Park Air Profiles - Glacier National Park

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

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.

Mycorrhizal community response

Many plants have a symbiotic relationship with mycorrhizal fungi (MF). Through the roots, the plants supply the fungi with carbon from photosynthesis and in exchange the MF enhance nutrient availability within soils, increase drought tolerance, and provide physical resistance to soil erosion (George et al., 1995; Cheng et al., 2021; Burri et al., 2013). Anthropogenic Nitrogen (N) deposition can disrupt this symbiotic relationship resulting in a shift from N sensitive to N tolerant mycorrhizal fungi and plant communities.

With increased N deposition to the soil, MF become less important for nutrient uptake and many plants will cease the exchange of nutrients altogether making them more vulnerable to stressors such as drought (Lilleskov et al., 2019). The CL-N for the shift in mycorrhizal community is 5-6 kg-N ha^-1 yr^-1 in coniferous forests and 10-20 kg-N ha^-1 yr^-1 broadleaf forests.

Glacier National Park has 2675.2 km² of coniferous forests, 20.4 km² of broadleaf forests, and 75.2 km² of mixed forests. Using the range in critical loads above, the minimum CL is exceeded in 49.1% of forested area and the maximum CL is exceeded in 17.2% of forested area based on 2019-2021 TDep Total N deposition.

Change in N and S deposition from 2000 to 2021

The maps below show how the spatial distribution of estimated Total N and Total S deposition in GLAC has changed from 2000-2002 to 2019-2021 (TDep MMF version 2022.02). Slide the arrows in the middle of the image up and down to compare N and S deposition between the two years (Yearly Data).

• Minimum N deposition increased from 2.4 to 2.7 kg-N ha^-1 yr^-1 and maximum N deposition remained at 6.4 kg-N ha^-1 yr^-1.
• Minimum S deposition decreased from 0.8 to 0.5 kg-S ha^-1 yr^-1 and maximum S deposition decreased from 2.6 to 1.5 kg-S ha^-1 yr^-1.

Estimated total nitrogen and sulfur deposition levels from 2000-2002 (top) compared to the 2019-2021 (bottom) average at GLAC. Estimated values were developed using the National Atmospheric Deposition Program - Total Deposition (TDep) approach that combines measured and modeled data. Estimated values are valuable for analyzing gradients of deposition and the resulting ecosystem risks where monitors are not present.

Persistent Pollutants

Pollutants like mercury and pesticides are concerning because they are persistent and toxic in the environment. These contaminants can travel in the air thousands of miles away from the source of pollution, even depositing in protected places like national parks. In addition, while some of these harmful pollutants may be banned from use, historically contaminated sites continue to endure negative environmental consequences.

When deposited, airborne mercury and other toxic air contaminants are known to harm wildlife like birds and fish, and cause human health concerns. Many of these substances enter the food chain and accumulate in the tissue of organisms causing reduced reproductive success, impaired growth and development, and decreased survival.

• Mercury concentrations in fish sampled from Glacier NP did not exceed any thresholds for fish toxicity, bird toxicity, or US EPA’s human consumption guidance. Fish were analyzed for mercury from one site (Lake McDonald) at the park and compared to data across 21 western parks. The average park fish mercury concentration (232.4 ng/g ww) was higher than the study-wide mean (77.7 ng/g ww). However, the data may not reflect the risk at other unsampled locations in the park (Eagles-Smith et al. 2014). Fish consumption advisories may be in effect for mercury and other contaminants (NPS 2022).
• Older studies found fish mercury concentrations in the park that exceeded safe consumption thresholds for human and wildlife health, prompting guidelines for fish consumption in Glacier NP, and specifically at Lake McDonald and Lake St. Mary (Schwindt et al. 2008; Downs and Stafford 2009; GNP 2009; Downs et al. 2011). At select sites (Snyder Lake and Oldman Lake), levels of historic-use pesticides dieldrin and DDT in fish also exceeded 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. 2008; Landers et al. 2010; ).
• One fish sampled from the park was found to be intersex (Schwindt et al. 2009; Schreck and Kent 2013). Reproductive abnormalities such as intersex, the presence of both male and female reproductive structures in the same fish, can signify exposure to contaminants.
• Some dragonfly larvae sampled at Glacier NP had mercury concentrations at moderate impairment levels. Dragonfly larvae have been sampled and analyzed for mercury from three sites in the park; 67% of the data fall into the moderate (100-300 ng/g dw) impairment categories for potential mercury risk. An index of moderate impairment or higher suggests some fish species may exceed the US EPA benchmark for protection of human health (Eagles-Smith et al. 2018; Eagles-Smith et al. 2020).
• Mercury, pesticides, and other contaminants have been found in park water, snow, vegetation, and lake sediments (Watras et al. 1995; Krabbenhoft et al. 2002; Hageman et al. 2006; Mast et al. 2006; Ingersoll et al. 2007). In 2021, the average mercury concentration found in snowpack was 1.3 ng/L at Apgar Lookout (USGS 2021).
• 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).

