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Quantification of Biodegradable Dissolved Organic Carbon in Soil Solution with Flow-Through Bioreactors

Dep. of Forest Science, Oregon State Univ., Corvallis, OR 97331

William H. McDowell

Dep. of Natural Resources, Univ. of New Hampshire, Durham, NH 03824

Nancy E. Kinner

Dep. of Civil Engineering, Univ. of New Hampshire, Durham, NH 03824

*Corresponding author (yanoy{at}fsl.orst.edu).

ABSTRACT

A flow-through bioreactor method for drinking water or stream water was modified for the rapid determination of biodegradable dissolved organic C (BDOC) in small, discrete samples such as soil solutions collected in lysimeters. Biodegradable dissolved organic C was measured as the difference in dissolved organic C (DOC) concentration between the inlet and outlet when a sample was pumped through a column colonized by indigenous soil microbes. Both feed water and sample solutions were adjusted to 10 mg C L^-1 to maintain a consistent environment in the column, and inorganic nutrients (N, P, S, and K) were added to avoid a nutrient limitation on C degradation. Biodegradable dissolved organic C values obtained by this method were consistent for a year and were insensitive to changes in ambient temperature (13–24°C) and flow rate (0.36–0.42 mL min^-1). Dextrose, humic acid, and dextrose-humic acid solutions were used to test the bioreactors. Only 5% or less of the humic acid C was lost in the bioreactor, suggesting limited abiotic sorption of C. Nearly 100% loss of dextrose, coupled with large increases in dissolved inorganic C (DIC), suggested biotic degradation of BDOC within the bioreactors.

Received for publication July 2, 1997.