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Air Pollution Impacts

Bryce Canyon National Park

Natural and scenic resources in Bryce Canyon National Park (NP) are susceptible to the harmful effects of air pollution. Nitrogen, sulfur, ozone, and fine particles impact natural resources such as surface waters and vegetation, and scenic resources such as visibility. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at Bryce Canyon NP.

  • Visibility
  • Nitrogen & Sulfur
  • Ozone

Visitors come to Bryce Canyon NP to experience the “hoodoo-iferous” terrain of the Bryce Amphitheater against the Paunsaugunt Plateau, blanketed with forests and meadows, and the spectacular nighttime sky. Park staff members lead world-class interpretive programs on geology, astronomy, and climate for visitors. Unfortunately, park vistas are sometimes obscured by haze caused by fine particles in the air. Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition contribute to this haze and visibility impairment. Additionally, organic compounds, soot, dust, and fires reduce visibility.

Visibility effects at Bryce Canyon NP include:

  • Reduced visibility, at times, due to human-caused haze from fine particles of air pollution;
  • Reduction of the average natural visual range from about 170 miles (without pollution) to about 130 miles because of pollution at the park;
  • Reduction of the visual range to below 85 miles on high pollution days.

(Source: IMPROVE 2013)

Images of good and poor visibility at Bryce Canyon National Park, Utah
Air pollutants can affect visibility at Bryce Canyon NP, Utah (clear to hazy from left to right)

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***Need BRCA vegetation photo***
Excess nitrogen inputs can promote the growth and spread of invasive, exotic plants such as cheatgrass – pictured here at Bryce Canyon NP – where it often dominates disturbed grasslands and displaces native plants.

Nitrogen (N) and sulfur (S) compounds deposited from air pollution can harm vegetation, soils, and surface waters throughout Bryce Canyon NP. Ammonium, a species of N that often indicates nearby agricultural sources, has been increasing in wet deposition at the park (Lehmann et al. 2007). Nitrogen acts as a fertilizer; disrupting soil nutrient cycling, altering plant communities, and contributing to overenrichment and eutrophication in surface waters. Ecosystem sensitivity to nutrient N enrichment at Bryce Canyon NP relative to other national parks is moderate (Binkley et al. 1997 [pdf, 839 KB]; Sullivan et al. 2011a; Sullivan et al. 2011b [pdf, 7.71 MB]). Arid ecosystems are particularly vulnerable to changes caused by nitrogen deposition. Invasive grasses tend to thrive in areas with high nitrogen deposition, displacing native vegetation adapted to low nitrogen conditions. Increases in N have been found to promote invasions of fast-growing exotic annual grasses (e.g., cheatgrass) and forbs (e.g., Russian thistle) at the expense of native species (Brooks 2003; Allen et al. 2009; Schwinning et al. 2005). Increased cover of exotic grasses can increase fire risk (Rao et al. 2010). N may also increase water use in plants like big sagebrush (Inouye 2006).

N, together with S, can also acidify surface waters and soils. Given the abundance of base cations in underlying park soils and rocks, surface waters in Bryce Canyon NP are generally well-buffered from acidification. However, the park’s seeps and springs may be sensitive to incoming acid inputs. Additionally, small streams with steep-sided canyon walls in the park have little ability to retain nutrients and water, offering the landscape little opportunity to buffer potentially acidic run-off. The ecosystem sensitivity to acidification from N and S at Bryce Canyon NP relative to other national parks is also moderate (Sullivan et al. 2011c; Sullivan et al. 2011d [pdf, 2.4 MB]).

How much nitrogen is too much?

Nitrogen (N) is a fertilizer and some N is necessary for plants to grow. However, in natural ecosystems, too much N disrupts the balance of communities, allowing weedy plants to thrive. Studies are now underway to estimate the “critical load” of N for plant communities in the park. A critical load is the level of deposition below which harmful effects to an ecosystem are not expected. Critical loads for certain ecoregions in the U.S. - including the North American Desert Ecoregion and the Northwestern Forested Mountains Ecoregion, both present at Bryce Canyon NP - are available. A critical load of 3 –8.4 kilograms N per hectare per year (kg N/ha/yr) has been suggested to protect shrublands and grasslands in the North American Desert Ecoregion (Allen and Geiser 2011), and a critical load of 4–10 kg/ha/yr has been suggested to protect shrublands and grasslands in the Northwestern Forested Mountains Ecoregion (Bowman et al. 2011). To maintain the highest level of protection in the park, the lower end of the ranges would be an appropriate management goal. Other critical loads for lichens and forest health are available (Pardo et al. 2011). Total N deposition at Bryce Canyon NP is currently 2–5 kg/ha/yr, suggesting that native plant communities are at elevated risk for harmful effects.

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Photograph of healthy Ponderosa Pine needles.
Elevated ground-level ozone concentrations can potentially affect ozone-sensitive plants, such as quaking aspen, along riparian zones at Bryce Canyon NP, Utah.

Naturally-occurring ozone in the upper atmosphere absorbs the sun‘s harmful ultraviolet rays and helps to protect all life on earth. However, in the lower atmosphere, ozone is an air pollutant, forming when nitrogen oxides from vehicles, power plants, and other sources combine with volatile organic compounds from gasoline, solvents, and vegetation in the presence of sunlight. In addition to causing respiratory problems in people, ozone can injure plants. Ozone enters leaves through pores (stomata), where it can kill plant tissues, causing visible injury, or reduce photosynthesis, growth, and reproduction.

A risk assessment that considered ozone exposure, soil moisture, and sensitive plant species concluded that plants in Bryce Canyon NP were at low risk of foliar ozone injury (Kohut 2004 [pdf, 220 KB]). However, estimated ozone concentrations and cumulative doses at the park are high enough to induce foliar injury to sensitive vegetation under certain conditions. The park‘s often arid conditions cause plant stomates to close, limiting ozone uptake. However, scientists found that in moist areas along streams and seeps in the Intermountain West, plants may keep stomates open more often, allowing ozone uptake and subsequent injury (Kohut et al. 2012). Ozone sensitive plants at the park include Apocynum androsaemifolium (spreading dogbane), Populus tremuloides (quaking aspen), and  Amelanchier alnifolia ( Saskatoon serviceberry). Additional research specific to the park’s riparian bioindicators (e.g., A. alnifolia, P. tremuloides) may be warranted. Past surveys at the park located probable ozone injury on Sambucus caerulea (blue elderberry) (NPS 2000).

Search the list of ozone-sensitive plant species (pdf, 184 KB) found at each national park.

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Studies and Monitoring icon

Studies and monitoring help the NPS understand the environmental impacts of air pollution. Access air quality data and see what is happening with Studies and Monitoring at Bryce Canyon NP.

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Last Updated: December 30, 2016