Most recently, studies have found that vegetated bioreactors can reduce phosphorus concentrations from subsurface agricultural drainage water to near zero. In addition, they have gained notoriety for their penchant for eliminating nitrogen. Nayar’s co-authors, researchers Laura Christianson and Richard Cooke, conducted the study. They monitored the performance of 10 full-size bioreactors throughout Illinois and uncovered a two-fold advantage of these systems. What’s next With Illinois struggling with some of the worst agricultural runoff in the nation, the study’s results can potentially lead to improved conservation practices.
At their core, bioreactors work as denitrifying agents, usually in the form of large basins filled with woodchips. These purifying structures are effective at removing nitrate pollution from agricultural drainage. The research shows that bioreactors have significant benefits beyond nitrogen removal. They play a very important role in reducing phosphorus that is so important to protecting our environmental health. Illinois has one of our country’s largest agricultural production landscapes, with approximately 9 million tile-drained acres. Doing so with bioreactors could mean a big boost in water quality across Iowa’s rural landscape.
The Mechanics of Bioreactors
The process of operating bioreactors includes inflow and outflow measurements that help determine the daily water flow rate through the reactor. This is because bioreactors will have a significant flush of phosphorus leaching from the woodchips in the first few months of operation. This unexpected phenomenon is due to the fact that woodchips inherently have phosphorus. Trees, like all plants, absorb nutrients, including phosphorus during their growth.
Laura Christianson, a key figure in the development of the TSP mentioned, stressed the need for tracking this leaching process. She highlighted that woodchips have phosphorus. This important nutrient is taken in by the trees while they are growing. We wanted to assess whether or not woodchip bioreactors are leaching phosphorus, because it’s important to reduce the amount of phosphorus we’re sending downstream.
Science indicates that bioreactors first flush a short-term pulse of phosphorus. Over their roughly ten-year lifespan, they can eliminate much more phosphorus than they leak. Cooke stated, “The life of a bioreactor is about 10 years, so if there is a brief phosphorus surge in the first few months, after that it removes more than it releases for most of its lifespan, then it is worth it.”
Addressing Environmental Concerns
Phosphorus pollution is a large, looming issue for water quality managers. All too often, it instead contributes to toxic harmful algal blooms in our waterways that are difficult and expensive to remove. The research points to an exciting advantage of bioreactors. They help with phosphorus removal without compromising their primary duty of transportation and safety.
Christianson pointed out the irony in this benefit: “First, when phosphorus gets into the waterways, it’s difficult and expensive to clean out. Second, bioreactors aren’t supposed to provide this benefit at all, so it’s like a freebie we’re getting.” This dual functionality highlights the bioreactors’ potential role in greater environmental management strategies.
Additionally, intense rainfall events increase the bioreactor’s capacity to remove phosphorus. Cooke noted, “When there is heavy rainfall, there is a spike in phosphorus removal, especially after manure application in the field.” This feature makes bioreactors powerful assets in addressing runoff due to increased extreme weather events.
Future Implications for Agriculture
The research complements Illinois’ grand ambition of cutting its nitrogen pollution entering the Mississippi River Basin by 45%. As farmers and other agricultural producers look for cost-effective practices to minimize nutrient runoff, bioreactors can be a good solution. Cooke encourages farmers to consider various approaches tailored to their specific needs: “Producers should consider what would be the best option for their farm and maybe use a combination of practices if possible.”
Bioreactors are an impactful approach to addressing pressing environmental challenges. They very much connect with farmers’ values around stewardship, around legacy. As Cooke remarked, “In my experience, farmers are good stewards of the land. They will think about their legacy and what they are leaving for their children, so they will be interested in practices that work well.”