Woodchip denitrifying bioreactors (WDBR) reduce off-field tile drainage nitrogen (N) losses from agricultural fields. Limited evaluation exists regarding the influence of flow direction through WDBRs. Changing flow direction could reduce short circuiting. This study evaluated the dependency of nitrate-N removal and dissolved nitrous oxide (dN2O) production rates on vertical flow direction in triplicate column bioreactors at 12-h (without carbon dosing) and 2-h (with carbon dosing) hydraulic residence times. Results presented demonstrate that there was no significant difference in overall N removal rates from these column bioreactors as a function of flow direction. There was the suggestion of lower N2O production in the downflow direction, although this was not statistically significant due to the high variability of the N2O production observed in the upflow direction. Carbon addition led to bioclogging of downflow columns; future work needs to identify dosing rate, placement, and conditions that prevent biofilm formation.
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We express gratitude to Todd Schumacher, Marta Roser, Lizzy Selvik, Olivia Richter, Martin DuSaire, and Sam Okkema for their technical assistance. We acknowledge and thank the Minnesota Agricultural Utilization Research Institute for partially funding this work. We also thank the two peer reviewers whose constructive comments contributed to a stronger manuscript. Use of manufacturers’ names does not represent endorsement by the USDA. The USDA is an equal opportunity provider and employer.
© 2020 The Authors. Agricultural & Environmental Letters published by Wiley Periodicals LLC on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America