By Mary Hightower
University of Arkansas System Division of Agriculture
FAYETTEVILLE, Ark. — Imagine a dump truck dropping 13 tons of dirt into the waters of Brush Creek, a waterway that feeds northwest Arkansas' primary drinking water source, Beaver Lake.
That's how much soil and sediment researchers measured going into the stream as runoff due to a single large storm event.
Finding the amount of storm-washed sediment entering Brush Creek was one of the goals of a recent study, " Watershed-scale controls outweigh local crossing effects on sediment loss from unpaved roads ," published in the Journal of Environmental Quality.
Water quality scientist Shannon Speir said the study was an outgrowth of other stream monitoring work. She and her students are regulars in the watersheds of northwest Arkansas, examining runoff, sediments and other issues that affect area rivers, creeks and lakes.
"We were already out there regularly doing sampling — wading through the creek, collecting water samples up and down the watershed — and we kept driving over these unpaved roads to get to our sites," Speir said. "It was hard to ignore — ruts, loose gravel washing toward the stream, ditches routing runoff directly toward the water."
Speir is an assistant professor of crop, soil and environmental sciences for the Dale Bumpers College of Agricultural, Food and Life Sciences at the University of Arkansas and for the Arkansas Agricultural Experiment Station, the research arm of the University of Arkansas System Division of Agriculture.
Northwest Arkansas is a study of contrasts. It is one of the 20 fastest growing metros in the United States, yet it is also very rural, with Ozarkian hills and valleys supporting cattle and poultry agriculture. Its pastures, farms and forests are crisscrossed with dirt roads. Its waterways are home to low-water crossings, culverts and "direct crossings," in which vehicles drive through the water.
"We knew that 85 percent of Arkansas county roads are unpaved," Speir said. "Previous research on unpaved road impacts had almost entirely been done in Pacific Northwest forestry settings — not in pasture-dominated, rural watersheds like ours.
"We were already in the right place asking adjacent questions, and it felt like a natural and necessary extension of the work," she said.
Testing the hypothesis
Speir, along with lead author and program associate Kathleen Cutting, Bumpers College master's student Karessa De La Paz, recent University of Arkansas graduate Caroline Anscombe, and Alana Strauss, a program associate with the Division of Agriculture, set out to see how crossings affected water quality.
Speir's team sampled Brush Creek for total suspended solids, including silt, clay, animal wastes and other particles, being carried in the water. They tested for particles upstream and downstream of crossings.
"We hypothesized that being downstream of a road crossing would increase sediment yields, and that direct crossings would be the worst offenders," Speir said.
However, "the data just didn't support that cleanly," she said. "What did matter — a lot — was what was happening at the watershed scale: how much unpaved road network existed in a sub-watershed, how much pastureland was present and what the flow conditions were.
"The crossings matter locally under certain conditions, but the bigger story turned out to be what's happening across the whole watershed," Speir said.
Broader focus, next steps
Speir said the study findings helped create "a meaningful shift in how you'd prioritize management."
"It moves the focus from 'fix the crossing' to 'think about the whole landscape and when water is moving through it,'" she said.
The study will dovetail into projects already in motion.
"Within Brush Creek, we have nearly three years of baseline water quality data now, and we're building on that through Project BEACON , which is testing biochar-amended poultry litter as a way to reduce nutrient runoff at the farm and watershed scale," Speir said.
Biochar is a carbon-rich material created from agricultural waste through a specialized heating process. When mixed with poultry litter and applied to pastures, it acts like a sponge, capturing nutrients and reducing runoff into nearby streams.
The U.S. Environmental Protection Agency recently awarded $1.9 million to Speir to study how adding biochar to poultry litter may help improve water quality.
Speir said "the unpaved roads findings will help us think more strategically about where on-farm conservation practices need to be paired with road and pastureland best management practices for maximum effect."
Consequences
Speir said the "study reinforces that sediment loading to streams is already significant under current conditions. During large storm events, we measured up to 13 tons of sediment loss in a single day — basically an entire dump truck of sediment" going into the waterway.
In true land-grant fashion, Speir is taking the research to the Cooperative Extension Service and others who can turn research findings into practices that support local water quality.
"We're also committed to making sure this work reaches people who can act on it," she said. "That means working with extension agents, the Arkansas Unpaved Roads Program, and groups like the Beaver Watershed Alliance, which has already estimated that implementing road BMPs could reduce sediment loads by over 800 tons per year to Beaver Lake. These findings support that kind of targeted investment."
Speir said, "this work wouldn't be possible without the landowners in the Brush Creek watershed who let us access their land and whose conversations helped us understand the road management landscape."
This research was supported by an Arkansas Agricultural Experiment Station Research Innovation Grant. Additional support came from the U.S. Department of Energy Office of Science under contract #DE-SC002463 and the Arkansas Section 319(h) Grant Program through the EPA and Arkansas Department of Agriculture's Natural Resources Division.
To learn more about ag and food research in Arkansas, visit aaes.uada.edu
