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Studies and Monitoring

Isle Royale National Park

Isle Royale National Park (NP), Michigan, has its own unique environmental concerns based on its particular ecology. Air quality studies and monitoring programs at Isle Royale NP focus on the deposition and effects of mercury and other air toxics, and nitrogen. Click on the tabs below to review air quality studies and key scientific references at Isle Royale NP, as well as to access information on air quality monitoring in or near the park.

  • Studies & Projects
  • Monitoring & Data
  • Key References

Ongoing research in Isle Royale NP, Michigan:

Update: Mercury in the Great Lakes Region

As the world’s largest freshwater system, the Great Lakes are a unique natural resource, and Isle Royale NP is a treasured site within that system. Since the early to mid-1800s, mercury has been released into the air and waterways of the Great Lakes region. This has led to fish consumption advisories in the eight U.S. states that border the lakes, including Michigan and Isle Royale NP, and the province of Ontario (Wiener et al. 2012). Efforts to control mercury pollution in the Great Lakes region have included cross-jurisdiction cooperation within the region and beyond, and the promotion of regulatory and voluntary action (Cain et al. 2011). Substantial progress has resulted, but mercury pollution remains a major concern in the region. While many measurements show declining mercury concentrations in fish and wildlife over time, some observations have found recent increases in mercury concentrations in particular species in certain areas (Evers et al. 2011a [pdf, 8.3 MB]). Further controls on air emission sources and focusing reduction efforts on sources with the highest emissions should lower mercury concentrations in aquatic food webs, yielding multiple benefits to fish, wildlife, and people in the region.

Airborne Toxic Impacts

The Great Lakes region and Isle Royale NP have been heavily researched regarding the effects of air toxics such as DDT, PCBs, and mercury. While the park is an island in the vastness of Lake Superior, mainland power plants and other sources contribute to the deposition of toxics at Isle Royale NP. Moreover, the abundance of wetlands, low pH lakes, complex food webs, and predatory fish creates an environment susceptible to bioaccumulation of these contaminants. The first study documenting the presence of air toxics at the park was conducted in 1978 and assessed concentrations of PCBs, DDT, and more in fish. Since then, more than three decades of scientific studies at the park continue to show elevated concentrations of many contaminants—specifically mercury and PCBs—in air, precipitation, sediment, fish, and loons (Swackhamer and Hornbuckle 2004 [pdf, 4.5 MB]). Mercury and PCB concentrations in fish exceed thresholds established for human health (MDNR 2011); particularly concerning because fishing is a top recreational activity for park visitors. Wildlife health is also affected as mercury concentrations in fish and loons are at levels known to affect behavior and reproduction (Drevnick et al. 2008; Sandheinrich et al. 2011; Evers et al. 2011b; Evers et al. 1998; Scheuhammer and Blancher 1994).

Projects throughout the Great Lakes monitor air toxics and impacts in or near Isle Royale NP. The University of Wisconsin at La Crosse, in partnership with the NPS Inventory and Monitoring Program, are assessing mercury in fish, larval dragonflies, zooplankton, water, and sediment at national parks in the Great Lakes area (including Isle Royale NP) in an effort to better understand methylmercury production and transfer through aquatic food webs (Issue Brief [pdf, 211 KB]; Resource Brief [pdf, 368 KB]). Samples collected from Angleworm, Harvey, Richie, and Sargent lakes aid in this effort. Additionally, the Michigan Department of Natural Resources monitors fish at Siskiwit Lake and issues statewide fish consumption guidance (pdf, 1.3 MB). There are also many ongoing multi-agency, binational collaborative efforts pertaining to air toxics and mercury in the Great Lakes environment, including: The Great Lakes Binational Toxics Strategy (U.S. Environmental Protection Agency, Environment Canada), U.S. EPA-funded Great Lakes Air Deposition Program (GLAD), Regional Air Pollutant Inventory Development System (RAPIDS), and Great Lakes Mercury Connections (Biodiversity Research Institute, the Great Lakes Commission, and the University of Wisconsin-La Crosse): four-page summary (pdf, 3.9 MB) or the full report (pdf, 8.3 MB). These efforts are all improving understanding of contaminant pollution in the Great Lakes region and using partnerships to address the problem.

Nitrogen and Sulfur Impacts

Nitrogen (N) and sulfur (S) deposition at the park can be particularly harmful to sensitive boreal lakes. The low buffering capabilities of thin soils place the boreal ecosystem at high risk from acidification effects (Sullivan et al. 2011a; Sullivan et al. 2011b [pdf, 2.3 MB]). Boreal lakes in the park are also highly sensitive to nutrient effects from excess N enrichment (Sullivan et al. 2011c; Sullivan et al. 2011d [pdf, 6.2 MB]). A current study at Isle Royale NP is investigating the fertilization effects of excess N loading, including changes to the species composition of sensitive aquatic communities (Saros 2008). These efforts aim to define a nitrogen critical load, the threshold at which a community shifts from undisturbed species to weedy, nitrogen-loving species (Saros et al. 2010).

