Park Air Profiles - Carlsbad Caverns National Park

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.

Nitrogen and Sulfur

Visitors come to Carlsbad Caverns National Park to enjoy scenic views of numerous caves and the Chihuahuan desert landscape.

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 Carlsbad Caverns National Park (CAVE) relative to other national parks is very 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 CAVE relative to other national parks is very high (Sullivan et al. 2016); to search for acid-sensitive plant species, see: NPSpecies.

From 2017-2019 total N deposition in CAVE ranged from 3.6 to 4.0 kg-N ha^-1 yr^-1 and total S deposition ranged from 1.2 to 1.4 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 CAVE.

Arid ecosystems and grasslands have shown variable responses to excess N. About a third of CAVE is covered in grasslands. Increases in N 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). N may also increase water use in plants like big sagebrush (Inouye 2006).

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 21.8 km² (11.5%) of the land area of Carlsbad Caverns National Park.

• N deposition exceeded the 3.1 kg-N ha^-1 yr^-1 critical load to protect N-sensitive lichen species richness in 100% 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, Carlsbad Caverns National Park contains:

• 4 N-sensitive tree species and 14 N-sensitive herbaceous species.
• 5 S-sensitive tree species and 10 S-sensitive herbaceous species.

Mycorrhizal fungi community response

Many plants have a symbiotic relationship with mycorrhizal fungi (MF). Through the roots, the plants supply the fungi with carbon from photosynthesis and in exchange the MF enhance nutrient availability within soils, increase drought tolerance, and provide physical resistance to soil erosion (George et al., 1995; Cheng et al., 2021; Burri et al., 2013). Anthropogenic Nitrogen (N) deposition can disrupt this symbiotic relationship resulting in a shift from N sensitive to N tolerant mycorrhizal fungi and plant communities.

With increased N deposition to the soil, MF become less important for nutrient uptake and many plants will cease the exchange of nutrients altogether making them more vulnerable to stressors such as drought (Lilleskov et al., 2019). The CL-N for the shift in mycorrhizal community is 5-6 kg-N ha^-1 yr^-1 in coniferous forests and 10-20 kg-N ha^-1 yr^-1 broadleaf forests. Carlsbad Caverns National Park has 48 km² of coniferous forests. Using the range in critical loads above, the minimum CL is exceeded in 0% of forested area and the maximum CL is exceeded in 0% of forested area based on 2019-2021 TDep Total N deposition.

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 CAVE 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 remained at 2.4 kg-N ha^-1 yr^-1 and maximum N deposition decreased from 3.3 to 2.8 kg-N ha^-1 yr^-1.
• Minimum S deposition decreased from 1.4 to 0.9 kg-S ha^-1 yr^-1 and maximum S deposition decreased from 2.0 to 1.0 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 CAVE. 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.

• Bats – the most famous mammal at Carlsbad Caverns NP – may be vulnerable to toxic accumulation given their large 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. Other contaminants like mercury in bats may also decrease immune function and increase susceptibility to diseases like White Nose Fungus (Kurunthachalam et al. 2010).
• Dragonfly larvae sampled at Carlsbad Caverns NP had mercury concentrations at sub-impairment or low impairment levels. Dragonfly larvae have been sampled and analyzed for mercury from two sites in the park. No data from the park fall in the moderate or higher (>100 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. 2018; Eagles-Smith et al. 2020). However, the data may not reflect the risk at other unsampled locations in the park.
• Emissions from power plants and oil and gas development are likely the biggest influences on air quality around Carlsbad Caverns NP. While local sources are important, mercury also travels via regional and global pathways, namely gold mining operations (Struthers et al. 2022).

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 Carlsbad Caverns NP.

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.

Ground-Level Ozone

White sagebrush is one of the ozone sensitive species found at 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 grow and store carbon. Ozone causes leaf injuries like bleaching or dark spots on some sensitive plants. An ozone risk assessment concluded that plants in Carlsbad Caverns are at low risk of foliar ozone injury as dry conditions during peak ozone concentrations are likely to limit ozone uptake by plants (Kohut 2007; Kohut 2004). However, plants growing in moist areas along streams and seeps can have higher ozone uptake and higher risk of leaf injury (Kohut et al. 2012). There are four plants that may display ozone leaf injury at Carlsbad Caverns National Park. Search ozone-sensitive plant species found at Carlsbad Caverns National Park.

US Environmental Protection Agency and NPS found in ozone exposure experiments that ozone slowed tree seedling growth. NPS uses W126 values from averaged seedling responses in those experiments to describe park condition in terms of Vegetation Health. Ozone affects actively growing plants, so the W126 metric weights a sum of ozone concentrations during daylight hours over three months in the growing season.

