Park Air Profiles - Voyageurs National Park

Park visitors canoeing on a historic water route
Visitors come to Voyageurs NP to explore scenic views while traveling on an interconnected water highway.

Air quality at Voyageurs National Park

Most visitors expect clean air and clear views in parks. Given its remote location on the northern edge of Minnesota’s border with Canada, Voyageurs National Park (NP) experiences relatively good air quality. However, the park lies downwind of pollution from sources in the Midwest and Canada, as well as nearby industrial sources like paper mills. Air pollutants blown into the park can harm natural and scenic resources such as soils, surface waters, plants, wildlife, and visibility. The National Park Service works to address air pollution effects at Voyageurs NP, and in parks across the U.S., through science, policy and planning, and by doing our part.

Mercury and toxics

Bald eagle in the water at Voyageurs NPElevated levels of mercury have been found in bald eagles at Voyageurs NP.

Airborne mercury, and other toxic air contaminants, when deposited are known to harm birds, salamanders, fish and other wildlife, and cause human health concerns. These substances enter the food chain and accumulate in the tissues of organisms causing reduced reproductive success, impaired growth and development, and decreased survival.

While Voyageurs NP is in a remote location on the Minnesota-Canada border, nearby and distant sources contribute to the deposition of toxics at the park, including mercury. Mercury levels in lake sediment, fish, birds, and mammals in the Great Lakes region have been declining in recent decades in response to pollution controls on mercury discharge to surface waters and decreased air emissions (Evers et al. 2011a). However, mercury pollution remains a major concern (Evers et al. 2011a; Weiner et al. 2011) and air emissions are now the primary source of mercury pollution (Evers et al. 2011a). Voyageurs NP is particularly sensitive to mercury pollution. The abundance of wetlands, low pH lakes, complex food webs, and predatory fish create an environment susceptible to the bioaccumulation of toxics.

Mercury and toxics effects:

  • Widespread mercury in the park’s aquatic ecosystems, originating primarily from coal-fired power plants and taconite processing emissions. Elevated concentrations have been documented in fish as well as water, lake sediments, zooplankton, aquatic plants, benthic organisms, fish-eating birds, bald eagles, and river otters (Kallemeyn et al. 2003; Wiener et al. 2006; Swackhamer and Hornbuckle 2004);
  • High mercury concentrations in fish from nearly all of Voyageur NP’s 30 lakes (Sorensen et al. 2001). The average mercury level in fish exceeds the State of Minnesota fish consumption advisories. This is a concern since approximately 70% of visitors fish in the park (Kallemeyn et al. 2003);
  • Mercury levels in walleye, pike, bass, and other fish from lakes in the park exceed thresholds known to damage fish health (Sandheinrich et al. 2011; NPS 2010), and are at levels also known to harm fish-eating loons (Sorensen et al. 2001);
  • Concentrations of mercury in loon blood are high enough to reduce reproductive success (Evers et al. 2011a; Evers et al. 1998), and adult loon feather mercury concentrations are above a level associated with toxic effects (Scheuhammer and Blancher 1994);
  • Detectable levels of contaminants including mercury, PCBs, DDE, and dieldrin in feathers of bald eagle nestlings at the park (Pittman 2010). Mercury concentrations in nestling feathers have declined from the mid-1980s to the late 1990s, but recent samples suggest an increasing trend (Pittman et al. 2011);
  • Elevated concentrations of toxic elements including mercury, cadmium, and chromium in lichens (Bennett 1997);
  • PFOS, a by-product in the manufacture of fabric protectors, firefighting foams, and other chemicals, detected in water samples at the park (Simcik and Dorweiler 2005).

Nitrogen and sulfur

Nitrogen and sulfur compounds deposited from the air may have harmful effects, including acidification on soils, lakes, ponds, and streams. The park’s thin, undeveloped soils, underlying granitic rock, and low buffering capacity result in surface waterways and soils at high risk from acidification by atmospheric nitrogen and sulfur (Sullivan et al. 2011a; Sullivan et al. 2011b). Also, some plants are sensitive to acidification, search for acid-sensitive plant species found at Voyageurs NP.

