Air Quality at Capitol Reef National Park
Most visitors expect clean air and clear views in parks. Located in the heart of Utah’s red rock country, Capitol Reef National Park (NP) is filled with cliffs, canyons, domes, and bridges. The park enjoys relatively good air quality, but upwind emissions from disturbed drylands, urban areas, and industrial sources can degrade air quality. 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 Capitol Reef NP, and in parks across the U.S., through science, policy and planning, and by doing our part.
Nitrogen and Sulfur
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 Capitol Reef National Park (CARE) 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 CARE 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 CARE ranged from 2.1 to 3.3 kg-N ha-1 yr-1 and total S deposition ranged from 0.5 to 0.9 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 CARE.
Arid ecosystems have shown variable responses to excess N. 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). In contrast, a recent study showed little vegetation response to fertilization, but did see a decline in the stability of the soil crust community (Phillips et al. 2021). N may also increase water use in plants like big sagebrush (Inouye 2006).
Given the abundance of base cations in park soils and rocks, surface waters at CARE are generally well-buffered from acidification (Binkley et al. 1997).
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 88 km2 (8.9%) of the land area of Capitol Reef National Park.
- N deposition exceeded the 3.1 kg-N ha-1 yr-1 critical load to protect N-sensitive lichen species richness in 17.3% 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, Capitol Reef National Park contains:
- 10 N-sensitive tree species and 21 N-sensitive herbaceous species.
- 16 S-sensitive tree species and 18 S-sensitive herbaceous species.
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 some fish sampled at Capitol Reef NP exceeded the thresholds for fish toxicity and bird toxicity. Prey fish were sampled and analyzed for mercury from three sites at the park and compared to data across 21 western parks. The average fish mercury concentration (325.6 ng/g ww) was higher than the study-wide mean (77.7 ng/g ww). Mercury concentrations exceeded the thresholds for fish toxicity and bird toxicity in 49% and 98% of fish sampled, respectively (Eagles-Smith et al. 2014). The data may not reflect the risk at other locations in the park.
- Some dragonfly larvae sampled at Capitol Reef NP had mercury concentrations at moderate or higher impairment levels. Dragonfly larvae have been sampled and analyzed for mercury from three sites in the park; 33% of the data fall into the moderate (100-300 ng/g dw) and 66% fall into the high/severe (>300 ng/g dw) impairment categories for potential mercury risk. An index of moderate impairment or higher suggests some fish may exceed the US EPA benchmark for protection of human health (Eagles-Smith et al. 2020, Eagles-Smith et al. 2018).
Visitors come to Capitol Reef NP to view the area’s remarkable geology, including a dramatic monocline, large number of arches and natural bridges, high-walled canyons, and large rock domes. 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 2000’s. Overall, visibility in the park still needs improvement to reach the Clean Air Act goal of no human caused impairment.
- Reduced visibility, at times, due to human-caused haze from fine particles of air pollution
- Reduction of the average natural visual range from about 175 miles (without pollution) to about 130 miles because of pollution at the park
- Reduction of the visual range to below 90 miles on high pollution days
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. An ozone risk assessment concluded that plants in Capitol Reef NP were at low risk of ozone injury (Kohut 2004). However, estimated ozone concentrations and cumulative doses at the park may be high enough to damage the leaves of sensitive vegetation under certain conditions (NPS 2012). Generally, dry conditions in the park during peak ozone concentrations are likely to limit ozone uptake by plants. However along streams and seeps, where conditions are wetter, plants may have higher ozone uptake and injury (Kohut et al. 2012). Some plants are more sensitive to ozone than others. Ozone sensitive plants in Capitol Reef NP include Amelanchier alnifolia (serviceberry), Populus tremuloides (quaking aspen), and Salix gooddingii (Goodding’s willow). Search for additional ozone-sensitive plant species found at Capitol Reef NP.
Visit the NPS air quality conditions and trends website for park-specific ozone information.
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 8. Capitol Reef 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
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
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., Willacker, J.J., and Flanagan Pritz, C.M., 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. http://dx.doi.org/10.3133/ofr20141051.
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, 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, Colorado. 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.
Phillips, M. L., D. E. Winkler, R. H. Reibold, B. B. Osborne, and S. C. Reed. 2021. Muted responses to chronic experimental nitrogen deposition on the Colorado Plateau. Oecologia 195:513-524.
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.