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Park Air Profiles - Glacier National Park

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Air Quality at Glacier National Park

Most visitors expect clean air and clear views in parks. Glacier National Park (NP), Montana, boasting glacial vistas and relatively pristine surface waters, is downwind of many pollutant sources, including power plants, agricultural areas, oil and gas development, and other industry. 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 Glacier NP, and in parks across the U.S., through science, policy and planning, and by doing our part.

Nitrogen and Sulfur

Hidden Lake
Visitors come to Glacier NP to view active glaciers and beautiful lakes and streams.

Nitrogen (N) and sulfur (S) compounds deposited from the air may have harmful effects on ecosystem processes. Healthy ecosystems can naturally buffer a certain amount of pollution, but once a threshold is passed the ecosystem may respond negatively. This threshold is the critical load, or the amount of pollution above which harmful changes in sensitive ecosystems occur (Porter 2005). N and S deposition change ecosystems through eutrophication (N deposition) and acidification (N + S deposition). Eutrophication increases soil and water nutrients which causes some species to grow more quickly and change community composition. Ecosystem sensitivity to nutrient N enrichment at Glacier National Park (GLAC) relative to other national parks is high (Sullivan et al. 2016); for a full list of N sensitive ecosystem components, see: NPS ARD 2019. Acidification leaches important cations from soils, lakes, ponds, and streams which decreases habitat quality. Ecosystem sensitivity to acidification at GLAC relative to other national parks is very high (Sullivan et al. 2016); to search for acid-sensitive plant species, see: NPSpecies.

From 2017-2019 total N deposition in GLAC ranged from 2.4 to 8.1 kg-N ha-1 yr-1 and total S deposition ranged from 0.5 to 1.8 kg-S ha-1 yr-1 based on the TDep model (NADP, 2018). GLAC has been monitoring atmospheric N and S deposition since 1980, see the conditions and trends website for park-specific information.

Watersheds that receive glacial runoff are less sensitive to acid deposition than others due to buffering minerals like calcium in the runoff (Ellis et al. 1992; Clow et al. 2002; Nanus et al. 2009; Peterson et al. 1998; Sullivan et al. 2016).

Alpine ecosystem effects

Alpine environments are particularly vulnerable to large inputs of reactive nitrogen because of the sparse cover of vegetation, short growing seasons, large areas of exposed bedrock and talus, and snowmelt nutrient releases (Williams et al., 1996; Nanus et al., 2012). Approximately 2% of the land area in GLAC is alpine (~328 km2 above 1550 m). McClung et al. (2020) compared the 2015 estimated total N deposition (TDep; NADP, 2018) to the critical load of N for an increase in alpine sedge growth (alpine plant critical load = 3 kg-N ha-1yr-1) and the critical load of N for alpine soil nitrate leaching (alpine soil critical load = 10 kg-N ha-1yr-1; Bowman et al., 2012). They found that deposition exceeded the alpine plant critical load in *% of the park’s alpine area, but was below the alpine soil critical load throughout the park’s entire alpine area.

Epiphytic macrolichen community responses

Epiphytic macrolichens grow on tree trunks, branches, and boles. Since these lichens grow above the ground, they obtain all their nutrients directly from precipitation and the air. Many epiphytic lichen species have narrow environmental niches and are extremely sensitive to changes in air pollution. Geiser et al. (2019) used a U.S. Forest Service national survey to develop critical loads of nitrogen (N) and critical loads of sulfur (S) to prevent more than a 20% decline in four lichen community metrics: total species richness, pollution sensitive species richness, forage lichen abundance, and cyanolichen abundance.

McCoy et al. (2021) used forested area from the National Land Cover Database to estimate the impact of air pollution on epiphytic lichen communities. Forested area makes up 2183 km2 (53.5%) of the land area of Glacier National Park.

  • N deposition exceeded the 3.1 kg-N ha-1 yr-1 critical load to protect N-sensitive lichen species richness in 70.2% of the forested area.
  • S deposition was below the 2.7 kg-S ha-1 yr-1 critical load to protect S-sensitive lichen species richness in every part of the forested area.