Excess nitrogen can also lead to nutrient enrichment, a process that changes nutrient cycling and alters plant communities. Some park resources may be sensitive to nutrient enrichment from deposition. For example, in boreal lakes, increased nitrogen can affect biodiversity, algal communities, and water clarity (Sullivan et al. 2011c; Sullivan et al. 2011d; Kallemeyn et al. 2003; Wiener et al. 2006; Swackhamer and Hornbuckle 2004). Healthy ecosystems can naturally buffer a certain amount of pollution, but as nitrogen and sulfur accumulate, a threshold is passed where the ecosystem is harmed. “Critical load” is a term used to describe the amount of pollution above which harmful changes in sensitive ecosystems occur (Porter 2005). Nitrogen deposition exceeds the critical load for one or more park ecosystems (NPS ARD 2018).

Sulfur emissions and sulfur levels in precipitation have significantly significantly declined in recent decades due to air pollution controls (Lehmann and Gay 2011). However, sulfur remains a concern at Voyageurs NP because it plays an essential role in the methylation of mercury, leading to toxic accumulation of methylmercury in fish and wildlife. Also, sulfur is a strong driver of acidification in the park’s vulnerable lakes and streams.

Visit the NPS air quality conditions and trends website for park-specific nitrogen and sulfur deposition information. Voyageurs NP has been monitoring atmospheric nitrogen and sulfur deposition since 1988. Explore air monitoring »

Ground-level ozone

Milkweed plant and butterfly Milkweed is one of the ozone sensitive species found at Voyageurs NP.

At ground level, ozone is harmful to human health and the environment. Ground-level ozone does not come directly from smokestacks or vehicles, but instead is formed when other pollutants, mainly nitrogen oxides and volatile organic compounds, react in the presence of sunlight.

Over the course of a growing season, ozone can damage plant tissues making it harder for plants to produce and store food. It also weakens plants making them less resistant to disease and insect infestations. Some plants are more sensitive to ozone than others. Ozone-sensitive plants in Voyageurs NP include Apocynum androsaemifolium (Spreading dogbane), Ascelpias syriaca (Common milkweed), and Prunus serotina (Black cherry). A risk assessment that considered ozone exposure, soil moisture, and sensitive plant species concluded that plants in Voyageurs NP were at low risk of damage to plant leaves (see network report: Kohut 2004). Ozone injury to plants has not been documented in regions near Voyageurs NP (Swackhamer and Hornbuckle 2004). Search ozone-sensitive plant species found at Voyageurs NP.

Visit the NPS air quality conditions and trends website for park-specific ozone information. Voyageurs NP has been monitoring ozone since 1987. View live ozone and meteorology data, and explore air monitoring »


Water vista at Voyageurs NP Clean, clear air is essential to appreciating the scenic vistas at Voyageurs NP.

Visitors come to Voyageurs NP to enjoy the spectacular “North Woods”, a wilderness of interconnected waterways, and the northern lights. Park vistas are sometimes obscured by haze, reducing how well and how far people can see. Visibility reducing haze is caused by tiny particles in the air, and these particles can also affect human health. Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition contribute to this haze. Organic compounds, soot, and dust reduce visibility as well. Smoke from nearby forest fires also contributes to particulate matter in the region. Significant improvements in park visibility have been documented since the 2000’s. Overall, visibility in the park still needs improvement to reach the Clean Air Act goal of no human caused impairment.

Visibility effects:
  • Reduced visibility, at times, due to human-caused haze and fine particles of air pollution;
  • Reduction of the average natural visual range from about 115 miles (without pollution) to about 100 miles because of pollution at the park;
  • Reduction of the visual range to below 50 miles on very hazy days.

Visit the NPS air quality conditions and trends website for park-specific visibility information. Voyageurs NP has been monitoring visibility since 1988. Explore scenic vistas of Lake Superior and other sites in the Great Lakes via live webcams, and explore air monitoring »

Bennett, J. P. and Wetmore, C. M. 1997. Chemical element concentrations in four lichens on a transect entering Voyageurs National Park. Environmental and Experimental Botany 37: 259–277.

