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Carbon Quality of Four-Year-Old Woodchips in a Denitrification Bed Treating Agricultural Drainage Water

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASABE. 61(3): 995-1000. (doi: 10.13031/trans.12642) @2018
Authors:   Ehsan Ghane, Gary W. Feyereisen, Carl J. Rosen, Ulrike W. Tschirner
Keywords:   Denitrifying bioreactor, Tile drainage, Water quality, Woodchip bioreactor.

Abstract. A denitrification bed is a system that can reduce the nitrate concentration in subsurface drainage water. There is a need to investigate the carbon quality of old woodchips to gain a better understanding of the effect of age on woodchip properties. The objectives of this study were to characterize the carbon quality and carbon to nitrogen (C/N) ratio of aged woodchips and to examine the suitability of a denitrification bed for a replicated experiment. To achieve these goals, we excavated four-year-old woodchips along the length of a 106.4 m long denitrification bed near Willmar, Minnesota, and analyzed them for particle size, C/N ratio, and carbon quality. Particle size analysis showed similarities from 12.5 to 106.4 m along the bed. We found a mean C/N ratio ranging from 58.4 ±3.17 to 153.4 ±9.57 (smallest at the inlet). The mean lignocellulose index (LCI, a measure of carbon quality) of the four-year-old woodchips ranged from 0.47 to 0.57 (highest at the inlet). The woodchip particle sizes, C/N ratios, and LCI from 25.9 to 106.4 m along the bed length were similar. In conclusion, the C/N ratio and LCI of the four-year-old woodchips showed effects of decomposition and increased woodchip carbon recalcitrance over time, respectively.

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