RELATIONSHIPS BETWEEN AQUIFER PROPERTIES AND MICROBIAL-POPULATIONS IN THE BORDEN AQUIFER

Microbial numbers and activity were determined for 9 sediment cores 1.5 m in length collected from a shallow sandy aquifer at Canadian Forces Base, Borden, Ontario. Cores were extracted from a pristine zone 0.5-1.0 m below the water table (1.5-3.0 m below the ground surface). Viable cell counts, electron transport system (ETS) activity, dissolved oxygen (DO), dissolved organic carbon (DOC), weight fraction of organic carbon (FOC), and hydraulic conductivity (K) were determined for contiguous samples of aquifer material removed at 10.0-cm intervals from the 9 cores. Viable cell counts (0-10(4) cfu/g aquifer material) and ETS activity, measured as the amount of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride formazan (INT-for) produced (0-70 mug/g INT-for), were found to be greatest in the upper region of the aquifer (1.55-2.15 m below ground surface). Microbial occurrence and activities were found to be predominantly correlated with depth and dissolved oxygen. Evaluation of these results revealed an oxygen threshold level, occurring at approximately 3.0 mg/L, below which bacterial populations isolated in this study were less able to proliferate. Further evaluation of the microbiological and geologic data collected in this study suggests that, in conjunction with low dissolved oxygen, the naturally occurring carbon may be unsuitable to support large numbers of microorganisms. Similarly, an increase in the production of INT-for when aquifer material was amended with nitrogen suggests that the low microbial numbers and activity obtained in this study may be the result of nitrogen-limited conditions in this aquifer.