The Wisconsin District Mercury Studies Team is currently funded by the Toxic Substances Hydrology Program of the USGS to conduct a general examination of mercury in the environment called Mercury Cycling in Aquatic Ecosystems. This multidiciplinary, national investigation is designed to examine geologic sources, historical trends in deposition, biogeochemical cycling processes, biological uptake, and biological effects of mercury in aquatic ecosystems.

Mercury is a problem of global extent because of the dominantly atmospheric pathways by which it is transported to even the most remote locations, and because naturally occurring processes convert a portion of mercury in aquatic ecosystems into methylmercury, a potent neurotoxin. In fact, if methylmercury were not produced in the environment, there probably would be no "mercury problem". Concerns about environmental mercury pollution and contamination of aquatic food webs stem largely from the human and wildlife health risks of dietary exposure to methylmercury, the dominant form of mercury in the edible flesh of fish and aquatic mammals. The wide-spread nature and adverse consequences of mercury pollution continue to prompt considerable scientific investigation, and the environmental sources, biogeochemistry, transformations, transport, fate, and effects of mercury in the environment are subjects of frequent symposia, workshops, and a large, steadily expanding body of scientific literature. The Mercury in Aquatic Ecosystems project, coordinated by the Wisconsin District Mercury Research Laboratory (WDMRL) has several overall goals that seek to provide critical information to aid in the definition of the mercury problem and seek possible solutions or mitigation strategies. These goals are: (A) to clarify the broader mercury problem from a scientific perspective; (B) conduct research that will provide critical (but previously unavailable) information for resource managers and decision makers on what should be done to improve environmental Hg conditions; (C) continue to provide scientific leadership (within the USGS and nationally and internationally) for the planning and execution of investigations of mercury biogeochemistry, transformations, transport, and fate in the environment; and (D) serve as an intra-agency and inter-agency communication and coordination point for mercury research.

Currently the Mercury Studies Team is working on a series of linked projects to accomplished these goals:

• Mercury Experiment to Assess Atmospheric Loading in Canada and the United States (METAALICUS)
• National Assessment Study of Mercury Contamination of Aquatic Ecosystems
• High Alpine Lakes
• Methylmercury Formation, Transport and Fate in the Yukon River, Alaska

• Acquire national information inventories on mercury sources
• Design and conduct regional assessments to determine patterns (and controlling factors) of mercury contamination in the nation's aquatic ecosystems
• Execute ecosystem investigations to determine the processes and factors influencing methylmercury exposure in aquatic ecosystems
• Conduct toxicological studies to determine the significance of methylmercury exposure in fish-eating wildlife, with emphasis on reproductive effects

• A National Pilot Study of Mercury Contamination of Aquatic Ecosystems along Multiple Gradients: Bioaccumulation in Fishes
• National Assessment of Mercury in Aquatic Ecosystems
• USGS Workshop on Mercury Cycling in the Environment Golden, Colorado, July 7-9, 1996

There is a broad consensus among mercury experts that the most widespread cause of high fish MeHg concentrations is elevated atmospheric deposition of mercury to lakes and their watersheds. Emissions from the US Midwest and southeastern Canada are transported and deposited in both countries in a pattern similar to the deposition of sulfuric and nitric acids. In addition, there is increased global circulation of Hg in the atmosphere and increased deposition even in remote locations. One of the major sources of anthropogenicmercury is mercury emitted from coal-fired utilities, and controls on these emissions have recently been proposed. On a North American basis, the estimated cost of these controlswould be several billion dollars per year (EPA, 1998). Despite these moves towards controls, mercury experts are in agreement that the relationship between atmospheric mercury deposition and MeHg concentrations in fish is unknown. Although emission reductions of 50% have been proposed (Conference of New England State Governors and Maritime Province Premiers), there is no understanding of whether this reduction would be inadequate or more than necessary, and this could result in the waste of billions of dollars on control technologies. The uncertainty comes from the fact that the amount of stored Hg in ecosystems is many times greater than annual deposition. If the newly deposited Hg is much more bioavailable than the stored Hg, ecosystems will respond quickly (1-2 yr.) to changes in atmospheric deposition, but if all the Hg is equally bioavailable, response time will be very slow.

We are addressing these fundamental questions by adding trace amounts of inorganic mercury (HgII) to ELA Lake 658 and its watershed at the Experimental Lakes Area (ELA), northwestern Ontario over a two or three-year period. The ELA is situated in a region of low atmospheric deposition of mercury, and we plan to temporarily increase the Hg loading to a small ELA watershed by a factor of 4 to simulate the atmospheric loading of mercury to lakes in Eastern Canada (Southern Ontario and the Maritime Provinces). This is a whole-ecosystem experiment, which, in addition to following changes in MeHg concentration of fish, will examine other key biological and chemical processes that determine the rate of MeHg production and its bioaccumulation into fish.

