MercNet—Establishing a Comprehensive 

National Mercury Monitoring Network

2008

Workshop 

Report
Workshop organized by the U.S. Environmental Protection Agency, U.S. Geological Survey, U.S. Fish and Wildlife Service, National 

Oceanic and Atmospheric Administration, National Park Service, Cherokee Nation, Florida Department of Environmental Protection, 

Minnesota Pollution Control Agency, BioDiversity Research Institute, National Atmospheric Deposition Program, Syracuse University, 

and University of Connecticut.

Report prepared by Christine Negra and Kathy Fallon Lambert, ICF International

Submitted to U.S. Environmental Protection Agency, Contract No. EP-W-08-018, November 2008

For more information or to receive a copy of this report, contact David Schmeltz at schmeltz.david@epa.gov. 

This report is also available at http://nadp.sws.uiuc.edu.

Acknowledgements

2008 National Mercury Monitoring Workshop Report

1

Table of Contents

Executive Summary ................................................................................................................. 3

Introduction.............................................................................................................................. 5

I. Benefits of a national monitoring network..............................................................................................5

II. 2008 National Mercury Monitoring Workshop.......................................................................................8

Elements of a National Mercury Monitoring Network......................................................... 11

I. Network goals and objectives.................................................................................................................11

II. Mercury measurements .........................................................................................................................12

III. Types of mercury monitoring sites........................................................................................................12

IV. Site selection ...........................................................................................................................................13

Mercury Monitoring: What’s in Place Now? ......................................................................... 15

I. Existing mercury monitoring programs and sites................................................................................15

II. Potential intensive sites...........................................................................................................................16

Developing the Mercury Monitoring Network: Selecting Sites............................................17

I. Preliminary intensive site selection .......................................................................................................17

II. Cluster site selection ...............................................................................................................................18

Opportunities for Collaboration: Next Steps........................................................................ 21

I. Refining network design.........................................................................................................................21

II. Community engagement and outreach ................................................................................................22

III. Building new monitoring capacity.........................................................................................................22

List of Appendices................................................................................................................... 23

A: Workshop Steering Committee and Participants .................................................................................25

B: Mercury and Ancillary Monitoring Programs......................................................................................27

C: Preliminary List of Candidate Intensive Sites—From Annapolis Workshop......................................29

D: Tables of Recommended Mercury and Ancillary Measurements ........................................................31

E: Glossary of Terms ...................................................................................................................................35
2008 National Mercury Monitoring Workshop Report

3

Executive Summary

Methylmercury levels in fish and other biota routinely 

exceed thresholds considered potentially harmful 

to people and fish-eating wildlife throughout much 

of the United States. Mercury emitted to the atmosphere 

by industrial activities (e.g. coal-fired power generation, 

chlorine production) deposits to watersheds, transforms into 

highly bioavailable methylmercury, and magnifies to high 

concentrations in food webs. Growing awareness of changing 

mercury levels in the environment has sparked widespread 

concern about ecological and human health effects. 

Federal agencies, states, and tribes—in partnership with 

academic researchers, non-governmental organizations, 

and industry—have been actively engaged in understanding 

and developing solutions to the mercury pollution problem. 

Developing regulatory policies designed to reduce mercury 

emissions from stationary sources, including coal-fired power 

plants, is one of the primary ways states and the federal 

government are addressing the mercury threat. 

Sufficient information is not currently available for many 

areas of the United States to fully and accurately assess the 

benefits and effectiveness of mercury reduction measures. 

Policymakers, scientists, and the public need a national 

monitoring program to accurately quantify regional and 

national changes in atmospheric deposition, ecosystem 

contamination, and bioaccumulation of mercury in fish 

and wildlife in response to changing mercury emissions. 

In the absence of a national mercury monitoring program, 

federal, state, and tribal agencies and other organizations are 

collaborating to understand mercury in the environment 

using limited existing data and monitoring capabilities. This 

report is the result of a multi-stakeholder, national mercury 

monitoring workshop, held May 5–7, 2008, to envision a 

comprehensive and integrated national mercury monitoring 

network. The report highlights strategies and partnerships 

for the design and implementation of a national network for 

tracking mercury pollution in ecosystems. 

The process by which mercury deposits to watersheds, 

transforms to methylmercury, and magnifies to high 

concentrations in food webs is complex, requiring monitoring 

of all components of the mercury cycle to assess how changing 

emissions and deposition affect fish, wildlife, and people. 

Federal, state, and tribal agencies and other institutions 

operate a number of programs that monitor how mercury 

enters, cycles, and impacts ecosystems. However, all parts 

of the mercury cycle are not monitored, leaving major data 

gaps nationwide. In addition, agency mercury monitoring 

and research programs, developed and implemented for a 

variety of reasons, often sample over different spatial scales 

and time periods using disparate data-gathering protocols. 

Consequently, this presents a challenge to effectively combine 

resulting datasets to provide a complete national view of 

mercury in the environment. 

Policymakers, resource managers, and the public have many 

questions about mercury in the environment. For example:

Q How are mercury emissions and deposition to the 

environment changing as a result of implemented 

policies and programs?

Q How are ecosystems responding to changes in 

mercury pollution?

Q What reductions in mercury emissions are needed 

before fish can be eaten safely? 

Q How will other factors such as land management, 

climate change, and acidic deposition influence the 

behavior of mercury in the environment and its 

accumulation in food webs?

We can answer some of these questions, in some places, 

but current resources cannot address these critical 

environmental policy questions on national and regional 

scales. Our existing monitoring infrastructure needs to 

be linked into a comprehensive, multimedia network with 

coverage in all regions of the country.

Photo credit: Daniel Poleschook, Jr., and Ginger Gumm
4

Executive Summary

In May 2008, scientists, policy analysts, and natural resource 

managers representing academia, federal and state agencies, 

tribes, industry, and non-governmental organizations met in 

Annapolis, Maryland, to refine the scientific and technical 

design of a standardized, national mercury monitoring 

network; explore potential implementation strategies; and 

share information on existing North American mercury 

monitoring and research programs. The workshop was 

an important step in building broad support around a 

Q Richard Artz, 

National Oceanic and Atmospheric Administration

Q Thomas Atkeson, 

Florida Department of Environmental Protection

Q Ryan Callison, Cherokee Nation

Q Charles Driscoll, Syracuse University

Q David Evers, BioDiversity Research Institute

Q David Gay, National Atmospheric Deposition Program

Q Richard Haeuber, U.S. Environmental Protection Agency

Q David Krabbenhoft, U.S. Geological Survey

Q Robert Mason, University of Connecticut

Q Gregory Masson, U.S. Fish and Wildlife Service

Q Kristi Morris, National Park Service

Q David Schmeltz, U.S. Environmental Protection Agency

Q Edward Swain, Minnesota Pollution Control Agency

National Mercury Monitoring

Workshop Steering Committee

conceptual design for MercNet—a comprehensive and 

integrated monitoring network for the United States. 

Workshop participants agreed that the network would 

require standardized, multimedia sampling (i.e., air, water, 

sediments, fish, and wildlife) through national distribution 

of approximately 20 intensive monitoring sites, each 

accompanied by about 10 to 20 cluster sites. The network 

would operate for an extended period (10–40 years) to 

quantify the range of responses expected among the nation’s 

diverse ecosystems.

A national mercury monitoring network must serve a wide 

range of constituencies and meet multiple objectives. In 

recent years, extensive planning by a broad-based consortium 

of scientists, resource managers, and policy analysts has 

created a foundation for MercNet. The network envisioned 

will facilitate collaboration among diverse programs and 

agencies to produce comprehensive, nationally consistent, 

long-term mercury data through a cost-effective approach. 

At this time, new funding mechanisms do not exist for 

expanded mercury monitoring. Thus, efforts to establish the 

network must leverage existing monitoring capabilities and 

infrastructure, while striving toward a robust and coordinated 

set of monitoring sites that will provide the full range of 

information needed. Should new funding become available, 

implementation of the monitoring infrastructure described 

in this report would provide the nationally consistent 

monitoring necessary for tracking changing mercury levels 

and understanding ecological effects and response.

Agreement emerged from the May 2008 workshop regarding 

mercury monitoring network goals, objectives, and major 

design elements. Workshop participants also came to 

agreement about how to focus collaborative efforts in the 

near term. Refinement of the monitoring network design will 

emphasize creation of a national framework for site selection 

and data sharing. Network planners will seek opportunities to 

leverage existing monitoring activities and funding sources 

through engagement with the broader mercury community. 

Outreach and support-building for existing and expanded 

monitoring will be directed toward policymakers and federal 

and state agencies.
2008 National Mercury Monitoring Workshop Report

5

Introduction

Within watersheds and lakes, natural processes convert 

inorganic mercury to a highly bioavailable and toxic organic 

form—methylmercury—that is readily magnified to high 

concentrations in the food web (see figure 1). Exposure to 

toxic levels of mercury largely occurs through consumption 

of organisms with elevated methylmercury. Adverse effects on 

reproduction and neurological function have been observed in 

humans and wildlife with elevated levels of methylmercury. 

Growing awareness of changes in mercury in the 

environment—in atmospheric transport and deposition, 

terrestrial and aquatic ecosystems, and aquatic food webs and 

wildlife—has sparked widespread concern about ecological 

and human health effects. Mercury concentrations in fish 

and other biota in the United States now routinely exceed 

thresholds considered potentially harmful, particularly to fisheating humans and wildlife (see figure 2). Fish consumption 

advisories, including significant coastal advisories, have been 

issued throughout the nation in response to high levels of 

mercury in fish. 

Researchers, natural resource managers, and policymakers 

working to address the mercury problem recognize the need 

for an integrated national mercury monitoring network to 

regularly provide accurate, standardized information about 

ambient concentrations, deposition, watershed cycling, 

bioaccumulation, and biological effects of mercury. 

Figure 1. How mercury enters, cycles, and impacts ecosystems (from Mercury Matters: Linking Mercury Science with Public Policy 

in the Northeastern United States, Hubbard Brook Research Foundation, 2007).

I. Benefits of a national monitoring network

Why do we need enhanced mercury monitoring? 

Human and wildlife exposure to mercury has increased, 

primarily through eating mercury-contaminated fish. Mercury 

is a naturally occurring element, yet industrial activities, 

such as fossil fuel combustion and waste incineration, release 

mercury to the atmosphere where it can be transported 

locally, regionally, and globally. Mercury in the atmosphere 

deposits to the Earth’s surface primarily in inorganic forms. 
6

Introduction

Mercury is released to the environment in 

several ways, but the dominant pathway 

is airborne emissions and deposition. 