The NPS Air Resources Division reports on park conditions and trends for mercury. Visit the webpage to learn more.

Visibility

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 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 grow and store carbon. Ozone causes leaf injuries like bleaching or dark spots on some sensitive plants. There are six plants that may display ozone leaf injury at Glacier National Park. Search ozone-sensitive plant species found at Glacier National Park.

US Environmental Protection Agency and NPS found in ozone exposure experiments that ozone slowed tree seedling growth. NPS uses W126 values from averaged seedling responses in those experiments to describe park condition in terms of Vegetation Health. Ozone affects actively growing plants, so the W126 metric weights a sum of ozone concentrations during daylight hours over three months in the growing season.

A recent re-analysis of the seedling experiments established critical levels of ozone protective of each tree species tested (Lee et al. 2022). The ozone critical levels are W126 values that will prevent 5% or greater deficit in tree seedling biomass. Air Quality Conditions and Trends reports a 5-year average of W126 for each park. In 2018-2022, the average W126 value for Glacier National Park was 2.6 ppm-h. Based on this ozone level, trees present in the park (NPSpecies) are at low risk of ozone effects:

• Tree species Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), and quaking aspen (Populus tremuloides) are at low risk from ozone despite their known sensitivity. Recent ozone levels in the park are below critical levels that protect these trees from 5% biomass deficit.

Ozone critical levels are for tree seedlings, which represent the regenerative capacity and long-term stability of sensitive species within a forest. These tree species are also known to be sensitive to ozone as adults (Bell et al. 2020), but critical values for seedling growth do not predict ozone effects on mature trees. ARD is currently working with collaborators to establish critical levels for mature trees using data from forest monitoring plots.

Visit the NPS air quality conditions and trends website for park-specific ozone information. Glacier NP has been monitoring ozone since 1992.

Explore Other Park Air Profiles

There are 47 other Park Air Profiles covering parks across the United States and its territories.

References

Ackerman, L. K., Schwindt, A. R., Massey Simonich, S. L., Koch, D. C., Blett, T. F., Schreck, C. B., Kent, M. L., Landers, D. H. 2008. Atmospherically Deposited PBDEs, Pesticides, PCBs, and PAHs in Western U.S. National Park Fish: Concentrations and Consumption Guidelines. Environmental Science and Technology 42: 2334–2341. https://irma.nps.gov/DataStore/Reference/Profile/652640

Bell MD, Felker-Quinn E, Kohut R. 2020. Ozone sensitive plant species on National Park Service lands. Natural Resource Report. NPS/WASO/NRR—2020/2062. National Park Service. Fort Collins, Colorado. https://irma.nps.gov/DataStore/Reference/Profile/2271702

Bowman W, Murgel J, Blett T, Porter E. 2012. Nitrogen critical loads for alpine vegetation and soils in Rocky Mountain National Park. Journal of Environmental Management. 103:165-171

Burri, K., C. Gromke, and F. Graf. "Mycorrhizal fungi protect the soil from wind erosion: a wind tunnel study." Land Degradation & Development 24.4 (2013): 385-392.

Cheng, Shen, et al. "Elucidating the mechanisms underlying enhanced drought tolerance in plants mediated by arbuscular mycorrhizal fungi." Frontiers in Microbiology 12 (2021): 809473.

Clark, C.M., Simkin, S.M., Allen, E.B. et al. Potential vulnerability of 348 herbaceous species to atmospheric deposition of nitrogen and sulfur in the United States. Nat. Plants 5, 697–705 (2019). https://doi.org/10.1038/s41477-019-0442-8

Clow, D. W., Striegl, R. G., Nanus, L., Mast, M. A., Campbell, D. H., Krabbenhoft, D. P. 2002. Chemistry of Selected High-Elevation Lakes in Seven National Parks in the Western United States. Water, Air, and Soil Pollution: Focus 2: 139–164.

Clow, D. W., Striegl, R. G., Nanus, L., Mast, M. A., Campbell, D. H., Krabbenhoft, D. P. 2002. Chemistry of Selected High-Elevation Lakes in Seven National Parks in the Western United States. Water, Air, and Soil Pollution: Focus 2: 139–164.

