It never ceases to amaze me how much we have to learn about the Chesapeake Bay and other estuaries like it. We have known for more than a decade that the air was a major source of the nitrogen that is over-enriching the Bay’s waters, creating blooms of algae that rob the water of oxygen. And we understood that the excess nitrogen originates from the tailpipes of cars and other mobile sources, as well as the stacks of powerplants.
But there was also talk of another form of airborne nitrogen, ammonia, which might be a contributor. This was a troublesome rumor, as we all knew that the major source of ammonia was likely to be animal agriculture, a sector of the economy that is just beginning to come under scrutiny from environmental regulators. We weren’t sure we really wanted to have to point the finger again at the farmers, who were already bearing a large part of the effort to help reduce nitrogen and phosphorous loads to the Bay. But it was a potential source that could not be ignored.
So the Chesapeake Bay Program, along with the Mid-Atlantic Regional Air Management Association and the EPA air deposition-focused Great Waters Program, sponsored a two-day workshop in November on the significance of airborne ammonia to coastal and estuarine waters. It was an excellent opportunity to learn from the experts what we know about this complicated but potentially important subject. And it is quite an emerging story to tell.
While there were plenty of people there to call for more studies and better monitoring of conditions, there were already some clear messages for the managers to take in.
First, it is clear that ammonia is an important source of nitrogen to waters like the Bay; it can account for more than half of the airborne nitrogen loads which arrive, either from direct deposition to tidal waters, or by deposition on the land and washing or seeping into the rivers and the Bay.
Although the portion of total nitrogen loads contributed from the air varies from estuary to estuary, in the Chesapeake watershed it is estimated at 20–25 percent. Equally important, ammonia is an especially “hot” form of nitrogen, readily available and preferred as a nutrient by algae.
Until the workshop, the general word on the street was that while ammonia might be a problem in limited areas, the concentrations were localized around large sources like chicken houses and pig farm lagoons, and didn’t travel far.
This proved to be a major misconception. Studies show that airborne ammonia can travel long distances. While there is an area of heavy deposition around the source, the remaining fraction spreads out quickly and far. In fact, the so-called “airshed” for ammonia is about two-thirds the size of the NOx airshed, or several times the size of the Chesapeake watershed, extending well into the Midwest and the South as source areas. Likewise, sources within our region are contributing to ammonia loadings to waterbodies to the Northeast, as well as the coastal ocean.
Finally, in our watershed as well as others, agriculture is the primary source of airborne ammonia.
One study of the Chesapeake region east of Interstate 95 attributed 35 percent to poultry, 22 percent to other livestock, 13 percent to fertilizer, 18 percent to mobile sources, 7 percent to sewage treatment plants, and 5 percent to other sources. This adds up to 70 percent agricultural sources, and seems to be reflected in data from other areas.
Ammonia is at least half of the airborne nitrogen and the air provides 20–25 percent of total nitrogen loadings, so it looks like we are dealing with a previously ignored source of almost 10 percent of the total. As I say, it is amazing what we don’t know.
So the next issue is what to do about it. If you look at the total of airborne nitrogen in all its forms, not just ammonia, there are three general source areas.
First are powerplants; while there is a potential issue of ammonia “slip” or unintended discharge from some of the technologies being installed to handle NOx, a nitrogen regulatory regime is already in place for these facilities.
Second are the mobile sources, where ammonia emissions are just becoming understood; but here, too, there is already a nitrogen regulatory regime in place, although it is also currently focused on NOx.
When we come to agriculture, no such regime is in place. On the one hand, this could be said to make the job of reductions more difficult. But it also provides, in the spirit of the Chesapeake Bay Program, an opportunity to undertake cooperative efforts to go after the problem. What might such a management regime look like?
Some steps have proved to be effective in other places — manure storage can be made airtight, biofilters can be put on poultry house ventilators, and manure applied on fields can be quickly incorporated into the soil with chisel plowing and other practices.
Looking at the timing of field application offers another set of potential control measures. Fortunately, the “good algae” for fish food bloom in the spring, when the application of manure on fields is often undertaken. But we need to watch it in the summer, when it supports the “bad algae” that robs the water of oxygen. And we need to recognize that episodic events like storms can cause heavy loads of ammonia from the atmosphere. Perhaps application could be better timed to meteorological predictions.
Other possibilities exist in producing more feed locally (instead of importing more nitrogen), changing the formulation of feed, and even biogenetics. Special attention to “hot spots” also makes sense, given the high local deposition rates.
At the heart of the agricultural issue is the question of application rates of manure and fertilizer. An incredible effort is under way with farmers throughout the Chesapeake watershed to develop nutrient management plans and to carefully measure the volume of nutrients put on the fields.
But as accurate as those plans may be, they do not account for the cultural bias of farmers to overapply in anticipation of a perfect growing year. It seems to be almost a matter of bragging rights at the local feed store — “Guess how many bushels an acre I got this year!” We need to undertake an effort to shift the mentality from productivity per acre to profit per acre. Otherwise, we will never achieve the results we calculate with our charts and our models.
One interesting angle on ammonia has to do with forest practices. It appears that a young forest absorbs nitrogen from the air more effectively than mature forests. And scientists say there is a real concern that the ability of forests to absorb nutrients is limited, that beyond a point, the nutrients will saturate the soils and move into the groundwater and eventually, the streams.
Maximizing the capacity of forests calls for active management, and is another opportunity to build partnerships with the forest products industry, whose work continues to be misunderstood by many who care about the environment.
We need to find new incentives for farmers and foresters to keep the nitrogen in the system and out of the air. As we shift to phosphorous-based nutrient management, for example, it should make farmers want to find ways to hold onto the nitrogen so they do not need to buy nitrogen fertilizer to make up for the substantially lower manure application rates. We need to be alert to other ways to make the system work for the Bay.
And we need to push the technologies, from reducing the imports and inputs of nitrogen to controlling the outputs to the atmosphere. If nothing else, we need to find ways to convert the wastes to inert nitrogen, like the biological nutrient removal processes at sewage treatment plants.
When all is said and done, knowing what we do now and imagining what we will be learning about ammonia in coming years, is more regulation of farmers on the way? If we do nothing to deal with this issue now, the inevitable answer is “yes.”
But in the spirit of the Chesapeake Bay Program, we have another way. We can get to work now and tackle this problem cooperatively, and get so far ahead of the regulations that they never catch up. We’ve done it before. Let’s get to it with ammonia!