Industrialized animal farms put inexpensive meat on Americans’ dinner tables, but these farms also have been linked to serious environmental and human health problems.
This summer, a long-awaited study on the effect of such farms on North Carolina water quality was released, but how its results will be interpreted by regulators remains unclear.
The study, conducted by Stephen Harden of the U.S. Geological Survey, found higher levels of ammonia and nitrates in streams near concentrated animal feeding operations, or CAFOs. Other water quality indicators, including phosphorous and total organic nitrogen, were not higher near CAFOs.
Ammonia and nitrates are forms of nitrogen, a component of animal waste and fertilizer. In streams, nitrogen acts as a fertilizer, causing algal blooms that can kill fish. In drinking water, high levels of nitrates can cause a potentially fatal blood disorder called “blue baby syndrome” in infants.
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Although elevated near CAFOs, the concentrations of ammonia and nitrates detected by the USGS are still much lower than what the U.S. Environmental Protection Agency and the state consider dangerous to human health.
The study was commissioned by the N.C. Environmental Management Commission in response to a petition filed in 2007 by several environmental groups.
Hog waste is typically stored in open lagoons and sprayed on cropland as fertilizer. In the 1990s, leaking unlined waste lagoons in North Carolina were found to contaminate groundwater. Fertilizer runoff – whether from CAFOs or elsewhere – also has been implicated in algal blooms and fish kills.
In 2007, the state legislature banned construction of new lagoons and mandated stricter rules for the way new CAFOs store and process waste.
Experts weigh in
The findings of Harden’s study have been met with a variety of reactions from scientists, water quality advocates and state officials.
“I hope DENR will look at these results and see that it shows significant differences between water quality impacts in areas where these animal feeding operations are present and areas where they are not,” said Gray Jernigan, an attorney with Waterkeeper Alliance, an international environmental group with offices in North Carolina.
But while the results may be statistically significant, they may not be biologically significant, said Deanna Osmond, a professor in the soil science department at N.C. State. In other words, it’s not clear that the higher nitrogen levels actually matter to ecosystems or individual organisms.
The USGS posted its raw data online well before the report was released, and the N.C. Pork Council commissioned its own examination of the data.
The Pork Council’s consulting firm hired Bill Showers, an N.C. State professor and director of the RiverNet program, which studies nitrogen in the state’s waters. His report, released before the USGS report, is critical of some of Harden’s methods and analysis.
Harden sampled streams only six times – once every two months for just under a year. That’s too few data points, Showers said.
Showers also was critical of the way Harden grouped watersheds for analysis. Harden classified the watersheds into three types: background, where no CAFOs are present; swine; and swine/poultry.
“The problem I have is that watersheds are much more complicated than one, two or three,” Showers said.
Because the background watersheds and CAFO watersheds differ in factors such as size, presence of wetland and types of soils, he said, the comparisons are untrustworthy.
In an interview with The News and Observer, Harden defended his analysis. The sites were selected and categorized carefully within the limitations of where CAFOs are located in the state, he said, and their comparisons are statistically valid.
He also said that his team took samples as frequently as possible, given that they looked at more than 50 sites.
Neither the Harden report for the USGS nor the Showers report for the Pork Council was published in a peer-reviewed journal, although Harden’s report was reviewed by other USGS scientists.
Ken Reckhow, a professor emeritus of water resources at Duke, reviewed both studies at the request of The N&O.
Reckhow did not agree with Showers that the water samples were taken too infrequently or that the sites were not comparable.
In fact, Reckhow’s major criticism of the USGS report was that Harden could have done more with the data he collected.
Because of the way Harden set up his statistical model, Reckhow said, he didn’t actually answer the question of how important the population of farm animals is when it comes to clean water.
“That struck me as strange because that would be one of the first things I would do with that data set,” he said.
What Harden’s analysis did show was that three key factors determine whether nutrients showed up in streams near CAFOs: density of swine barns (a different metric than number of animals), percentage of wetlands and total acreage available for applying swine waste manures.
“Some watersheds are better at processing nutrients than others,” he said.
Showers’s report came to a similar conclusion. “We recognize that different watersheds may require different modifications depending upon the geology, elevation, soil types and drainages,” he wrote.
But Showers concluded that wetland size rather than animal population is the most significant predictor of nutrients in streams – a different finding than Harden’s and a conclusion that Reckhow disagrees with.
“That statement on its own is incorrect,” Reckhow said. “A wetland really cannot be said in general terms to be a source of nitrogen or phosphorous unless something that is a source is flowing into the wetland, like a wastewater treatment plant, or discharge or runoff from a CAFO.”
Reckhow also pointed out that one of Showers’s own graphs shows that smaller wetlands have higher levels of nitrates when CAFOs are present.
“The conclusion from that graph is that CAFOs influence concentration in streams,” he said.
Study’s impact on policy unclear
The Pork Council commissioned the report to better understand the USGS data, said the group’s CEO, Deborah Johnson. The council funds water quality research, she said, including monitoring and analyzing surface water.
“We encourage and we support credible science and scientific research,” Johnson said, “because we want that information to make sure we’re safeguarding our natural resources.”
It’s too early to say what the state Department of Environment and Natural Resources will do with the USGS findings, said Christine Lawson, an environmental engineer in the Division of Water Resources.
“There’s not been an official action plan made,” Lawson said. “We’re still working on the results and determining how that will fit in our regulatory process.”
DENR could make regulatory changes within the framework of existing statutes, Lawson said, but changes to the statutes themselves would have to be done by the General Assembly.