America’s national parks receive harmful, accidental fertilization from air pollution. A recent study identified how this unwanted dose of nitrogen nutrients harms plants and disrupts aquatic environments in 38 U.S. national parks.

Much of this accidental fertilization comes from ammonia that evaporated from agricultural chemicals and livestock urine, according to the study published in Atmospheric Chemistry and Physics. Power plant and vehicle emissions also contribute nitrogen in the form of nitrous oxides.

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These nitrogen-containing gases enter the atmosphere, then fall back to earth in rain water or through other means.

“When we apply fertilizer in the United States, only about 10 percent of the nitrogen makes it into the food,” said lead author Daniel J. Jacob of Harvard University in a press release. “All the rest escapes, and most of it escapes through the atmosphere.”

Once that nitrogen escapes into the environment, it damages ecosystems.

In the east, the unwanted fertilizer most seriously affects the hardwood trees, such as oak, in Great Smoky Mountains National Park. The trees start to suffer when nitrogen input reaches 3 to 8 kilograms per hectare each year. However, the forest now receives far more than that, at 13.6 kilograms per hectare each year.

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On the other side of the nation in Washington’s Mount Rainier National Park, nitrogen input levels have reached 6.7 kg/ha/year. Lichens, the base of the ecosystem, start to suffer when levels reach 2.5 to 7.1 kg/ha/year.

In bodies of water across the nation, excess nitrogen alters the acidity of the waters and fuels explosions of algae growth.

Controlling the environmental effects of accidental over-fertilization from air pollution poses a legal challenge, noted Jacob.

“Air quality regulations in the United States have always focused on public health, because air pollution leads to premature deaths, and that’s something you can quantify very well. When you try to write regulations to protect ecosystems, however, the damage is much harder to quantify,” said Jacob. “At least in the national parks you can say, ‘There’s a legal obligation here.’”

The government has an obligation to maintain the national parks we all share. This gives regulatory agencies a legal foundation for fighting nitrogen air pollution.

IMAGE: Looking up into Redwoods and Rhododendron on a foggy morning in the Lady Bird Johnson area of Redwoods N.P., California. (Darrell Gulin/Corbis)