Effective Filters

New findings prove saturated buffers can reduce nutrient loading in the Gulf of Mexico.

(Progressive Farmer image by Bob Elbert)

Widespread installation of saturated buffers in the Midwest can effectively reduce nutrient loads in waterways and the Gulf of Mexico, according to a new study.

A collaborative research project by the Agricultural Drainage Management Coalition (ADMC) and U.S. Department of Agriculture's Farm Service Agency (FSA) shows how many miles can be installed in the Midwest and the overall nitrate-N load reduction.

The study also shows carbon-rich riparian buffers are one of the most cost-efficient ways to remove nitrates from water exiting field drainage tiles.

"This is the first stab at estimating the impact of wide-scale implementation of saturated buffers," ADMC executive director Keegan Kult says. "It gives people an idea or a road map of what needs to be done to achieve the overall goal of a 45% reduction of nitrogen and phosphorus entering the Gulf."

A saturated buffer is an edge-of-field practice designed to remove nitrates -- a form of organic nitrogen that's potentially dangerous to infants at high levels -- from tile water. Instead of water flowing directly into a stream, a control structure redirects a portion of the flow to a distribution line in the buffer that runs parallel to the waterway.

Water filters through the soil profile. The opportunities that exist for denitrification and plant nutrient uptake in the buffer with perennial vegetation are used.

"It doesn't work everywhere, but it's an effective practice," Kult says.


ADMC asked the University of Illinois Department of Crop Sciences to identify site potential in the Midwest as part of the study. The university developed a decision support tool that revealed a conservative estimate of 46,920 miles of cumulative stream bank suitable for saturated buffers. The practice requires suitable slope for drainage and the right soil.

The study shows saturated buffers could potentially treat nearly 9.5 million acres, or 22%, of tile-drained Midwest land. If fully implemented, the practices could:

> remove 5 to 10% of the tile-contributed nitrate load

> remove 2 to 5% of the overall nitrate load delivered to the Gulf of Mexico.

"Even though those numbers don't sound huge, that's a pretty significant amount," Kult explains. "Especially when you pair saturated buffers with other nutrient-reduction practices like cover crops and wetlands."

The 2008 Gulf Hypoxia Action Plan's 45% nutrient-reduction goal is aimed at shrinking the hypoxic or dead zone in the Gulf -- an oxygen-depleted area largely absent of aquatic life -- to less than 5,000 square kilometers, or 1,930 square miles, by 2035. The dead zone measured 2,720 square miles in 2018, the fourth smallest area since 1985, according to the EPA.

Point and nonpoint sources like wastewater treatment plants and nutrient runoff from farm fields, respectively, contribute to the problem. The latter is the primary contributor, experts contend.


Many Midwest states have implemented voluntary nutrient-reduction strategies to improve water quality. Plans include a suite of conservation practices to curb nonpoint pollution.

Studies show saturated buffers are an effective, low-cost edge-of-field practice.

The ADMC and FSA monitored seven sites in the Midwest from October 2017 to August 2018. Similar projects also were conducted from 2012-2015 and 2016-2017.

Average nitrate concentration reduction ranged from 41 to 98%. Nitrate load reductions ranged from 10 to 194 pounds.

Installation cost of the seven saturated buffers in Illinois, Iowa and Minnesota averaged $3,584. The buffers operated at an efficiency of $1.22 per pound of nitrate removed over the 20 collective site years of the monitoring process.

A denitrifying wood chip-filled bioreactor typically costs $8,000 to $12,000, averaging 95 cents per pound for nitrate removal, according to Iowa State University (ISU) data. A wetland costs more than $10,000 per acre to build with an average efficiency rate of $1.32 per pound of nitrate removed, ISU research shows.

"Saturated buffers are one of the top, most economical nitrogen reduction practices," says Chris Hay, Iowa Soybean Association (ISA) senior environmental scientist.

He says ADMC nitrate reduction data is consistent with the association's saturated buffer findings. ISA's Environmental Programs and Services advances science-based research to improve the environment and more efficient and profitable soybean production.

Hay told producers and landowners during the recent ISA Farmer Research Tour that saturated buffers are ideal for improving water quality.

"There's not a lot of management farmers have to do," he says. "By using existing buffers, you don't take land out of production."


Studies indicate converting a standard buffer into a saturated one could remove 13 times the annual amount of nitrate, while making the practice six to 10 times more efficient in terms of dollars per pound of nitrate removed.

A desire to help neighbors downstream prompted two research participants to upgrade existing buffers.

Mark Schleisman's saturated buffer is a couple hundred feet long on the banks of Elk Run Creek, in Carroll County, Iowa. It treats about 30 acres of farmland.

Saturated buffers don't provide an economic return. The Lake City grain and livestock farmer is fine with that.

Schleisman's ground eventually drains into the Raccoon River, a drinking-water source used by more than 500,000 people in the Des Moines metro area. The city's waterworks unsuccessfully sued three upstream counties for allegedly allowing nitrates coming from 10 drainage districts they control to pollute the river. The entity claimed ag nutrient runoff posed a public-health threat and a financial burden to its customers when its nitrate-removal facility operates.

The study concluded Schleisman's buffer reduced nitrate concentration of water entering the buffer by 74% and removed 194 pounds of nitrogen.

"I don't see a nitrate discharge over 10 parts per million anymore," Schleisman says of the treated tile water. "It takes us (farmers) all onboard to truly reduce the hypoxic zone and nitrate load in water." The federal drinking water standard is 10 parts per million.

David Legvold, of Northfield, Minnesota, a retired educator-turned-farmer, agrees with his colleague to the south.

The first steps to truly addressing water-quality concerns is acceptance there is a problem and implementing multiple conservation practices, even if they don't have a financial return, Legvold says.

He paid about one-third of his buffer that cost about $3,500, while federal and state grants picked up the rest. It's about 750 feet long and drains 75 acres. His land drains into the Cannon River, which dumps into the Mississippi River at Red Wing, Minnesota.

"The research assures farmers that they can do something with a buffer that enhances water quality," Legvold says.

His buffer averaged a 41% nitrate concentration reduction and removed 16 pounds of nitrates during the study period.


Environmental specialists say cost-share funds are available to pay for most, if not all, the cost of a saturated buffer.

The federal Environmental Quality Incentives Program, Conservation Reserve Program and Clean Lakes, Estuaries and Rivers Initiative are a few options.

States have funds available through various nutrient-reduction efforts and other initiatives. The Minnesota Department of Agriculture paid for a portion of Legvold's buffer.

Commodity and livestock groups contribute to clean-water efforts. The Iowa Pork Producers Association provided $25,000 last year to the Iowa Department of Agriculture and Land Stewardship to scale up edge-of-field practices.

Kit Paper, a former project coordinator for the Wright County, Iowa, Soil and Water Conservation District, says industry partners will often cover costs to install a saturated buffer that tax dollars and grants don't.

"There's a good chance for 100% funding in priority watersheds," Paper says. "If costs are covered, why wouldn't you do it?"