FACTORS INFLUENCING THE ABUNDANCE AND METABOLIC CAPACITIES OF MICROORGANISMS IN EASTERN COASTAL-PLAIN SEDIMENTS

The abundance and metabolic capacities of microorganisms residing in 4 9 sediment samples from 4 boreholes in Atlantic Coastal Plain sediment s were examined. Radiolabeled time-course experiments assessing in sit u mirobial capacities were initiated within 30 min of core recovery. A cetate (1-C-14- and H-3-) incorporation into lipids, microbial colony forming units, and nutrient limitations were examined in aliquots of s ubsurface sediments. Water-saturated sands exhibited activity and numb ers of viable microorganisms that were orders of magnitude greater tha n those of the low permeability dense clays. Increased radioisotope ut ilization rates were observed after 6-24-h incubation times when sedim ents were amended with additional water and/or nutrients. Supplements of water, phosphate, nitrate, sulfate, glucose, or minerals resulted i n the stimulation of microbial activities, as evidenced by the rate of acetate incorporation into microbial lipids. Additions of water or ph osphate resulted in the greatest stimulation of microbial activities. Regardless of depth, sediments that contained >20% clay particles exhi bited lower activities and biomass densities, and greater stimulation with abundant water supplementation than did sediments containing >66% sands and hydraulic conductivities >200 mu m sec.(-1).