Laura Christianson, agronomist and water quality engineer
Laura Christianson, PhD, PE, is an agronomist and professional engineer in the field of agricultural water quality. Her research involves growing food while making sure our water stays clean. One of her favorite things to study is a denitrifying woodchip bioreactor.
The Midwest United States often has very moist springs. The topography is also usually flat. The spring rains and snowmelt come at a time when farmers need to plant crops. Planting earlier in the spring means a longer growing season and the possibility of higher crop yields.
But driving heavy tractors over wet fields is not good for the soil. It causes soil compaction. One of the best solutions for this was to install drains below the soil. The drains direct water from soaked farm fields into nearby streams and ditches. The soil dries out faster, the plants don’t drown, and farmers get into their fields earlier in the spring.
But scientists started to notice problems in local streams–and even as far away as the Gulf of Mexico. They determined that too many chemicals called nitrates were getting into the streams. This is harmful to all water sources. Denitrifying woodchip bioreactors are one solution to this problem.
Woodchip bioreactors are trenches filled with–woodchips! Farmers direct their drains to move water through the trench before it gets to streams. They dig holes–often as large as about 1/3rd the size of a football field–and fill them with woodchips. They then cover the woodchips with soil. Water from rain or snowmelt flows down through the soil, into the drains, then through the woodchip bioreactors. The woodchips and bioreactor pits contain bacteria. (For more on that, read this blog.) As the water containing nitrates flows by the bacteria, they convert the nitrate in the water to harmless nitrogen gas. Since the bacteria do all the work in these systems, they are called bioreactors.
Christianson’s research lab verifies the amount of nitrates in the tile drainage water in the lab to make sure the bioreactors are working properly. Woodchip bioreactors decrease the amount of nitrates that get into streams. This means farmers can use the necessary drains to dry out their fields, plant earlier crops, and protect the environment. Christianson has traveled around the world to collaborate with scientists who are using woodchip bioreactors in other countries.
Denitrifying woodchip bioreactors are one practical solution that engineers and scientists have developed through research–and that farmers can use to keep our streams healthy while growing food to feed the world.
Watch Christianson in action. Besides being a researcher at the University of Illinois-Urbana, Christianson is an associate editor for the Journal of Environmental Quality, published by ASA, CSSA, and SSSA.
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