- Air quality at Isle Royale National Park
- Related references
Air quality at Isle Royale National Park
Most visitors expect clean air and clear views in parks. Isle Royale National Park (NP), Michigan, is a heavily forested, remote island in Lake Superior that experiences relatively good air quality. However, air pollution from mainland sources in Canada and the Midwest, including pollutants from industries along the Ohio River Valley, does affect the park. 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 Isle Royale NP, and in parks across the U.S., through science, policy and planning, and by doing our part.
Mercury and toxics
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.
Power plants and other sources of air pollution on the mainland contribute to the deposition of toxics at Isle Royale NP. 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. 2011). However, mercury pollution remains a major concern (Evers et al. 2011; Weiner et al. 2011) and air emissions are now the primary source of mercury pollution (Evers et al. 2011). Isle Royale NP is particularly sensitive to mercury pollution. The abundance of wetlands, low pH lakes, complex food webs, and predatory fish creates an environment susceptible to the bioaccumulation of toxics.
The first study documenting air toxics at the park assessed concentrations of PCBs, DDT, and more in fish in 1978. 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).
Mercury and toxics effects:
- Elevated mercury and PCB concentrations and State of Michigan fish consumption advisories for fish caught in Siskiwit Lake. Learn more about fishing at Isle Royale NP.
- Concentrations of mercury in pike at levels associated with adverse health and reproductive effects (NPS 2010; Sandheinrich et al. 2011) as well as cell damage and liver toxicity (Drevnick et al. 2008)
- Concentrations of mercury in loon blood and feathers are high enough to affect behavior and reduce reproductive success (Sandheinrich et al. 2011; Evers et al. 2011; Evers et al. 1998; Scheuhammer and Blancher 1994);
- Mercury detected in deer mice (Vucetich et al. 2001) and moose teeth (Vucetich et al. 2009), a sign that mercury is accumulating in the land-based food web;
- Elevated mercury in rain and snow at monitoring sites near Isle Royale NP (Risch et al. 2012);
- Pesticides including atrazine and cyanazine detected in rainfall at the park (Thurman and Cromwell 2000);
- Contaminants including pesticides, PCBs, and mercury detected in herring gull eggs (Bowerman et al. 2011);
- PCBs detected in tree bark, verifying long-range transport of persistent organic pollutants to the park (Hermanson and Hites 1990);
- PBDEs (flame retardants) found in freshwater mussels collected from 10 inland lakes in the park (Chernyk et al. 2002).
Nitrogen and sulfur
Nitrogen and sulfur compounds deposited from the air may have harmful effects, including acidification on soils, lakes, ponds, and streams. Thin, undeveloped soils, and low buffering capacity result in surface waterways and soils that are vulnerable to acidification in the park (Sullivan et al. 2011a; Sullivan et al. 2011b). Also, some plants are sensitive to acidification, search for acid-sensitive plant species found at Isle Royale NP.
Excess nitrogen can also lead to nutrient enrichment, a process that changes nutrient cycling and alters plant communities. Boreal lakes—including Sargent and Richie—may be particularly sensitive to nitrogen enrichment, which could rapidly affect algal communities and lake biodiversity (Saros 2008; Sullivan et al. 2011c; Sullivan et al. 2011d). A study at Isle Royale NP investigated the fertilization effects of excess nitrogen loading, including changes to the species composition of sensitive aquatic communities, and determined that lakes in the park are vulnerable to increasing nitrogen deposition compared to other national parks (Saros 2008; Saros 2014).
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 declined in recent decades due to air pollution controls (Lehmann and Gay 2011). However, sulfur remains a concern at Isle Royale NP because it plays an essential role in the methylation of mercury, leading to toxic accumulation of methylmercury in fish and wildlife.
Visit the NPS air quality conditions and trends website for park-specific nitrogen and sulfur deposition information.
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 Isle Royale 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 Isle Royale 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 Isle Royale NP (Swackhamer and Hornbuckle 2004). Search for more ozone-sensitive plant species found at Isle Royale NP.
Visit the NPS air quality conditions and trends website for park-specific ozone information.
Visitors come to Isle Royale NP to enjoy the spectacular remote islands in the vastness of Lake Superior, with forests, inland lakes, and opportunities to see wildlife. 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. Additionally, organic compounds, soot, and dust reduce visibility. 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, including dust;
- 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 45 miles on very hazy days.
Visit the NPS air quality conditions and trends website for park-specific visibility information. Isle Royale 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 »
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Last updated: September 27, 2018