Mercury Methylation and Climate Change in Lake Champlain

Nikkohl Luehm, Colin Penn, Polly Perkins, Adam Oliver, Jeremy Koslow

Problem Statement[LS1]

The effects of climate change on the rates of mercury methylation and bioaccumulation in Lake Champlain.

Purpose Statement

To evaluate environmental factors that influence mercury methylation rates[LS2] in freshwater, making it more available for accumulation and biomagnification[LS3]. This study will also investigate how climate change may manipulate these factors,further affecting methylation rates in the Lake Champlain Basin.

Justification

Mercury is a toxic trace metal commonly found in surface waters throughout the world. Although mercury is naturally occurring in the environment, due to an increase in human activity, such as fossil-fuel combustion and waste incineration, mercury has become a prominent pollutant. Once mercury enters an ecosystem microbial and abiotic processes convert elemental mercury (Hg) into methylmercury (CH3Hg) through the transfer of methyl groups to elemental mercury (Barkay et al, 1997). This conversion is of major significance seeing as methylmercury is the most toxic and bioavailable form of mercury. This conversion thusposes a threat to human and ecological health due to its accumulation in fish and wildlife. Methylmercury is a potent neurotoxin that will cause serious health problems if enough is ingested. It is especially dangerous for children and women of childbearing age to consume fish that may be contaminated with methylmercury; due to the adverse affects on the developing brain and nervous system. In Vermont it is currently advised that women of childbearing age and children under six do not consume more than one meal of large game fish from Lake Champlain per month. Everyone else should eat no more than three meals of these fish due to methylmercury and other contaminants present in these fish (VT department of Heath, 2007).

The transport and transformation of mercury is affected by a variety of environmental factors[LS4] that control the bioavailability of Hg to methylating bacteria. These factors that control the rate of methylmercury synthesis may therefore control the rate of methylmercury bioaccumulation. The fact that mercury enters the food web in a variety of ways leads to the need for management plans. Methylmercury is known to be absorbed more readily and excreted more slowly from a given system due to the tissues it is absorbed into and the paths it may take, which is what makes it such a dangerous contaminant. A study that may help stakeholders observe the possible future implications of mercury in a changing climate therefore becomes a valuable tool. Managers in areas such as Fish and Wildlife, Department of Public Health, Agency of Natural Resources, Lake Champlain Basin Program, and other related organizations can use the studied relationships of mercury and climate change to adapt their management and monitoring plans along with the changing environment we are bound to face in order to conserve and protect both ecological and human health.

Literature Review

  • Mass Balance Assessment for Mercury in Lake Champlain, Gao et. al. 2006
  • This article demonstrates how mercury currently circulates around Lake Champlain, as well as how it enters the lake and what the largest sources are. From this information it can be determined how these inputs, outputs, and sinks may change as the climate changes.
  • Mercury in the Aquatic Environment: A review of Factors Affecting Methylation, Ullrich et al. 2001
  • This paper will aid in the understanding of what the factors are that control the methylation of mercury forfreshwater and saltwater as well as abiotic and microbial factors.
  • Net Methylmercury Production as a basis for Improved Risk Assessment, Dott et al. 2007
  • This article provides insight to some of the processes that impact methylmercury synthesis through microbial processes.
  • Mercury bioaccumulation in green frog (Rana climitans) and bullfrogs (Rana catesbieana) tadpoles from Acadia National Park, Maine, USA. Bank, Michael et al. 2007
  • This paper examines the role of mercury bioaccumulation and access to biota. The results of this study discuss the relationship of measured DOM in streams and mercury levels measured in the frog tadpoles.
  • Potential effects of climate change on freshwater ecosystems of New England/Mid-Atlantic region. Moore, Marianne V. et al. 1997
  • This article is a general overview report, however it does have a section on what factors might influence mercury and bioaccumulation.
  • Potential effects of climate change on surface-water quality on North America. Murdoch, Peter S et al. 2000
  • This is also a general overview report that includes a section on factors influencing mercury methylation rates and bioavailability.
  • Mercury, Food Webs, and Marine Mammals: Implications of Diet and Climate Change for Human Health. Booth, Shawn and Zeller, Dirk. 2006.
  • This article, from Science, is a literature review of the culminating effects of mercury and climate change that will serve as a good basis for our further research.
  • Interactions between mercury and dissolved organic matter––a review. Ravichandran, Mahalingam. 2004
  • This is a great article that discusses the interactions of DOM and MeHg.
  • Concentration of mercury species in relationship to other site-specific factors in the surface waters of northern Wisconsin lakes. Watras, Carl J. et al. 1995.
  • This is a great article that discusses the many influences of mercury methylation, more specifically DOM and pH over specific ranges.
  • Regional and Seasonal Inputs of Mercury into Lake St. Pierre (St. Lawrence River), a Major Commercial and Sports Fisheries in Canada.Caron et al. 2008
  • This paper relates to our topic in that it is a very close study site which shares many of the characteristics of Lake Champlain. The study was conducted in Lake St. Pierre, Canada’s most important fresh water fishery, and shows how surface sediments and a changing hydrologic regime relate to MeHg concentrations.
  • Increase in Mercury Contamination Recorded in Lacustrine Sediments Following Deforestation in the Central Amazon. Roulet et al. 2000
  • This study was on the increasing MeHg concentration in surface sediments due to environmental changes brought on by the nearby human populations. They cite increased soil erosion to the the cause of increased sediment loading of the Tapajos River, and show how the highest concentrations of Mercury are occurring in the topmost layers of sediment.

