Australian pineapple, Danish trout and Midwestern U.S. corn farmers are not often lumped together under the same agricultural umbrella. But they and many others who raise crops and animals face a common problem — excess nitrogen in drainage water.
Whether it flows out to the Great Barrier Reef or the Gulf of Mexico, the nutrient contributes to harmful algal blooms that starve fish and other organisms of oxygen.
But there's a simple solution that significantly reduces the amount of nitrogen in drainage water, regardless of the production system or location — denitrifying bioreactors.
"Nitrogen pollution from farms is relevant around the world, from corn and bean farms here in Illinois to sugarcane and pineapple farms in Australia to diverse farms bordered by ditches in Belgium. We're all dealing with this issue. It's really exciting that bioreactors are bringing us together around a potential solution," said Laura Christianson, assistant professor in the Department of Crop Sciences at University of Illinois.
Denitrifying bioreactors come in many shapes and sizes, but in their simplest form, they're trenches filled with wood chips.
Water from fields or aquaculture facilities flows through the trench, where bacteria living in wood chip crevices turn nitrate into a harmless gas that escapes into the air.
20-40% Reduction in Nitrate
This edge-of-field conservation practice has been studied for at least a dozen years, but most of what scientists know about nitrogen removal rates is based on laboratory replicas and smaller-scale experimental setups.
USDA's National Resource Conservation Service published a set of standardized bioreactor guidelines in 2015, based in part on Christianson's early field-scale work, and now more and more U.S. farmers are adding bioreactors. They're catching on in other countries, too.
"After gathering all the data, the message is bioreactors work," Christianson said. "We've shown a 20-40% reduction in nitrate from bioreactors in the Midwest, and now we can say bioreactors around the world are pretty consistent with that."
She said bioreactors, like all conservation practices, have their limitations, but nitrous oxide emissions aren't one of them.
"People are worried we're just transferring nitrate in water for nitrous oxide, which is a greenhouse gas. We don't know the full story on nitrous oxide with bioreactors yet, but we can say with good confidence they're not creating a huge nitrous oxide problem," she said. "They're just not."
Christianson said farmers frequently ask her about monitoring the water in bioreactors, so she and her colleagues partnered with the Illinois Farm Bureau to create a series of step-by-step videos explaining how to test the water.
"For monitoring, there are two parts. You have to know how much water is flowing through the bioreactor and how much nitrogen is in the water," she said.
The short videos, which are aimed at non-researchers such as farmers and water quality volunteers, break the process down into five steps.
Christianson, who may just be the world's biggest cheerleader for bioreactors, admits the monitoring guidelines and video series are a little self-serving.
"We included recommended monitoring approaches so that more people will build them, and then more people will monitor them. And then we'll have more data to show how well bioreactors work and how we can make them work better."
Watch Dr. Laura Christianson's Videos on Denitrifying Bioreactors and Testing Water
This video series is intended for conservation professionals and water sampling volunteers who are monitoring woodchip bioreactors to estimate…
In the second video of this series, we explain how to use water depth sensors to measure flow rates in the field. The video covers how to conn…
If you want to know how much nitrate your woodchip bioreactor is removing, you need to know how much nitrate is in the water entering and leav…
In the fourth video of this series, we explain how to connect the water depth sensor to the transfer shuttle in the field , how to transfer th…