BACTERIA IN DEEP COASTAL-PLAIN SEDIMENTS OF MARYLAND - A POSSIBLE SOURCE OF CO2 TO GROUNDWATER

Nineteen cores of unconsolidated Coastal Plain sediments obtained from depths of 14 to 182 m below land surface near Waldorf, Maryland, were collected and examined for metabolically active bacteria. The age of the sediments cored range from Miocene to Early Cretaceous. Acridine orange direct counts of total (viable and nonviable) bacteria in core subsamples ranged from 10**8 to 10**4 bacteria/g of dry sediment. Direct counts of viable bacteria ranged from 10**6 to 10**3 bacteria/g of dry sediment. Three cores contained viable methanogenic bacteria, and seven cores contained viable sulfate-reducing bacteria. The observed presence of bacteria in these sediments suggest that heterotrophic bacterial metabolism, with lignitic organic material as the primary substrate, is a plausible source of CO//2 to groundwater.