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Air Pollution Impacts

Voyageurs National Park

Natural and scenic resources in Voyageurs National Park (NP) are susceptible to the harmful effects of air pollution. Mercury (and other air toxics), nitrogen, sulfur, ozone, and fine particles impact natural resources such as wildlife, surface waters, and vegetation, as well as visibility. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at Voyageurs NP.

  • Toxics & Mercury
  • Nitrogen & Sulfur
  • Ozone
  • Visibility
Bald eagle at Voyageurs National Park, Minnesota
Studies found elevated levels of airborne toxics including mercury and pesticides in bald eagles and other wildlife at Voyageurs National Park, Minnesota.

Toxics, including heavy metals like mercury, accumulate in the tissue of organisms. When mercury converts to methylmercury in the environment and enters the food chain, effects can include reduced reproductive success, impaired growth and development, and decreased survival. Other toxic air contaminants of concern include pesticides (e.g., DDT), industrial by-products like PCBs, and emerging chemicals such as flame retardants for fabrics (PBDEs). Some of these are known or suspected to cause cancer or other serious health effects in humans and wildlife.

Effects of Toxics/Mercury at Voyageurs NP include:

  • Mercury is currently widespread in the park’s aquatic ecosystems, and comes primarily from coal-fired power plant and taconite processing emissions. In addition to fish, elevated concentrations have been documented in water, lake sediments, zooplankton, aquatic plants, benthic organisms, fish-eating birds, bald eagles, and river otters (Kallemeyn et al. 2003 [pdf, 11.3 KB]; Wiener et al. 2006; Swackhamer and Hornbuckle 2004 [pdf, 4.5 MB]);
  • 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 (MN-DOH 2012), a concern since approximately 70 percent of visitors enjoy fishing in the park (Kallemeyn et al. 2003 [pdf, 11.3 KB]);
  • 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 [pdf, 337 KB]), and at levels also known to harm loons that eat those fish (Sorensen et al. 2001);
  • Concentrations of mercury in loon blood at a level sufficient to reduce reproductive success (Evers et al. 2011a; Evers et al. 1998), and adult loon feather mercury concentrations above a level associated with risk of 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 [pdf, 1.1 MB]). Mercury concentrations in nestling feathers have declined over time, but recent samples suggest a gradual increase (Pittman et al. 2011 [pdf, 1.8 MB]);
  • 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).

Additional Information:

Get Toxics/Mercury Data »


View of Cleary Lake at Voyageurs National Park
Boreal lakes at Voyageurs NP in Minnesota are particularly sensitive to sulfur and nitrogen deposition.

Nitrogen (N) and sulfur (S) compounds deposited from air pollution can harm surface waters, soils, vegetation, and ecosystem biodiversity. 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 N and S (Sullivan et al. 2011a; Sullivan et al. 2011b [pdf, 2.3 MB]).

Some park resources may be sensitive to nutrient N enrichment from deposition. For example, in N-limited boreal lakes, increased N can affect biodiversity, algal communities, and water clarity (Sullivan et al. 2011c; Sullivan et al. 2011d [pdf, 6.2 MB]; Kallemeyn et al. 2003 [pdf, 11.3 KB]; Wiener et al. 2006; Swackhamer and Hornbuckle 2004 [pdf, 4.5 MB]). Concentrations of ammonium, an N compound and indicator of nearby agricultural activity, have increased in precipitation in the Great Lakes region in recent decades. During that same period, declines in nitrate concentrations have been observed and as a result, total nitrogen deposition remains elevated above natural conditions and relatively unchanged (NPS 2010 [pdf, 337 KB]; Lehmann et al. In Prep; Lehmann and Gay 2011).

Sulfur emissions and resultant sulfate concentrations in precipitation have gone down more significantly 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. (more »). In addition, sulfur is a strong driver of acidification in poorly buffered lakes and streams, and ecosystems at the park have been identified as being very sensitive to acidification effects (Sullivan et al. 2011a; Sullivan et al. 2011b [pdf, 2.3 MB]).

How much nitrogen is too much?

Nitrogen is a fertilizer and some nitrogen is necessary for plants to grow. However, in natural ecosystems, too much nitrogen can disrupt the balance of plant communities, like diatoms, allowing weedy species to grow faster. Nitrogen deposited from air pollution may upset the balance of sensitive diatom communities in the boreal lakes of Voyageurs NP. A project is underway to analyze diatom community assemblages from 16 inland lakes at the park (Elias and Damstra 2011 [pdf, 2.1 MB]). Findings may shed light on possible changes in diatom community structure over time, and allow results to be compared to the critical load developed for similar boreal lakes near Voyageurs NP. Above that threshold of nitrogen deposition, communities may begin to change, with sensitive species gradually replaced by pollution-tolerant species. Critical loads for natural resources can be used to establish goals for ecosystem recovery.

Get Nitrogen & Sulfur Data »


Photo of Prunus serotina (Black cherry)
While ground-level ozone concentrations are generally low at Voyageurs NP, Minnesota, there are a few ozone-sensitive species present in the park, such as Prunus serotina (Black cherry).

Naturally-occurring ozone in the upper atmosphere absorbs the sun’s harmful ultraviolet rays and helps to protect all life on Earth. However, in the lower atmosphere, ozone is an air pollutant, forming when nitrogen oxides from vehicles, power plants, and other sources combine with volatile organic compounds from gasoline, solvents, and vegetation in the presence of sunlight. In addition to causing respiratory problems in people, ozone can injure plants. Ozone enters leaves through pores (stomata), where it can kill plant tissues, causing visible injury, or reduce photosynthesis, growth, and reproduction.

There are a few ozone-sensitive plants in Voyageurs NP including Apocynum androsaemifolium (Spreading dogbane), Ascelpias syriaca (Common milkweed), and Prunus serotina (Black cherry). Because ozone exposure levels at the park are low, there is a low risk of ozone damage to plants (Kohut 2004 [pdf, 187 KB]). A review of monitoring results found no ozone injury to plants in regions near Voyageurs NP (Swackhamer and Hornbuckle 2004 [pdf, 4.5 MB]).

Search the list of ozone-sensitive plant species (pdf, 184 KB) found at each national park.

Get Ozone Data »


Visitors come to Voyageurs NP to enjoy the spectacular “North Woods,” a wilderness of interconnected waterways, and the distant howls of wolves. Unfortunately, park vistas are sometimes obscured by haze caused by fine particles in the air. Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition contribute to this haze and visibility impairment. Additionally, organic compounds, soot, and dust reduce visibility. Smoke from nearby forest fires also contributes to particulate matter in the region.

Visibility effects at Voyageurs NP include:

  • Reduced visibility, at times, due to human-caused haze and fine particles of air pollution;
  • Reduction of the average natural visual range from about 110 miles (without pollution) to about 60 miles because of pollution at the park;
  • Reduction of the visual range to below 35 miles on very hazy days.

(Source: IMPROVE 2010)

Images of good and poor visibility at Voyageurs National Park, Minnesota
Air pollutants can affect visibility at Voyageurs NP, Minnesota (clear to hazy from left to right)

Explore regional vistas via live webcams located throughout the Midwest.

Get Visibility Data »


Featured Content

Studies and Monitoring icon

Studies and monitoring help the NPS understand the environmental impacts of air pollution. Access air quality data and see what is happening with Studies and Monitoring at Voyageurs NP.

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Last Updated: January 03, 2017