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Sharing success: bioreactors to reduce nitrate loss

Roger and Louise Van Ersvelde are passionate about conservation and land stewardship on their farm east of Brooklyn in Poweshiek County, IA.

They shared that passion with more than 50 attendees at a field day this past August, and highlighted the newest practice they are using on their farm – a denitrifying bioreactor.

“Installing the bioreactor was the next logical step for helping to do my best to help make sure the water leaving our farm is as clean as possible,” Van Ersvelde says.

Their denitrifying bioreactor was completed fall of 2017 with assistance from the local Natural Resource Conservation Service staff and Poweshiek County Soil and Water Conservation District. To measure the performance of the bioreactor, they partnered with Andrew Graham, assistant professor of chemistry at Grinnell College, to collect and analyze paired samples collected from the inlet and outlet structures.

1. Average nitrate removal is 46 percent from March to July 2018.
2. Higher removal efficiencies were observed during lower flow times (March-Early May and again in July). Removal efficiencies ranged from 10 to 30 percent during high-flow times.
3. Removals of total N are pretty comparable to nitrate removal. This indicates the bioreactor is promoting denitrification to primarily nitrogen gas and not generating ammonia.
4. The high nitrate removal tends to coincide with high-dissolved organic carbon concentrations, suggesting that the extent of denitrification is strongly dependent on the amount of readily degradable carbon.

“If you care about the environment, bioreactors are a great practice – even with no direct benefit to the landowner,” says Dave Maxwell, the contractor who helped install the bioreactor.

To learn more about bioreactors and other edge of field practices, visit www.iowalearningfarms.org/field-edge-practices.