Researchers in the Midwest are working on solutions to the problem of agricultural runoff -- a problem with a number of troublesome consequences, including massive annual "dead zones" in the Gulf of Mexico.

Recently, scientists have been testing the ability of woodchip-filled trenches to keep nitrogen, the main ingredient in fertilizer, from being carried into the Mississippi watershed.

Currently, most commercial farmers use a system of drainage pipes buried just a few feet beneath the soil surface to keep their fields from becoming waterlogged. This system keeps the soil dry, but it also helps funnel large amounts of nitrogen, leached from the soil by rain and irrigation, into the Mississippi River.

The river carries the nitrogen south, fueling expansive algae blooms in the Gulf of Mexico, which give off toxins and suck oxygen from the water, creating "dead zones" capable of suffocating thousands of fish and other marine organisms.

"There are 10 million acres of tile-drained fields in Illinois alone," Laura Christianson, a crop scientist and water quality expert with the University of Illinois, said in a news release.

Christianson and her colleagues are using wood-filled trenches, or bioreactors, to form a barrier between nitrogen-carrying drainage pipes and the Mississippi watershed.

The wood chips foster the growth of bacteria capable of neutralizing the nitrogen by turning it into a benign gas.

"Good bacteria colonize the woodchips, and use them as food," said Christianson. "We're enhancing a natural process. There's an elegance to it."

Christianson says there is also growing interest in the use of bioreactors for other uses, including incorporation into municipal water treatment facilities.

Researchers are currently experimenting with different bioreactor designs, varying the dimensions and ingredients. Carbon-rich sources like corn and woodchips are the preferred fuels for bacteria growth.

"We're constantly trying to improve the design," said Christianson.

A new proof-of-concept study in the Journal of Environmental Quality details the installation of a bioreactor on a soybean farm in Iowa.