ACWA Installs Tile Line Bioreactor Agriculture’s Clean Water Alliance (ACWA), a group of 16 ag retailers organized to reduce nutrient loss from farm fields in Raccoon River and Des Moines River watersheds and an Iowa Soybean Association partner, has installed a tile line bioreactor pilot project in the Raccoon River watershed in Greene County in central Iowa. Nitrogen is highly water-soluble so, as water moves off the farm landscape, it carries nitrogen with it. There are practices that capture and filter water at the surface (such as wetlands and retention ponds), but they can be costly and require land to be taken out of production. One alternative filtration practice gaining interest is bioreactors. Bioreactors are essentially underground trenches filled with a carbon source (commonly wood chips), through which tile water is allowed to flow. The carbon source provides material within which microorganisms can colonize. Using the wood chips as a food source, the microorganisms begin breaking down the nitrate through a denitrification process and expel the nitrate as a gas. The systems are easy to construct, relatively inexpensive, take little or no land out of production and are believed to require little maintenance. There are no adverse effects on crop production, and they can be designed to not restrict drainage. Early research has found nitrate removal efficiency averaging between 25 to 35 percent. The Greene County bioreactor project will be heavily researched. ACWA will be observing nitrate levels in its water monitoring network above and below each site to evaluate the performance. If the bioreactors are proven as a practice in the Raccoon River watershed, they could become one of several integrated solutions for improved water quality. The identity and community dynamics of microorganisms participating in denitrification in tile drain bioreactors are unknown, apart from findings that both bacterial and fungal species are important to the process. Researchers surmise that the fungi break the cellulose in the wood into smaller organic molecules, which the bacteria then use in their metabolic processes.