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.

Elias, J. E. and Damstra, R. A. 2011. Monitoring water quality of inland lakes, Great Lakes Network, 2009 and 2010: Data summary report. Natural Resource Data Series NPS/GLKN/NRDS—2011/163. National Park Service, Fort Collins, Colorado. Available at

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

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.

Kallemeyn, L. W., Holmberg, K. L., Perry, J. A., and Odde, B. Y. 2003. Aquatic Synthesis for Voyageurs National Park: U.S. Geological Survey, Information and Technology Report 2003—0001. 95 pp. Available at

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

Kohut R.J. 2007. Ozone Risk Assessment for Vital Signs Monitoring Networks, Appalachian National Scenic Trail, and Natchez Trace National Scenic Trail. NPS/NRPC/ARD/NRTR—2007/001. National Park Service. Fort Collins, Colorado. Available at

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.

[MN-DOH] Minnesota Dept. of Health. 2012. Fish Consumption Advice.Site-specific meal advice for tested lakes and rivers available at

[NPS] National Park Service. 2010. Monitoring Persistent Contaminants at Voyageurs. Resource Brief, Great Lakes Network.

Pittman, H. T. 2010. Using Nestling Bald Eagles to Assess Temporal and Spatial Trends of Environmental Contaminants, Voyageurs National Park, Minnesota. MS Thesis, Clemson University. Available at

Pittman, H. T., Bowerman, W. W., Grim, L. H., Grubb, T. G., and Bridges, W. C. 2011. Using nestling feathers to assess spatial and temporal concentrations of mercury in bald eagles at Voyageurs National Park, Minnesota, USA. Ecotoxicology 20: 1626–1635. Available at

Porter, E., Blett, T., Potter, D.U., Huber, C. 2005. Protecting resources on federal lands: Implications of critical loads for atmospheric deposition of nitrogen and sulfur. BioScience 55(7): 603–612.[0603:PROFLI]2.0.CO;2

Rowe, A.S. 2001. The Development of an Avian Biosentinel Program for Michigan using the Bald Eagle (Haliaeetus leucocephalus). MS Thesis, Clemson University.

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

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.

Simcik, M. F. and Dorweiler, K. J. 2005. Ratio of Perfluorochemical Concentrations as a Tracer of Atmospheric Deposition to Surface Waters. Environmental Science and Technology. 39(22): 8678–8683.

Sorensen, J. A., Kallemeyn, L. W., Sydor, M. 2005. Relationship between Mercury Accumulations in Young-of-the-Year Yellow Perch and Water-Level Fluctuations. Environmental Science and Technology. Environmental Science & Technology 39 (23): 9237–9243.

Sorenson, J. A., Rapp Jr., G., Glass, G. E. 2001. The effect of exotic rainbow smelt (Osmerus mordax) on nutrient/trophic pathways and mercury contaminant uptake in the aquatic food web of Voyageurs National Park, a benchmark study of stable element isotopes. NPS Final Report. 52 pp.

Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011a. 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., 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

Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011c. 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., 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

Sullivan T.J. 2016. Air quality related values (AQRVs) in national parks: Effects from ozone; visibility reducing particles; and atmospheric deposition of acids, nutrients and toxics. Natural Resource Report. NPS/NRSS/ARD/NRR—2016/1196. National Park Service. Fort Collins, Colorado. Available at

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

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.

Wiener, J. G., Knights, B. C., Sandheinrich, M. B., Jeremiason, J. D., Brigham, M. E., Engstrom, D. R., Woodruff, L. G., Cannon, W. F., and Balogh, S. J. 2006. Mercury in soils, lakes, and fish in Voyageurs National Park (Minnesota): Importance of atmospheric deposition and ecosystem factors. Environmental Science & Technology 40 (20): 6261–6268.

Part of a series of articles titled Park Air Profiles.

Voyageurs National Park

Last updated: September 27, 2018