Atmospheric deposition of ammonium from regional agriculture is elevated and increasing at sites near to the park (NPS 2010 [pdf, 2.8 MB]; Lehmann et al. In Prep). Recent proposals for a new power plant, a copper processing facility, and a combined taconite processing-steel making facility in northern Minnesota also raise concerns about the potentail for additional emissions of both N and S from future development.

Air quality monitoring information and data access:

Air Pollutant/Impact

Monitoring Program

Sites and Data Access

Toxics & Mercury IADN
  • Two sites on Lake Superior: Brule River, WI and Eagle Harbor, MI
Nitrogen & Sulfur NPS Air Quality Inventory
OzoneNPS Air Quality Inventory
Visibility IMPROVE

Abbreviations in the above table:

    IADN: Integrated Atmospheric Deposition Program
    IMPROVE: Interagency Monitoring of Protected Visual Environments
    MDN: Mercury Deposition Network
    NADP: National Atmospheric Deposition Program
    NPS: National Park Service
    NTN: National Trends Network
    RAPIDS: Regional Air Pollutant Inventory Development System
    VIEWS: Visibility Information Exchange Web System

For more information regarding monitoring and data assessments conducted by the National Park Service, link to the NPS Air Quality Monitoring Program or to the NPS Air Quality Monitoring History Database for a history of active and inactive monitoring sites at Isle Royale NP.

Key air quality related references from Isle Royale NP, Michigan:

Bennett, J. P. 1995. Abnormal Chemical Element Concentrations in Lichens of Isle Royale National Park. Environmental and Experimental Botany 35 (3): 259–277.

Bowerman, W., Moore, L., Leith, K., Drouillard, K., Sikarskie, J., Best, D., Allan, T., Garvon, J., Scharf, W., Perlinger, J., and Romanski, M. 2011. Concentrations of Environmental Contaminants in Herring Gull Eggs from Great Lakes Colonies in Michigan, 2002–2006. MI/DEQ/WRD—12/007. Michigan Department of Environmental Quality: Lansing, MI. 68 pp. Available at (pdf, 2.3 MB).

Caine, A., Morgan, J. T., and Brooks, N. 2011. Mercury policy in the Great Lakes states: past successes and future opportunities. Ecotoxicology 20: 1500–1511.

Chernyk, S., Hickey, J., and Benoche, I. 2002. PBDEs in Great Lakes Biota. Proceedings from Society of Environmental Toxicology and Chemistry: North America. Salt Lake City, UT: 16–20.

Drevnick P. E., Roberts, A. P., Otter, R. R., Hammerschmidt, C. R. Klaper, R., and Oris, J. T. 2008. Mercury toxicity in livers of northern pike (Esox lucius) from Isle Royale, USA. Comparative Biochemistry Physiology Part C 147: 331–338.

Evers, D. C., Kaplan, J. D., Meyer, M. W., Reaman, P. S., Braselton, W. E., Major, A., and Burgess, N., Scheuhammer, A. M. 1998. Geographic trend in mercury measured in common loon feathers and blood. Environmental Toxicology & Chemistry 17 (2): 173–183.

Evers, D. C., Wiener, J. G., Driscoll, C. T., Gay, D. A., Basu, N., Monson, B. A., Lambert, K. F., Morrison, H. A., Morgan, J. T., Williams, K. A., and Soehl, A. G. 2011a. Great Lakes Mercury Connections: The Extent and Effects of Mercury Pollution in the Great Lakes Region. Biodiversity Research Institute. Gorham, Maine. Report BRI 2011—18. 44 pp. Available at (pdf, 8.3 MB).

Evers, D. C., Williams, K. A., Meyer, M. W., Scheuhammer, A. M., Schoch, N., Gilbert, A., Siegel, L., Taylor, R. J., Poppenga, R. and Perkins, C. R. 2011b. Spatial gradients of methylmercury for breeding common loons in the Laurentian Great Lakes region. Ecotoxicology 20: 1609–1625.

Gorski, P. R., Cleckner, L. B., Hurley, J. P., Sierszen, M. E., and Armstrong, D. E. 2003. Factors affecting enhanced mercury bioaccumulation in inland lakes of Isle Royale National Park, USA. Science of the Total Environment 304 (1–3): 327–348.

Gotelli, N. J. and Ellison, A. M. 2002. Nitrogen deposition and extinction risk in the northern pitcher plant, Sarracenia purpurea. Ecology 83: 2758–2765.

Hermanson, M. and Hites, R. 1990. Polychlorinated biphenyls in tree bark. Environmental Science & Technology 24: 666–671.