Purposed Approach

Mercury conversion and movement through a lake system is very complex. There are various ways that mercury poses a threat to human and ecosystem health. We plan to investigate the factors which could change the availability and concentration of methylmercury, the most toxic form of this heavy metal.

The factors that affect the inputs of mercury that will be considered include: wet deposition, dry deposition, and erosion. There are other factors which may affect mercury inputs, but these should be more closely related to the effect of climate change. The magnitude of these sources has been studied for the Lake Champlain Basin Project and we plan to use them as a source for our paper.

Since the methylated form of mercury is the most harmful and mobile, the rate of conversion to that form is extremely important. Conditions that affect methylation include temperature, dissolved oxygen concentration, amount of organic matter, sulfate concentration and pH. These affect the activity of and competition amongst sulfate reducing bacteria which methylate mercury. These factors could all be influenced by changing temperatures and precipitation patterns, i.e. climate change. Several of these factors are connected by climatic conditions and have been studied in various ecosystems.

It will be necessary for us to form some assumptions to connect all of these factors under the lens of climate change. Although it seems difficult to model all of the factors currently at work and how they might change, it is crucial to our understanding of potential risk. Looking at just one of the factors that influence methylmercury availability overlooks too much. It will not be possible to specifically quantify all of the forces and feedbacks which interact in this process. We intend to establish relative magnitudes for the factors that influence methylation and availability. We will consult experts Alan McIntosh, a professor and water expert at UVM, and Neil Kamman of the Vermont Department of Environmental Conservation to gain more insight on the physical factors affecting mercury methylation.

As a concluding point to our project we will briefly overview bioaccumulation within fish species of Lake Champlain and the northeast at large. We will then follow mercury’s path through the food web (biomagnification), ending at humans. Mercury’s adverse affects on human health will be highlighted as well.

Effort Assignment

In order to cover the vast array of categories dealing with the methylation of mercury and how these processes relate to climate change in Lake Champlain, our group has broken down the research into sections. Each person is focusing on a different aspect of mercury in Lake Champlain from inputs to factors influencing methylation to the impact of human activity.Research will be done on current data from peer reviewed sources on assigned topics. Once each person collects current information they will then refer to models and studies that infer how climate change will impact the Northeast. From this data, each member can extrapolate their current information to determine the impact climate change will have of their area of focus. As information is collected our group will have weekly or bi-weekly meetings to discuss our findings, progress, and direction of the project. From these meetings we hope to clearly address our problem in order to successfully report our conclusions of how climate change will influence the synthesis of methylmercury.The research topics assigned to each person are as follows:

Polly Perkins- Bioaccumulation and impacts on human health

Adam Oliver- Mercury inputs into Lake Champlain

Colin Penn & Nikkohl Luehm- Factors influencing the methylation of inorganic mercury

Jeremy Koslow- Erosion/Sedimentation and human developmental impacts on MeHg[LS5]

WORKS CITED

Barkay, T, Gillman, M, & Turner, R Effects of dissolved organic carbon and salinity on bioavailability of mercury. Applied and Environmental Microbiology, 63, from

Vermont Department of Health, (2007, June). Health Alert. Retrieved February 27, 2009, from Vermont Department of Health Web site:

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[LS1]Could this be rearranged to make a more strong statement? The changing climate will have several effects on mechanisms controlling the rate of mercury methylation, thereby possibly increasing rates of bioaccumulation of methylmercury in Lake Champlain. (Or something along those lines)

[LS2]As well as the processes of Hg input into water bodies?

[LS3]I feel that the Problem and Purpose statements should be as strong as possible. Perhaps word this differently: (…freshwater, which affect methylmercury concentrations and therefore biomagnification). Something along those lines? Just my thought.

[LS4]What are these and how might the changing climate pose a problem (increase in methylmercury synthesis rates)?

[LS5]Overall, I think this Proposal looks good:

Kept to the proper format

Clear problem and goal, might have been reworded to sound stronger

Justification Okay

Lit Review has very relevant/recent works

Well described proposed effort and e. assignment