Park Air Profiles - Everglades National Park

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Air Quality at Everglades National Park

Most visitors expect clean air and clear views in parks. Everglades National Park (NP), Florida, the “River of Grass” and home to the only subtropical preserve in North America, often experiences relatively poor air quality. The park is affected by many sources of air pollution, including power plants, urban areas, agriculture, and industry. Pollutants from these sources can harm the park’s natural and scenic resources such as surface waters, vegetation, birds, fish, and visibility. The National Park Service works to address air pollution effects at Everglades NP, and in parks across the U.S., through science, policy and planning, and by doing our part.

Nitrogen and Sulfur

A crane wading in Everglades NP
Visitors come to Everglades NP for opportunities to see unique and diverse wildlife and plant communities.

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 changes community composition. Ecosystem sensitivity to nutrient N enrichment at Everglades National Park (EVER) 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 EVER relative to other national parks is low (Sullivan et al. 2016); to search for acid-sensitive plant species, see: NPSpecies.

From 2017-2019 total N deposition in EVER ranged from 4.8 to 10.1 kg-N ha-1 yr-1 and total S deposition ranged from 3.1 to 5.7 kg-S ha-1 yr-1 based on the TDep model (NADP, 2018). EVER has been monitoring atmospheric N and S deposition since 1980, see the conditions and trends website for park-specific information.

At EVER, emissions of ammonium from nearby agricultural sources contribute to increased N deposition in the park (NPS 2010). These nutrient inputs can cause changes to soil nutrient cycling (Sullivan et al. 2016). Wetland plant species adapted to low N environments are sensitive to the effects of nutrient N enrichment because species relationships are altered, which sometimes increases numbers of non-native species at the expense of rare species.

The freshwater and saltwater ecosystems at EVER are well-buffered from the effects of acidification (Sullivan et al. 2016). Of note for EVER is the essential role of S in the methylation of mercury. A process that leads to toxic accumulation of mercury in fish and wildlife. Although the main source of S is runoff from agriculture north of the park, local emissions from coal-burning power plants might contribute to this problem.

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. 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 only 18.6 km2 (0.3%) of the land area of Everglades National Park as this analysis did not include woody wetlands.

  • 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 exceeded the 2.7 kg-S ha-1 yr-1 critical load to protect S-sensitive lichen species richness in 100% 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, Everglades National Park contains:

  • 3 N-sensitive tree species and 9 N-sensitive herbaceous species.
  • 5 S-sensitive tree species and 8 S-sensitive herbaceous species.

Persistent Pollutants

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 tissues of organisms causing reduced reproductive success, impaired growth and development, and decreased survival.

Everglades NP and the surrounding South Florida region have extremely high levels of mercury contamination. The NPS conducts research to assess mercury cycling in the environment and accumulation in sediments, fish, and wildlife in the park. Long-term studies on mercury in Everglades NP include: Mercury Cycling in the Everglades and the South Florida Mercury Science Program (USGS).

Despite improved understanding of how mercury cycles in the Everglades marsh from these efforts, a significant question remains: Why is mercury in Everglades NP’s biota much higher than in biota from almost everywhere else in south Florida? The NPS collects tissue, feather, or unhatched egg samples from birds, along with water and sediment samples, to answer this question.

Studies have also been conducted on other airborne toxics, including endosulfan. Elevated levels of this agricultural pesticide in sediment, surface waters, and native fish in the Everglades, nearby Biscayne Bay, and several western national parks, led to a ban on endosulfan. Phased implementation of this ban began in 2010.

Mercury and toxics effects:

  • High mercury deposition at the park (NPS 2010), likely because of large nearby sources of mercury such as coal-burning power plants and waste incinerators
  • Elevated mercury levels in sediment, vegetation, and in all levels of the food chain, from frogs, fish, wading birds, to fish-eating birds such as the great egret and the bald eagle, pythons, alligators, and the endangered Florida panther (Guentzel et al. 1998; Krabbenhoft 2010; Rumbold et al. 2002; Rumbold 2005; Sundlof et al. 1994; Ugarte et al. 2005)
  • Mercury levels in wading birds at concentrations associated with neurologic and reproductive impairment (Sundlof et al. 1994)
  • Mercury levels in frogs and pythons above human health thresholds (Krabbenhoft 2010; Ugarte et al. 2005), a concern for areas that permit harvesting and consumption
  • Fish consumption advisories by waterbody are in effect for mercury and other contaminants such as dioxin, PCBs, and pesticides (Florida DOH, EPA)
  • Elevated concentrations of pesticides, particularly endosulfan, in sediment, surface waters, and several native fish (Carriger et al. 2006; Carriger and Rand 2008a and b; Rand and Carriger 2004; Rand et al. In Prep)

Everglades NP has been monitoring atmospheric mercury deposition since 1996. Explore air monitoring »

Highlight: Mercury and the endangered Florida panther

Florida Panther
Florida Panthers in Everglades NP are vulnerable to high levels of airborne mercury because their preferred diet consists of fish-eating animals.

The Florida panther (Puma concolor coryi), a state and federally-listed endangered species, has suffered severe declines in population numbers because of environmental stressors, low genetic variability, and habitat loss. Mercury contamination could contribute to the species’ poor reproductive success. High mercury levels found in panthers in Everglades NP have been attributed to a preferred diet of fish-eating wildlife such as raccoons and alligators, rather than of herbivores such as deer. Detectable levels of mercury in panthers have been evident since 1978, with the highest levels found in panthers from Everglades NP (Roelke et al. 1991). Everglades NP continues to have the highest concentrations of mercury in panther hair and blood of all four South Florida regions (SFER 2011). Also, mercury in panther hair samples from the 1990s was significantly higher than in museum specimens dating back to the 1890s (Newman et al. 2004). A study in the early 2000s concluded that risks of mercury exposure to panthers had decreased somewhat from the 1990s (Barron et al. 2004), likely because of better controls on sources of airborne mercury. However, there is evidence that regions in the Everglades with high levels of mercury still exist, and could increase because of marsh restoration activities.


