The Ogallala Aquifer, the water source for much of western Kansas, is being replenished at a rate of less than 2 inches per year, and areas where resupply is greatest contain higher amounts of underground contaminants, according to new research.
Marios Sophocleous, a water scientist at the Kansas University-based Kansas Geological Survey, said researchers found recharge, or the movement of water from the surface down into the aquifer, was consistently higher under irrigated farmland as opposed to rangeland.
"Irrigation is now so widespread that it seems to contribute more to recharge than does precipitation," Sophocleous said. "But this recharge is coming at the expense of groundwater that was previously stored in the aquifer, and more irrigation is not the answer."
The research, which was conducted with the U.S. Geological Survey, also revealed that water returned to the aquifer beneath irrigated land was higher in contaminants, such as herbicides and nitrates.
Bob Hooper, a water conservation activist from Bogue and past chairman of the Solomon River Basin Advisory Committee, said the report reinforced his belief the state should expect the aquifer to continue to drop, with the remaining water in it becoming increasingly tainted.
Widespread irrigation from the aquifer has been a boost to agriculture but that "addiction" has hurt the Kansas environment, Hooper said.
"If we're looking at the short term, then exploiting the resource makes money," he said. "It just doesn't make a hell of a lot of sense environmentally for the long term. What the state of Kansas has done, by and large, is turn a blind eye to that."
Hooper has called for a zero-depletion policy for the aquifer, which would require that pumping not exceed the recharge rate. But he has been rebuffed at the Kansas Water Office.
Since the onset of widespread irrigation several decades ago, water levels in the aquifer generally have been declining. Those declines range from a few feet to more than 100 feet in some parts of southwestern Kansas. Knowing the amount of water that replenishes the aquifer is crucial to water management in the area, experts said.
The study found recharge under irrigated land ranged from 1.1 inches to 1.8 inches per year. Under rangeland, it was 0.17 inches to 0.21 inches per year.
"In the rangeland, it appears that precipitation is captured by evaporation or by plants before it can get to the water table," Sophocleous said.
Higher amounts of contaminants were found in the water beneath irrigated land. Nitrate concentrations range from 20 to 24 parts per million in water beneath irrigated land. Atrazine, a commonly used herbicide, was found at levels slightly above 0.9 parts per billion. The survey didn't find contaminants in the water under rangeland.
"These results make it clear that levels of nitrate and herbicides are elevated in the water beneath land that is used for irrigated agriculture," Sophocleous said. The amounts of contaminants beneath irrigated land aren't huge, he said, but are still a problem.
The research, conducted in 2000 and 2001, was based on three instrumented wells in southwestern Kansas. Two were under irrigated farmland in southern Finney County and one was under rangeland in the Cimarron National Grasslands in Morton County.
The wells, each about 150 feet deep, were equipped with sensors that tracked movement of water underground to the water table.