For exceedances of other lichen metrics and the predicted decline of lichen communities see Appendices A and B of McCoy et al. (2021).

Additional modeling was done on 459 lichen species to test the combined effects of air pollution and climate gradients (Geiser et al. 2021). A critical load indicative of initial shifts from pollution-sensitive toward pollution-tolerant species occurred at 1.5 kg-N ha-1 yr-1 and 2.7 kg-S ha-1 yr-1 even under changing climate regimes.

Plant species response

Plants vary in their tolerance of eutrophication and acidification, and some plant species respond to nitrogen (N) or sulfur (S) pollution with declines in growth, survival, or abundance on the landscape. Horn et al. (2018) used the U.S. Forest Service national forest survey to develop critical loads of N and critical loads of S to prevent declines in growth or survival of sensitive tree species. Clark et al. (2019) used a database of plant community surveys to develop critical loads of N and critical loads of S to prevent a decline in abundance of sensitive herbaceous plant species. According to NPSpecies, Glacier National Park contains:

  • 6 N-sensitive tree species and 40 N-sensitive herbaceous species.
  • 8 S-sensitive tree species and 35 S-sensitive herbaceous species.

Persistent Pollutants

Fishing at Glacier National Park
Fish consumption advisories are in effect for some lakes at Glacier NP due to fish found with levels of mercury that exceed safe human consumption thresholds.

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.

Research findings from the Western Airborne Contaminants Assessment Project (WACAP), Rocky Mountain Regional Snowpack Chemistry Monitoring Study, Glacier National Park Fisheries Inventory and Monitoring, and other studies found airborne contaminants in fish, vegetation, snow, and lake sediments in the park (Downs and Stafford 2009; Downs et al. 2011; Hageman et al. 2006; Ingersoll et al. 2007; Krabbenhoft et al. 2002; Landers et al. 2010; Landers et al. 2008; Mast et al. 2006; Watras et al. 1995).

The park is investigating the presence of selenium in fish (Downs et al. 2011). Growing scientific evidence suggests that selenium affects the fate of mercury in aquatic food chains and may moderate its toxicity. However, the protective effects of selenium against mercury toxicity rely on a fine balance of selenium in the diet as it can also be toxic to organisms (Peterson et al. 2009).

Mercury and toxics effects:

  • Concentrations of a combustion by-product, Polycyclic aromatic hydrocarbons (PAHs), in snow, lichen, and sediment is 3.6 to 60,000 times greater in the park’s Snyder Lake watershed than in other western and Alaskan national park watersheds; levels attributable to emissions from a local aluminum smelter. Although the smelter is now closed, PAHs deposited from its emissions persist in the park’s ecosystems (Usenko et al. 2010).
  • Levels of historic-use pesticides dieldrin and DDT in fish exceed safe consumption thresholds for human and wildlife health, and concentrations of current-use pesticides in fish are higher than in other western U.S. national parks (Ackerman et al. 2008; Landers et al. 2010; Landers et al. 2008).
  • Concentrations of mercury in fish from numerous lakes in the park exceed safe consumption thresholds for human and wildlife health (Downs and Stafford 2009; Downs et al. 2011), prompting guidelines for fish consumption (GNP 2009).
  • Mercury levels associated with tissue damage in fish kidney and spleen (Schwindt et al. 2008);
  • Male intersex fish (the presence of both male and female reproductive structures in the same fish) found in the park, a response that indicates exposure to contaminants (Schwindt et al. 2009). Follow-up research is examining the extent to which contaminants are disrupting reproductive organs in park fish.

Glacier NP has been monitoring atmospheric mercury deposition since 2003. Explore air monitoring »

Visibility

View at Glacier National Park
Clean, clear air is essential to appreciating the scenic vistas at Glacier NP.

Visitors come to Glacier NP to enjoy spectacular views of active glaciers and the rugged topography and stunning lakes and streams left by the colossal glaciers of the past. 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, dust, and wood smoke reduce visibility as well. Significant improvements in park visibility have been documented since the late 1980’s. Still, visibility in the park is a long way from the Clean Air Act goal of no human caused impairment.