Coal-fired power plants are the largest 

single source of anthropogenic mercury in 

the United States, followed by industrial 

boilers and electric arc furnaces. Mercury 

emissions from some sources have decreased 

substantially since passage of the 1990 Clean 

Air Act Amendments. However, emissions 

from coal-fired power plants remain largely 

unchanged. Developing regulatory policies 

designed to reduce mercury emissions from 

coal-fired power plants and other sources 

is one of the primary ways states and the 

federal government are addressing the 

mercury problem. Sufficient information is 

not currently available for many areas of the 

country to fully and accurately assess the 

benefits and effectiveness of these mercury 

reduction measures. Policymakers, scientists, 

and the public need a comprehensive and 

integrated mercury monitoring network to 

accurately quantify regional and national 

changes in atmospheric deposition, ecosystem contamination, 

and bioaccumulation of mercury in fish and wildlife in 

response to changing mercury emissions. 

Who needs mercury monitoring data and why?

As mercury regulations are implemented, a wide range 

of constituencies need information about mercury in the 

environment. It is clear that a mercury monitoring network 

must serve multiple objectives given the types of information 

needed by federal agencies, states, tribes, academic 

researchers, non-governmental organizations, the private 

sector, and the public. 

Informing federal and state mercury policy. The desired 

outcome of mercury emission reduction policies and 

programs is reduced mercury risks to humans and wildlife. 

Critical information is needed to understand and quantify 

the linkages between mercury emissions, ecosystem response, 

Methylmercury contamination has adversely affected the 

benefits derived from fishery resources in many of the 

nation’s inland and coastal waters. In 2006, methylmercury 

was responsible for 80 percent, or 3,080, of the fish 

consumption advisories posted in the United States. 

In addition, 48 states, one territory, and two tribes had 

advisories attributed to mercury. The number of statewide 

fish consumption advisories issued for coastal waters, lakes, 

and rivers in the United States has increased substantially 

in the past two decades. In 2006, 23 states had mercuryrelated, statewide fish consumption advisories for lakes; 21 

had statewide advisories for rivers, and 13 had statewide 

advisories for coastal waters. More than 57,400 km2

 of lake 

area and 1,420,000 km of rivers in the United States were 

under advisory for mercury in 2006. Based on more recent 

data from the National Fish and Wildlife Contamination 

Program, fish consumption advisories now blanket the entire 

nation, as shown on the map above. 

Sources: 2005/2006 national listing of fish advisories. EPA, 

Fact Sheet EPA-823-F-07-003, Office of Water, Washington, 

DC. Available at www.epa.gov/waterscience/fish/

advisories/2006/tech.pdf; USEPA National Fish and Wildlife 

Contamination Program, 2008. 

Figure 2. States with mercury-fish consumption advisories (EPA, 2008).

“Where will we get the biggest bang for our buck? It 

may be domestic, regional, or international sources. 

The network is necessary to tell policymakers how well 

programs are working and where to go next. Getting 

that information systematically from the network will be 

a real challenge.”

Samuel Napolitano

U.S. Environmental Protection Agency
2008 National Mercury Monitoring Workshop Report

7

and human health concerns. Since consumption of fish is the 

primary exposure pathway in humans, a primary focus of 

the scientific effort has been on mercury contamination of 

aquatic food webs. Consumption of fish is also an important 

pathway of methylmercury exposure for wildlife at the top of 

the food webs. Additional monitoring information is needed 

to help determine whether observed changes in mercury 

concentrations in fish and other biota are related to regulatory 

controls on mercury emissions.

Providing data for the development and refinement of 

predictive models. Producing answers to policy and 

management questions about the sources and effects 

of mercury emissions requires the development and 

application of computer models. Advancing understanding 

of atmospheric transport, deposition, and ecological 

transformation of mercury requires spatially and temporally 

rich monitoring data. High-resolution atmospheric mercury 

data are needed to improve atmospheric model estimates of 

wet, dry, and total mercury deposition, and to assess sourcereceptor relationships. Models can help in understanding 

the spatial and temporal variability of mercury in the 

atmosphere, although local, regional, and international 

sources and variable forms of mercury in the atmosphere 

greatly complicate this task. Ecological models combine 

mercury deposition data with indicators of ecosystem 

sensitivity, such as high capacity for mercury methylation, 

and help in understanding bioaccumulation of mercury in 

fish and other biota.

Characterizing biological effects of mercury exposure.

To implement and assess conservation strategies, resource 

managers need information about mercury exposure 

and resulting adverse effects on biological organisms, 

species, and communities. While there has been significant 

work to understand mercury transfer through ecological 

systems and food webs, expanded datasets are needed to 

understand the relationship between changing mercury 

concentrations and biological effects. Measurements of 

environmental mercury that are comparable over time and 

location are particularly important. 

What is the context for a national mercury 

monitoring network?

The regulatory context for mercury emissions is changing. 

Federal agencies, states, and tribes are developing plans and 

policies for reducing mercury emissions from stationary 

sources and will continue to pursue important partnerships 

in this effort. Under any regulatory scenario, there is a 

clear need for a monitoring network that can accurately 

evaluate the impact of changing mercury emissions on 

the environment. For example, implementation of Total 

Maximum Daily Loads (TMDLs) by the states requires 

tracking and managing mercury levels in aquatic ecosystems. 

Similarly, development and implementation of federal and 

state mercury emission control regulations requires detailed 

data on mercury in the environment.

At this time, new funding mechanisms are not in place for 

expanding monitoring of ecological responses to mercury 

contamination. Given funding constraints, design of a 

mercury monitoring network will initially emphasize 

coordination across existing monitoring activities. Where 

possible, the network will leverage infrastructure that 

is already in place while striving towards a robust and 

coordinated set of sites that will meet the full range of 

monitoring objectives. Despite funding shortages and other 

challenges, the mercury research and monitoring community 

has successfully worked together on data-gathering and 

modeling to advance scientific understanding of this critical 

environmental and public health issue. 

What has been done to develop a comprehensive, 

integrated mercury monitoring network?

Considerable progress already has been made in the design 

of a national mercury monitoring network. In 2003, more 

than 30 mercury specialists with expertise in atmospheric, 

terrestrial, and aquatic processes gathered in Pensacola, 

Florida for the North American Workshop on Mercury 

Monitoring and Assessment. This workshop, sponsored by 

the U.S. Environmental Protection Agency (USEPA) and 

the Electric Power Research Institute (EPRI) and convened 

by the Society of Environmental Toxicology and Chemistry 

(SETAC), proposed a framework for a national-scale 

program to monitor changes in mercury concentrations in 

the environment. Workshop participants recommended a set 

of environmental measurements and indicators to monitor 

trends in mercury concentrations in air, land, water, and 

biota to assess ecosystem responses to reductions in mercury 

emissions. They also recommended a general nested sampling 

design for the monitoring network that will enable integrated 

assessment of mercury in the environment on a national scale. 

“It is important to ensure that the detection of mercury 

can be tangibly tied to environmental effects. 

Congress wants to know whether the presence of a 

pollutant in the environment translates into effects 

in the environment. FWS is interested in monitoring 

mercury trend data because they will affect our 

management actions and improve prevention and 

restoration activities.”

Tiffany Parsons

U.S. Fish and Wildlife Service
8

Introduction

A peer-reviewed journal article (2005)1 and a subsequent book 

(2007)2 published recommendations from this workshop.

Much more has been accomplished since 2003. New work, 

organized through the National Atmospheric Deposition 

Program (NADP) Atmospheric Mercury Initiative, facilitated 

collaboration among federal, state, and academic research and 

monitoring groups to provide high-resolution, high-quality 

data at 10 sites to estimate changes in atmospheric mercury 

concentrations and dry mercury deposition. In Congress 

the House and the Senate have put forth authorization bills 

that charge multiple federal agencies with establishing a 

national mercury monitoring program (H.R.1533 and S.843, 

respectively)3. In the Northeast, a team of scientists convened 

by the Hubbard Brook Research Foundation synthesized 

regional mercury data under a Northeastern Ecosystem 

Research Cooperative initiative, and modeled mercury 

emissions from local coal-fired power plants. This work 

generated important findings about the presence of biological 

mercury “hot spots” and implications of mercury deposition 

reductions for mercury levels in biota, and highlighted the 

need for an enhanced mercury monitoring program to assess 

the response to emissions reductions. This team produced 

a special issue of the peer-reviewed journal Ecotoxicology

(Vol. 14, Issues 1–2, March 2005), two synthesis papers in the 

1 Mason RP, Abbott ML, Bodaly RA, Bullock Jr. OR, Driscoll CT, Evers 

D, Lindberg SE, Murray M, Swain EB. 2005. Monitoring the response of 

changing mercury deposition. Environ. Sci. Technol. 39:14A-22A.

2 Harris R, Krabbenhoft DP, Mason R, Murray MW, Reash R, Saltman T. 

2007. Ecosystem responses to mercury contamination: indicators of change. 

SETAC, Boca Raton, FL.

3 Full text of these bills is available from the Government Printing Office: 

H.R.1533 http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=110_

cong_bills&docid=f:h1533ih.txt.pdf; and S.843 http://frwebgate.access.gpo.

gov/cgi-bin/getdoc.cgi?dbname=110_cong_bills&docid=f:s843is.txt.pdf 

peer-reviewed journal BioScience4, as well as Mercury Matters5, 

a report communicating these scientific findings to general 

audiences.

II. 2008 National Mercury 

Monitoring Workshop

Who was involved in the workshop?

In 2007, EPA’s Office of Atmospheric Programs organized a 

13-person National Mercury Monitoring Workshop Steering 

Committee, with representatives from research and monitoring 

organizations and federal, state, and tribal agencies (see 

Appendix A for membership list). The purpose of the Steering 

Committee was to convene a workshop to explore options to 

design and implement a comprehensive, national mercury 

monitoring network. Since the mandate to monitor, assess, and 

report on mercury in the environment cuts across numerous 

federal, state, and tribal agencies, the steering committee 

recognized the need to expand coordination and agreement 

among a broad-based consortium of stakeholders about nearand medium-term monitoring needs for tracking mercury 

pollution in ecosystems.

4 Driscoll, C.T., Y.-J. Han, C.Y. Chen, D.C. Evers, K.F. Lambert, T.M. Holsen, 

N.C. Kamman, and R.K. Munson. 2007. Mercury contamination in forest 

and freshwater ecosystems in the Northeastern United States. BioScience. 

57:17-28.

Evers, D.C., Y-J Han, C.T. Driscoll, N.C. Kamman, M.W. Goodale, K.F. 

Lambert, T.M. Holsen, C.Y. Chen, T.A. Clair, and T. Butler. 2007. Biological 

Mercury Hotspots in the Northeastern United States and Southeastern 

Canada. BioScience. 57(1):29-43.

5 Driscoll, C.T., D. Evers, K.F. Lambert, N. Kamman, T. Holsen, Y-J. Han, 

C. Chen, W. Goodale, T. Butler, T. Clair, and R. Munson. Mercury Matters: 

Linking Mercury Science with Public Policy in the Northeastern United States. 