Visitors come to Everglades NP to enjoy sights of some of the most rare and endangered species in the U.S., including the manatee and American crocodile, as well as plant communities such as mangrove and cypress swamps. Park views 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, and dust reduce visibility as well. Significant improvements in park visibility on clearest days 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:

  • Reduction of the average natural visual range from about 110 miles (without the effects of pollution) to about 65 miles because of pollution at the park
  • Reduction of the visual range to below 40 miles on high pollution days.

Visit the NPS air quality conditions and trends website for park-specific visibility information. Everglades NP has been monitoring visibility since 1988. Explore air monitoring »

Ground-Level Ozone

Buttonbush is one of the ozone sensitive species found at Everglades 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. The low levels of ozone exposure at Everglades NP make the risk of foliar ozone injury to plants low (Kohut 2004). Still, some plants are more sensitive to ozone than others. There are a few ozone-sensitive plants in Everglades NP including Cephalanthus occidentalis (common buttonbush) and Rhus copallinum (flameleaf sumac). Search ozone-sensitive plant species found at Everglades NP.

Visit the NPS air quality conditions and trends website for park-specific ozone information.

Barron, M. G., Duvall, S. E., Barron, K. J. 2004. Retrospective and Current Risks of Mercury to Panthers in the Florida Everglades. Ecotox. 13: 233–229.

Carriger, J. F. and Rand, G. M. 2008a. Aquatic Risk Assessment of Pesticides in Surface Waters in and Adjacent to the Everglades and Biscayne National Parks: I. Hazard Assessment and Problem Formulation. Ecotoxicology 17 (7): 660–679.

Carriger, J. F. and Rand, G. M. 2008b. Aquatic Risk Assessment of Pesticides in Surface Waters in and Adjacent to the Everglades and Biscayne National Parks: II. Probabilistic Analyses. Ecotoxicology 17 (7): 680–696.

Carriger, J. F., Rand, G. M., Gardinali, P. R., Perry, W. B., Tompkins, M. S., Fernandez, A. M. 2006. Pesticides of Potential Ecological Concern in Sediment from South Florida Canals: An Ecological Risk Prioritization for Aquatic Arthropods. Soil and Sediment Contamination 15 (1): 21–45.

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).

[EPA] U.S. Environmental Protection Agency. 2008. The National Listing of Fish Advisories. Available at

Florida [DOH] Department of Health. 2016. Your Guide To Eating Fish Caught In Florida. Available at

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.

Guentzel, J. L., Landing, W. M., Gill, G. A., Pollman, C. D. 1998. Mercury and major ions in rainfall, throughfall, and foliage from the Florida Everglades. The Science of the Total Environment 213: 43–51.

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.

Kohut, B. 2004. Assessing the Risk of Foliar Injury from Ozone on Vegetation in Parks in the South Florida / Caribbean Network. Available at

Krabbenhoft, D. P. 2010. Mercury Bioaccumulation in Everglades Pythons. Poster, Greater Everglades Ecosystem Restoration Conference: July 12–16, 2010. Naples, FL.

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. Natural Resource Report NPS/NRSS/ARD/NRR—2021/2299. National Park Service, Fort Collins, Colorado.

[NADP] National Atmospheric Deposition Program. 2018. NTN Data. Accessed January 20, 2022. Available at

Newman, J., Zillioux, E., Rich, E., Liang, L., Newman, C. 2004. Historical and Other Patterns of Monomethyl and Inorganic Mercury in the Florida Panther (Puma concolor coryi). Arch. Environ. Contam. Toxicol. 48: 75–80.

[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

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.[0603:PROFLI]2.0.CO;2

Rand, G. M. and Carriger, J. F. 2004. Screening Level Ecological Risk Assessment (SERA): Canal-111 and Adjacent Coastal Areas. Report submitted to Everglades National Park.

Rand, G.M. et al. South Florida Freshwater Ecological Risk Assessment: 1990–2007. In Prep.

Roelke, M. E., Schultz, D. P., Facemire, C. F., Sundlof, S. F., Royals, H. E. 1991. Mercury Contamination in Florida Panthers. Report of the Florida Panther Technical Subcommittee to the Florida Panther Interagency Committee.

Rumbold, D. G. 2005. A probabilistic risk assessment of the effects of methylmercury on great egrets and bald eagles foraging at a constructed wetland in South Florida relative to the Everglades. Human and Ecological Risk Assessment 11 (2): 365–388.

Rumbold, D. G., Fink, L. E., Laine, K. A., Niemczyk, S. L., Chandrasekhar, T., Wankel, S. D., Kendall, C. 2002. Levels of mercury in alligators (Alligator mississippiensis) collected along a transect through the Florida Everglades. Science of the Total Environment 297 (1–3): 239–252.

[SFER] South Florida Environmental Report. 2011. Volume I The South Florida Environment. South Florida Water Management District, West Palm Beach, Florida. Available at

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.

Sundlof, S. F., Spalding, M. G., Wentworth, J. D., Steible, C. K. 1994. Mercury in Livers of Wading Birds (Ciconiiformes) in Southern Florida. Archives of Environmental Contamination and Toxicology 27 (3): 299–305.

Ugarte, C. A., Rice, K. G., Donnelly, M. A. 2005. Variation of total mercury concentrations in pig frogs (Rana grylio) across the Florida Everglades, USA. Science of the Total Environment 345 (1–3): 51–59.

Part of a series of articles titled Park Air Profiles.

Everglades National Park

Last updated: November 29, 2022