The USGS research on this project is funded by the TOXICS program, and is primarily focused on the biogeochemcial processing and transport of the mercury isotopes that are delivered to the upland forests and the wetland, and then to the lake itself. We have instrumented the water shed with four flow monitoring and automated sampling stations that take runoff samples in response to rain event, which typically arrive suddenly and do not allow for adequate time get to the field site to sample during storms. In addition, we have water level recorders in the lake and wetland, which will be essential to calculating hydrologic and mercury isotope mass balances.

• METAALICUS

Mercury contamination of environment and toxicological exposure to wildlife and humans is a complex problem that is unlike any other contaminant issue mankind has ever been confronted with, and requires a special level of holistic, interdisciplinary research before we will be able to take effective steps toward improving environmental conditions. First, it is unique among all known elements in that at ambient pressure and temperature its stable phase is as a metallic liquid that is highly vaporous. Thus, unlike all other heavy metals of general concern, it is effectively distributed in the gaseous state to literally any location, including sensitive ecosystems. Second, because mercury is an element, releases from both natural and anthropogenic sources are difficult to discriminate and mutually accumulate in various pools in the environment (primarily soils and sediments) where unlike most other contaminants of widespread concern it does not degrade over time and potentially presents a contamination problem for very long periods of time. Third, unlike most contaminants where biogeochemical processes generally serve to moderate its expressed toxicity, several key natural processes actually served to exacerbate mercury toxicity by converting it to methylmercury, a highly potent neurotoxin that is the focus of most environmental mercury research today. In fact, if mercury were not methylated in the environment, there essentially would be no mercury problem, and as such the "mercury problem" is really a "methylmercury problem". Mercury methylation is the net result of a vexing series of physical, chemical and microbiological processes, which in an unfortunate twist originate at or near the base of food webs in aquatic ecosystems and effectively serve to "inject" it into the food web from the point of orgination. Although mercury methylation is the focus of intense research currently, it is still poorly understood especially at the national scale. The challenge currently confronting resource managers, lawmakers, and the scientific community at large is to bring this complex problem into a more complete understanding that will allow for the proper and responsible actions to not only reduce new releases to the environment, but also prescribe effective land management strategies to deal with existing inventories.

This proposal seeks to bring together the expertise of an interdisciplinary team of scientists and programs to execute an integrated monitoring and research plan that will take a holistic approach toward examining mercury cycling and bioaccumulation at a set of NAWQA [hot link to NAWQA program] watersheds across the United States, which exhibit widely ranging ecosystem conditions, mercury sources, and biological components (food webs). The project employs the combined talents, interests, and funding of scientists from the NAWQA, Toxics, and NRP programs of the Water Resources Discipline, as well as scientists and programs from the Biological Resources Discipline of the USGS. In essence, this proposal distills the "mercury problem" down two three forcing functions that we believe control mercury toxicity in aquatic ecosystems: source characterization, apportionment and quantification; the biogeochemical processes that lead to the formation of methylmercury; and, the introduction of methylmercury into the food web (bioaccumulation) and biomagnification steps that follow. These three forcing functions are referred to here as the Mercury Triad. Our overall research objective is to determine what environmental and biological factors govern the methylation of mercury and its resulting bioaccumulation in aquatic ecosystems. We have identified five NAWQA study basins (CONN, GAFL, WMIC, WILM, and NVBR) that present a unique opportunity to extend the three apices of the Mercury Triad in such a way that we be able elucidate the relative importance of these forcing functions under varying environmental conditions. A primary strength of this proposed effort is the adoption of a consistent set of research questions and field and laboratory methods that will be applied to each of the study basins, such that the results will not only be comparable among basins but transferable to other locations in the US.

• Evaluate if trends in mercury accumulation and methylmercury production can be identified at national and regional scales across the United States
• To identify ecosystem characteristics that favor the production and bioaccumulation of methylmercury.
• Study design looks at a national scope with emphasis on multimedia sample collection (water, sediment, and predator fish) with consistent use of trace metal clean sampling methods and low-level mercury and methylmercury analytical procedures.

• Toxic Substances Hydrology, US Geological Survey
• National Water Quality Assessment (NAWQA) Program

Studies worldwide have shown that mercury (Hg) is a ubiquitous contaminant, reaching even the most remote environments such as high-altitude lakes via atmospheric pathways. However, very few studies have been conducted to assess Hg contamination levels of these systems. The study area consists of ninety-three mid-latitude, high-altitude lakes from seven national parks in the western United States which were sampled in September, 1999 for basic water quality parameters, carbon gases and mercury. In addition to the synoptic survey, routine monitoring and experimental studies were conducted at one of the lakes (Mills Lake) to quantify MeHg flux rates and important process rates such as photo-demethylation.

• Acquire data from an array of high-altitude lakes from across the western United States for the purposes of providing a baseline on the current Hg and MeHg contamination levels of these sensitive ecosystems.
• Provide a detailed assessment of photo-demethylation as a protective agent for high-altitude lakes.
• Construction of a seasonal mass-balance for MeHg for one of the study lakes by conducting a more detailed assessment including repeated sampling of the lake, stream inflow and outflow, and sediment coring.