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. Available at: https://irma.nps.gov/DataStore/Reference/Profile/661541

Downs, C. C., Stafford, C., Langner, H., and Muhlfeld, C. C. 2011. Glacier National Park Fisheries Inventory and Monitoring Bi-Annual Report, 2009–2010. National Park Service, Glacier National Park, West Glacier, Montana. Available at: https://irma.nps.gov/DataStore/Reference/Profile/2170299

Eagles-Smith, C.A., J.J. Willacker, and C.M.Flanagan Pritz. 2014. Mercury in fishes from 21 national parks in the Western United States—Inter and intra-park variation in concentrations and ecological risk: U.S. Geological Survey Open-File Report 2014-1051, 54 p. Available at: http://dx.doi.org/10.3133/ofr20141051.

Eagles-Smith, C.A., S.J. Nelson., C.M. Flanagan Pritz, J.J. Willacker Jr., and A. Klemmer. 2018. Total Mercury Concentrations in Dragonfly Larvae from U.S. National Parks (ver. 6.0, June 2021): U.S. Geological Survey data release. https://doi.org/10.5066/P9TK6NPT

Eagles-Smith, C.A., J.J. Willacker, S.J. Nelson, C.M. Flanagan Pritz, D.P. Krabbenhoft, C.Y. Chen, J.T. Ackerman, E.H. Campbell Grant, and D.S. Pilliod. 2020. Dragonflies as biosentinels of mercury availability in aquatic food webs of national parks throughout the United States. Environmental Science and Technology 54(14):8779-8790. https://doi.org/10.1021/acs.est.0c01255

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.

Geiser, Linda & Nelson, Peter & Jovan, Sarah & Root, Heather & Clark, Christopher. (2019). Assessing Ecological Risks from Atmospheric Deposition of Nitrogen and Sulfur to US Forests Using Epiphytic Macrolichens. Diversity. 11. 87. 10.3390/d11060087.

Geiser, Linda & Root, Heather & Smith, Robert & Jovan, Sarah & Clair, Larry & Dillman, Karen. (2021). Lichen-based critical loads for deposition of nitrogen and sulfur in US forests. Environmental Pollution. 291. 118187. 10.1016/j.envpol.2021.118187.

George, Eckhard, Horst Marschner, and Iver Jakobsen. "Role of arbuscular mycorrhizal fungi in uptake of phosphorus and nitrogen from soil." Critical reviews in biotechnology 15.3-4 (1995): 257-270.

[GNP] Glacier National Park. 2009. Contaminants in Fish and the Human Health Perspective. National Park Service, Glacier National Park, West Glacier, Montana. https://irma.nps.gov/DataStore/Reference/Profile/2171880

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. https://irma.nps.gov/DataStore/Reference/Profile/2207989

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. https://irma.nps.gov/DataStore/Reference/Profile/648386

Landers, D. H., Simonich, S. M., Jaffe, D. A., Geiser L. H., Campbell, D. H., Schwindt, A. R., Schreck, C. B., Kent, M. L., Hafner, W. D., Taylor, H. E., Hageman, K. J., Usenko, S., Ackerman, L. K., Schrlau, J. E., Rose, N. L., Blett, T. F., and Erway, M. M. 2008. The Fate, Transport, and Ecological Impacts of Airborne Contaminants in Western National Parks (USA). EPA/600/R—07/138. U.S. Environmental Protection Agency, Office of Research and Development, NHEERL, Western Ecology Division, Corvallis, Oregon. Available at https://irma.nps.gov/DataStore/Reference/Profile/660829.

Landers, D. H., Simonich, S. M., Jaffe, D. A., Geiser L. H., Campbell, D. H., Schwindt, A. R., Schreck, C. B., Kent, M. L., Hafner, W. D., Taylor, H. E., Hageman, K. J., Usenko, S., Ackerman, L. K., Schrlau, J. E., Rose, N. L., Blett, T. F., and Erway, M. M. 2010. The Western Airborne Contaminant Assessment Project (WACAP): An Interdisciplinary Evaluation of the Impacts of Airborne Contaminants in Western U.S. National Parks. Environmental Science and Technology. Vol 44: 855–859. Available at: https://irma.nps.gov/DataStore/Reference/Profile/2171893

Lee EH, Anderson CP, Beedlow PA, Tingey DT, Koike S, Dubois J, Kaylor SD, Novak K, Rice RB, Neufeld HS, Herrick JD. 2022. Ozone Exposure-Response Relationships Parametrized for Sixteen Tree Species with Varying Sensitivity in the United States. Atmospheric Environment. 284:1-16. https://irma.nps.gov/DataStore/Reference/Profile/2294221

Lilleskov, Erik A., et al. "Atmospheric nitrogen deposition impacts on the structure and function of forest mycorrhizal communities: a review." Environmental Pollution 246 (2019): 148-162.

