Southern Illinois University (SIU) researchers are finding structures that reduce soil erosion also influence water quality, and a unique saturated buffer design works well.
Jon Schoonover, SIU hydrology professor, recently reported on research projects with Karl Williard, SIU watershed management and hydrology professor. The Illinois Nutrient Research and Education Council (NREC) funds the research.
The two scientists, along with colleagues and many graduate students, are studying water quality impacts from water and sediment control basins or WASCOBs in Menard County and saturated buffers, including a unique pitchfork design, in Moultrie County.
“These (WASCOBs) are ubiquitous across the landscape. There are tons of them out there,” Schoonover said. “They’re designed for water and sediment control, but there is very little evidence what they do in terms of water quality.”
Researchers had planned to install WASCOBs into frozen soil during the 2018-19 winter, but weather delayed installation until late June. In the study, WASCOBs with and without cereal rye cover crops are compared with two ephemeral gullies also with and without cover crops. Automated water samplers pull samples from drains.
WASCOBs intercept and detain runoff in a basin where sediment settles. Runoff water is slowly released through an underground outlet that moves the water through a pipe to a stream.
Schoonover reported the project WASCOBs are settling out sediment compared to the ephemeral gullies. But the summer installation plus weather conditions caused an ephemeral gully to form in the field because the newly built structures don’t control rill or sheet erosion elsewhere, he added.
The WASCOBs also reduced the amount of phosphorus and nitrate moving from the field compared to the ephemeral gullies. As expected, the upper WASCOB basins captured more nitrogen and phosphorus than lower ones. “That’s what we wanted to see, to see them functioning,” he said.
In Moultrie County, the research compares a standard saturated buffer with a pitchfork design that has a set of three dispersion lines, which treats three times the amount of drainage water.
Saturated buffers are vegetated strips between tile drained fields and waterways. A saturated buffer uses denitrification and vegetative uptake to remove nutrients from drainage water.
The Moultrie County saturated buffers were installed March 15 near Lake Shelbyville, and results presented were from Oct. 28 through Jan. 14 samples.
Backflow valves installed on pitchfork laterals prevented backflow, especially when water tables were high, Schoonover noted. “During storms, we’re seeing water going the wrong way in the standard (buffer) design and coming back,” Schoonover explained. “Anytime (ground)water levels are above tile lines, I think a saturated buffer needs to have a backflow valve.”
In addition, the outside pitchfork lateral includes a check valve that allows the farmer to control water levels and do fieldwork.
Water samples from the saturated buffer show a reduction in nitrate levels, Schoonover reported. However, the pitchfork design worked more efficiently, removing 11 pounds of nitrate per acre per year in early data.
The researcher speculated water tests will show different results when a cover crop mix with seven species is planted as part of the research.
In addition to NREC, Schoonover thanked Illinois Farm Bureau, the Natural Resources Conservation Service and Illinois Land Improvement Contractors Association for helping with the research.
Hear Schoonover’s research presentation.