Bioreactors showing success
BOONE — Bioreactors are gaining popularity as an edge-of-field conservation drainage practice and have proven to help reduce the amount of nitrates in drainage tile water before it is released to surface waters.
In order to help bring more awareness to edge-of-field conservation practices such as bioreactors and saturated buffers, Prairie Rivers of Iowa and Iowa Learning Farms hosted a field day last week at the Field Extension Education Laboratory (FEEL) near Boone.
The event included a tour of a bioreactor that is being used for research purposes for Iowa State University and presentations from an engineer, Iowa Learning Farms and a local landowner who has recently had a bioreactor installed on this farm.
Jace Klein, an engineer with Ecosystems Services Exchange (ESE), spoke at the event.
ESE, according to the company, can assist with the planning, design, managing and monitoring of agricultural land. They help by implementing in-field or edge-of-field water management practices that improve productivity and conservation.
The company claims they are able to determine which practice will be most effective and economically feasible for your land and will utilize a combination of real-time nitrogen sensing, automation and DRAINMOD to analyze and model the nutrient reductions in the field.
Klein said that, although they are a conservation company within the private sector, they are also technical service producers for the NRCS.
“We are able to do NRCS-approved practices, so if you cost share through them, we are able to do that,” he said.
Klein said 30 to 80 acres is a suitable site for a bioreactor.
“If you have anything larger than that, we might want to look into something like a wetland,” he said, adding they also look for an area that doesn’t have much surface drainage.
“We worry about sediment plugging up the tile lines, so that is pretty important,” Klein said.
Having too many low depressions or low spots in the field can also be a reason to stray away from having a bioreactor installed.
“You are creating a higher water table when you put those structures in, so when you create that higher water table, if you have a low spot in your field, you are at risk of flooding some of that crop out,” he said. “There are a lot of reasons with some sites we have to turn down or we just have to say that you can have this bioreactor, but you might have a two acre wetland out there.”
The design process
Klein said if a producer or landowner is interested in an edge-of-field conservation practice, such as a bioreactor or saturated buffer, the first step is initial site selection.
“Either you guys as landowners come to us with interest, or a watershed coordinator gets a hold of you, then the next thing to do is, we come out, or whoever is designing your bioreactor or saturated buffer, and do a site survey,” he said. “We just kind of take into consideration all of the conditions of the site. We have to find that tile outlet.”
Locating tiles can sometimes be a daunting task.
“Tile maps seem to be the unicorn of the Midwest,” he said. “Some exist. Some don’t. Some are really good and some are hand-drawn on a napkin that someone’s great-grandpa put down. But any time there is a map that is great, but finding the outlet and knowing what has to be done with it is the big part.”
Klein said after the tile outlets are found and taken into consideration how that will effect the design; they then process all of the data and begin making plans.
Installing a bioreactor
Klein said after the bioreactor plans are made, they dig a trench, put a plastic liner down to help avoid any water getting lost outside of the bioreactor, then a 2 to sometimes 4-foot pile of woodchips is loaded into the trench.
A geotextile landscape fabric is then installed before it is covered up with earth fill.
Klein said bioreactors can be extremely effective, with an average of 50 percent total nitrate reduction.
“On average, 50 percent is a pretty common number out there,” he said. “Of that water that actually enters the bioreactor, they are extremely efficient for what water goes in there. A lot of times there is a 90 percent reduction of nitrates in the water that makes it to the bioreactor, but because we have bypass flows during high flow events, that is where we get the 50 percent overall of total reduction on average.”
Klein said the jury is out on the lifespan of the woodchips that are installed into bioreactors.
“We haven’t had very many bioreactors long enough,” he said, adding that the first bioreactor built by the Iowa Soybean Association recently had its woodchips dug up to find out they were much deteriorated.
Research continues to be done on woodchips to find the ideal size and consistency that will work best in a bioreactor.
“This was the first one,” he said. “We have a bigger process now. The things that really kill these woodchips are extremes in weather, too wet or too dry. That will really break them down and the way we try to design them now is to keep them saturated more times of the year, so hopefully the more current bioreactors that have been designed since the standard one has been out will see a longer lifespan of the woodchips.”
Joseph Reutter, a Boone-area landowner, said he and his brother own a 100-acre parcel of farmland where they have a bioreactor treating about 40 acres.
Reutter said they recently took some measurements with test strips and they found the water coming into the bioreactor was measuring at 10 to 20 parts per million (ppm) of nitrates.
“You don’t want it much over 10 for safe drinking water and algae bloom,” he said.
The water tested coming out of the bioreactor was down to between 3 to 5 ppm of nitrates.
“That’s actually safe enough for a newborn baby or a pregnant mother to drink and that’s actually better than tap water at the farmhouse faucet which is part of the rural water district,” he said. “It seems to be working, but we are still learning.”
Kayla Bergman, watersheds and waterways program coordinator for Prairie Rivers of Iowa, said Reutter’s bioreactor was put in last November.
“This is only nine months in and is already effective in reducing nitrates,” said Bergman.
Klein said saturated buffers use the same process at helping to clean up surface waters — denitrification.
“Except it uses the vegetation with all of the organic matter in the soil,” he said. “And most of the denitrification does come from that organic matter. I’m sure there is some uptake of nitrates from the actual buffer system itself, but most of that denitrification we are getting is actually in the soil, but again, it is the same type of removal efficiencies.”
He added there is a saturated buffer they are monitoring right now and said it is not uncommon that close to 100 percent of the nitrates that actually goes into the buffer is removed.
“It’s not common to see that all,” he said. “But, then again, looking at the bypass flows, on average there is 50 percent again of total reduction. Some people think only 50 percent, but, for me, that is a pretty big number. If you can take out 50 percent of the total loading on average per year, I think that is really significant.”