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/.

McClung JJ, Bell MD, Felker-Quinn E. 2021. Extrapolating critical loads of nitrogen for alpine vegetation and assessing exceedance in national parks based on TDep Total N from 2002–2016. Natural Resource Report. NPS/NRSS/ARD/NRR—2021/2240. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/nrr-2284914

McCoy K., M. D. Bell, and E. Felker-Quinn. 2021. Risk to epiphytic lichen communities in NPS units from atmospheric nitrogen and sulfur pollution: Changes in critical load exceedances from 2001‒2016. Natural Resource Report NPS/NRSS/ARD/NRR—2021/2299. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/nrr-2287254.

[NADP] National Atmospheric Deposition Program. 2018. NTN Data. Accessed January 20, 2022. Available at http://nadp.slh.wisc.edu/NADP/

Nanus L, Clow D, Saros J, Stephens V, Campbell D. 2012. Mapping Critical Loads of Nitrogen Deposition for Aquatic Ecosystems in the Rocky Mountains, USA.. Environmental Pollution. 166:125-135

Nanus, L., Williams, M. W., Campbell, D. H., Tonnessen, K. A., Blett, T., and Clow, D. W. 2009. Assessment of lake sensitivity to acidic deposition national parks of the Rocky Mountains. Ecological Applications 19(4): 961–973.

[NPS] National Park Service. 2022. Fish Consumption Advisories. https://www.nps.gov/subjects/fishing/fish-consumption-advisories.htm

Peterson, D. L., Sullivan, T. J., Eilers, J. M., Brace, S., Horner, D., Savig, K., and Morse, D. 1998. Assessment of air quality and air pollutant impacts in national parks of the Rocky Mountains and northern Great Plains. Report NPS/CCSOUW/NRTR—98/19. National Park Service, Air Resources Division, Denver, CO. Chapter 6: Glacier National Park. Available at https://irma.nps.gov/DataStore/Reference/Profile/11733.

Peterson, S. A., Ralston, N. V. C., Peck, D. V., Van Sickle, J., Robertson, D. V., Spate, V. L., Morris, J. S. 2009. How might selenium moderate the toxic effects of mercury in stream fish of the western U.S.? Environ Sci Technol 43: 3919–3925.

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. https://doi.org/10.1641/0006-3568(2005)055[0603:PROFLI]2.0.CO;2

Saros, J. 2009. Inferring Critical Nitrogen Deposition Loads to Alpine Lakes of Western National Parks and Diatom Fossil Records. NPS Final Report. 13 pp.

Schreck, C.B. and M. Kent. 2013. Extent of Endocrine Disruption in Fish of Western and Alaskan National Parks. NPS-OSU Task Agreement J8W07080024. NPS Final Report, 72 pp. https://irma.nps.gov/DataStore/DownloadFile/469831

Schwindt, A. R., Fournie, J. W., Landers, D. H., Schreck, C. B., Kent, M. 2008. Mercury Concentrations in Salmonids from Western U.S. National Parks and Relationships with Age and Macrophage Aggregates. Environmental Science and Technology 42(4): 1365–1370. https://irma.nps.gov/DataStore/Reference/Profile/664114

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. https://irma.nps.gov/DataStore/Reference/Profile/662018

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, CO.

Usenko, S., Massey Simonich, S. L., Hageman, K. J., Schrlau, J. E., Geiser, L., Campbell, D. H., Applyby, P. G., Landers, D. H. 2010. Sources and Deposition of Polycyclic Aromatic Hydrocarbons to Western U.S. National Parks. Environmental Science and Technology 44: 4512–4518. https://irma.nps.gov/DataStore/Reference/Profile/2257820

Watras, C. J., Morrison, K. A., Bloom, N. S. 1995. Mercury in remote Rocky Mountain Lakes of Glacier National Park, Montana, in comparison with other temperate North American regions. Canadian Journal of Fisheries and Aquatic Sciences 52(6): 1220–1228. https://irma.nps.gov/DataStore/Reference/Profile/338651

Williams MW, Baron JS, Caine N, Sommerfeld R, Sanford R. 1996. Nitrogen saturation in the Rocky Mountains. Environmental Science & Technology. 30(2):640-646