First bioreactor in Iowa gets a recharge11/09/2017 | Soil Health, Water Quality
By Carol Brown, ISA environmental communications specialist
Nearly a decade ago, Mike Bravard agreed to have a backhoe dig a large hole alongside one of his soybean fields in Greene County near Jefferson. The hole would become the first bioreactor installed in Iowa.
A denitrification bioreactor is an edge-of-field structure designed to reduce nitrates in subsurface drainage before the water enters a river or stream. It consists of a shallow pit, approximately four feet deep, lined with plastic, filled with woodchips and covered with soil. A tile line is routed so it drains into the woodchips and exits the other side into the nearest water body. The microorganisms on the woodchips use the nitrates carried by the water as a food source. This process converts the nitrates into nitrogen gas, thus reducing the amount of nitrate remaining in the water.
Agriculture’s Clean Water Alliance (ACWA) funded the project and helped ISA collect water samples entering and exiting the bioreactor to monitor how much nitrogen was removed. If it worked, bioreactors could be another tool for farmers to use to remove nutrients lost from the ag landscape and improve water quality in receiving waters.
On Nov. 7 and 8, this inaugural bioreactor received major attention. The bioreactor was excavated on Nov. 7 to remove what was left of the original woodchips that have been working hard and decomposing for nearly a decade.
On Nov. 8, a field day was held at the bioreactor site hosted by ACWA, ISA, in cooperation with Capital Crossroads through "Conservation Conversations" — a joint effort to help people understand the upstream and downstream efforts needed to improve water quality. ACWA chairman Harry Ahrenholtz also recognized landowner Mike Bravard. “Oftentimes, being the first to do something like this — folks can be skeptical. Mike has been a great partner in this,” said Ahrenholtz. “It does take a certain amount of bravery to be the first. I give Mike and his family credit for that.”
ISA Environmental Scientist Keegan Kult spoke about the beginnings of this bioreactor and its performance. Chris Hay, senior environmental scientist for ISA Environmental Programs and Services, reviewed the nutrient reduction practices that can be used to help achieve the goals in the Nutrient Reduction Strategy.
“We monitored it closely and we are able to show about a 1,500-pound reduction of nitrogen over those first seven years,” said Kult. “That puts us in the $6–8 ballpark when we talk about the cost per pound of nitrogen removed. With bioreactors now, we can get closer to the $2–3 mark, even down to $1. Of the water that we pushed through the bioreactor, the average concentration reduction was 51 percent.”
New woodchips were added to recharge the bioreactor, the soil cap replaced, and now the bioreactor is ready for at least another 10 years of nitrate removal.
The bioreactor was the first of six installed and monitored as part of the ACWA project. Since then, numerous bioreactors have been installed across Iowa. ISA has overseen the installation of close to 30 since this first one.
Because of that experimental bioreactor installed in Bravard’s field in 2008, farmers and landowners now have another tool to reduce nitrogen entering rivers and streams.
“This bioreactor was the first that actually had the science, the data and the information for them to become a cost-sharable practice with the USDA,” said Wolf. “It also enabled bioreactors to be included in the Iowa Nutrient Reduction Strategy (INRS) as one of the eligible practices.”
As with all the INRS recommendations, using a combination of in-field and edge-of-field conservation practices will be the most effective in reducing nutrients from Iowa’s waterbodies and for those downstream.
For more details about the first bioreactor, read the article in the upcoming December Iowa Soybean Review. To see a time lapse video of a bioreactor being installed, click here.
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