Hubbard Brook Research Foundation. 2007. Science Links Publication. 

Vol. 1, no. 3.

2003 2004 2005 2006 

Mason et al.

2005, ES&T

39:14A-22A

USEPA/SETAC North American 

Workshop on Mercury Monitoring

and Assessment, Pensacola, FL

Comprehensive mercury

monitoring bills introduced 

in House and Senate
2008 National Mercury Monitoring Workshop Report

9

On May 5–7, 2008, the Steering Committee held a National 

Mercury Monitoring Workshop of approximately 50 

participants in Annapolis, Maryland, to share mercury 

monitoring information, refine the scientific and technical 

basis for the design of a national mercury monitoring 

network, and explore potential implementation strategies.6

Participants represented diverse perspectives and 

disciplines, with specific types of mercury-related expertise 

and involvement in mercury monitoring, modeling, and 

research in academia, federal and state agencies, tribes, nongovernmental organizations, and other sectors.6

What were the goals of the workshop?

The workshop focused on three goals: 

Q Distill recommendations from previous work on 

measurement parameters for tracking ecological responses 

to mercury; 

Q Share information and explore potential collaboration 

among existing North American sites and programs that 

monitor chemical and biological endpoints of mercury 

contamination (e.g., air, water, watershed, sediments, 

biota); and 

Q Identify mercury monitoring data gaps and explore options 

for eliminating those gaps. 

The workshop focused on atmospheric, terrestrial, freshwater, 

and coastal ecosystems in the United States, although linkages 

to ecosystems and monitoring programs in Canada and 

Mexico were encouraged. 

6 See http://nadp.sws.uiuc.edu/.

How was the workshop organized? 

The workshop was organized around a set of key monitoring 

network design questions. For some of these questions, 

substantial progress already had been made, and workshop 

discussions focused on refinement of earlier work: 

I. What are the goals and objectives of a national mercury 

monitoring network?

II. What are the major elements needed to meet network 

goals and objectives?

For other network design questions, robust preliminary work 

was used to inform discussion of major remaining issues.

III. What monitoring capabilities are already in place? 

IV. What existing sites can meet monitoring objectives?

V. How can we develop the network?

In the workshop, a range of panelists and presenters shared 

ideas and information about network goals, objectives, 

and major elements. In breakout groups and full group 

discussions, participants reflected on preliminary options 

presented by the Steering Committee for selection of 

monitoring sites. Participants helped to fill information 

gaps for existing and potential sites, in addition to exploring 

options for near-term strategies to develop the network.

2007 2008 2009 2010

Harris et al.

2007, CRC Press 

National Mercury Monitoring Workshop

May 5–7, 2008, Annapolis, MD

Northeastern mercury scientists from the Hubbard Brook Research 

Foundation published two papers in BioScience on mercury in the 

environment. Both papers indicated the need for a comprehensive 

and integrated nationwide mercury monitoring program.

2008 National Mercury Monitoring Workshop Report

11

Elements of a National

Mercury Monitoring Network

Mercury cycling is complex. To quantitatively document 

the full range of ecosystem responses to changing mercury 

emissions, more robust monitoring of terrestrial, freshwater, 

estuarine, and coastal ecosystems—and greatly enhanced 

integration of data gathering—is needed. 

To support national environmental policy development 

and assessment, it is essential that the monitoring network 

provide nationally consistent data that are comparable across 

ecosystems over time. Establishment of clearly defined site 

selection criteria and standardized measurement protocols—

that are sufficiently flexible to allow the use of reliable, 

historical data to document trends—will be important to 

the success of the network. Scientific collaboration will 

require development of effective data management systems, 

accessible databases, and diverse reporting mechanisms. 

Finally, transparent processes for quality assurance are 

necessary to ensure scientific defensibility. 

I. Network goals and objectives

What is the overall goal of the mercury monitoring 

network?

Prior to the workshop, the Steering Committee proposed the 

following goal:

To establish an integrated, national network to 

systematically monitor, assess, and report on policy-relevant 

indicators of atmospheric mercury concentrations and 

deposition, and mercury levels in land, water, and biota in 

terrestrial, freshwater, and coastal ecosystems in response to 

changing mercury emissions over time.

Workshop discussions expanded on this statement to 

emphasize the importance of linking monitoring activities 

explicitly to the information needs of policymakers, 

resource managers, and researchers for managing risk and 

predicting outcomes. 

Other key attributes of the desired monitoring network 

include national-scale coordination to enable an integrated 

view of changes in mercury associated with emission control 

policies. This will require comprehensive measurement of 

key variables and should include monitoring of ecosystems 

expected to be sensitive to changes in mercury deposition. 

What are the main objectives of the mercury 

monitoring network?

The Steering Committee proposed monitoring network 

objectives. The workshop participants reviewed and revised 

the objectives to align with the full range of mercury 

information needs. The result was the following list:

1. Establish baseline mercury concentrations in multiple 

ecosystem compartments that document environmental 

conditions before implementation of new mercury 

emissions controls to detect temporal trends that might 

be attributable to these controls. This entails building on 

historical datasets and accounting for baseline conditions 

that vary in space and time. 

Workshop participants reviewed goals, objectives, and 

proposed network design strategies, and emphasized the 

importance of national-scale coordination and comprehensive 

measurement of key ecosystem variables related to mercury 

pollution. To enable an integrated view of ecosystem 

responses to emission control policies, focus should be 

placed on systems expected to respond rapidly to changes 

in mercury deposition. There was broad agreement with 

proposed measurement parameters and a nested sampling 

strategy involving intensive and cluster sites.

Site selection should be focused on the ability to document 

trends and establish causal links between mercury emissions 

and ecosystem responses, and to provide useful input data 

for predictive atmospheric and watershed models.

Monitoring 

network

Measurements

and models

Informed

policy and 

management

“The idea is to get everyone to operate the technologies 

in the same fashion.”

David Gay

National Atmospheric Deposition Program
12

Elements of a National Mercury Monitoring Network

2. Track spatial patterns and long-term trends in mercury 

concentrations in specific ecosystem compartments including 

airsheds and watersheds, aquatic ecosystems, aquatic biota, 

and wildlife as mercury emissions controls are implemented. 

This entails a comprehensive geographic approach that 

accounts for spatial variability, and a long-term, consistent set 

of measurements to assess temporal response.

3. Provide data to assess linkages between atmospheric 

mercury emissions and methylmercury concentrations 

in biota, and how these change over time. This entails 

quantifying relationships between mercury emission 

sources and aquatic receptors, and accounting 

for ecological ‘lags’ with particular attention to 

contamination of aquatic food webs and fish to provide 

information needed for health risk assessment and fish 

consumption advisories.

4. Document trends in biological indicators of mercury 

exposure and effects relative to changes in mercury 

loadings to ecosystems, including ecotoxicological effects 

on organisms and populations. 

5. Provide mercury and ancillary data to evaluate predictive 

and diagnostic models and to advance the development 

of mercury cycling models and models to assess sourcereceptor relationships. This entails integration of 

monitoring and modeling activities to ensure that data 

can be efficiently used to build, test, and run models that 

account for the full range of factors affecting mercury 

abundance and methylation rates.

6. Assess potential ecological harm and linkages to air 

emission sources for sites and wildlife of conservation 

concern. This entails quantifying cause-and-effect 

relationships among mercury emissions, deposition, and 

wildlife exposure. 

7. Connect national mercury monitoring efforts to other 

monitoring programs in North America and adjacent 

waters, where feasible, to maximize integration of 

expertise and monitoring capacity. Strive for effective 

interaction with mercury monitoring programs, both in 

North America and globally.

II. Mercury measurements 

Major network design concepts were originally developed at 

the 2003 Pensacola workshop and subsequently published in 

Harris et al. (2007). Presentations provided by Robert Mason 

(University of Connecticut) and David Krabbenhoft (U.S. 

Geological Survey) summarized these concepts and were 

supplemented by workshop discussions.

What mercury parameters should be measured?

Monitoring should focus on environmental features expected 

to respond to changes in mercury deposition and exposure 

over management-relevant timescales. Measurements 

should be made with proven methods, provide data that 

can be defensibly interpreted, and be optimized to enable 

differentiation among ecosystem factors related to mercury 

methylation (e.g., sulfate deposition; mercury loading vs. 

wetland alteration). 

Recommended measurements, as detailed in Harris et al. 

(2007), include concentrations of total and methylated 

forms of mercury in air, soils, forest litter, sediments, surface 

and ground water, snow, yearling fish, adult predatory fish, 

and mercury-sensitive wildlife species (see appendix D). 

Monitoring sites should also measure speciated ambient 

mercury concentrations, wet and dry mercury deposition, and 

mercury in throughfall and litterfall.

In addition to monitoring changes in mercury 

concentrations, measurement of ancillary parameters—

atmospheric and aquatic chemistry, hydrology, climate, 

and trophic conditions—is needed to defensibly interpret 

mercury trends and dynamics. Recommended ancillary 

measurements include physical features (e.g., watershed 

area, land cover, wetland area, rainfall), other chemical 

constituents (e.g., sulfate, nutrients, oxygen, organic carbon) 

and parameters (e.g., pH, temperature, acid-neutralizing 

capacity), as well as characteristics of sampled biota (e.g., 

size, age, trophic position). 

III. Types of mercury monitoring sites

Where should mercury parameters be measured?

There is broad agreement about the utility of a nested 

sampling approach that includes a small number of intensively 

monitored sites with a larger number of more sparsely 

monitored sites clustered around them.

Intensive sites are intended to provide a sound foundation 

for understanding mechanistic, cause-and-effect responses, 

“We would like to measure everything everywhere, but 

that is impractical.”

Rob Mason

University of Connecticut
2008 National Mercury Monitoring Workshop Report

13

measuring trends, and allowing for development and 

refinement of models. Emphasis at these sites would be given to 

process-level monitoring and research and to comprehensive, 

high-resolution measurements in air, soil, water, and biota. 

Selection of approximately 20 nationwide intensive sites 

would emphasize areas likely to undergo change in response 

to altered mercury loading, highly sensitive sites, and possibly 

“global background” sites. Capitalizing on existing monitoring 

programs will maximize opportunities for establishing needed 

baselines and ongoing institutional support.

Cluster sites are intended to provide a more general 

understanding of environmental responses for a defined 

geographic area or ecosystem type, and to allow observations 

to be transferable to the population of the resource. Emphasis 

at these sites would be given to expanding geographic coverage 

of monitoring data through lower resolution and more limited 

types of measurements than at intensive sites. Approximately 

10 to 20 cluster sites would be selected in the vicinity of each 

intensive site to provide a general understanding of the range of 

ecosystem responses within the area. 

