Air Pollution Impacts

Nitrogen and sulfur compounds deposited from air pollution can harm surface waters, soils, and vegetation. In some ecosystems, nutrient effects from nitrogen deposition can cause changes to soil nutrient cycling and the species composition of plant communities. Nitrogen and sulfur deposition can also cause acidification of soils, streams, and springs. There are significant point sources of airborne nitrogen and sulfur located near Mesa Verde NP. Soils and streams are generally well-buffered and unlikely to be acidified by atmospheric deposition (Binkley et al. 1997 [pdf, 592 KB]).

However, arid shrublands in the park are particularly vulnerable to changes caused by nitrogen (N) deposition (Sullivan et al. 2011a; Sullivan et al. 2011b [pdf, 7.4 MB]). N deposition may disrupt soil nutrient cycling and alter plant communities. Invasive grasses thrive in areas with high N deposition, displacing native vegetation adapted to low N conditions. The fire risk subsequently increases due to extensive areas of weedy grasses (Fenn et al. 2003).

Wildfires in or near Mesa Verde NP also contribute increased nitrogen to park ecosystems by re-emitting formerly deposited nitrogen from power plants and other sources. Weed density at Mesa Verde NP increases in post-fire environments that tend to support higher soil nitrogen levels (Floyd-Hanna et al. 2004).

Concentrations of ammonium in wet deposition from regional agricultural sources are elevated and increasing in the park, and nitrate concentrations in wet deposition are among the highest of all national parks measured (NPS 2010 [pdf, 2.8 MB]), a finding likely associated with nearby power plants.

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Toxics, including heavy metals like mercury, accumulate in the tissue of organisms. When mercury converts to methylmercury in the environment and enters the food chain, effects can include reduced reproductive success, impaired growth and development, and decreased survival. Other toxic air contaminants of concern include pesticides, industrial by-products, and emerging chemicals such as flame retardants for fabrics, some of which are known or suspected to cause cancer or other serious health effects in humans and wildlife.

While mercury in wet deposition at Mesa Verde NP is among the highest of western U.S. sites (NADP 2010), a pilot study at the park did not find elevated mercury levels in songbirds, invertebrates, stream fish, or crayfish (Nydick and Williams 2010). Sample sizes were very small, however, and the study did not preclude the possibility of mercury accumulation in park wildlife. Mercury levels in fish from other parts of the region exceed wildlife and human health consumption thresholds (Peterson et al. 2007; CDPHE 2009), and a nearby high elevation site indicates elevated levels of mercury in lake sediments and zooplankton (Nydick 2010).

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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.

Ozone concentrations have increased significantly at Mesa Verde NP since monitoring began in 1994 (NPS 2010 [pdf, 2.8 MB]), and there are a few ozone-sensitive plant species in Mesa Verde NP including Populus tremuloides (quaking aspen), Apocynum androsaemifolium (spreading dogbane), and Rhus trilobata (skunkbush). The risk of injury to plants is generally low in the park (Kohut 2004 [pdf, 254 KB]) partly because in arid areas plants close their stomata to limit moisture loss, which also limits ozone uptake by the plant. No signs of ozone foliar injury have been reported for vegetation in or near to the park (Binkley et al. 1997 [pdf, 592 KB]; Nydick 2009 [pdf, 2.4 MB]).

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

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Visitors come to Mesa Verde NP to enjoy a spectacular look into the lives of the park’s early inhabitants, the Ancestral Puebloans who made it their home from A.D. 600 to A.D. 1300. 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, and dust reduce visibility. Smoke from forest fires sometimes contributes significantly to haze in the region.

Unimpaired visibility has special importance at Mesa Verde from an historical context. The Ancestral Puebloans were highly dependent on visual contact for long-distance communication. Thus, preserving visibility is an important means of enhancing visitor understanding of this culture. A more thorough appreciation of the prehistoric landscape at Mesa Verde NP is more attainable when park visitors immerse themselves in it. Regional haze forms a barrier to that experience.

Visibility effects at Mesa Verde NP include:

• Reduced visibility sometimes due to human-caused haze and fine particles of air pollution, including dust;
• Reduction of the average natural visual range from about 170 miles (without the effects of pollution) to about 100 miles because of pollution at the park;
• Reduction of the visual range to below 60 miles on high pollution days.

(Source: IMPROVE 2010)

Explore scenic vistas through a dust monitoring webcam at Mesa Verde National Park.

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