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Webinar Series on "Mercury in Reservoirs"

   01 February 2018

The U.S. Geological Survey (USGS), in collaboration with the California Water and Environmental Modeling Forum (CWEMF), presented a series of free webinars on mercury in reservoirs. Seven webinars were given from February 14 through May 2, 2018.

Scientists presented a series of webinars on mercury in reservoirs, with the goal of informing stakeholders in the State of California's Statewide Mercury Control Program for Reservoirs. Stakeholders include reservoir owners and operators (including federal, state, and local agencies, and irrigation districts), water-quality regulators, and the scientific community.

Topics included mercury sources from historical gold mining, mercury methylation and bioaccumulation in food webs, management tools, and current scientific studies in California and elsewhere in the western U.S. that are addressing mercury issues.


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Webinar Series on Mercury in Reservoirs
February – May 2018
Presented by the U.S. Geological Survey (USGS), in collaboration with the
California Water and Environmental Modeling Forum (CWEMF)

Weds. Feb. 14 – Mercury transport and bioaccumulation in California reservoirs affected by historical gold mining

(C. Alpers, R. Stewart, J. Fleck, M. Marvin-DiPasquale)

Information was presented on mercury in California reservoirs as it relates to historical gold mining. Case studies from the Yuba and Bear River watersheds in the northwestern Sierra Nevada were used as examples. Data from USGS studies at Englebright Lake, Camp Far West Reservoir, and Lake Combie were discussed. Lessons learned from these studies were considerd along with possible management options to control methylmercury formation and bioaccumulation in reservoirs, and to maintain reservoir capacity.

Weds. Feb. 28 – The biogeochemical cycling of mercury within Lake Powell, Glen Canyon National Recreation Area, Utah-Arizona

(M. Marvin-DiPasquale, D.L. Naftz, D.P. Krabbenhoft, G. Aiken, E.S. Boyd, C.H. Conaway, J. Ogorek & M. Anderson)

Elevated Striped-bass mercury concentrations found in the downstream portion of Lake Powell resulted in a 2012 fish-consumption advisory for the lower ~100 km of the reservoir. The USGS conducted two detailed reservoir sampling events (late spring during high-flow conditions, and late summer during stratified, low-flow conditions) to collect chemical, physical, and biological data needed to test hypotheses associated with a conceptual model developed to explain the observed spatial gradient in fish mercury concentration. This presentation details the major findings of that study.

Weds. Mar. 7 – The Hells Canyon Complex mercury study, Snake River, Idaho-Oregon, USA

(D. Krabbenhoft, C. Eagles-Smith, A. Baldwin, B. Poulin, M. Marvin-DiPasquale, R. Myers, J. Naymik, & R. Harris)

The Hells Canyon Complex (HCC) Mercury Study was initiated in 2014 following an initial pre-study that revealed elevated levels in game fish. The HCC is a relatively unusual setting in that it consists of three reservoirs (Brownlee, Oxbow, and Hells Canyon) in series over about a 100-mile section of the Snake River along the Idaho-Oregon border. During summer, the two largest reservoirs (Brownlee and Hells Canyon) exhibit strong thermal and chemical stratification, which carries well into the fall and early winter periods. Elevated levels of methylmercury accumulate in the hypolimnion of these reservoirs, and an important goal of this project is to resolve the key factors controlling mercury methylation and the fate of methylmercury during the fall destratification period. This large, multi-disciplinary project has eight guiding hypotheses, all of which point the effort toward understanding how reduced methylmercury production and bioaccumulation might be achieved.

Weds. Mar. 21 – Mercury bioaccumulation and food web studies in lakes and reservoirs

(C. Eagles-Smith, J. Ackerman, R. Stewart, R. Harris)

Ecological pathways of mercury bioaccumulation and biomagnification matter because mercury in animals is rarely driven by sources alone, due to the unique cycling of mercury in the environment. This presentation describes four critical mechanisms of mercury bioaccumulation: primary productivity, habitat use, bioenergetics, and food-web structure. The importance of these mechanisms is discussed in the context of reservoir management, including processes that affect mercury methylation in the anoxic part of the water column (hypolimnion), water-level fluctuations, and other factors that affect the food web. The strong seasonality of phytoplankton and zooplankton are discussed in relation to their important influence on mercury bioaccumulation in top predator fish.

Weds. Apr. 4 – Mercury isotopes – an emerging tool for science and management in reservoirs

(D. Krabbenhoft)

The recent development of methodologies to make high-precision measurements of mercury stable-isotope ratios in tissues, sediment, water, and air have revolutionized mercury science. Now, scientists have an independent means by which sources, pathways, and processes can be assessed using the results of mercury stable-isotope measurements. Initial applications of this methodology were limited to tissue and sediment samples with relatively high concentrations; today, however, we can utilize samples with lower concentrations, and measurements on water and air samples are readily achievable. Mercury stable-isotope measurements are a new and powerful tool, but should not be viewed as a panacea; rather, they are another tool available to help inform difficult questions regarding mercury in the environment.

Weds. Apr. 18 – Appraising long-term mercury concentration and loading trends in the Carson River-Lahontan Reservoir system

(E. Morway, C. Thodal, A. Paul, K. Thomas, M. Marvin-DiPasquale, R. Hirsch, C. Alpers, D. Krabbenhoft, J. DeWild)

An estimated 15,000,000 pounds of mercury were released to the Carson River system during extraction of silver and gold from the Comstock Lode in western Nevada during the late 19th century and early 20th century. At the Fort Churchill gaging station on the Carson River, located downstream of the mining and milling activity, there is a continuous data set of mercury and methylmercury concentrations in river water from 1997 through 2013. Trend analysis reveals that total mercury concentrations in the water column remained relatively constant, but the partitioning coefficient trended downward, indicating a greater proportion of filter-passing mercury in the water column through time. Water samples also were collected downstream of Lahontan Reservoir, enabling analysis of the trap efficiency of mercury and suspended sediment.

Weds. May 2 – Synthesis of mercury case studies in reservoirs – matching study design to research and management questions

(J. Fleck, M. Marvin-DiPasquale, C. Eagles-Smith, R. Stewart, C. Alpers, R. Harris, D. Krabbenhoft)

The previous presentations in this webinar series demonstrated that there are wide variations in sources of inorganic mercury and in-reservoir biogeochemical and hydrologic processes affecting mercury methylation and bioaccumulation in reservoirs in California and other western states. This presentation emphasizes that sampling design for mercury and methylmercury in reservoirs should be driven by the characteristics of a given reservoir and its catchment, and the scientific objectives. If the dominant source of methylmercury is from upstream of the reservoir, efforts should be focused on eliminating methylmercury loading from upstream sources and/or optimizing in-reservoir loss mechanisms (particle settling and photo-degradation). If the dominant source of methylmercury is from in-reservoir production, efforts should be focused on determining the relative importance of benthic and pelagic processes to optimize the potential success of mitigation strategies.


Recordings

Recordings of the webinar presentations are available to watch on demand. For links to the recordings, please contact Gabe Lopez (glopez@usgs.gov, 916-278-3026).

For additional information, contact: Charlie Alpers (cnalpers@usgs.gov, 916-278-3134).

Contact Information

Mark Desio
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(916) 278-3111

Steve Ackley
Outreach and Special Events
Office: (916) 278-3130
Cell: (916) 431-8359

Gabriel Lopez
USGS Data and Report Requests
(916) 278-3026

Laurel Rogers
Communications Chief
Office: (619) 225-6104
Cell: (619) 980-6527


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