Highlights A denitrifying woodchip bioreactor (DWB) was evaluated for performance in western Oregon. Nitrogen attenuation was observed within 16 h internal estimated retention time. Hydrogen sulfide production was routinely observed, indicating over-reducing conditions. High volumetric flow rates and other considerations may require an alternative DWB design for the Willamette Valley, Oregon. ABSTRACT. Denitrifying woodchip bioreactors (DWBs) have been studied as an edge-of-field method of intercepting and removing nitrogen constituents in agricultural runoff; however, most research has been conducted in the U.S. Midwest, which has a significantly different climate from the Mediterranean climate found in the Willamette Valley of Oregon. A DWB unit was installed at the Oregon State University Dairy Center in Corvallis, Oregon, to evaluate performance under climate conditions found during the winter rain season (daily temperatures of 11.7°C ± 5.6 (mean ± SD), monthly precipitation inputs of 154 ± 30.8 mm/month, cumulative precipitation of 772 mm over 6 months). Frequent sample collection over three operating seasons demonstrated that good reductions in nitrate-N were achievable, although with rates at the low end of the range reported in literature (2.7 g N m -3 d -1 ± SD 2.3). A moderate degree of “active management” to adjust for changing weather conditions proved to be a critical factor in improving nitrogen (N) removal. Internal measurements show that nitrogen attenuation is generally achieved at an estimated hydraulic retention time of 16 hours (at water temperatures of 9.5°C ± SD 1.8, mean inlet NO 3 -N concentrations of 4.0 to 4.7 mg N/L, and a total range of 0.0 – 24.0 mg N/L), at which point production of hydrogen sulfide routinely occurs. A discussion of factors and features to consider for DWB operation in a high winter rainfall climate regime is provided. Keywords: Active management, Agricultural runoff, Hydraulic retention time, Hydrogen sulfide production, Internal measurements, Mediterranean climate, Oregon, Subsurface drainage, Woodchip bioreactor.
Weisshaar et al. (2026) studied this question.