Quantification of biodegradable dissolved organic carbon in soil solution with flow-through bioreactors

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 approximate 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 gear and were insensitive to changes in ambient temperature (13-24 degrees C) and flow rate (0.36-0.42 mt 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.