IV. Site selection 

What major objectives should guide selection of 

intensive sites?

Candidate intensive sites will be selected to meet as many 

network monitoring objectives as possible. However, previous 

monitoring and research suggests that some candidate intensive 

sites will have attributes that make them suitable for meeting 

some monitoring objectives more effectively than others. The 

following general categories can be used to inform site selection:

Documenting trends. Sites that lend themselves to 

establishment of baseline mercury concentrations in multiple 

ecosystem compartments (prior to implementation of 

atmospheric mercury control measures) will be especially 

useful for documenting changes in mercury concentrations 

and determining spatial patterns and long-term trends. Such 

sites will have existing longer term mercury datasets (both 

atmospheric and ecosystem data) and supporting information 

on site characteristics and ancillary measurements (e.g., 

meteorology). A nationally distributed network of trends sites 

will be needed to cover a range of ecological regions and span 

major ecosystem types (e.g., forests, wetlands, streams, lakes, 

coastal areas, the Great Lakes).

Establishing causality. Sites that are anticipated to exhibit a 

clearly defined response to changes in mercury deposition 

(in particular, sites where confounding by other disturbances 

will be minimal) will be especially useful for establishing 

mechanistic linkages among changes in atmospheric mercury 

emissions; deposition rates; and mercury concentrations in 

soil, water, or biotic compartments. Sites will span a range 

of expected response times to changing mercury deposition 

Table 1. Types of measurements for cluster or intensive 

sites adapted from Mason et al., 2005. (Note that these 

recommended measurements may be adapted as the mercury 

monitoring network is implemented. For more detailed 

descriptions, refer to appendix D.)

Indicator Site Frequency

Air and Watershed

Atmospheric mercury speciation; wet 

and dry deposition flux

IN C

Weekly wet deposition and fluxa CL W

Mercury evasion/fluxa IN M

Watershed yield (surface water and 

ground water flux)

CL M

Sediment and Water

Historic sediment depth profileb IN I

Total mercury, methylmercury, and 

percent methylmercury in surface 

(0–2 cm) sediment

CL S

Total mercury, methylmercury in 

surface water

CL S

Total mercury, methylmercury in 

water-column profiles

IN S

Aquatic Biota

Phytoplankton and algaec IN M

Zooplankton/benthic invertebratesc IN M

Yearling fish CL A

Piscivorous/commercial fishc CL A

Wildlifed CL A

Site: IN = intensive sites; CL = cluster and intensive sites

Frequency of sampling: C = continuously; W = weekly; M = monthly; S = 

every 6 months; A = annually; I = every 3–5 years.

a

 Event-based wet deposition collection at intensive sites, weekly integrated 

sampling at cluster sites. At intensive sites, flux estimates would include 

wet, dry, gaseous, and particulate deposition; throughfall and litterfall; and 

snowpack sampling as appropriate. Mercury concentration and evasion 

fluxes would be for both aquatic and terrestrial environments.

b

 Intensive sites and a subset of cluster sites would be sampled to determine 

historic mercury trends.

c Sampling not recommended by the biological indicators workgroup at 2003 

SETAC workshop (as summarized in chapter 4, Harris et al., 2007).

d

 Birds, small and larger mammals; both short-term and integrative sampling.

Note that mercury evasion/flux values frequently change substantially on even 

an hourly basis. The Draft Standard Operating Procedures for Analysis of 

Gaseous and Fine Particulate-Bound Mercury, developed from a best practices 

questionnaire distributed by the NADP, describes standard operation and 

maintenance of an automated, speciated ambient mercury monitoring unit.
14

Elements of a National Mercury Monitoring Network

(e.g., rapid response in perched seepage lakes, slow response 

in sites with substantial groundwater input). Study sites will 

also include areas of high conservation concern and sites near 

emission sources. 

regional emission sources that produce a range of atmospheric 

concentrations and plume “episodes.” Mercury emissions 

inventories, ambient measurements, and meteorological data are 

also needed to interpret trends in measurements.

What site characteristics should be used 

to evaluate potential monitoring sites? 

While the rationale for including any individual monitoring 

site in the national network might be based on unique site 

characteristics, general considerations for evaluating how 

well a potential site could contribute to network objectives 

have been identified. Site selection should be informed by the 

following criteria:

1. Sensitivity to mercury inputs. Ecosystem characteristics 

(e.g., water quality and land use) play a significant role 

in determining the “mercury sensitivity” of any potential 

monitoring location. Mercury sensitivity is the relative 

efficiency of an ecosystem to transform an inorganic 

mercury load into bioaccumulated methylmercury. 

Mercury-sensitive ecosystems are more efficient in 

conducting the transformation. In addition, it is likely 

that more sensitive ecosystems will be more responsive to 

changes in mercury loading in terms of both the magnitude 

and timing of the response. Chosen monitoring sites will 

need to have characteristics known to promote greater 

sensitivity, although some low mercury-sensitivity sites 

should also be included to quantify the broad range of 

responses across ecosystem types.

2. Data and modeling. Are longer-term mercury or ancillary 

data available for this site? Does this site have potential for 

evaluating atmospheric and ecosystem mercury models? 

3. Suitability as a reference site. Does this site have 

potential for characterizing the influence of other 

global sources of mercury?

4. Site resources. Does this site have existing scientific 

facilities and institutional infrastructure to support 

monitoring? Are there intra-agency and interagency 

operations and strong prospects for obtaining funding and 

sustaining monitoring efforts at this site? 

5. Logistical, personnel, and other issues. Does the site 

have (or have potential for) access, power supply, and 

telecommunications? Is this site vulnerable to vandalism 

or extreme weather? Is this site close to site operators and 

researchers? Is the land ownership stable?

Design and implementation of a mercury monitoring network 

will inevitably emphasize coordination across existing 

monitoring capabilities and infrastructures. Understanding 

the capacity of current mercury monitoring activities and 

programs to meet the full range of monitoring objectives 

and data needs is a key step in building the foundation for an 

expanded, integrated network.

“To have national relevance, we need to have a national 

distribution of monitoring sites. We have to include 

definitions of ecosystems that are threatened, including 

information about ecosystem types, mercury sensitivity, 

and proximity to sources and urban areas.”

David Krabbenhoft

U.S. Geological Survey

Characterizing the influence of other global sources. To 

differentiate other global (i.e., non-U.S.) sources of mercury 

from domestic emission sources, it is desirable to include one 

or more sites that can assist in characterizing, quantifying, 

and tracking the impacts of atmospheric mercury imported 

to the United States. It is important to evaluate the influence 

of mercury from other global sources because emissions are 

rapidly increasing due to industrialization elsewhere in the 

world, particularly in China and India. A suitable “global 

background” site for a national mercury monitoring network 

would be a location where it can be reasonably assumed 

from field data and models that mercury inputs are solely 

or primarily from sources outside of the United States. It is 

critical that this monitoring network is aware of and tracks 

other environmental factors—climate, vegetation, soils, land 

cover, including wetland cover, hydrologic flowpaths, water 

chemistry, and surface water productivity—that significantly 

affect mercury transformation and bioaccumulation. 

Thus, great care will be necessary when identifying one or 

more “global background” sites for the national mercury 

monitoring network.

How should modeling needs guide site selection?

Development of models to predict and explain the observed 

magnitude and timing of ecological responses to changes in 

mercury emissions (e.g., changing methylmercury levels in fish) 

requires supporting data. Selection of monitoring sites should be 

informed by model input needs as well as the need to distinguish 

the effects of multiple environmental factors.

Watershed Models. For successful application and rigorous testing 

of watershed mercury models, preferred site characteristics 

include relatively uniform sites with well-characterized land 

cover, meteorology, hydrology, soils, and biology, and a relatively 

long time series of mercury measurements. Data need to include 

measurement of evasion, throughfall, litterfall, methylation, 

demethylation, and soil adsorption.

Atmospheric models. For successful development of atmospheric 

mercury models, preferred site characteristics include simple 

terrain with few confounding variables (e.g., vehicle traffic), 

existing meteorological simulations, and well-characterized 
2008 National Mercury Monitoring Workshop Report

15

Mercury Monitoring:

What’s in Place Now? 

I. Existing mercury monitoring programs 

and sites

What monitoring programs are already in place?

Mercury monitoring efforts vary greatly across the United 

States, ranging from one-time sampling events, to repeat 

long-term sites that monitor mercury in one ecosystem 

compartment, to established intensive study sites that 

monitor mercury in the atmosphere, surface water, fish, 

sediment, vegetation, wildlife, and other environmental 

media. (See appendix B for a summary of major existing 

and emerging monitoring initiatives.) Monitoring efforts 

conducted by researchers, federal agencies, states, tribes, and 

other organizations to support distinct objectives are often 

uncoordinated and use disparate sampling and analytical 

methods. In many instances, resulting mercury data from 

these efforts are not entirely comparable. This can present 

a challenge to establishing regional and national baselines, 

assessing spatial patterns and temporal trends, and evaluating 

causal links between mercury emissions and bioaccumulation 

in aquatic food webs.

High-quality mercury measurements are made in many 

places throughout the country. From a national perspective, 

the use of nonstandardized sampling and analytical methods 

impede assessment of spatial patterns and temporal trends 

of mercury in the environment. As a first step toward 

understanding the comparability of mercury sampling 

data across the United States, EPA, in partnership with 

the BioDiversity Research Institute and other institutions, 

developed the MercNet metadatabase. The metadatabase 

documents information about the location and type of 

mercury sampling activities nationwide, including methods 

used to make mercury measurements. The metadatabase 

was used primarily to identify potential network monitoring 

sites, based on preliminary analysis of locations where 

more than one ecosystem compartment (e.g., air, water, 

fish, sediment) was sampled. The metadatabase is also 

being used to explore opportunities to standardize network 

methods on regional and national scales.

Where has mercury data been collected?

To characterize the landscape in which a national mercury 

monitoring network could be implemented and to identify 

gaps in data gathering, EPA’s Office of Atmospheric Programs 

and the BioDiversity Research Institute have catalogued 

sites where mercury concentrations and related parameters 

have been measured nationwide. The MercNet metadatabase 

houses information about the geographic location, dates, 

and other attributes of mercury sampling events in various 

media such as air, water, sediment, fish, plants, and wildlife 

conducted by many agencies and researchers.

The metadatabase was populated through several approaches, 

including a broad survey of scientific literature, data mining 

from federal agency datasets,7

 and informally surveying 

7 These include: NOAA National Status and Trends Program (NS&T), 

EPA Environmental Monitoring and Assessment Program (EMAP), EPA 

STOrage and RETrieval (STORET), USFWS Environmental Contaminant 

Data Management System (ECDMS), USGS National Water-Quality 

Assessment Program (NAWQA), USGS Contaminant Exposure and 

Effects-Terrestrial Vertebrates (CEE-TV), and BioDiversity Research 

Institute (BRI) Wildlife Data.

