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Grazing to protect water quality

By Staff | Oct 29, 2009

AMES – In the past decade, the public’s increased concerns about water quality have prompted cattle producers and researchers to take a new look at how they manage land along streams.

Grazing animals in pastures along streams and other riparian areas can have a significant impact on water quality, one animal science research said, due to sediment loss, nutrient transport and more. Proper grazing management of beef cows, however, can limit non-point sources of pollution in the steams, according to years of research at Iowa State University.

“Improper grazing management may increase bare ground near pasture streams,” said Jim Russell, an ISU animal scientist, “manure concentration near pasture streams, and sediment and nutrient loading of precipitation runoff.

“The greatest risk of non-point source pollution may be controlled by rotational grazing to restrict access to the stream and by using stabilized crossings with riparian buffers.”

In addition, research shows that stream bank erosion seems primarily related to stream hydrology, not grazing. “Streams are machines,” said Tom Isenhart with ISU’s Department of Natural Resource Ecology and Management. “The amount of water in the stream and the slope of the stream influence the stream’s power.”

Streams dissipate energy by following a meandering path and will cut bends and curves along their route, Isenhart said, even if humans intervene and try to straighten the streambed.

Isenhart explained that the South Skunk River near Ames was straightened in the 1930s. “By the 1990s, the stream was meandering again.”

Streambank stabilization can help manage streambank erosion by reducing the stream’s power, Isenhart noted. Weirs in the stream that function as pool-riffle structures to slow down water velocity can also reduce a stream’s erosive power.

Examples of these options can be seen at the Ann Smeltzer Charitable Trust and Iowa Learning Farm south of Otho, he said.

“The Smeltzer demonstration farm is unique, because it has a number of features that are ideal to showcase a variety of conservation and environmental practices,” said Jim Patton, Region 7 director for ISU Extension. Patton noted that a stream running through the farm provides a unique opportunity to illustrate various streambank stabilization and buffer strip techniques.

“These practices will have the ability to reduce sediment and nutrients in surface water, which ultimately improves water quality,” he said.

A national model

ISU-sponsored research on the use of riparian buffers for soil and water quality in central Iowa’s Bear Creek watershed has shown that dramatic improvements in the condition of the streambanks can be achieved in just a few seasons.

The Agroecology Issue Team of the Leopold Center for Sustainable Agriculture developed a riparian management system model that integrates a buffer of trees, shrubs and grasses, technologies for streambank stabilization and more.

These components work together to reduce the load of nitrates and other pollutants released into the stream. They also provide habitat for wildlife.

In years past, Bear Creek’s wildlife habitat had been adversely affected by high sediment loads, Isenhart said, while water quality had been degraded by high concentrations of suspended solids, nutrients and agricultural chemicals.

The long-term goal of the project was to restore functioning riparian zones along the creek, which would improve aquatic habitat, water quality and the aquatic community in the creek.

Why worry about the health of the aquatic community in the creek?

“Fish and invertebrates are indictors of the health of our streams,” Isenhart said.

Streambank stabilization was the first component to be completed at Bear Creek. Researchers used stakes of quick-growing willow to add structure and stability to the bank.

Biodegradable erosion control fabric was used to hold soil to the bank. After the streambanks were stabilized, the multi-species buffer strip was established.

The first zone of the strip, pastures closest to the stream, included a 33-foot wide and made up of several species of trees, including the willows anchoring the banks.

The second zone included a 12-foot wide area planted with many shrub species. The third zone featured a 21-foot wide strip of grasses. The widths of a buffer strip are flexible, depending on factors such as erosion levels, pollution potential and landowner preferences, according to ISU.

“When all else is held equal, land use around streams can be very important,” said Isenhart, who urges landowners and livestock producers to understand how grazing management impacts water quality. “Grass filters and riparian buffers and can play a key role in controlling sediment and nutrient loss.”

Contact Darcy Dougherty Maulsby by e-mail at yettergirl@yahoo.com.

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