[IMPROVE] Interagency Monitoring of Protected Visual Environments. 2010. Improve Summary Data. Available at

Kohut, R. 2004. Assessing the Risk of Foliar Injury from Ozone on Vegetation in Parks in the Great Lakes Network. Available at (pdf, 187 KB).

Lehmann C. M. B. and Gay,D. A. 2011. Monitoring Long-Term Trends of Acidic Wet Deposition in U.S. Precipitation: Results from the National Atmospheric Deposition Program. PowerPlant Chemistry 13 (7): 386–393.

Lehmann, C. M. B., Gay, D. A., and Bowersox, V. C. (in preparation). Trends in NADP/NTN Precipitation Chemistry and Wet Deposition, 1985–2009. Illinois State Water Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, IL.

[MDNR] Michigan Department of Natural Resources. 2011. 2011–2012 Michigan Fish Advisory. Available at (pdf, 1.3 MB).

[NADP] National Atmospheric Deposition Program. 2010. Inorganic nitrogen wet deposition from nitrate and ammonium, 2009. Available at (pdf, 1.9 MB)

[NPS] National Park Service. 2010. Air Quality in National Parks: 2009 Annual Performance and Progress Report. Natural Resource Report NPS/NRPC/ARD/NRR—2010/266. National Park Service, Denver, Colorado. Available at Parks_2009_Final_Web.pdf (pdf, 2.8 MB).

Risch M. R., Gay, D. A., Fowler, K. K., Keeler, G. J., Backus, S. M., Blanchard, P., Barres, J. A., Dvonch, J. T. 2012. Spatial patterns and temporal trends in mercury concentrations, precipitation depths, and mercury wet deposition in the North American Great Lakes region, 2002–2008. Environmental Pollution 161: 261–271.

Sandheinrich, M. B., Bhavsar, S. P., Bodaly, R. A., Drevnick, P. E., and Paul, E. A. 2011. Ecological risk of methylmercury to piscivorous fish of the Great Lakes region. Ecotoxicology 20: 1577–1587.

Saros, J. E. 2008. Determine critical nitrogen loads to boreal lake ecosystems using the response of phytoplankton. NPS Implementation Plan. 10 pp.

Saros, J. E., Clow, D. W., Blett, T., and Wolfe, A. P. 2010. Critical nitrogen deposition loads in high-elevation lakes of the western U.S. inferred from paleolimnological records. Water, Air, and Soil Pollution 216 (1–4): 193–202.

Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., and Moore, D. 2011a. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/349. National Park Service, Denver, Colorado. Available at

Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., and Moore, D. 2011b. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: Great Lakes Network (GLKN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/356. National Park Service, Denver, Colorado. Available at (pdf, 2.3 MB).

Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., and Moore, D. 2011c. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/313. National Park Service, Denver, Colorado. Available at

Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., and Moore, D. 2011d. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: Great Lakes Network (GLKN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/309. National Park Service, Denver, Colorado. Available at (pdf, 7.4 MB).

Scheuhammer, A. M. and Blancher, P. J. 1994. Potential risk to common loons (Gavia immer) from methylmercury exposure in acidified lakes. Hydrobiologia 279/280: 445–455.

Swackhamer, D. L. and Hornbuckle, K. C. 2004. Assessment of Air Quality and Air Pollutant Impacts in Isle Royale National Park and Voyageurs National Park. NPS Report. Available at (pdf, 4.5 MB).

Thurman, E. M. and Cromwell, A. E. 2000. Atmospheric Transport, Deposition, and Fate of Triazine Herbicides and their Metabolites in pristine areas at Isle Royale National Park. Environmental Science and Technology 34 (15): 3079–3085.

Vucetich, L. M., Vucetich, J. A., Cleckner, L. B., Gorski, P. R., and Peterson, R. O. 2001. Mercury concentrations in deer mouse (Peromyscus maniculatus) tissues from Isle Royale National Park. Environmental Pollution 114 (1): 113–118.

Vucetich, L. M., Outridge, P. M., Peterson, R. O., Eide, R., and Isrenn, R. 2009. Mercury, lead and lead isotope ratios in the teeth of moose (Alces alces) from Isle Royale, U.S. Upper Midwest, from 1952 to 2002. Journal of Environmental Monitoring 11 (7): 1352–1359.

Wiener, J. G., Evers, D. C., Gay, D. A., Morrison, H. A., and Williams, K. A. 2012. Mercury contamination in the Laurentian Great Lakes region: introduction and overview. Environmental Pollution 161: 243–251.

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Pollutants including mercury and other toxics, nitrogen, sulfur, ozone, and fine particles affect resources such as wildlife, lakes, soils, and scenic vistas. Find out how on our Isle Royale NP Air Pollution Impacts web page.

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Last Updated: February 20, 2013