“MercNet can be considered a shared resource for 

everyone and will provide a valuable benchmark for 

future needs by scientists, landscape managers, 

and policymakers.”

David Evers

BioDiversity Research Institute

Photo credit: Mario Montesdeoca, Syracuse University
16

Mercury Monitoring: What’s in Place Now?

the research community.8 This resource might be used to 

search for potential intensive or cluster sites that meet key 

monitoring objectives, as well as to identify major gaps in 

existing monitoring coverage. Preliminary queries of the 

MercNet metadatabase were conducted to demonstrate 

its potential for identifying sites that could be appropriate 

for trends analysis—by identifying sites with repeat 

sampling—and sites that might be appropriate for establishing 

causality—by identifying sites with measurements for multiple 

environmental compartments. Sites with higher resolution 

ecological analysis have overlapping measurements for fish 

and other wildlife, as well as for information about mercury 

concentrations associated with adverse biological effects. 

Future applications of the MercNet metadatabase might 

include identification and analysis of data suitable to support 

development of mercury baselines. However, more work is 

needed to fully populate the metadatabase and evaluate the 

mercury datasets. 

II. Potential intensive sites

What has been done to characterize potential 

intensive sites?

A key step in implementing a national mercury monitoring 

network is to select intensive sites where a broad suite 

of mercury and ancillary measurements should occur. 

8 These include: Syracuse University comprehensive mercury monitoring 

activities at Huntington Wildlife Forest and Sunday Lake in the 

Adirondacks; sediment core mercury monitoring activities in the upper 

Midwest; over 100,000 records for fish-sampling activities, including data 

from state environmental agencies/departments, USGS programs (e.g. 

NAWQA, BEST), and private research institutions. 

A compilation exercise to characterize current sampling 

programs at existing mercury monitoring sites was performed 

by staff in EPA’s Office of Atmospheric Programs. While not 

yet complete, this compilation was intended to synthesize 

background information and allow objective site comparisons 

based on the richness of monitoring data collected at each 

site and suitability for meeting monitoring objectives. Rich 

datasets produced by site-specific mercury research are a 

valuable asset; however, the stability of funding for continued 

data collection will be a key consideration in selecting 

intensive sites.

To identify sites with strong potential for contributing to 

a national monitoring network, the list of recommended 

measurement parameters (from Harris et al., 2007) and site 

selection criteria (described on pp. 13–14) were applied to 

existing monitoring sites. Specifically, sites in the MercNet 

metadatabase, sites identified through the primary literature 

(approximately 120 journal articles), and sites in known 

monitoring networks9

 were filtered to identify geographic 

locations where more than one ecosystem compartment (e.g., 

air, water, fish, sediment) is measured within a defined area. 

A preliminary, semi-qualitative assessment led to the 

identification of 69 potential intensive sites for evaluation by 

the Data Task Group (see p. 17). Notably, results of this initial 

compilation suggest that most sites have better potential to 

function as cluster sites than as intensive sites.

A key objective of the Annapolis workshop was to refine 

selection criteria and identify candidates for a comprehensive 

mercury monitoring network of intensive and cluster sites, 

based on agreed upon network elements and objectives. 

In preparation for the workshop, the Steering Committee 

convened the Data Task Group on March 4, 2008, to 

undertake a planning exercise for identifying potential 

monitoring sites based on preliminary site characterizations 

developed by EPA. In breakout groups and full group 

discussions, participants at the Annapolis workshop reflected 

on the preliminary options developed by the Data Task Group 

and helped to more fully characterize potential intensive and 

cluster sites.

9 Such as the National Atmospheric Deposition Program (NADP), the 

Clean Air Status and Trends Network (CASTNET), and the Temporally 

Integrated Monitoring of Ecosystems (TIME).

Photo credit: Adirondack Ecological Center
2008 National Mercury Monitoring Workshop Report

17

Developing the Mercury

Monitoring Network: Selecting Sites

I. Preliminary intensive site selection

What progress has been made in selecting 

intensive sites?

Based on their professional judgment and the preliminary 

compilation of existing sites described above, the Data 

Task Group developed a list of 21 candidate sites to further 

characterize and review at the Annapolis workshop. The 

group focused on identifying a limited set of potential 

intensive monitoring sites that would represent key site 

types and meet a range of network monitoring objectives 

and site selection criteria. The group recommended further 

site characterization and a gap analysis to examine the 

monitoring capacity of each potential site relative to network 

monitoring objectives and siting considerations. 

Data Task Group members noted that it was difficult to 

identify existing sites where the full range of measurements 

needed to meet overarching network objectives were currently 

being made. However, a number of sites were included by 

multiple experts in their recommended sites lists (developed in 

preparation for the March 4th meeting). 

At the Annapolis workshop, participants worked in breakout 

groups—based on geographic regions—and in full group 

discussions to evaluate the proposed list of 21 intensive sites and 

expand the underlying site characterization (e.g., by applying 

region-based knowledge of specific sites). These discussions 

produced a next iteration of candidate intensive sites (appendix 

C). This preliminary list will be explored through regional 

meetings and further refined by network planners. 

Workshop participants evaluated preliminary intensive site 

characterization and selection work performed by the Data 

Task Group. Outcomes included a refined list of potential 

intensive sites and identification of next steps for further 

refinement. Additional work is needed to refine definitions 

of intensive sites (e.g., appropriate areal extent) and cluster 

sites (e.g., geographic criteria, national consistency). 

Characterization and selection of intensive sites require 

evaluation of sites’ existing and potential monitoring activity 

as well as the ability to meet network objectives. Participants 

also explored general issues, potential criteria, and alternative 

approaches for selection of cluster sites.

“We [the Data Task Group] tried to identify and 

characterize existing sites through a series of criteria, 

including distribution, sensitivity to mercury deposition, 

proximity to sources (i.e., elevated loading), previous 

studies and monitoring, conservation concerns, and the 

region around the sites.”

Charles Driscoll

Syracuse University

What issues remain unresolved for intensive sites?

Discussions by the Data Task Group and Annapolis workshop 

participants outlined a set of questions that should be 

addressed to support further development of the list of 

potential intensive sites: 

1. The list of potential intensive sites includes ‘sites’ that range 

widely in geographic extent from fairly localized areas 

with established monitoring to multi-state regions. Further 

work is needed to define the areal extent that is considered 

appropriate for a designated intensive site. For example, is 

it possible and appropriate to combine adjacent sites with 

complementary data into a single large site? A geographic 

definition has implications for the range of landscape 

variability that is included within a designated intensive site, 

as well as the pool of historical mercury and ancillary data 

that would be considered relevant. 

2. Selection of intensive sites will draw upon a number 

of considerations, and some degree of prioritization 

among these might be necessary. For example, what 

are the tradeoffs in site selection to achieve objectives 

of documenting trends versus establishing causality? 

Some types of data collection (e.g., atmospheric, biota) 

might lend themselves more easily to establishment of 

baselines, and this might affect comparisons of potential 

sites with different types of baseline data. The answer 

may depend on whether the site is selected to establish 

trends—and therefore requires strong baseline data—or 

to determine causal links between mercury deposition 

and ecological response. 

3. Agreement is needed about how to evaluate sites that 

are well suited to meeting a single monitoring objective 

relative to sites that provide a more balanced set of 

capabilities. For example, should a site be included in the 

small set of intensive sites with a primary site objective 
18

Developing the Mercury Monitoring Network: Selecting Sites

of characterizing the influence of other global sources 

if it does not contribute usefully to other monitoring 

network objectives?

What are the next steps toward selection of 

intensive sites?

Although preliminary characterization of potential 

intensive sites has been used to inform stakeholder 

efforts to select a useful set of sites, more in-depth and 

quantitative site characterization is needed. For each of 

the candidate intensive sites, substantial work is needed to 

fully characterize current and potential monitoring capacity 

and evaluate how the site would contribute to network 

monitoring objectives. This will involve evaluating the 

coverage of recommended measurement parameters, as well 

as potential confounding factors, at a more comprehensive 

set of existing sites and performing some form of geographic 

gap analysis to understand where existing monitoring 

infrastructure is lacking. Selection of the full set of intensive 

sites requires definition of the geographic regions to be used 

in distributing sites across the United States. As part of a 

geographic analysis, basic site categorization by ability to 

support documentation of trends and establish causal links 

between mercury emissions and ecological response will 

be critical to ensure the national network can meet the core 

objectives with robust spatial relevance.

II. Cluster site selection

What progress has been made in cluster 

site selection?

The Data Task Group also discussed several different 

approaches for selecting cluster sites. The proposed objectives 

to guide cluster site selection include assisting in national 

assessments and evaluation of policy impacts, contributing 

to ecological baselines, and providing information needed 

for model development and process-level research. At the 

Annapolis workshop, presentations and discussions explored 

key concepts and tradeoffs in locating cluster sites. Presenters 

provided alternative approaches for optimizing selection 

of cluster site locations, anchored in case studies of specific 

existing monitoring efforts. 

Random Stratified Sampling Design—Case Study in the 

Everglades. To illustrate the utility of cluster siting based on 

random sampling sites established through major monitoring 

programs, David Krabbenhoft (U.S. Geological Survey) described 

the extensive sampling program for mercury in the Florida 

Everglades. The U.S. Geological Survey led a study to monitor 

nine intensive sites running north-south through the Everglades 

over time. Beginning in 1995, a fleet of helicopters was used to do 

random stratified design sampling to spatially extrapolate from 

these nine intensive sites, through EPA’s Regional Environmental 

Monitoring and Assessment Program (REMAP) with multiagency support. The intensive and cluster site monitoring in 

the Everglades program has enabled the following important 

observations: (1) methylation rate varies across the landscape 

and corresponds closely to mercury abundance; and (2) between 

1995 and 2005, 20 percent of the land area that formally exceeded 

human health benchmarks for mercury in tiny fish are no longer 

exceeding those levels. It is believed that a decrease in sulfate 

entering the Everglades has played a key role.

Ecosystem Subtype Sampling Design—Case Study in Acadia 

National Park. To illustrate how cluster siting could account 

for spatial variability around intensive sites, David Evers 

(BioDiversity Research Institute) presented ideas for siting 

mercury monitoring in the vicinity of Acadia National Park 

on Mount Desert Island in Maine. This area has diverse habitat 

and a range of existing mercury-related biological datasets. 

The emphasis in this presentation was on connecting mercury 

data gathering to different habitat types and food webs—with 

different levels of mercury sensitivity—and locating cluster sites 

to track how mercury has moved through freshwater, terrestrial, 

and marine habitats. This approach, it was noted, represents a 

more geographically constrained strategy.

Figure 4. Conceptual map of a potential mercury monitoring network. 