Visibility effects:

  • Reduction of the average natural visual range from about 145 miles (without the effects of pollution) to about 95 miles because of pollution at the park;
  • Reduction of visual range to below 50 miles on high pollution days.

Visit the NPS air quality conditions and trends website for park-specific visibility information. Glacier NP has been monitoring visibility since 1988. View live webcams and explore air monitoring »

Ground-Level Ozone

Quaking Aspen Trees showing fall colors
Quaking Aspen is one of the ozone sensitive species found at Glacier 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. Relatively low ozone exposure levels at Glacier NP make the risk of vegetation injury to plants low (Kohut 2004). Ozone-sensitive plants in Glacier NP include Populus tremuloides (quaking aspen) and Salix scouleriana (Scouler’s willow). Search ozone-sensitive plant species found at Glacier NP.

Visit the NPS air quality conditions and trends website for park-specific ozone information. Glacier NP has been monitoring ozone since 1992. View live ozone and meteorology data, and explore air monitoring »

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Downs, C. C. and Stafford, C. 2009. Glacier National Park Fisheries Inventory and Monitoring Annual Report, 2008. National Park Service, Glacier National Park, West Glacier, Montana.

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Ellis, B. K., Stanford, J. A., Craft, J. A., Chess, D. W., Gregory, G. R., and Marnell, L. F. 1992. Monitoring of water quality of selected lakes in Glacier National Park, Montana: Analysis of data collected, 1984–1990. Open File Report 129-92 in conformance with Cooperative Agreement CA 1268-0-9001, Work Order 6, National Park Service, Glacier National Park, West Glacier, Montana. Flathead Lake Biological Station, The University of Montana, Polson.

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Hageman, K. J., Hafner, W. D., Campbell, D. H., Jaffe, D. A., Landers, D. H., Massey Simonich, S. L. 2010. Variability in Pesticide Deposition and Source Contributions to Snowpack in Western U.S. National Parks. Environmental Science and Technology 44: 4452–4458.

Horn KJ, Thomas RQ, Clark CM, Pardo LH, Fenn ME, Lawrence GB, et al. (2018) Growth and survival relationships of 71 tree species with nitrogen and sulfur deposition across the conterminous U.S.. PLoS ONE 13(10): e0205296. https://doi.org/10.1371/journal.pone.0205296

Ingersoll, G. P., Mast, M. A., Nanus, L., Handran, H. H., Manthorne, D. J., and Hultstrand, D. M. 2007. Rocky Mountain snowpack chemistry at selected sites, 2004: U.S. Geological Survey Open-File Report 2007-1045, 15 p. Available at http://pubs.usgs.gov/of/2007/1045/.

Kohut, R. 2004. Assessing the Risk of Foliar Injury from Ozone on Vegetation in Parks in the Rocky Mountain Network. Available at https://irma.nps.gov/DataStore/Reference/Profile/2181542.

Krabbenhoft, D. P., Olson, M. L., Dewild, J. F., Clow, D. W., Striegl, R. G., Dornblaser, M. M., and VanMetre, P. 2002. Mercury loading and methylmercury production and cycling in high-altitude lakes from the western United States. Water, Air, and Soil Pollution, Focus 2: 233–249.

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Mast, M. A., Foreman, W. T., and Skaates, S. V. 2006. Organochlorine compounds and current-use pesticides in snow and lake sediment in Rocky Mountain National Park, Colorado, and Glacier National Park, Montana, 2002–03. U.S. Geological Survey, SIR 2006-5119. Reston, VA. Available at https://pubs.usgs.gov/sir/2006/5119/.

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Schwindt, A. R., Kent, M. L., Ackerman, L. K., Massey Simonich, S. L., Landers, D. H., Blett, T., Schreck, C. B. 2009. Reproductive Abnormalities in Trout from Western U.S. National Parks. Transactions of the American Fisheries Society 138: 522–531.

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Part of a series of articles titled Park Air Profiles.

Glacier National Park

Last updated: December 2, 2022