Measurement of biodegradable dissolved organic carbon (BDOC) in lake water with a bioreactor

Once-through, plug-flow bioreactors were colonised and maintained with a microbial community from a mesotrophic lake and used to measure the concentration of biodegradable dissolved organic carbon (BDOC). A BDOC measurement can be done within 3-4h by this method. Glucose was used to test whether oxygen consumption (BOD) could substitute for measurements of dissolved organic carbon (DOC). All added glucose was utilised, however, without a concomitant increase in oxygen demand. Oxygen consumption should not be used in bioreactor measurements. The site-specificity was tested by comparing DOC utilisation in bioreactors with batch cultures inoculated with indigenous bacteria and incubated for 28 days. The bioreactors were not site-specific and required no acclimation to measure BDOC from three different systems. However, humic substances were adsorbed in the reactors and about two days were needed to equilibrate the reactors. The BDOC concentrations in two lakes varied 2-fold over diurnal cycles and 3-fold during the period February-June. No significant relations to the light, dark cycle, chlorophyll, and DOC were found. The absolute BDOC concentrations ranged from 20 to almost 200 microM and averaged 13% of the DOC in the lakes. It is concluded that BDOC in lakes and other fresh waters can be measured quickly and reliably with a bioreactor.