passing methylmercury (MeHgF) at Brownlee Outflow during the destratification period (August to December) [ng/L, nanograms per liter; mg/L, milligrams per liter; m3, cubic meters; DO, dissolved oxygen].
Figure 5
Figure 5
Relationship between methylmercury (MeHg) in filter-passing water and zooplankton samples from Brownlee Outflow and Oxbow Outflow. (A) Samples from the entire study period June 2018 to September 2019; (B–D) samples binned based on the stratification state of Brownlee Reservoir. Linear regressions are shown as solid lines, and confidence intervals of the fit are shaded [ng/L, nanograms per liter; ng/g, nanograms per gram dry weight; r = Spearman correlation; p = p value on the Spearman correlation].
Figure 6
Figure 6
Brownlee Outflow (A,B) biomass and (C,D) biological (bio) methylmercury (MeHg) loads in individual biological compartments, and (E,F) total biological MeHg load compared with aqueous (filter-passing and particulate) MeHg loads. Load estimates based on biweekly samples, June 2018 to September 2019. A companion figure for Oxbow Outflow is provided in Figure S13 [Mg, megagrams; g, grams].
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References

    1. Louis St. V.; Kelly C. A.; Duchemin É.; Rudd J. W. M.; Rosenberg D. M. Reservoir Surfaces as Sources of Greenhouse Gases to the Atmosphere: A Global Estimate: Reservoirs Are Sources of Greenhouse Gases to the Atmosphere, and Their Surface Areas Have Increased to the Point Where They Should Be Included in Global Inventories of Anthropogenic Emissions of Greenhouse Gases. BioScience 2000, 50, 766–775. 10.1641/0006-3568(2000)050[0766:RSASOG]2.0.CO;2. - DOI
    1. Zarfl C.; Lumsdon A. E.; Berlekamp J.; Tydecks L.; Tockner K. A Global Boom in Hydropower Dam Construction. Aquat Sci 2015, 77, 161–170. 10.1007/s00027-014-0377-0. - DOI
    1. Bohada-Murillo M.; Castaño-Villa G. J.; Fontúrbel F. E. Effects of Dams on Vertebrate Diversity: A Global Analysis. Diversity 2021, 13, 528.10.3390/d13110528. - DOI
    1. Ekka A.; Pande S.; Jiang Y.; der Zaag P. Anthropogenic Modifications and River Ecosystem Services: A Landscape Perspective. Water (Switz.)) 2020, 12, 2706.10.3390/w12102706. - DOI
    1. Jane S. F.; Hansen G. J. A.; Kraemer B. M.; Leavitt P. R.; Mincer J. L.; North R. L.; Pilla R. M.; Stetler J. T.; Williamson C. E.; Woolway R. I.; Arvola L.; Chandra S.; DeGasperi C. L.; Diemer L.; Dunalska J.; Erina O.; Flaim G.; Grossart H.-P.; Hambright K. D.; Hein C.; Hejzlar J.; Janus L. L.; Jenny J.-P.; Jones J. R.; Knoll L. B.; Leoni B.; Mackay E.; Matsuzaki S.-I. S.; McBride C.; Müller-Navarra D. C.; Paterson A. M.; Pierson D.; Rogora M.; Rusak J. A.; Sadro S.; Saulnier-Talbot E.; Schmid M.; Sommaruga R.; Thiery W.; Verburg P.; Weathers K. C.; Weyhenmeyer G. A.; Yokota K.; Rose K. C. Widespread Deoxygenation of Temperate Lakes. Nature 2021, 594, 66–70. 10.1038/s41586-021-03550-y. - DOI - PubMed

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