CSU Fisheries Ecology Laboratory
Management of Mercury Bioaccumulation in Colorado Reservoirs
Funded by: Colorado Division of Wildlife
2007-2011

Students and Postdocs

Dr. Jesse Lepak

Collaborators
Dr. Nicole Vieira, Ken Kehmeier, Colorado Division of Wildlife

Background/Rationale

Mercury contamination in sport fish is an emerging human health concern in Colorado.  Over the last decade, a handful of Colorado waters were posted with fish consumption advisories; however, a statewide testing program initiated in 2004 by the Colorado Department of Public Health and Environment (CDPHE) has found that mercury contamination is a widespread problem. As a result of the CDPHE study, an increasing number of Colorado water bodies have been posted with fish consumption advisories due to mercury contamination (CDPHE 2006). To date, 16 water bodies were found to contain fish with mercury concentrations that exceeded 0.5 mg/kg and another seven waters contained fish with mercury concentrations ranging between 0.3 and 0.5 mg/kg (CDPHE 2006). News of these consumption advisories has alarmed the public due to the relatively limited experience with fish consumption advisories by comparison with other areas such as the Midwest and Northeast U.S.

Mercury occurs naturally in some rock types and certain events such as forest fires and volcanic eruptions contribute mercury to the atmosphere, but human activities like gold mining and coal-fired power generation have increased the amount of mercury that is introduced into the environment. In freshwater systems, certain water quality conditions (e.g. high dissolved organic carbon, low dissolved oxygen and low pH) and water level fluctuations promote the transformation of inorganic mercury to its most toxic form; methylmercury (MeHg). MeHg is the most toxic form of mercury because it is a potent neurotoxin that has the potential to accumulate to harmful levels in organisms. Humans and animals, including fish, bioaccumulate methylmercury by absorbing it from the food they eat.  Although MeHg is gradually eliminated from organisms, it can accumulate over time if consumption levels exceed the organisms’ capacity for excretion.

Achieving meaningful reductions in mercury levels in fish in Colorado simply by reducing local power plant emissions is probably not a practical solution given that atmospheric mercury is dispersed globally and mercury already present in our water bodies will continue to contaminate fish for a long time via mobilization of mercury from soils and sediments (Munthe et al. 2007). More practical solutions include managing systems to reduce bioaccumulation rates in fish and methylation rates in the water bodies themselves.

Theoretically, the factors under human control that are affecting mercury inputs and its uptake by fish include: a) manipulating the food web to minimize bioaccumulation in sport fishes, b) reducing inputs from water diversions (if it can be shown that source water is an important component of mercury loading), and c) manipulating water management regimes to minimize the likelihood of physicochemical conditions that promote methylation. System-wide alterations to fisheries and water management are potentially very expensive endeavors, and the relative efficacy and practicality of these approaches is uncertain.  Clearly, it would be prudent to invest in research before advocating for major departures from current management practices.

Because mercury contamination in fish is driven by dietary exposure, it should be possible to reduce mercury body burdens in sport fish without reducing mercury levels in the water, simply by manipulating food webs.  This approach is the basis of the present study. 

Study Goals

The overall goal of this project is to evaluate the efficacy of a variety of fishery management strategies for minimizing mercury bioaccumulation in sport fishes.  We will conduct food web and bioenergetics modeling, and gather field data to 1) identify the “risk factors” that drive methylmercury concentrations in reservoirs; 2) evaluate the prospects for fishery management strategies (e.g., prey base manipulation, stocking, and harvest regulation scenarios) to mitigate mercury contamination across a wide range of reservoirs throughout the state; and 3) aid in development of a manipulative experiment in Horsetooth Reservoir (and/or other reservoirs with mercury Fish Consumption Advisories) to reduce mercury loads in walleye.

Literature Cited

CDPHE (Colorado Department of Public Health and Environment) 2006. Colorado Fish Tissue Study.  Water Quality Control Division. http://www.cdphe.state.co.us/wq/FishCon/analyses/index.html.  (May 29, 2007).

Munthe, J., R. A. Bodaly, B. A. Branfireun, C. T. Driscoll, C. C. Gilmour,  R. Harris, M. Horvat, M. Lucotte, and O. Malm.  2007.  Recovery of mercury-contaminated fisheries.   Ambio 36:33-44.

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Dr. Brett M. Johnson
Department of Fish, Wildlife and Conservation Biology
1474 Campus Delivery, Colorado State University,

Fort Collins, CO 80523-1474
voice: 970-491-5002, fax: 970-491-5091
email: brett.johnson"at"colostate.edu (replace “at” with @)

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