Chicken Farming, Ammonia, and Coastal Threats

April 21, 2004 at 12:27 pm

As anyone knows who’s changed a wet diaper or cleaned a cat litter box, ammonia is a volatile natural waste that animals produce in substantial amounts. Indeed, where animals are raised in confinement—such as large chicken houses—indoor concentrations of ammonia, if not vented properly, can damage a chicken’s or even a person’s eyes.

WASTE SOURCE. Livestock operations such as chicken farming can release large amounts of ammonia gas into the environment. When it returns to Earth in rain or dust, this nitrogen source can overfertilize algae, the decomposition of which can deplete the oxygen in bodies of water.

Despite its stinky reputation, ammonia represents a mighty nutrient for plant life. This volatile gas is the main nitrogen source in fertilizers that farmers apply to row crops. Ammonia from that source or livestock waste can pollute the air and, when the chemical comes back to Earth via rain or dust, waterways.

Ammonia can thus fertilize the algae in estuaries such as the Chesapeake Bay. As overabundant algae die in such waters, they fall to the bottom and decompose in sediments. There, they fuel the growth of microorganisms that suck oxygen out of the lower layers of water, creating “dead zones” that are void of fish for part of each year.

Last year’s Chesapeake dead zone, one of the largest since scientists began monitoring the condition there 2 decades ago, affected some 40 percent of the bottom waters of the estuary, the nation’s largest. The Chesapeake—some 200 miles long and from 3 to 35 miles wide—is the source of half a billion pounds of seafood for dinner tables each year. As such, it’s a major economic driver to coastal communities throughout Delaware, Maryland, and Virginia, a region known as Delmarva.

That’s why understanding human-influenced sources of nitrogen to the bay has become essential. And a new study by researchers in Maryland and Delaware now concludes that chicken farming—a Delmarva industry valued at $1.5 billion per year—could be contributing a whopping 18,000 metric tons of airborne ammonia to the Chesapeake Bay and the waters that feed it.

If true, that would amount to around 8 percent of the nitrogen falling upon the watershed from all sources—including combustion emissions from traffic and commercial smokestacks. Less than a tenth of the total may not sound like much, but officials throughout the Chesapeake watershed, some 64,000 square miles in six states, are looking for every way possible to cut nutrient emissions into the bay. In that context, an airborne chemical measured in thousands of metric tons is a significant source of nitrogen, the researchers say.

Tracking ammonia plumes

Ronald L. Siefert of the University of Maryland’s Center for Environmental Science and his colleagues set up ammonia-sampling devices about 60 meters downwind of two large Delmarva chicken houses—facilities holding some 11,500 birds each. In seven separate 6-to12-hour sessions, his team collected ammonia readings at various heights above ground near one or the other of the houses.

In the atmosphere, ammonia doesn’t exist independently for very long. The compound is “relatively sticky” and readily adheres to almost any material it encounters, says Siefert. That’s why his team set up its equipment so close to the birds; the researchers wanted to measure ammonia emissions before they diffused or attached to plants, soil, or particles in the air.

The ammonia tallies the team recorded were about 50 percent larger than the few values that have been reported near chicken houses by other scientists, principally researchers in Europe. “We don’t know why ours are higher,” Siefert told Science News Online. That’s a question that will be probed in follow-up research. His suspicion is that the answer will trace to the Delmarva birds’ diet or how their wastes are managed within the chicken houses.

The rectangular buildings emitting the fumes studied by the University of Maryland team have open windows all along their long outside walls. Another popular chicken-house-ventilation design places windows only on a building’s ends. The latter design would be more conducive to an ammonia-recycling effort based on air scrubbers, if officials ever demand such an effort of chicken growers, Siefert says.

He adds that growers probably won’t volunteer to install such pollution controls. “Incorporating that kind of technology would add a lot to the cost of the operations,” Siefert observes, and the profit margins on chicken farms are small. Moreover, he notes, scrubbing ammonia gas from chicken houses would create yet another waste stream for farmers to deal with—liquid ammonia.

Siefert notes that livestock operations are an important source of nitrogen in the environment nationally, so pollution-management demands are headed the way of many farmers. “Basically, it comes down to social and political economics, what people are willing to do to protect our resources,” he says. “I’m just trying to give [farmers and officials] better numbers to work with.”