A recent re-analysis of the seedling experiments established critical levels of ozone protective of each tree species tested (Lee et al. 2022). The ozone critical levels are W126 values that will prevent 5% or greater deficit in tree seedling biomass. Air Quality Conditions and Trends reports a 5-year average of W126 for each park. In 2018-2022, the average W126 value for Capitol Reef National Park was 18 ppm-h. Based on this ozone level, trees present in the park (NPSpecies) are at risk of the following ozone effects:

• The tree species black cherry (Prunus serotina), with an ozone critical level of 2.5 ppm-h, is at risk of 31% biomass deficit in seedlings. The tree species winged sumac (Rhus copallinum), with an ozone critical level of 8.5 ppm-h, is at risk of 23% biomass deficit in seedlings. The tree species ponderosa pine (Pinus ponderosa), with an ozone critical level of 6 ppm-h, is at risk of 13% biomass deficit in seedlings. Recent ozone levels in the park exceed critical levels that protect these species.

• Tree species Douglas-fir (Pseudotsuga menziesii) is at low risk from ozone despite its known sensitivity. Recent ozone levels in the park are below critical levels that protect these trees from 5% biomass deficit.

Ozone critical levels are for tree seedlings, which represent the regenerative capacity and long-term stability of sensitive species within a forest. These tree species are also known to be sensitive to ozone as adults (Bell et al. 2020), but critical values for seedling growth do not predict ozone effects on mature trees. Air Resources Division is currently working with collaborators to establish critical levels for mature trees using data from forest monitoring plots.

Visit the NPS air quality conditions and trends website for park-specific ozone information. Carlsbad Caverns NP has been monitoring ozone since 2006. View live ozone and meteorology data.

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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.

Bell MD, Felker-Quinn E, Kohut R. 2020. Ozone sensitive plant species on National Park Service lands. Natural Resource Report. NPS/WASO/NRR—2020/2062. National Park Service. Fort Collins, Colorado. https://irma.nps.gov/DataStore/Reference/Profile/2271702

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.

Burri, K., C. Gromke, and F. Graf. "Mycorrhizal fungi protect the soil from wind erosion: a wind tunnel study." Land Degradation & Development 24.4 (2013): 385-392.

Cheng, Shen, et al. "Elucidating the mechanisms underlying enhanced drought tolerance in plants mediated by arbuscular mycorrhizal fungi." Frontiers in Microbiology 12 (2021): 809473.

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

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. https://doi.org/10.1007/s002440010207

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., 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

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.

George, Eckhard, Horst Marschner, and Iver Jakobsen. "Role of arbuscular mycorrhizal fungi in uptake of phosphorus and nitrogen from soil." Critical reviews in biotechnology 15.3-4 (1995): 257-270.

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 Sonoran Desert Network. Available at https://irma.nps.gov/DataStore/Reference/Profile/2181558

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. https://irma.nps.gov/DataStore/Reference/Profile/2187617

Krabbenhoft, D. P. Modeling Surface-Water Methylmercury in National Parks. In Review.

Kurunthachalam Kannan, Se Hun Yun, Robert J. Rudd, and Melissa Behr. 2010.High concentrations of persistent organic pollutants including PCBs, DDT, PBDEs and PFOS in little brown bats with white-nose syndrome in New York, USA. Chemosphere 80(6):613-618.https://doi.org/10.1016/j.chemosphere.2010.04.060

Lee EH, Anderson CP, Beedlow PA, Tingey DT, Koike S, Dubois J, Kaylor SD, Novak K, Rice RB, Neufeld HS, Herrick JD. 2022. Ozone Exposure-Response Relationships Parametrized for Sixteen Tree Species with Varying Sensitivity in the United States. Atmospheric Environment. 284:1-16. https://irma.nps.gov/DataStore/Reference/Profile/2294221

Lilleskov, Erik A., et al. "Atmospheric nitrogen deposition impacts on the structure and function of forest mycorrhizal communities: a review." Environmental Pollution 246 (2019): 148-162.

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.

[NADP] National Atmospheric Deposition Program. 2018. NTN Data. Accessed January 20, 2022. Available at http://nadp.slh.wisc.edu/NADP/

Natural Resource Report NPS/NRSS/ARD/NRR—2021/2299. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/nrr-2287254

[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. Available at 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.

Struthers, K., L. Baril, and M. Brunson. 2022. Natural resource conditions at Capitol Reef National Park: Findings & management considerations for selected resources. Natural Resource Report NPS/NCPN/NRR—2022/2406. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/nrr-2293700

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.