Series: Park Air Profiles

Park Air Profiles - Mammoth Cave National Park

Mammoth Dome in Mammoth Cave NP
Visitors come to Mammoth Cave NP to enjoy scenic views of the Green River Valley and the world's longest cave system.

Air quality at Mammoth Cave National Park

Most visitors expect clean air and clear views in parks. However, Mammoth Cave National Park (NP), Kentucky, home to the world’s longest recorded cave system and scenic river valleys, experiences relatively poor air quality. The park is downwind of many sources of air pollution, including power plants, urban areas, and industry in Kentucky and Tennessee. Pollutants emitted from these sources can harm the park’s natural and scenic resources such as upland surface waters, plants, fish, bats, and visibility. The National Park Service works to address air pollution effects at Mammoth Cave NP, and in parks across the U.S., through science, policy and planning, and by doing our part.

Visibility

Green River in Mammoth Cave NP Clean, clear air is essential to appreciating the scenic vistas at Mammoth Cave NP.

Visitors come to Mammoth Cave NP not only to explore the vast and complex underground labyrinths, but also to enjoy vistas of the Green River valley and hill country of South Central Kentucky. Unfortunately, these scenic views are often affected by haze that reduces 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, and dust reduce visibility as well. Significant improvements in park visibility have been documented since the 1990’s. Still, visibility in the park is a long way from the Clean Air Act goal of no human caused impairment.

Visibility effects:
  • Reduced visibility due to human-caused haze
  • Reduction of the average natural visual range from about 110 miles (without the effects of pollution) to about 50 miles because of pollution at the park
  • Reduction of the visual range to below 25 miles on high pollution days

Visit the NPS air quality conditions and trends website for park-specific visibility information. Mammoth Cave NP has been monitoring visibility since 2000. Check out the live air quality webcam and explore air monitoring »

Ground-level ozone

Milkweed is one of the ozone sensitive species found at Great Smoky Mountains NP. Milkweed is one of the ozone sensitive species found at Mammoth Cave 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.

Ozone levels in the park have come down significantly over the past 10 years but still occasionally exceed the National Ambient Air Quality Standard set by the U.S. Environmental Protection Agency to protect public health. Ozone is a respiratory irritant, causing coughing, sinus inflammation, chest pains, scratchy throat, lung damage, and reduced immune system functions. Children, the elderly, people with existing health problems, and active adults are most vulnerable. When ozone levels exceed, or are predicted to exceed, health standards, Mammoth Cave NP staff post health advisories cautioning visitors of the potential health risks associated with exposures to elevated levels.

Ground-level ozone also weakens plants making them less resistant to disease and insect infestations. There are several ozone-sensitive plants in Mammoth Cave NP including Asclepias syriaca (common milkweed), Liquidambar styraciflua (sweetgum), and Liriodendron tulipifera (tulip poplar). A risk assessment concluded that plants in at Mammoth Cave NP were at high risk for ozone damage (Kohut 2007; Kohut 2004). Assessments in the park have also documented visible ozone injury on the leaves of approximately 25% of Common milkweed plants surveyed (CUPN 2010). Sweetgum and Tulip poplar have also shown ozone damage on leaves. Search ozone-sensitive plant species found at Mammoth Cave NP.

Visit the NPS air quality conditions and trends website for park-specific ozone information. Mammoth Cave NP has been monitoring ozone since 1997. Check out the live ozone and meteorology data from Mammoth Cave, NP and explore air monitoring »

Nitrogen and sulfur

Nitrogen and sulfur compounds deposited from the air may have harmful effects, including acidification, on soils, lakes, ponds, and streams. Seeps and surface waters that flow from limestone bedrock in the park are well-buffered from acidification effects. Some soils, sandstone ridges, and dry upland areas may be more sensitive to acid deposition. There is a particular concern that during rainstorms, when there is little opportunity for rainwater to come into contact with deep soils, episodic acidification could occur. Some plants are sensitive to acidification, search for acid-sensitive plant species found at Mammoth Cave NP.

Excess nitrogen can also lead to nutrient enrichment, a process that changes nutrient cycling and alters plant communities. 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). Mammoth Cave NP receives high levels of nitrogen deposition. However, ecosystems in the park are not typical of nitrogen-sensitive systems and are rated as having very low sensitivity to nutrient-enrichment effects relative to all Inventory & Monitoring parks (Sullivan et al. 2011c; Sullivan et al. 2011d). Nevertheless, nitrogen deposition exceeds the critical load for one or more park ecosystems (NPS ARD 2018).

Visit the NPS air quality conditions and trends website for park-specific nitrogen and sulfur deposition information. Mammoth Cave NP has been monitoring atmospheric deposition of nitrogen and sulfur since 2002. Explore air monitoring »

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.

Effects of mercury and toxics:
  • Mercury deposition at Mammoth Cave NP is a concern given numerous nearby coal-burning power plants, which are significant sources of airborne mercury
  • Mercury deposition at the park is high compared to other parks (NPS 2010)
  • Kentucky has issued a statewide fish consumption advisory for mercury
  • Elevated levels of mercury have been found in bats, fish, insects, water, and sediment samples in the park (NPS 2009)

Mammoth Cave NP has been monitoring mercury since 2006. Explore air monitoring »

[CUPN] Cumberland Piedmont Network. 2010. Summary of Results of 2009 Foliar Injury Surveys by Cumberland Piedmont Network. Presented at the National Park Service Air Quality Planning Meeting. January 5-7, 2010. Denver, CO.

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

[NPS] National Park Service. 2009. Assessing the Impact of Mercury Bioaccumulation in Cumberland Piedmont Park Units. PMIS 110144. National Park Service Annual Report.

[NPS] National Park Service. 2010. Air Quality in National Parks: 2009 Annual Performance and Progress Report. Natural Resource Report NPS/NRPC/ARD/NRR–2010/266. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2166247

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

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: Cumberland Piedmont Network (CUPN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/330. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2168619

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: Cumberland Piedmont Network (CUPN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/360. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2170577

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://www.nps.gov/articles/aqrv-assessment.htm