Agricultural ammonia emissions disrupt Earth's delicate nitrogen balance

May 9, 2016
Credit: NASA

When considering human impacts on earth systems, disturbance to the carbon cycle grabs the headlines. But another critically important earth process, the nitrogen cycle, has also seen major disruption from human activity.

It turns out the nature of that disruption in the U.S. has changed over the last several decades. New Colorado State University research indicates that nitrogen cycle disturbance from emissions of agriculture-related now exceeds the effects of emissions.

And no matter what the source, in the atmosphere, as it cycles through terrestrial and aquatic ecosystems in both wet and dry processes, has debilitating environmental impacts. These include increased soil acidification, decreased biodiversity, and changes to the chemistry of lakes and streams.

The research team was led by Jeffrey Collett, professor and head of CSU's Department of Atmospheric Science, and includes collaborators from the Environmental Protection Agency, the National Park Service and the National Atmospheric Deposition Program.

Publishing May 9 in Proceedings of the National Academy of Sciences, the researchers describe a slow, measurable shift in sources of nitrogen deposition - the input of reactive nitrogen from the atmosphere to the biosphere - that continue to wreak havoc on ecosystems. The paper's first author is Yi Li, a recent CSU Ph.D. graduate who now works for the state of Arizona.

Starting in the 20th century, human-made nitrogen deposition has come from two main sources: nitrogen oxides from fossil fuel emissions, which become nitrates in the atmosphere; and ammonia, which derives mostly from livestock waste and from , and which cycles through ecosystems as ammonium.

Over recent decades, most attention has been focused on the fossil fuel side of the equation. In that time, major strides have been made to stem those emissions, through technological improvements and government regulations. Tailpipe emissions are cleaner than ever today, and power plants are tightly regulated for nitrogen oxide pollutants.

In contrast, ammonia from agricultural processes has received little attention, and ammonia is not a regulated pollutant. The CSU researchers have found that ammonium has now surpassed nitrates as the dominant source of nitrogen deposition and subsequent disruption to the nitrogen cycle.

"We are used to thinking of nitrates as driving a lot of the nitrogen deposition, and that was true in the 1980s," Collett said. "But largely because we've reduced nitrates so much while ammonium deposition has increased, the balance is now shifted, and ammonium is now a bigger contributor to nitrogen deposition."

Ammonia emissions, while not toxic to humans at current atmospheric levels, also have secondary effects, the researchers say. Ammonia is a chemical precursor to many particulate matter pollutants that are harmful to humans, including ammonium nitrate and ammonium sulfate.

In the paper, the researchers analyzed the shift in nitrogen deposition sources from nitrates to ammonia in the context of what's called wet deposition, which is nitrogen that enters the in the form of rain or snow.

Nitrogen can also undergo dry deposition, which is when a gas molecule or particle in the atmosphere is directly deposited to the earth's surface. Quantification of dry deposition is more challenging, Collett said, and less data is available to analyze those effects. A recent expansion in U.S. ammonia measurements allowed the team to more fully quantify nitrogen dry deposition inputs. These findings further emphasize the importance of ammonia as a main contributor to ecosystem inputs of .

The takeaway? "Policymakers need to be thinking about ammonia, not just nitrates," Collett said. "We've worked hard at decreasing nitrates by reducing emissions of from fossil fuel combustion, but if we want to continue to make progress on reducing , we need to think about ammonia as well."

Explore further: Atmospheric nitrogen leads to loss of plant diversity in sites across US

More information: Increasing importance of deposition of reduced nitrogen in the United States, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1525736113

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7 comments

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IronhorseA
1.9 / 5 (9) May 09, 2016
Seems like eventually all farms will have to be fully enclosed.
jonnyrox
1.4 / 5 (9) May 09, 2016
Easy solution to all of these environmental problems....stop supporting people who either can't or won't take care of themselves. This is now proving to be a luxury that the planet cannot afford !!!
kochevnik
1.4 / 5 (10) May 09, 2016
Yesterday carbon. Today nitrogen. Well in any case I have never advocated fossil fuels and I have always said that there can never be too many abortions. If only because some diseases like psychopathy are untreatable, easily tested, and far more immediately dangerous to humanity than flooded islands

Organic food tastes much better. It has fewer lectins which cause senility, arthritis and coronary disease in particular the Monsanto GMO variants
tblakely1357
1.4 / 5 (10) May 09, 2016
Funny how a couple of hundreds years ago there were vast herds of buffalo numbering in the millions roamed the plains in the US. Ditto in Africa. I guess they didn't poop.
BartV
1 / 5 (8) May 10, 2016
I guess since Nitrogen makes up about 80% of the atmosphere, where are going to have to start restric it.

HeloMenelo
5 / 5 (5) May 10, 2016
i guess since you are an antigoracle sockpuppet, you will have to be fed a bannana
AGreatWhopper
2.3 / 5 (3) May 17, 2016
Of course that's an obscene metaphor.

(I don't think antisciencegorilla's socks are smart enough to have gotten that.)

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