Dealing with ammonia volatilization could add another layer of complexity to animal waste management, which historically has focused mainly on curbing nutrient runoff that pollutes surface and ground water.
Ultimately, farmers could be asked to control not only what runs off the land, but what goes up in the air.
In some cases, that could prove to be a delicate balancing act as efforts to control one form of pollution sometimes may contribute to another.
Consider the North Carolina example. Ammonium deposition in coastal waters may have increased as a result of efforts to control runoff from industrial hog operations by building large manure storage "lagoons."
But the lagoons also allowed large amounts of ammonia to volatilize into the air and ultimately fall into the water - thereby contributing to a water pollution problem the lagoons were intended to prevent. It's an impact that caught most people by surprise.
"No one, I don't believe - whether they were regulators or in the environmental community - really thought about the secondary impacts [from the lagoons], certainly not secondary impacts that might relate to air quality," said Jonathan Howes, former secretary of the state's Department of Environment, Health and Natural Resources, at a conference earlier this year that focused on air pollution impacts on coastal waters.
Similar questions could crop up in the Bay watershed. Some people, for example, are concerned that certain recommendations for dealing with animal manure stemming from last year's pfiesteria outbreak have the potential to increase ammonia volatilization.
The amount of ammonia lost through various agricultural practices has been examined for years, though not from a water quality standpoint. Farmers applying fertilizers on the fields need to know how much nitrogen is lost into the air in the form of ammonia gas - and take that into account - to make sure they place enough nitrogen on the ground.
As a rule of thumb, said Jack Meisinger, of the U.S. Department of Agriculture's Agricultural Research Service, about 30 percent to 50 percent of the nitrogen in animal wastes volatilizes into the air as ammonia from the time it is excreted until it is placed into storage. "There's a substantial loss from our livestock system," he said, "but you really can't avoid some of those losses."
More ammonia is lost into the air when the manure is spread onto fields.
Exactly how much is lost depends on a variety of factors. Warm, windy or low humidity weather can increase volatilization.
Under such conditions, a third to half of the remaining nitrogen could vanish from the manure. But if the farmer plows the manure into the soil, the loss during application can be reduced to almost zero. Urea-based fertilizers, the most common in the watershed, can also lose a large portion of their nitrogen to ammonia volatilization, depending on their method of application. If the fertilizers are sprayed onto the fields and not incorporated into the soil, 15 percent to 20 percent of the nitrogen can be lost, said Richard Fox, an agronomy professor at Penn State University.
If it is applied directly to the soil as a liquid through a hose, that can be reduced. Quickly incorporating it into the soil reduces it even further.
But plowing the fertilizer into the ground is more costly - both in time and labor - to the farmer. And it may not be an option in areas with steep slopes where "no till" agriculture is practiced to reduce erosion.
"There's a lot of pros and cons," said Greg Roth, an extension specialist in Penn State's Agronomy Department. "It's typical of a lot of issues that we've got to deal with."
While reducing ammonia volatilization can reduce the fertilizer needed for a crop, those savings may not always offset the added cost of plowing the fertilizer in, Roth said.
"On a lot of dairy farms in Pennsylvania, farmers are in a daily haul-type situation," Roth said. "They will spread a couple of loads of manure a day.
They can't go out and work that in every day."
Dealing with volatilization, he said, "is one priority among many. It may not always come out on top."
Because of such complexities, some actions suggested in the wake of last year's pfiesteria outbreak - intended to reduce phosphorus runoff - could increase ammonia volatilization.
Historically, manure has been placed on crops based on the nitrogen need of the plants. But because of the high phosphorus-to-nitrogen ratio in chicken manure, this has resulted in large phosphorus accumulations in the soils of some areas. That, in turn, may contribute to elevated phosphorus levels in the water.
Spreading that manure over more land could reduce the phosphorus buildup, but it may also increase ammonia volatilization unless it is quickly plowed into the soil.
"It's really a question of time management," Meisinger said. "If you're spreading it over more acres, does the fellow have the time and the equipment and the labor to incorporate those additional acres?"
Efforts to get rid of excess manure through composting could also increase ammonia volatilization. "When you compost material, you drive off a large part of the ammonia," said Tom Simpson, Chesapeake Bay Coordinator with theMaryland Department of Agriculture.
But Simpson expressed optimism that efforts to deal with phosphorus could be developed without increasing ammonia volatilization.
"Certainly, we will be looking at all aspects of it environmentally," he said. "And I have no reason to think that we're going to leave it on the surface longer than we have before."
Simpson said evidence increasingly suggests that incorporating phosphorus into the soil is important to controlling phosphorus runoff. If that practice becomes important for phosphorus management, he said, it will also reduce the loss of ammonia.
Also, some efforts to reduce phosphorus, he said, such as the addition of the enzyme phytase to chicken feed, would reduce the need to spread manure over more acres.
Research about other additives to manure that are intended to reduce phosphorus runoff - such as alum - have also shown they can dramatically reduce ammonia volatilization. In fact, the Bay Program is considering funding a research effort about the potential use of adding alum to animal waste to control phosphorus and reduce ammonia volatilization.