The addition of up to 50,000 dairy cows in Northern Colorado in the next few years will mean more air pollution in the region.

That includes ammonia emissions, which contribute to the build-up of nitrogen in Rocky Mountain National Park, an outdoor icon and key Front Range tourist draw.

The cows' digestives processes also will lead to more methane, a greenhouse gas that the Environmental Protection Agency says traps heat in the atmosphere more effectively than carbon dioxide.

Weld County already boasts a total of 550,000 cattle including 50,000 dairy cows.

Spread throughout the region, the additional cows are expected to produce 4.5 million pounds of milk by the end of next year, said Wade Meek, member services director for Dairy Farmers of America in Colorado.

The farmer-owned cooperative has agreed to supply that milk to the new Leprino cheese plant in Greeley. That level of production will require 30,000 more dairy cows, but the plant someday will have capacity for additional production, which would require 50,000 cows, Meek said.

Now fully operational in its first phase with 100 workers, Leprino is building its plant in three phases, company spokesman Ted Wietecha said. The company will ramp up production based on demand and the availability of milk.

Dairy Farmers of America will coordinate with Leprino to align the number of incoming cows with the plant's growth, said David Darr, vice president of sustainability and public affairs.

Regardless of the specific number of cows headed for Weld County, scientists believe nitrogen levels in Rocky Mountain National Park have already risen to twice the acceptable amount.

Upslope weather — winds from the east — carries ammonia particles to the park, leading to nitrogen deposition in soil, plants and lakes.

Livestock, including dairy and beef cattle, emit the most ammonia of any pollution source, according to a 2002 analysis published in a recent state report.

Depending on the weather, the ammonia can head in any direction, including farms where it fertilizes crops.

But it harms the national park's fragile alpine environments, in part by creating more algae in lakes that could kill fish and favoring grasses that crowd out flowering plants, diminishing alpine flowers, according to the National Park Service.

"It's very, very subtle," said Jay Ham, professor at CSU's Department of Soil and Crop Science. But, "Since it's a pristine national park, a lot of effort is going in to protect it."

Ham has measured ammonia emissions from dairy farms that have agreed to be monitored. Livestock has contributed to the problem, but it represents just one of many sources of pollution, he said.

"Will adding these animals really add that much to the total?" he asked. "We don't really know."

Ham doubts a significant change in air quality would result. However, how much additional air pollution the cows will cause depends on their location, how farmers manage them, the kinds of waste handling system they use and other factors.

The state, which does not regulate cow emissions, has collaborated with industry to minimize any environmental issues.

In fact, the state Department of Public Health and Environment has worked with the dairy industry for years to reduce ammonia emissions in the park, said Phyllis Woodford, manager of the state environmental agriculture program.

Moving forward, state regulators want dairy farmers to commit to voluntary "best management practices" to limit cow emissions, Woodford said.

State officials also are considering a system to warn farmers of upslope weather that could carry ammonia to the mountains. That way, farmers could avoid moving manure around those times.

Some Northern Colorado dairy farmers have responded by adopting some of these practices.

Sensitive to the issue, the Colorado Livestock Association hosted an air-quality symposium in Fort Morgan in February, though turnout was lower than expected.

"There wasn't as many producers there as I had hoped," said Jon Slutsky, owner of a 1,500-cow dairy farm near Wellington.

A member of the Colorado Air Quality Control Commission, Slutsky said that because the park is supervised by the federal government, dairy farmers run the risk of violating the federal Clean Air Act.

Upslope winds do not occur very often, but when they do, "we have the potential to really affect the ecosystem," he said.

"If we were very diligent in these periods of time, we could make a big impact on the park," he said.

Slutsky believes that dairy farmers can prevent additional nitrogen deposition in the park by ensuring that cow urine does not combine with an enzyme in manure to produce additional ammonia. That means frequently moving manure as soon as possible from cows' stalls to manure piles, which seal themselves and prevent nitrogen from escaping.

Dairy farmers also can avoid feeding their cows too much nitrogen, which combines with cow urine to create ammonia. Many farmers already work with nutritionists to do this to maintain milk quality, he said.

Beyond dairy farms, crop farmers should incorporate manure from dairy operations used for fertilizer into their soil as quickly as possible, he added.

As for methane, the state does not have immediate plans to address the greenhouse gas. Worldwide, livestock produce about 80 million metric tons of methane annually, making them "one of the largest methane sources," according to the EPA.

In the United States, cattle emit about 5.5 million metric tons of methane annually, accounting for one fifth of the nation's methane emissions.

Agricultural activities are exempt under state air regulations, said Kirstin King, program manager for stationary sources at the state environment department.

However, citing a U.S. Department of Agriculture study, King said any dairy farm with 6,700 or more cows may emit enough methane and nitrous oxide to warrant a permit from the federal government.

A dairy farm of that size would emit 100,000 tons of carbon dioxide equivalent annually, or about 8,000 tons of methane, she said. Scientists are conducting additional studies that should help the department better understand cattle emissions.

EPA is "still working through what sources and how they would be regulated," she said. "Ag is one of those that's in a little bit of a gray area. We're waiting for clarification on that."

King said her department plans to tell dairy farmers what the state will require when they determine who might need a permit.

"The greenhouse gas rules are new, so we're still getting a handle on what sources are out there and how large they really are," she said. "It's certainly something we will be looking into and watching over time."

Darr said emissions from dairy cows have decreased through the years: As cow-milking operations have become more efficient, fewer cows overall are needed, even as milk production has risen.

As for odor and dust, Weld County requires dairy farmers to control those issues and officials investigate when complaints are made, said Troy Swain, waste program coordinator for the county Department of Public Health and Environment.

In addition, dairy farms are located in agricultural zones away from populated areas and newer facilities are designed to minimize the problem, Swain said.

New operations can take steps like using siding that prevents odor and dust from blowing into populated areas during prevailing winds, Ham said.

Ham hopes that dairy farmers in the area will work with CSU, which could help them maintain cleaner air.

"That's one thing nice thing about new operations is you can be proactive and take care of issues before they even start," he said.