This map illustrates how monitoring sites could be distributed across 

the United States to achieve comprehensive regional and national 

coverage. (Note: The areas identified in this map are preliminary and do 

not represent a final set of sites to be included in the national mercury 

monitoring network.)

Area discussed at the Annapolis Workshop 

as a potential candidate intensive site
2008 National Mercury Monitoring Workshop Report

19

Process-Level Sampling Design—Case Study in the 

Adirondacks. To illustrate the benefits of process-level 

sampling strategies, Charles Driscoll (Syracuse University) 

described intensive and cluster monitoring sites in the 

Adirondacks region of New York. This large forested 

area includes an intensive study site at the Huntington 

forest, a 300-hectare area with an NADP National Trends 

Network site, and a Mercury Deposition Network (MDN) 

site for mercury data collection. Process-level studies in 

uplands, wetlands, and lakes have used mass balance and 

tracer studies to understand the processing and transport 

of mercury across the landscape. A series of lakes (and 

surrounding terrestrial areas) were monitored in the early 

1990s and later to document physical and chemical changes 

through measurements of total mercury, methylmercury, 

pH, sulfate, and other information. Resulting observations 

were mixed: mercury concentrations in fish decreased in 

half the lakes, increased in one-quarter of the lakes, and 

remained unchanged in one-quarter of the lakes.

deposition only). In considering where to locate intensive sites 

and any surrounding comprehensive atmospheric cluster sites, 

ideal sites would be ringed by different sources and therefore 

be affected by episodic high levels of mercury deposition from 

known sources as well as regional and distant (global) sources.

“The clearest change in the deposition of mercury that can 

be biologically measured is likely in terrestrial systems, 

primarily because there are fewer biogeochemical hurdles 

for detecting a clear response. Even though ecological risk 

is likely greatest in wetlands, mountaintops may be the 

best habitat to monitor such changes.”

David Evers

BioDiversity Research Institute

Atmospheric Modeling Sampling Design. Mark Cohen 

(National Oceanic and Atmospheric Administration) 

described key concepts for locating and designing 

atmospheric measurement cluster sites. For areas that are 

remote from major emission sources, spatial gradients in 

atmospheric concentration and deposition might be relatively 

small; therefore, the need for cluster sites may be minimal. 

That is, measurements at the intensive site may be reasonably 

representative of the surrounding areas. However, for sourceimpacted areas, there may be large spatial gradients. While 

MDN-type cluster sites measuring wet deposition may be cost 

effective, it would be prohibitively expensive—with currently 

available approaches—to measure ambient concentrations 

and rigorously estimate dry deposition at a sufficient number 

of cluster sites to characterize the atmospheric concentrations 

and total deposition in the area surrounding the intensive site. 

Thus, for the atmospheric pathways, models will be crucial, 

and to the extent possible, atmospheric intensive and cluster 

site design should optimize development, evaluation, and 

improvement of atmospheric fate and transport models. From 

the modeling perspective, it would likely be more useful to 

have a few “comprehensive” measurement sites than a number 

of cluster sites with very incomplete measurements (e.g., wet 

“You cannot measure everything that you want 

to measure everywhere, which is why models 

are necessary. Given resource constraints, a few 

comprehensive monitoring sites may be more useful for 

atmospheric model development and evaluation than a 

lot of minimally instrumented cluster sites.”

Mark Cohen

National Oceanic and Atmospheric Administration

What issues remain unresolved for cluster sites?

It is anticipated that selection of cluster sites will occur after 

selection of intensive sites, yet some conceptual guidance 

is needed to advance the selection process. Discussions by 

the Data Task Group and Annapolis workshop participants 

clarified the set of considerations and challenges yet to be 

resolved to develop selection criteria: 

1. The definition of geographic criteria for cluster sites 

should specify the maximum distance of cluster sites from 

intensive sites that is considered useful for extending 

the spatial relevance of measurements at intensive 

sites. Consideration should be given to how map-based 

proximity analyses can be used to consider monitoring 

within a certain radius from potential intensive sites.

2. Geographic definitions will affect the degree to which 

intensive sites and their associated cluster sites provide 

comprehensive spatial coverage across the United States. 

Some specific questions:
20

Developing the Mercury Monitoring Network: Selecting Sites

Q Should the full set of cluster sites be located to achieve 

comprehensive national representation (i.e., cluster sites 

“fill in” areas across the entire United States)? Or should 

cluster sites be optimized to support process-level 

research conducted at individual intensive sites by more 

fully characterizing localized variability?

Q Should cluster sites be selected to achieve 

characterization of ecological regions?

Q How should plans for modeling to achieve spatial 

extrapolation be incorporated into site selection? How 

should down-scaling capability be included?

3. Guidance is needed with regard to how cluster sites 

should be chosen to account for variability in landscape 

and habitat types around intensive sites. For example, is 

it more important that cluster sites represent all major 

ecological systems surrounding an intensive site, or that 

they represent those ecological systems most sensitive to 

changing mercury deposition (and related factors)? 

4. Ideally, cluster sites would be located in a highly consistent 

manner across the country; however, regional differences 

in landscape type might affect the comparability of cluster 

sites and the information they contribute to a national 

monitoring network. For example, in some areas, the 

absence of natural lakes might inhibit establishment of 

cluster sites as they have been defined to date. Further 

clarification is needed regarding how to maximize 

consistency in cluster site selection while allowing room 

for regionally appropriate selection strategies. 

5. Finally, as the small set of intensive sites are identified, 

selection of cluster sites will require choices about 

maximizing the use of existing probabilistic monitoring 

networks to provide data for ancillary parameters 

or optimizing for sites that best align with mercury 

monitoring objectives. 
2008 National Mercury Monitoring Workshop Report

21

Opportunities for Collaboration: 

Next Steps

A number of areas of agreement emerged from the 

Annapolis workshop. Goals and objectives for 

the monitoring network were refined to include 

greater focus on provision of information to key policy and 

management audiences and linkage to emission control 

policies. A nested sampling approach, based on intensive 

and cluster sites that emphasizes coordination of existing 

monitoring capabilities and infrastructure achieved broad 

agreement. The need to move forward in developing an 

integrated national monitoring system that produces 

comparable and high-quality data, and to establish baseline 

information in advance of impending changes in mercury 

regulations and emissions, was widely acknowledged. 

At this time, major new funding programs for expanded 

mercury monitoring are unavailable, and additional network 

design issues remain. However, opportunities exist in the near 

term to move forward in building the foundation of a national 

mercury monitoring network. Expanded collaboration to 

integrate existing and emerging monitoring activities through 

a national network can substantially improve the delivery of 

nationally consistent mercury data.

With representation by federal agencies, states, and tribes, 

as well as academic and private-sector scientists, network 

planners are poised to further develop the national 

monitoring network through a range of partnerships. Key 

activities will likely include convening subcommittees and 

task groups to address network design challenges, engaging 

the mercury community and reaching out to potential 

supporters, and identifying opportunities to build new 

monitoring capacity.

I. Refining network design

A national framework 

There is a clear need for a national framework to guide 

the integration of local, state, tribal, federal, private, and 

research-scale mercury monitoring efforts into a nationally 

coherent network. In addition to identifying intensive and 

cluster sites, such a framework should provide mechanisms 

for harmonizing data from existing monitoring programs, as 

well as informing implementation of emerging monitoring 

efforts. As a diverse consortium of monitoring efforts that 

adhere to common sampling and data management protocols 

to routinely deliver high-quality, nationally consistent 

environmental data products, the NADP provides a useful 

organizational model. 

Site evaluation and selection

Intensive sites. Workshop participants saw a clear need for 

quantitative assessment of the ability of potential intensive 

sites to meet monitoring objectives, and for a consistent 

description of the rationales for inclusion of specific sites 

in the network. Building on the MercNet metadatabase and 

other preliminary work, participants recommended continued 

compilation of site characteristics for a broader range of 

existing North American monitoring sites and programs. 

Agreement emerged from the Annapolis workshop regarding 

mercury monitoring network goals, objectives, and major 

design elements. In the final workshop session, participants 

came to agreement about how to focus collaborative efforts 

in the near term. Refinement of the monitoring network 

design will emphasize creation of a national framework 

for site selection and data sharing. Network planners will 

seek opportunities to leverage existing monitoring activities 

and funding sources through engagement with the broader 

mercury community. Outreach and support-building for 

existing and expanded monitoring will inform federal and 

state decision-making.

“We need someone to pull data together to get a good 

product. The Northeast area did a great job. We need to 

scale up and bring the information together so that we 

can make regional or national assessments, as opposed 

to the current piecemeal approach.”

Darren Rumbold

Florida Gulf Coast University

Workshop participants also widely acknowledged that a 

wealth of mercury data has been collected at many potential 

intensive sites over time—although in many cases the absence 

of repeat sampling or other limitations constrains the utility 

of data for meeting national monitoring objectives. Some 

assessment of the opportunities for creating high-value 

information, such as mercury baselines, by further mining 

of existing literature and databases should be part of rich site 

characterization. With leadership from network planners, 
22

Opportunities for Collaboration: Next Steps

a mechanism will be needed for selecting intensive sites for 

inclusion in the network once richer characterization work 

has been completed.

Cluster sites. While substantial progress has been made in 

identifying selection criteria and specific potential intensive 

sites, more work is needed to produce similar progress for 

selection and identification of cluster sites. Network planners 

will work with stakeholders to clarify the characteristics and 

deliverables that will be expected from a cluster site in the 

national mercury monitoring network. Similar to intensive 

sites, a mechanism for cluster site selection will be needed—

such a mechanism could be located at the level of major 

regions or even individual intensive sites if clear guidance is 

available to ensure national consistency.

Integrating monitoring data and emerging 

monitoring efforts

Development of specific technical resources for integrating 

mercury monitoring data is needed to build on the 

expanding interest and activity for mercury monitoring at 

many levels. To guide monitoring by individual states, tribes, 

and other site operators, a manual that outlines common 

protocols for collection, configuration, storage, and quality 

control of data is an essential tool for producing nationally 

consistent datasets. 

Historically, many types of environmental research and 

monitoring data have not been made widely available 

beyond the data-gathering institution or agency, and this has 

constrained our ability to more fully understand mercury 

dynamics. To facilitate data exchange, a clearinghouse for 

mercury data that standardizes existing datasets could be 

developed with the MercNet metadatabase as a platform. 

Development of data-sharing mechanisms and cooperation 

with national monitoring and research programs such as the 

NADP or the National Ecological Observatory Network could 

contribute to this effort. 