Our synoptic sampling effort of 90 mid-latitude, high-altitude lakes from eight national parks in the western United States during a four-week period in September 1999 showed that overall these ecosystems have low Hg and MeHg levels (1.07 and 0.05 ng L-1, respectively). Compared to most other studies, we observed a very good correlation of Hg to MeHg (r2= 0.82), suggesting that inorganic Hg(II) loading is a primary controlling factor of MeHg production in mountain lakes, and that any future changes to atmospheric Hg loads would likely be detected in these sensitive systems. Positive correlations were also observed for DOC and both Hg and MeHg, although to a much lesser degree. Glacier National Park, Montana, had the lowest overall MeHg levels we observed (0.02 ng L-1), and we suspect this is related to naturally elevated pH values in the lakes there, although among the national parks sampled pH exhibited a relatively narrow range of values and showed little control of either HgT or MeHg. A more detailed study of Hg and MeHg was conducted at Mills Lake, Rocky Mountain National Park, Colorado. This study showed rates of photo-demethylation were quite fast, and this process was of equal importance to sedimentation and stream flow for removing MeHg. We suspect that enhanced rates of photo-demethylation are likely an important reason why high-altitude lakes, with typically high water clarity and sunlight exposure, are low in MeHg.

• Toxic Substances Hydrology, US Geological Survey
• The National Park Service

Although all ecosystems on the planet are surficially contaminated with mercury to some degree, generally the most remote locations are the least contaminated. However, very little is known about the actual contamination levels of extremely remote locations such as the Yukon Basin, and establishing an accurate baseline for such locations is important for monitoring possible future changes from emissions reductions, as well as changes that may also arise from other global phenomenon like global warming. For example, vast areas of the still relatively pristine Yukon Basin are permafrost peatlands, and if global warming predictions are accurate, widespread melting of the peat may occur and release mercury that has been accumulating for long periods of time, or potentially worse, melting could catalyze mercury methylation in the peat that is now not likely occurring. For the Yukon River Basin study, we have accomplished or started several tasks that will allow for establishment of several critical baselines to detect possible future changes, and for establishing what currently contamination levels are in this extremely remote location.

• In the spring, summer and fall of 2001, we participated in a larger effort to plan and conduct a complete water chemistry sampling along the more than 2200 miles of the Yukon River, including mercury.
• In June, 2001, we participated in a survey of the Yukon River, including many of its important tributaries that drain possible mining enriched mercury areas.
• We participated in the scientific plan development for the Yukon River study, including providing the text for a fact sheet (published by Ed Landa) describing the mercury investigations for this study

1. Mercury methylation:

1a. Methylmercury is produced in the multitude of intra- and lateral-stream sloughs and wetlands of the Yukon River, and the annual flushing of these sub-ecosystems during spring runoff regulates observed fluxes of MeHg in the River itself. 

1b. No new MeHg formation is currently active in the Yukon basin, and measurable fluxes of MeHg at the present are the result of mobilization of relic MeHg formed during warmer, wetter historical times, retained in frozen peat lands, and only recently mobilized by melting permafrost.

1c. Because MeHg formation is microbially mediated, warmer conditions would likely yield higher methylation rates in native soils and peat.

1d. Methylmercury levels in the Yukon Basin are generally low, and are reflective of abiotic methylation in the atmospheric and subsequent deposition of MeHg.

2. Mercury and methylmercury sources and transport in the Yukon River:

2a. Clear water tributaries and sloughs contribute "reactive" Hg and MeHg to the Yukon River, however, the high particulate loads quickly scavenge the Hg and MeHg from aqueous solution and limit the methylation and bioaccumulation processes.

2b. Glacial erosion and melt water mobilize "geologic" particulate mercury from watershed sources (both intact natural mineralized areas and areas contaminated by past or current mining activity) down gradient to the Yukon River, where sedimentation in methylmercury forming environments (sloughs and wetlands).

2c. Annual flooding and flushing of the Yukon Basin wetlands by snow and glacial melt water enriched in particulate mercury stimulates methylation due to the combined influences of inundation and mercury loading.

2d. Although spring floods bring high loads of particulate, inorganic mercury to the Yukon Basin, this mercury pool is largely unreactive and the more reactive and bioavailable mercury in rainfall is what drives MeHg formation.

3. Gaseous mercury production and fluxes: 

3a. Gaseous mercury production and evasion is a result of photo reduction by UV light, and due to the continual sunlight conditions of high latitude sites, mercury depletion of wetland surfaces will results and limits MeHg formation.

3b. Gaseous mercury production and subsequent evasion from the water column is an important process in most ecosystems, however, the high turbidity of the Yukon River prevents (or greatly limits) this process.

3c. Although significant total mercury levels exist in the Yukon River, the majority is particulate and not sensitive to photo reduction by ultraviolet sunlight.

Photos taken during field work for the Yukon project.