A new study commissioned by the Chesapeake Bay Foundation (CBF) and conducted by researchers at North Carolina State University has determined an estimate for the amount of nitrogen that reaches the Chesapeake Bay due to ammonia emissions from poultry farms on Maryland’s Eastern Shore. However, the Delmarva Poultry Industry Inc. challenged the modeling and pointed out actions area farmers have taken to reduce runoff.

The study, published in the journal Science of the Total Environment, determined that more than 600 poultry houses emit an estimated 33.8 million lb. of ammonia per year and that about 24.4 million lb. of that ammonia were deposited to land and water on the Eastern Shore. The ammonia comes from chicken litter and is emitted as a gas from poultry houses. Ammonia contains nitrogen, which is a pollutant in the Chesapeake Bay.

Holly Porter, executive director of the Delmarva Poultry Industry, noted in a follow-up statement that Maryland’s family farmers raising chickens have played a key role in achieving the state’s well-documented progress in reducing nutrients escaping to the Chesapeake Bay and improving water quality. Maryland has met its water quality goals for reduced phosphorus seven years ahead of the 2025 deadline, in part because of reduced phosphorus loads from agriculture and despite rising phosphorus loads from cities and suburbs. Farmers in the watershed have reduced their nitrogen contribution to the bay by 24% since the 1980s, even while nitrogen runoff from developed areas has risen, Potter pointed out.

Related:Delmarva ag industry supports next phase of phosphorus management

The study does have some limitations, CBF noted. “The model didn’t account for litter amendments or other practices to reduce ammonia emissions that are in use but the extent of which is unknown. Due to the lack of publicly available information, the study also assumed the poultry houses were at full capacity for 365 days a year, which is often not the case,” CBF said.

Potter noted that, in reality, the use of litter amendments is widespread on U.S. chicken farms because they reduce ammonia, producing a better environment for chickens and farmers.

The research also assumes that every Maryland chicken house contains birds 365 days a year, without pause, but Potter said the reality is that several times a year, there are “layout” periods between flocks when the houses are empty so all chicken farmers can perform maintenance and upgrades.

Also, the model doesn’t account for any forested land in Delmarva and assumes that all of Maryland’s Eastern Shore is farmland. “In reality, forests absorb ammonia, as do vegetative buffers on chicken farms,” she said.

As the researchers acknowledged in a published paper, these assumptions were “not a realistic approach” and caused their model to overestimate ammonia levels, Potter added. “The researchers did not approach [Delmarva Poultry Industry] or our members to get data about the use of litter amendments or the frequency of layouts before publishing conclusions based on their incomplete model. We look forward to working with the Chesapeake Bay Foundation to correct those flawed assumptions in the model,” she said.

Another key finding of the study is that the ammonia gas doesn’t travel far from the poultry house where it was created. About 30% of emitted ammonia is deposited to land or water within a third of a mile of the poultry house, and about 70% is deposited within 31 miles. This means that much of the pollution is staying within the bay watershed after being emitted, CBF said.

Potter noted, “Even with these flawed assumptions in place, the model’s predicted ammonia levels on Delmarva fell far short of concentrations noticeable by people, or concentrations with any effect on human health. When the researchers performed limited air monitoring on Delmarva, they recorded the highest levels of ammonia in a city and at a waterfront point close to southern Maryland – not in rural, farmed areas. That’s no surprise to Delmarva family farmers raising chickens who live and work on their farms, right alongside their flocks. After all, they care deeply about air quality, since they breathe the same air their neighbors do.”

During the past 20 years, total pounds of chickens processed on the Delmarva Peninsula have grown by 36%, according to Delmarva Poultry Industry Inc.

Poultry operations on the Eastern Shore also contribute to phosphorus pollution — another primary bay pollutant that, like nitrogen, can fuel algal blooms that cause dead zones devoid of oxygen in the water. Phosphorus runs off farm fields during and after rains if farmers apply too much chicken manure to fields.