Negligible nitrate escapes
By LARRY KERSHNER
ELLSWORTH – A relatively inexpensive water quality practice in Hamilton County appears to have been successful in keeping 142 pounds of nitrates from reaching a creek that empties into the South Skunk River 1.5 miles away.
Bob and Leah Maass’ 15-year-old buffer strip was converted two years ago into a saturated environment, with the intent to see if the buffer’s switchgrass vegetation would use the nitrates leaching from a 16-acre corn and soybean crop.
The buffer was originally designed to reduce surface erosion from the field as it slopes northward to the stream, as well as provide a more stable creek embankment.
The saturated buffer is fed by a century-old tile line, Bob Maass said.
According to Dan Jaynes, of the U.S. Department of Agriculture’s Agricultural Research Service lab in Ames, weekly water quality testing of 16 monitoring wells in the 200-foot saturated buffer indicated the buffer took in 142 pounds of nitrates during 2014, primarily from three rain events, but the amount of nitrates found at stream side were negligible.
The weekly test results, taken when the tile is running, found nitrate levels as high as 18 to 27 parts per million from May through June, when tile ran the most. Nitrate levels must be 10 ppm or less to be considered safe for drinking or bathing.
But the 16 monitoring wells in the upper, middle and lower levels of the buffer were showing almost no nitrates.
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Jaynes said the well on the field side of the system contains 5 ppm nitrate (from corn/bean production), but as this groundwater flows into the buffer, the nitrate is removed by the buffer.
“That we are infiltrating more nitrate with the tile water we are introducing into the buffer,” he said, “and still seeing no nitrate in the shallow wells installed in the buffer, indicates the buffer is removing this added load just as we had hoped.
“It’s been real effective.”
He said the absence of nitrates in buffer’s various zones and at stream side indicates that the plants are denitrifying the nutrient.
“We didn’t think it would work this well,” said Tom Isenhart, a natural ecology specialist at Iowa State University.
Leah Maass said she’s been a longtime advocate for water quality initiatives in the region, which is why the buffer strip was planted 15 years ago in the federal Conservation Reserve Program.
Maass said she joined the Southfork Watershed Alliance 12 years ago and has been part of several water quality initiatives in Hamilton County. She is current chair of the Alliance’s fund committee.
A graduate of ISU with an ag education degree, Maass said she was excited to hear how well the saturated buffer worked during 2014.
“But it does make sense,” she said, “that water can be routed to be filtered. It’s exciting to have this opportunity, and it’s a fascinating thing to look at.”
The Maasses hosted a field day last summer talking to visitors about how the saturated buffer works.
“We’re just this close to ISU,” Leah Maass said, “so we should be doing something.”
Jaynes said the saturated buffer’s effectiveness is for nitrates, and not other nutrient escapes; although the buffer’s surface helps prevent stream bank erosion withholding phosphorus from the creek.
Jaynes said this spring USDA-ARS and ISU will team up to run a test and see how much nitrogen gas is being released from the buffer.
Nitrogen gas, or N2, is the result of plant material and carbon breaking down nitrates. Nitrates are a pollutant, but N2 is a harmless gas.
However, Jaynes said, 2015’s efforts will see if the amount of N2 would add to green house gas effects in the atmosphere.
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