Some leaching might not be a bad thing, Burton said, since excess nitrogen could be taken up by plants in nearby areas.  But people who drink water with too much nitrogen face health risks, most notably so-called blue baby syndrome, a potentially fatal blood disease that affects infants.

And once it enters waterways, nitrogen makes its way to lakes and oceans where it can contribute to "dead zones," coastal areas where excess nutrients cause explosive phytoplankton growth, robbing water of oxygen and suffocating the aquatic creatures that need it.

Finally, and perhaps most worrisome, saturating forests with nitrogen "will very likely" lead to more nitrous oxide emissions - a potent greenhouse gas - said Nathaniel Ostrom, co-director of the Biogeochemistry Environmental Research Initiative at Michigan State University. 

Nitrous oxide emissions in other areas, scientists say, could even offset the climate benefit of northern forests as carbon sinks.

The jury is still out on whether human-caused nitrogen deposition accelerates climate change through those emissions or slows it by boosting plant growth and slowing decomposition, said Townsend."But I suspect that we're accelerating it," he said.  "The speed and scale at which we're changing the nitrogen cycle are pretty scary."

This article originally ran at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.