OSU Research Counteracts Effects of Nitrogen in Agricultural Runoff

The Willamette River flows through many of Oregon’s most populous cities, including, of course, Corvallis. It also happens to be the most polluted river in Oregon.   

Agricultural runoff is a huge contributor to the pollution in the Willamette River. With the Willamette Valley’s rich farmland, which accounts for nearly half of Oregon’s annual farm sales, this might come as no surprise.   

You’ve likely heard of the issue of agricultural runoff: put simply, water from irrigation or precipitation makes contact with farmland, and then absorbs into the ground, or makes its way into surrounding bodies of water. This runoff often ends up carrying a variety of pollutants into large bodies of water, like the Willamette.   

High levels of nitrogen, a common component in fertilizers and manure, tend to make their way into water bodies this way. As a result, algal blooms and other negative environmental impacts arise, posing a threat to aquatic plants and animals, as well as to humans.   

Oregon State University’s Dr. Frank Chaplen and Ph.D. student Elsie W. are currently working on research that may offer a promising solution. Their work takes advantage of naturally occuring denitrifiers, a type of bacteria that convert nitrogen from one form to another.   

Bacteria often get a bad rap, but in this case, they are immensely helpful. Eventually, these nitrogen-fixing bacteria convert the nitrogen found in runoff to its gaseous state. This allows the nitrogen to safely enter the atmosphere, which is composed of approximately 78% nitrogen already.  

Here is where the real work comes in: these bacteria offer a solution, but they do not naturally work on a scale large enough to match that of agricultural production. Not on their own, that is.   

The research done by Chaplen and Weisshaar utilizes something called a Denitrifying Woodchip Bioreactor. The name sounds intimidating, but the concepts behind it are quite simple: a large pit, equipped with plumbing that allows water to flow in one end and out the other, is filled with woodchip particles that act as a “home” for denitrifying bacteria.   

As agricultural drainage enters the system, carrying high levels of nitrogen, the bacteria begin to do their part, and the water eventually drains out the other end. The water that flows out from this system typically has much lower levels of nitrogen nutrients than the water that flowed in, making the agricultural runoff much less of a threat to surrounding ecosystems.   

Denitrifying Woodchip Bioreactors are not totally new, having been studied most heavily in places like New Zealand and the Midwestern United States. Chaplen and Weisshaar are testing this system in a vastly different climate — that of the Willamette Valley — where most agricultural runoff occurs in our rainy, cold winter months.   

Weisshaar and Chaplen reflected on the study so far, calling the results “very promising”. Weisshaar, who oversaw the construction of the system while Chaplen was in New Zealand, is now focused on finding the optimal flow rate for the water that passes through the bioreactor. Increasing the flow rate results in decreasing the contact time between the water and the bacteria, so the solution is not as simple as it might initially seem.  

The Willamette Valley could benefit greatly from systems like the Denitrifying Woodchip Bioreactor. Though some aspects of their research require further study, Chaplen and Weisshaar’s work provides a potential solution to an issue that is growing in importance.   

This research project was made possible through funding received by the Oregon Dairy Farmers’ Association, the Oregon Department of Agriculture, and OSU’s Agricultural Research Foundation.  

By Olivia Goodfriend 

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