II. Community engagement and outreach 

Engaging the mercury research and monitoring 

community 

While the May 2008 Annapolis workshop was an important 

step in building broad support around a conceptual design 

for a comprehensive, integrated monitoring network in 

the United States, many researchers and natural resource 

managers across the country have not yet been engaged in 

network design efforts. These individuals and their agencies 

and institutions can enhance characterization of potential 

monitoring sites and identify opportunities for leveraging 

existing data-gathering activities and funding sources to 

efficiently and effectively meet network objectives. 

Strategic engagement and collaboration will be fostered 

through sessions at national meetings (e.g., NADP’s annual 

scientific symposium), as well as specially convened regional 

meetings. These meetings will provide opportunities to engage 

regional experts who can provide richer information about 

the possibilities and constraints of existing sites, as well as 

areas for consideration for establishment of new monitoring 

activity. By engaging broader stakeholder groups within 

regional contexts, it may be possible to lay the foundation for 

regionally based evaluation and selection of cluster sites. 

Reaching out to potential supporters

Throughout the workshop, discussions emphasized the 

importance of communicating the need for improved 

and expanded mercury monitoring beyond the mercury 

research and monitoring community. To assist in 

communicating with policymakers and potential funding 

entities about the need to develop a comprehensive 

mercury monitoring network, participants recommended 

producing and distributing several straightforward and 

engaging communications pieces to key audiences through 

briefings, conferences, and other settings. In addition, 

these materials can assist in building institutional support 

within federal and state agencies for long-term datasets and 

regular information products by clarifying the rationale 

for sustaining existing efforts. This report serves as one 

product. An executive summary of this report serves as a 

fact sheet or brochure. 

III. Building new monitoring capacity

As the network design and suite of monitoring sites 

are refined, gaps in geographic coverage and mercury 

measurements will likely be identified. To fill these gaps, new 

monitoring capacity and the resources to support it will be 

needed. In some cases, this might involve implementing new 

mercury measurement capability at existing facilities where 

baseline information and ongoing data collection already are 

in place. In other cases, this might require the establishment 

of new monitoring sites to fill in geographic gaps. As new 

funding sources become available, implementation of 

new monitoring infrastructure will provide important 

new capabilities for tracking changing mercury levels and 

understanding ecological and human health effects.
2008 National Mercury Monitoring Workshop Report

23

List of Appendices

A. Workshop Steering Committee and Participants

B. Mercury and Ancillary Monitoring Programs

C. Preliminary List of Candidate Intensive Sites—from Annapolis Workshop

D. Tables of Recommended Mercury and Ancillary Measurements 

E. Glossary of Terms

Photo Credit: Joseph Bushey, Syracuse University

2008 National Mercury Monitoring Workshop Report

25

Appendix A

Workshop Steering Committee and Participants

National Mercury Monitoring Workshop 

Steering Committee

Rick Artz, National Oceanic and Atmospheric Administration

Tom Atkeson, Florida Department of Environmental 

Protection

Ryan Callison, Cherokee Nation

Charles Driscoll, Syracuse University

Dave Evers, BioDiversity Research Institute

David Gay, National Atmospheric Deposition Program

Rick Haeuber, U.S. Environmental Protection Agency

Dave Krabbenhoft, U.S. Geological Survey

Rob Mason, University of Connecticut

Greg Masson, U.S. Fish and Wildlife Service

Kristi Morris, National Park Service

David Schmeltz, U.S. Environmental Protection Agency

Ed Swain, Minnesota Pollution Control Agency

Workshop Participants

Rick Artz, National Oceanic and Atmospheric Administration

Jesse Bash, U.S. Environmental Protection Agency

Mark Brigham, U.S. Geological Survey

Russ Bullock, U.S. Environmental Protection Agency

Neil Burgess, Environment Canada

Mark Castro, University of Maryland Center for 

Environmental Sciences

Mark Cohen, National Oceanic and Atmospheric 

Administration

Jay Davis, San Francisco Estuary Institute

Charles Driscoll, Syracuse University

Dan Engstrom, Science Museum of Minnesota

Dave Evers, BioDiversity Research Institute

David Gay, National Atmospheric Deposition Program

Cindy Gilmour, Smithsonian Environmental Research Center

John Goodrich-Mahoney, Electric Power Research Institute

Mae Gustin, University of Nevada

Rick Haeuber, U.S. Environmental Protection Agency

Colleen Haney, U.S. Environmental Protection Agency

Chad Hammerschmidt, Wright State University

Reed Harris, Tetra Tech

Susan Holdsworth, U.S. Environmental Protection Agency

Neil Kamman, Vermont Department of Environmental 

Conservation

Chris Knightes, U.S. Environmental Protection Agency

Dave Krabbenhoft, U.S. Geological Survey

Ellen Kurlansky, U.S. Environmental Protection Agency

Greg Lampman, New York State Energy Research and 

Development Authority

Dixon Landers, U.S. Environmental Protection Agency

Matt Landis, U.S. Environmental Protection Agency

Tony Lowery, National Oceanic and Atmospheric 

Administration

Winston Luke, National Oceanic and Atmospheric 

Administration

Rob Mason, University of Connecticut

Mike Meyer, Wisconsin Department of Natural Resources

Bruce Monson, Minnesota Pollution Control Agency

Kristi Morris, National Park Service

Sam Napolitano, U.S. Environmental Protection Agency

Christine Negra, ICF International

Tiffany Parson, U.S. Fish and Wildlife Service

Eric Prestbo, Tekran Instruments Corporation

Barnett Rattner, U.S. Geological Survey

Darren Rumbold, Florida Gulf Coast University

Tony Scheuhammer, Environment Canada

David Schmeltz, U.S. Environmental Protection Agency

Larry Scrapper, Cherokee Nation

Tim Sharac, U.S. Environmental Protection Agency

Darell Slotton, University of California

Bob Stevens, Florida Department of Environmental 

Protection

Ed Swain, Minnesota Pollution Control Agency

Robert Wayland, U.S. Environmental Protection Agency

Jim Wiener, University of Wisconsin-La Crosse

2008 National Mercury Monitoring Workshop Report

27

Appendix B

Mercury and Ancillary Monitoring Programs

This compilation represents information shared at the Annapolis workshop about major existing and emerging monitoring 

programs and does not account for all programs and efforts that monitor mercury in the United States. 

Agency/Program Mercury monitoring activity

National Atmospheric 

Deposition Program (NADP), 

Mercury Deposition Network 

(MDN) 

NADP currently monitors mercury in wet deposition at more than 100 MDN sites 

throughout North America. Under the new NADP Atmospheric Mercury Initiative, federal 

agencies (e.g., EPA, USGS, NOAA), states, tribes, universities, and other institutions are 

collaborating to measure air concentrations of mercury in its gaseous and particulate 

forms. Data generated are used to support mercury dry deposition estimates, assessment 

of mercury source impacts, atmospheric model evaluation, and long-term trends 

assessment. Fifteen sites are currently participating, with several more expected to join 

in 2009. Participants operate mercury speciation instrumentation in accordance with a 

standard operating procedure developed by NADP and the mercury measurement scientific 

community. NADP maintains quality-assured site data in a centralized database. Data will 

be available online at http://nadpweb.sws.uiuc.edu/amn/. 

U.S. Geological Survey (USGS) 

National Water Quality 

Assessment Program (NAWQA)

Detailed mercury cycling studies in streams in Oregon, Wisconsin, Florida, the coastal 

plain of South Carolina, and the Adirondacks monitor food web, water quality, sediment 

geochemistry, and wet deposition. Currently developing models of mercury transport and 

cycling for South Carolina and New York studies, in collaboration with EPA. Large-scale 

synoptic studies use one-time sampling of mercury in the water column, sediments, and 

fish tissue at several hundred stream sites across the United States. Selected other USGS 

mercury studies have been done for Lake Champlain tributaries, California streams and 

rivers, high-elevation lakes in the West, and lakes in northern Minnesota (Voyageurs 

National Park).

National Oceanic and 

Atmospheric Administration 

(NOAA)

Monitoring and modeling of mercury in air, water, sediments, and biota in U.S. coastal 

regions and the Great Lakes focuses on understanding the fate and cycling of mercury. 

Atmospheric measurements are gathered at several long-term sites and via aircraft. Several 

NOAA programs gather data on mercury in biota. Mussel Watch provides a long-term, 

nationwide dataset for mercury in bivalves. Fish and dolphin monitoring data have been 

gathered for regional and national surveys. Additional work looks at mercury in seafood, as 

well as integrated ecological assessments.

National Park Service (NPS) NPS hosts 14 MDN sites at different parks across the United States. Extensive studies on 

the ecological effects of mercury have been completed or are in progress at several national 

parks. The recently completed, 5-year Western Airborne Contaminants Assessment Project 

(WACAP) examined mercury and other contaminants in air, snow, water, sediments, lichen, 

conifer needles, and fish at eight parks in the western United States: Denali, Gates of the 

Arctic, Glacier, Mount Rainier, Noatak, Rocky Mountain, Glacier, and Sequoia. The final 

report is available at www.nature.nps.gov/air/Studies/air_toxics/wacap.cfm.
28

Appendix B

Agency/Program Mercury monitoring activity

U.S. Environmental Protection 

Agency (EPA) 

EPA supports several collaborative monitoring programs: 

Q The EPA Office of Air and Radiation (OAR) collaborates with the NADP and other 

and other organizations to establish a new, national, standardized network to monitor 

mercury in the atmosphere (see above). Related to NADP, EPA-OAR administers the 

Clean Air Status and Trends Network (CASTNET), a long-term network of more than 

80 atmospheric monitoring sites that provide ancillary measurements useful for mercury 

monitoring and model development. 

Q The EPA Office of Water (OW) recently initiated the National Rivers and Streams 

Assessment, which will include fish tissue sampling for mercury. Field collection will 

occur over 2 years (2008–2009) at approximately 2,000 sites including wadeable and 

non-wadeable water bodies. EPA-OW has also been working with states to standardize 

protocols for monitoring mercury in water. 

Q The EPA Office of Research and Development (ORD) is conducting an ongoing 

investigation of mercury fish tissue concentrations. In 2005, ORD re-sampled 42 sites 

from the original Mid-Atlantic Highlands Assessment (MAHA), where fish-tissue 

mercury samples were collected in 1993–1994. In 2005, ORD sampled 60 Temporally 

Integrated Monitoring of Ecosystems (TIME) sites in the mid-Atlantic region for the first 

time for fish tissue mercury. ORD intends to re-sample these sites for fish tissue mercury 

every 2–3 years, as funds allow.

States States have expended more than $50 million on mercury research and monitoring over 

the past 15 years. The primary focus has been on studies of mercury in fish and other 

biota, mercury emission inventories, lake sediment core analyses, atmospheric deposition 

modeling and monitoring, and research on mercury attributable to consumer products. 

Of 47 states, two tribal agencies, and one Canadian province that responded to a recent 

survey (percentages refer to proportion of respondents for each question):

Q All have fish consumption advisories because of mercury in fish.

