Constructed wetlands meet expectations

CULLOM, Ill. — A constructed wetland designed to receive tile drainage water from 73 acres of corn and soybeans is doing its job of removing nitrates.

The 1.1-acre wetland treatment area of Fulton Farms was constructed in August 2018. It also includes an adjacent 2.45-acre buffer area of pollinator habitat.

“After a couple of years, it’s removing over 1 ton of nitrate from the water annually. The nitrogen gets processed through the wetland and converted into nitrogen gas,” Jill Kostel, The Wetlands Initiative water resource program director, said at a recent Livingston County Soil and Water Conservation District tour.

TWI has been involved with installing six constructed wetlands on working farms in Illinois. Kostel noted other examples of like success.

An 0.8-acre constructed wetland that is 3.6% of the total acres drained into the system in Bureau County removed 8 tons of nitrate in 2019 and an average annual removal efficiency of 80%.

Another Bureau County system that was 0.8 acres and 1.8% of the total acres drained removed 1.6 tons of nitrate in 2019 and a four-year average removal efficiency of 20%.

“Usually in year two and three is when it gets near to where it should be for nitrate removal once the carbon builds up,” Kostel said. “The Nature Conservancy has 20 years of monitoring that show basically the same thing.”

TWI’s role is to work with farmers and help them address their nutrient loss issues and concerns.

“Being The Wetlands Initiative, we know one practice real well — wetlands. We’re trying to take that knowledge and use it to design constructed wetlands for cropland tile drainage treatment,” Kostel said.

“They are considered constructed because we are forcing and making them artificial ecosystems. We’re bringing the water into an area with the purpose of removing nitrate from the tile drainage.

“We try to put these on acres that are obviously not the most profitable — that would be ridiculous — but on the least profitable or underperforming acres.”

Design

The system is designed to intercept the tile main from the field and construct the wetland to intercept the tile water before it is discharged into a ditch, waterway, or creek and on downstream. The size is based on the amount of tile drainage entering the main.

Wetlands are able to remove nitrogen through a combination of physical, chemical and biological processes. These naturally occurring processes adsorb and absorb, transform, sequester and remove the nutrients and other chemicals as water slowly flows through the wetland.

The main physical processes of nutrient removal are particle settling, or sedimentation; volatilization, releasing as a gas into the atmosphere; and sorption. Sorption includes a nutrient adhering to a solid, adsorption, or diffusing into another liquid or solid, absorption, according to Kostel.

Chemical processes include transformations of nutrient forms and chemical precipitation, in which a solid compound is formed out of a liquid through a chemical reaction.

The main biological processes are uptake, or assimilation, by plants, algae and bacteria and transformation processes conducted by microbes.

All of these processes occur throughout the different wetland compartments, which include water; biota, or plants, algae and bacteria; litter; and soil.

“It does remove phosphorous in terms of phosphate or phosphorous attached to sediment. It’s just that wetlands do not have a biological process for that. Yes, plants do take up the phosphate, as well as other nutrients, but plants die and when they die they release everything back out. So, it’s just temporary storage,” Kostel said.

“Overall, constructed wetlands are very cost-effective. They are a capital outlay. It’s a one-time payment, but wetlands will work forever.

“As long as there’s water going into the wetland, it’s going to be removing nitrogen. As long as you have some plants in there, it’s happy removing nitrogen.

“So, if you look at the cost over, say, a span of 50 years, you find that tile treatment practices are the most cost-effective way of removing nitrogen.”

Financial Programs

There is financial assistance programs through the farm bill, including the Environmental Quality Incentive Program used by Jim Fulton or the Conservation Reserve Program.

Kostel estimates about 96% of the project’s cost is for excavation.

“There are incentive payments out there that are very attractive. We realize a $60,000 to $80,000 cash outlay is not real feasible for most people. So, if we can use the farm bill, The Wetlands Initiative provides some grant money, but we always needs some money buy-in from the farmer,” Kostel said.

“CRP provides cost-share on the construction, but also gives you that soil rental payment for 15 years. This is a continuous practice and as long as there’s acres available and you go in the office you can sign your contract that day. There’s no bidding, there’s no waiting,” she said.

“You can also sign up after your 15-year contract expires for another 15 years under the current farm bill.

“We never say these practices are permanent. We don’t intend them to be permanent, per se. We don’t know what’s happening in the world in 20 years. Maybe you want to farm this area once again. Of course, you’re going to have to find the material to fill it in.”

TWI’s Role

TWI provides free technical assistance and “boots on the ground” to help get the project completed.

“Every one is designed differently. We sat down with Jim at his kitchen table. We had a rough idea, a preliminary concept, and worked with him to adjust things,” Kostel said.

“We handle the paperwork, any permits. We got the Army Corps of Engineers permit for this one to say that it’s not a real wetland. The Corps recognize it’s an artificial wetland, so they don’t have any jurisdiction. So, he can fill this in after his contract periods is over if he wishes and there’s no penalty.

“However, if we’re in a 100-year floodplain we have to get permits from the state to make sure we’re not impacting threatened and endangered species, as well as not impacting the land across the stream by raising water levels.”

Numerous models are developed by TWI to show how the creek and wetland reacts. The modeling also addresses any concerns for the landowner and upstream landowners have related to an impact on tile drainage.

“We don’t do designs that impact tile drainage. Water is always free-flowing,” Kostel added.

There are no permanent easements in the construction project.

“This is your land. This is your practice operating for you as part of your tile drainage system,” Kostel said.

“We know there’s a lot more tile going in these days in response to our changing climate, our new rainfall pattern. We want to make sure we can get in there to plant and harvest.

“We want to work with those tiling contractors ahead of time as you’re planning that system, make a space for a tile treatment practice. It would be great if there’s a wetland, but there’s also bioreactors, saturated buffers, drainage water management options, as well.

“You just need a plan so you don’t have to do everything at the same time. You just need to plan for it, but usually the practice is a very small percentage of what you’re paying for the tile system installation. Add it into your loan if you’re getting a loan for a tile drainage system.”