Factors influencing the abundance and metabolic capacities of microorganisms in Eastern Coastal Plain sediments

The abundance and metabolic capacities of microorganisms residing in 49 sediment samples from 4 boreholes in Atlantic Coastal Plain sediments were examined. Radiolabeled time-course experiments assessing in situ mirobial capacities were initiated within 30 min of core recovery. Acetate (1-¹⁴C- and³H-) incorporation into lipids, microbial colony forming units, and nutrient limitations were examined in aliquots of subsurface sediments. Water-saturated sands exhibited activity and numbers of viable microorganisms that were orders of magnitude greater than those of the low permeability dense clays. Increased radioisotope utilization rates were observed after 6–24-h incubation times when sediments were amended with additional water and/or nutrients. Supplements of water, phosphate, nitrate, sulfate, glucose, or minerals resulted in the stimulation of microbial activities, as evidenced by the rate of acetate incorporation into microbial lipids. Additions of water or phosphate resulted in the greatest stimulation of microbial activities. Regardless of depth, sediments that contained >20% clay particles exhibited lower activities and biomass densities, and greater stimulation with abundant water supplementation than did sediments containing >66% sands and hydraulic conductivities > 200 μm sec.^?1.