Q 94 percent have ongoing fish contaminant monitoring programs (FCMPs).

Q In 67 percent, the FCMP is intended only for fish consumption advisories.

Q 63 percent use FCMP data for trend analysis.

Q 65 percent use trend monitoring at fixed stations (x-sites every y-years); all but two of 

these fixed station FCMPs have a 1 to 5- year sample cycle.

Q The average period of record for monitoring is 14 years.

Q 54 percent have prepared monitoring reports.

Q 60 percent use largemouth bass as the indicator fish species, 37 percent use walleye, and 

33 percent use trout species.

(Based on 2008 surveys of states by C. Mark Smith, Massachusetts Department of 

Environmental Protection, and Bruce Monson, Minnesota Pollution Control Agency)

Tribes Tribes with MDN sites: Potawatomi Nation, WI; Menominee Indian Tribe of Wisconsin; 

Cherokee Nation (Stillwell, OK; Newkirk, OK); Yurok Tribe, CA; Makah Nation, WA; 

Cheyenne River Sioux Tribe, SD; Grand Traverse Band of Ottawa and Chippewa Indians, 

MI; Micmac Tribe, ME; Sac and Fox Nation, KS. Pending MDN sites: Penobscot Nation, 

ME. Possible MDN sites: Mille Lacs Band of Ojibwe, MN (might start again); Zuni Nation, 

NM. Inactive MDN sites: Mille Lacs Band of Ojibwe, MN; Passamaquaddy, ME.

Several tribes are monitoring mercury in fish and other media within their tribal lands.
2008 National Mercury Monitoring Workshop Report

29

APPENDIX C

Preliminary List of Candidate Intensive Sites—From Annapolis Workshop

This list represents the recommendations from regionally based breakout groups at the Annapolis workshop and does 

not represent the final list of intensive monitoring sites to be proposed for inclusion in a national network. Further 

characterization of these and other potential intensive sites is planned (see details on pages 18 and 21). Parentheses 

indicate sites that the breakout groups considered to be of secondary priority.

Southeast

Everglades National Park, FL 

Coastal South Carolina [ACE Basin]

Northern Gulf Coast

Grand Bay NERR, MS

Pensacola, FL

(Atlanta/Yorkville, GA)

Mid-Atlantic

Chesapeake Bay [Beltsville, SERC]

Northeast

Huntington Wildlife Forest, NY 

Acadia National Park, ME 

Proctor Center, Underhill, VT

Neversink Watershed, NY 

Cape Cod National Seashore, MA

Long Island Sound, NY

(Mt. Washington, NH)

(Kejimkujik, NS)

Ohio River Valley

Steubenville, OH 

(Frostburg, MD) 

(Canaan Valley Institute, WV)

(Athens, OH)

Upper Midwest

Voyageurs National Park, MN

Experimental Lakes Area, Canada

Dexter, MI

Marcell Experimental Forest, MN

(Northern Highland Forest, WI)

West

Rocky Mountain National Park, CO

Toolik, AK

Glacier Bay, AK

Stilwell, OK

Sierra Nevada, CA/NV

Mt. Rainier, WA

(Four Corners-Mesa Verde, CO)

(Mt. Bachelor, OR, as a “global background” site)

2008 National Mercury Monitoring Workshop Report

31

APPENDIX D

Tables of Recommended Mercury and Ancillary Measurements 

Note that these recommended measurements may be adapted as the mercury monitoring network is implemented. 

Mercury Measurements for Documenting TrendS—ADAPTED FROM TABLE 6.2, P. 199 IN HARRIS ET AL., 2007

Indicator Location (intensive, 

cluster, or both)

Frequency

Soil solutions (Total Hg and MeHg) Intensive Quarterly

Sediment (Total Hg and MeHg) Both Annual and quarterly, 

respectively

Percent MeHg in sediment Both Annual and quarterly, 

respectively

Instantaneous methylation rate Both Annual and quarterly, 

respectively

Total Hg accumulation rate in sediment Cluster Every 5-10 years

Surface water (Total Hg and MeHg) Both Annual and quarterly, 

respectively

Stream Intensive Weekly

Total Hg in whole prey fish Both Annual or semi-annual

Total Hg in predatory fish (axial muscle)b Both Annual

Total Hg in mammal blood and fur a Both Annual

Total Hg in bird blood, feather, and egg a Both Annual a

 Species of birds and mammals vary in distribution and habitat preferences and can only be used as indicators where present.

b

 Not included in Table 6.2 in Harris et al., 2007.
32

Appendix D

Mercury Measurements for Assessing Causality—Adapted from Table 6.3, p. 200 in Harris et al., 2007

Indicator Location (intensive, 

cluster, or both)

Frequency

Atmospheric Hg Intensive Continuous

Wet deposition (Total Hg) Intensive Weekly

Throughfall (Total Hg and MeHg) Intensive Weekly

Litterfall (Total Hg and MeHg) Intensive Weekly

Snowpack (Total Hg) Cluster Annual

Soil (Total Hg and MeHg) Intensive Once to characterize 

pools

Soils solutions (Total Hg and MeHg) Intensive Quarterly

Forest floor surveys Intensive 10 years

Sediment (Total Hg and MeHg) Both Quarterly

Percent MeHg in sediments and soils Both Quarterly

Instantaneous sediment methylation rate Intensive Biannual

Total Hg accumulation in cores (Total Hg and MeHg) Intensive 5-10 years

Ground water (Total Hg and MeHg) Intensive Quarterly

Surface water (Total Hg) Both Quarterly

MeHg/Total Hg ratio in surface water Both Quarterly

Raccoon Cluster (when feasible) Annual

Mink Both (when feasible) Annual

Harbor porpoise Cluster (when feasible) Annual

Common loon Both (when feasible) Annual

Herring gull Cluster (when feasible) Annual

Common tern Cluster (when feasible) Annual

Leach’s storm petrel Cluster (when feasible) Annual

Belted kingfisher Both (when feasible) Annual

Tree swallow Both (when feasible) Annual

Bicknell’s thrush Cluster (when feasible) Annual

Saltmarsh sharp-tailed sparrow Cluster (when feasible) Annual

Note: Species of birds and mammals vary in distribution and habitat preferences and can only be used as indicators where present.
2008 National Mercury Monitoring Workshop Report

33

Ancillary Monitoring Parameters—Adapted from Table 6.4, p. 204 in Harris et al., 2007

Parameter Location 

(intensive, 

cluster, or 

both)

Frequency Type 

(A or B)a

Atmospheric deposition of sulfate Both Weekly B

Rainfall Both Weekly B

Watershed area Both Once B

Land cover Both Once B

Percent wetlands in watershed area Both Once B

Lake morphometry Both Once B

Water chemistry (pH, dissolved organic carbon, sulfate, total suspended 

solids, chlorophyll, temperature, acid-neutralizing capacity, color, 

nutrients, dissolved oxygen, stratification status)

Both Quarterly A, B

Characteristics of fish (size, age, stomach contents, sex, condition) Both Annual for prey 

fish; 1 to 3-year 

intervals for 

piscivorous fish

A, B

Characteristics of mammals (size, age, sex, condition) and tissues for 

nonlethal sampling (fur and blood) and lethal sampling (fur, brain, 

muscle, and liver)b

Both Annual A, B

Characteristics of birds (size, age, sex, condition) and tissues for 

nonlethal sampling (blood, feathers, and eggs) and lethal sampling 

(feathers, brain, muscle, liver, and eggs)b

Both Annual A, B

a

 Type A = for trends assessment; Type B = for causality assessment

b

 Species of birds and mammals vary in distribution and habitat preferences and can only be used as indicators where present.

2008 National Mercury Monitoring Workshop Report

35

Appendix E

Glossary of Terms

Ancillary measurements: Environmental measurements that 

supplement data on mercury concentrations to accurately 

characterize mercury trends and dynamics. Examples include 

weather patterns; physical features of watersheds; chemical 

constituents of air, soil, and water; and characteristics of 

sampled organisms. See appendix D for more detailed 

description of recommended ancillary measurements.

Atmospheric deposition: Transfer of pollutants, such as 

mercury, from the air to vegetation, soil, water, and the built 

environment through wet (e.g., rain, snow) and dry (e.g., 

falling particles, gas exchange) mechanisms.

Baseline: Initial comprehensive environmental measurements 

against which subsequent measurements, made using the 

same protocols and techniques, can be compared.

Biota: The biological organisms, including microbes, plants, 

and animals, inhabiting a given area.

Cluster sites: Locations in the vicinity of an intensive site 

where a limited set of environmental measurements are made 

in order to expand the geographic relevance of intensive 

measurements.

Ecosystem sensitivity: Ecosystem properties (e.g., abundance 

of wetlands) that increase the likelihood of mercury 

movement, methylation, and uptake by organisms.

Intensive sites: Locations where comprehensive, highresolution measurements are made in air, soil, water, and biota 

to produce a robust understanding of ecological responses to 

changes in mercury loading.

Mercury bioaccumulation: Increased concentration of 

mercury in the tissues of an organism.

Mercury biomagnification: Increased concentration of 

mercury in the tissues of organisms at higher trophic levels of 

a food web.

Mercury cycling: Transfer of mercury across environmental 

compartments such as the atmosphere, soils, water, 

sediment, and biota, and associated alteration of mercury’s 

chemical form.

Mercury indicators: Environmental measurements that can 

be compared across time and space to understand changes in 

mercury exposure, concentration, and ecological effects. 

Mercury methylation: Transformation of oxidized forms of 

mercury by microorganisms under oxygen-poor conditions, 

forming highly toxic methylmercury (MeHg+).

Mercury speciation: Different chemical forms of mercury in 

air, soil, water, and biota, including elemental mercury (Hg0

), 

reactive gaseous mercury (RGM), particulate mercury (Hg-P), 

and methylmercury (MeHg+), that exhibit different behaviors 

in the environment.

Nested sampling design: Data-gathering strategy in which each 

type of measurement is made for only a single level of the 

sampling scheme.

Probabilistic monitoring: Environmental survey in which a 

randomly selected subset of sites or features is measured and 

the resulting data are used to estimate actual environmental 

conditions.

Sampling protocols: A consistent set of procedures for 

gathering and managing data.

Site characterization: Information about geographic location, 

site properties, and current and historical sampling activities 

that can assist in evaluating potential mercury monitoring sites. 

Source-receptor relationships: Characterization of principal 

mercury sources that influence atmospheric mercury 

deposition to specific locations.

Spatial extrapolation: Projection of data from measured locations 

to estimate environmental conditions at nonmeasured locations 

or at larger scales using statistical techniques. 

Total Maximum Daily Loads: The calculated maximum 

amount of a pollutant that a water body can receive from all 

point, nonpoint, and natural background sources and still 

meet water quality standards.


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