OSU Research Team Investigates Streambank Erosion and Phosphorus SourcesTue, 09 Dec 2014 11:56:08 CST
To protect water quality in eastern Oklahoma streams, Oklahoma State University researchers are studying sources of phosphorus and ways to limit phosphorus input to streams.
One project led by Garey Fox, Oklahoma Water Resources Center interim director, and funded by United States Geological Survey and U.S. Environmental Protection Agency Region VI programs, explored phosphorus concentrations in the soil and streambank erosion in the Barren Fork Creek watershed.
The BFC watershed is home to a regional poultry industry that generates litter. Because it is expensive to ship, poultry litter was historically applied to nearby fields as fertilizer. Phosphorus accumulates in the soil, which can wash into streams as sediment, reducing the water quality.
Streams in the BFC watershed have composite streambanks made of a silty topsoil overlaying an unconsolidated gravel layer. When a bank’s gravel layer is undercut by the streamflow, it can fail rapidly. This erosion can remove acres of property annually. The combination of phosphorus-laden sediment washing into streams and large-scale streambank erosion is proving to be a serious environmental issue, said Fox.
”Streambanks can represent a majority of the sediment and nutrient loads for some watersheds,” he said. “In extreme cases, streambanks can account for as much as 80 percent to 90 percent of the total sediment load, making them a clear choice for investigating phosphorus sources.”
Oklahoma emphasizes and invests in riparian protection as a best management practice, especially in the Illinois River watershed. A protected riparian zone has astrip of plant life growing alongside its streambanks, reducing erosion through the additional soil strength the plant roots provide.
Composite streambanks tend to be weaker because roots only hold onto the upper soil layer and leave the gravel beneath vulnerable to erosion. The team tested the effectiveness of riparian protection on this more volatile type of streambank. If proven beneficial, the research could support future installation of buffers or filter strips.
Of the 10 eroding areas studied, seven had a protected riparian zone and threewere unprotected. National Agricultural Imagery Program images, taken in 2003, 2008 and 2010 showed streambank erosion occurred at nearly every site—most prominently at sites without a historically protected riparian zone. Sites with riparian protection still eroded, but at slower rates than the unprotected banks.
“Though it was hypothesized these unprotected zones also would have higher phosphorus levels, the soil sample results of an onsite test revealed no significant differences,” Fox said. “Interestingly, phosphorus levels appeared to be related to the distance from the Illinois River; closer sites had higher levels. It’s likely the sandier upstream soils were not as buffered for phosphorus as the silt-dense downstream soils, creating an extra variable in the study.”
Approximately 29 percent of soil samples had phosphorus levels high enough to be of environmental concern. With a combination of soil analysis and video reconnaissance, the team determined that more than a third of the BFC watershed has unstable banks that likely provided 10 percent of the estimated dissolved phosphorus load and a larger percentage of the total phosphorus load.
“Streambanks with riparian buffers have three to four times less sediment and phosphorus entering the stream,” Fox said. “The results give quantifiable evidence for the value of riparian protection.”
Installed and maintained riparian buffers are important for reducing property loss due toerosion, filtering out pollutants before they reach the stream and shading stream channels, all of which improve water quality and aquatic habitat.
Landowners may receive financial and technical assistance for the installation of riparianbuffers from the Conservation Reserve Enhancement Program or the Environmental Quality Incentives Program. You can learn more about the CREP program from the Oklahoma Conservation Commission by clicking here and about the EQIP program from the USDA Natural Resources Conservation Service by clicking here.
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