- Air quality at Carlsbad Caverns National Park
- Related references
Air quality at Carlsbad Caverns National Park
Most visitors expect clean air and clear views in parks. Carlsbad Caverns National Park (NP), New Mexico, is a wonder of canyons, shrublands, and more than 100 caves beneath the surface. Although the park is rural and surrounded by the Chihuahuan Desert, there are some nearby and regional sources of air pollution, including oil and gas operations, mineral extraction and processing, agricultural activities, refineries, and power plants. 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 Carlsbad Caverns NP, and in parks across the U.S., through science, policy and planning, and by doing our part.
Many visitors come to Carlsbad Caverns NP to experience the large cave chambers deep underground, and to enjoy panoramic vistas of the Guadalupe Mountains as well as one of the few protected portions of the northern Chihuahuan Desert ecosystem. 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 improvement in visibility on the clearest days has been documented since the late 1980’s. Still, regional visibility has not improved significantly on the haziest days and is a long way from the Clean Air Act goal of no human caused impairment.Visibility effects:
- Reduced visibility, at times, due to human-caused haze and fine particles of air pollution, including dust
- Reduction of the average natural visual range from about 175 miles (without pollution) to about 90 miles because of pollution
- Reduction of the visual range to below 55 miles on high pollution days
Visit the NPS air quality conditions and trends website for park-specific visibility information. The NPS has been monitoring visibility at Guadalupe Mountains NP, Texas since 2000 these data are considered representative of regional visibility conditions for Carlsbad Caverns 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. Some plants are more sensitive to ozone than others. There are a few ozone-sensitive plants in Carlsbad Caverns NP including Rhus trilobata (skunkbush), Artemisia ludoviciana (white sagebrush), and Pinus ponderosa (ponderosa pine). A risk assessment that considered ozone exposure, soil moisture, and sensitive plant species concluded that plants in Carlsbad Caverns NP were at low risk of damage to plant leaves (see network report: Kohut 2004). Generally, dry conditions in the park during peak ozone concentrations are likely to limit ozone uptake by plants. However along springs and seeps, where conditions are wetter, plants may have higher ozone uptake and injury (Kohut et al. 2012). Search ozone-sensitive plant species found at Carlsbad Caverns NP.
Visit the NPS air quality conditions and trends website for park-specific ozone information. Carlsbad Caverns NP has been monitoring ozone since 2006. Check out the live ozone and meteorology data from Carlsbad Caverns NP and explore air monitoring »
Nitrogen and sulfur
Nitrogen and sulfur compounds deposited from the air may have harmful effects. Excess nitrogen can lead to nutrient enrichment, a process that changes nutrient cycling and alters plant communities. Ecosystem sensitivity to nutrient enrichment at Carlsbad Caverns NP relative to other national parks is very high (Sullivan et al. 2011a; Sullivan et al. 2011b). Healthy ecosystems can naturally buffer a certain amount of pollution, but as nitrogen and sulfur accumulate, a threshold is passed where the ecosystem is harmed. “Critical load” is a term used to describe the amount of pollution above which harmful changes in sensitive ecosystems occur (Porter 2005). Nitrogen deposition exceeds the critical load for one or more park ecosystems (NPS ARD 2018).
Arid ecosystems and grasslands are particularly vulnerable to changes caused by nitrogen deposition. About a third of the park is covered in grasslands. Increases in nitrogen have been found to promote invasions of fast-growing exotic annual grasses and forbs (e.g., Russian thistle) at the expense of native species (Brooks 2003; Allen et al. 2009; Schwinning et al. 2005). Fire is a natural component of the northern Chihuahuan Desert (Gebow and Halvoson 2004), but exotic grasses can increase fire risk (Rao et al. 2010) and affect plant biodiversity. Nitrogen may also increase water use in plants like big sagebrush (Inouye 2006).
Nitrogen, together with sulfur, can also acidify surface waters and soils. Given the abundance of base cations in underlying park soils and rocks, surface waters in Carlsbad Caverns NP are generally well-buffered from acidification. Some plants are sensitive to acidification, search for acid-sensitive plant species found at Carlsbad Caverns NP.
Visit the NPS air quality conditions and trends website for park-specific nitrogen and sulfur deposition information.
Mercury and toxics
Airborne mercury, and other toxic air contaminants, when deposited are known to harm birds, salamanders, fish and other wildlife, and cause human health concerns. These substances enter the food chain and accumulate in the tissue of organisms causing reduced reproductive success, impaired growth and development, and decreased survival.
Bats – the most famous mammal at Carlsbad Caverns NP – may be vulnerable to toxic accumulation given their voracious appetite for insects. Findings from Clark (2001) indicate that DDT played a major role in the severe population decline of Brazilian (Mexican) Free-tailed Bats at Carlsbad Caverns since 1936. Furthermore, a mercury risk assessment based on water chemistry and physical parameters rated the potential for methylmercury production in the park very high compared to other NPS units (Krabbenhoft, In Review).
Allen, E. B. and L. H. Geiser. 2011. North American Deserts. In L.H. Pardo, M.J. Robin-Abbott and C.T. Driscoll (Eds.). Assessment of Nitrogen Deposition Effects and Empirical Critical Loads of Nitrogen for Ecoregions of the United States. General Technical Report NRS–80. U.S. Forest Service, Newtown Square, PA. pp. 133–142. Available at: http://nrs.fs.fed.us/pubs/38109.
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.
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, D.R., Jr. 2001. DDT and the decline of free-tailed bats (Tadarida brasiliensis) at Carlsbad Cavern, New Mexico. Arch Environ Contam Toxicol 40(4):537–543.
Gebow, B. S., and W. L. Halvoson. 2004. Managing Fire in the Northern Chihuahuan Desert: A Review and Analysis of the Literature. USGS Open-File Report SBSC-SDRS–2004–1001. U.S. Geological Survey, Southwest Biological Science Center, Sonoran Desert Research Station, University of Arizona, Tucson, AZ. Available at https://pubs.usgs.gov/of/2005/1157/
Inouye, R.S. 2006. Effects of shrub removal and nitrogen addition on soil moisture in sagebrush steppe. Journal of Arid Environments. 65: 604–618.
Krabbenhoft, D. P. Modeling Surface-Water Methylmercury in National Parks. In Review.
Kohut, B. 2004. Assessing the Risk of Foliar Injury from Ozone on Vegetation in Parks in the Sonoran Desert Network. Available at https://irma.nps.gov/DataStore/Reference/Profile/2181558
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., 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.
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. Available at https://doi.org/10.1641/0006-3568(2005)055[0603:PROFLI]2.0.CO;2.
Rao, L. E., E. B. Allen, and T. Meixner. 2010. Risk-based determination of critical nitrogen deposition loads for fire spread in southern California deserts. Ecological Applications 20: 1320–1335.
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., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011a. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/313. National Park Service, Denver, Colorado. Available at https://www.nps.gov/articles/nitrogen-risk-assessment.htm.
Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011b. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: Chihuahuan Desert Network (CHDN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/313. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2168613.
Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011c. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/349. National Park Service, Denver, Colorado. Available at https://www.nps.gov/articles/acidification-risk-assessment.htm.
Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011d. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: Chihuahuan Desert Network (CHDN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/349. National Park Service, Denver, Colorado. Available at https://www.nps.gov/articles/acidification-risk-assessment.htm.
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, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2170574.