Park Air Profiles - Black Canyon of the Gunnison National Park

Air Quality at Black Canyon of the Gunnison National Park

Most visitors expect clean air and clear views in parks. Black Canyon of the Gunnison National Park (NP), Colorado, the “greatest combination of depth, narrowness, sheerness of any canyon in North America,” is in a relatively remote location on the Colorado Plateau. Still, upwind urban and industrial sources can degrade air quality at 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 Black Canyon of the Gunnison NP, and in parks across the U.S., through science, policy and planning, and by doing our part.

Nitrogen and Sulfur

Visitors come to Black Canyon of the Gunnison NP to enjoy scenic views of Black Canyon, including steep cliffs, rock spires, and rivers.

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 Black Canyon of the Gunnison National Park (BLCA) relative to other national parks is moderate (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 BLCA relative to other national parks is moderate (Sullivan et al. 2016); to search for acid-sensitive plant species, see: NPSpecies.

From 2017-2019 total N deposition in BLCA ranged from 2.0 to 2.6 kg-N ha^-1 yr^-1 and total S deposition ranged from 0.4 to 0.5 kg-S ha^-1 yr^-1 based on the TDep model (NADP, 2018). See the conditions and trends website for park-specific information on N and S deposition at BLCA.

Invasive grasses tend to thrive in areas with high N deposition, displacing native vegetation adapted to low N conditions. Increases in N have been found to promote the spread of fast-growing non-native annual grasses (like cheatgrass) and forbs (like Russian thistle) at the expense of native species (Brooks 2003; Allen et al. 2009; Schwinning et al. 2005). N may also increase water use in plants like big sagebrush (Inouye 2006).

Given the abundance of base cations in underlying park soils and rocks, surface waters in BLCA are generally well-buffered from acidification. However, steep-sided canyon walls in the park have little ability to retain nutrients and water, limiting the landscapes to buffer acidic run-off that may discharge to the inner canyon (Sullivan et al. 2016).

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. Epiphytic lichen communities are less diverse in arid areas, but are still impacted by 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 83 km² (66%) of the land area of Black Canyon of the Gunnison National Park.

• N deposition was below the 3.1 kg-N ha^-1 yr^-1 critical load to protect N-sensitive lichen species richness in every part 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, Black Canyon of the Gunnison National Park contains:

• 3 N-sensitive tree species and 19 N-sensitive herbaceous species.
• 6 S-sensitive tree species and 16 S-sensitive herbaceous species.

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 BLCA 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 decreased from 1.8 to 1.6 kg-N ha^-1 yr^-1 and maximum N deposition increased from 2.7 to 3.0 kg-N ha^-1 yr^-1.
• Minimum S deposition decreased from 0.6 to 0.3 kg-S ha^-1 yr^-1 and maximum S deposition decreased from 0.8 to 0.4 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 BLCA. 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.

The NPS Air Resources Division reports on park conditions and trends for mercury. Visit the webpage to learn more. Fish consumption advisories may be in effect for mercury and other contaminants (NPS 2022).

Visibility

Clean, clear air is essential to appreciating the scenic vistas at Black Canyon of the Gunnison NP.

Visitors come to Black Canyon of the Gunnison NP, a high desert on the Colorado Plateau, to enjoy scenic views of the deep, steep, and narrow canyon carved by the Gunnison River. 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 visibility have been documented since the 1990’s. Overall, visibility still needs improvement to reach the Clean Air Act goal of no human caused impairment.

In the region, average natural visual range is reduced from about 175 miles (without the effects of pollution) to about 140 miles because of pollution. The visual range is reduced to below 95 miles on high pollution days.

Visit the NPS air quality conditions and trends website for park-specific visibility information. Visibility monitoring at Weminuche Wilderness has been active since 1988, and these data are considered representative of regional visibility conditions for Black Canyon of the Gunnison NP. Explore park vistas through live webcams.

Ground-Level Ozone

Ponderosa Pine trees are one of the ozone sensitive species found at Black Canyon of the Gunnison 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. A risk assessment that considered ozone exposure, soil moisture, and sensitive plant species concluded that plants in Black Canyon of the Gunnison NP were at low risk of ozone injury (Kohut 2007; Kohut 2004). However, estimated ozone concentrations and cumulative doses at the park are high enough to damage the leaves of sensitive vegetation under certain conditions. The park’s semi-arid conditions cause stomates on plant leaves to close, limiting ozone uptake. At the nearby Rocky Mountain National Park in Colorado, scientists found that in moist areas along streams and seeps, plants may keep stomates open more often, allowing ozone uptake and injury (Kohut et al. 2012). Some plants are more sensitive to ozone than others. Ozone sensitive plants at the park include Amelanchier alnifolia (Saskatoon serviceberry), Populus tremuloides (quaking aspen), and Pinus ponderosa (ponderosa pine) (Binkley et al 1997). Search for more ozone-sensitive plant species found at Black Canyon of the Gunnison NP.

Visit the NPS air quality conditions and trends website for park-specific ozone information.

Explore Other Park Air Profiles

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

References

Allen, E. B., L. E. Rao, R. J. Steers, A. Bytnerowicz, and M. E. Fenn. 2009. Impacts of atmospheric nitrogen deposition on vegetation and soils in Joshua Tree National Park. Pages 78–100 in R. H. Webb, L. F. Fenstermaker, J. S. Heaton, D. L. Hughson, E. V. McDonald, and D. M. Miller, editors. The Mojave Desert: ecosystem processes and sustainability. University of Nevada Press, Las Vegas, Nevada, USA.

Binkley et al. 1997. Status of Air Quality and Related Values in Class I National Parks and Monuments of the Colorado Plateau. Chapter 5. Black Canyon of the Gunnison National Park. National Park Service, Air Resources Division, Denver, CO. Available at https://irma.nps.gov/DataStore/Reference/Profile/167034.

Brooks, M.L. 2003. Effects of increased soil nitrogen on the dominance of alien annual plants in the Mojave Desert. Journal of Applied Ecology. 40:344–353.

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

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.

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

Inouye, R.S. 2006. Effects of shrub removal and nitrogen addition on soil moisture in sagebrush steppe. Journal of Arid Environments. 65: 604–618.

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 https://www.nps.gov/articles/ozone-risk-assessment.htm.

Kohut, B. 2004. Assessing the Risk of Foliar Injury from Ozone on Vegetation in Parks in the Northern Colorado Plateau Network. Available at https://irma.nps.gov/DataStore/Reference/Profile/2181489.

Kohut, B., C. Flanagan, E. Porter, J. Cheatham. 2012. Foliar Ozone Injury on Cutleaf Coneflower at Rocky Mountain National Park, Utah. Western North American Naturalist 72(1): 32–42.

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/

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

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

Schwinning, S., B. I. Starr, N. J. Wojcik, M. E. Miller, J. E. Ehleringer, R. L. Sanford. 2005. Effects of nitrogen deposition on an arid grassland in the Colorado plateau cold desert. Rangeland Ecology and Management. 58: 565–574.

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.