The state is looking at research in fields near Rocky Ford to determine if irrigation practices could improve Arkansas River water quality.
On Thursday, officials from Colorado and Kansas health agencies and researchers looked at how intercepting water from fields through irrigation drains could prevent deeper leaching of water and nitrates into the soil. That leaching action, when it reaches bedrock layers of shale, triggers suspended selenium releases that are harmful to wildlife, explained Tim Gates, a Colorado State University- Fort Collins researcher who has spent 15 years investigating Arkansas Valley irrigation systems.
“Excess irrigation percolates through to the shales and soils around them and the nitrates in the soil from excessive fertilization causes the selenium to dissolve out,” Gates said.
To a large degree, the increase of sprinkler systems and drip irrigation has reduced the amount of water applied to fields, meaning less water to percolate deeply in the soil.
But in fields still flood irrigated, drains could provide a means to reduce selenium buildup.
Many of the farms in the Lower Arkansas Valley have tile drains installed in the first part of the 1900s under federal programs as a way to reduce waterlogging.
A two-year study funded by the Colorado Department of Public Health and Environment is looking at how effectively those drains can prevent selenium concentration.
“What it’s looking at is whether there’s a better way to intercept and control it,” said Jim Valliant, a retired CSU Extension researcher who is working on the project. Valliant also represents Crowley County on the Lower Arkansas Valley Water Conservancy District board.
Part of the problem rests with state water law, he added.
“Farmers are told to use it or lose it, so it encourages over-irrigation,” Valliant said. “But I think younger farmers are more willing to adapt. I think we can work together to improve the quality of the water returning to the Arkansas River.”
Cutting down on fertilizer application, which releases nitrates, could also save farmers money, Valliant said.
The levels of selenium in the Arkansas River are exacerbated by higher base flows on Fountain Creek, along with storms on Fountain Creek and Wild Horse Creek in the Pueblo area. But return flows from irrigation also react with shale that lies on the surface and up to 40 feet below throughout the valley.
It also creates a problem for downstream users, because the selenium accumulates as water moves along the river.
“Lakin, Kan., is a small community of about 1,800, and we had to build a $6 million water treatment plant,” said Randy Hayzlett, who represents Kansas on the Arkansas River Compact Administration. “I think the problem is getting worse. What dilutes it is high flows, and we just haven’t had them for a while.”