As a part of our study on microbial heterogeneity in subsurface environments, we have examined the microbial respiration of sediment samples obtained from a coastal site near Oyster, VA. The sediments at the site are unconsolidated, fine to coarse beach sand and gravel. A Columbus Instruments Micro-Oxymax Respirometer was used to measure the rate of carbon dioxide (CO2) production during the respiration of the sediment samples. The rate of respiration of the Sediment samples ranged from 0.035-0.6 mu L CO2/h/g of the sediment. The sediment samples showing maximum (0.6 mu L CO2/h/g) and minimum (0.035 mu L CO2/h/g) production of CO2 were selected to study the effect of micronutrient-yeast extract (0.5 and 1.0 mu g/g of the sediment) and water (0.5 and 1.0 mL) on the rate of CO2 production. The rate of CO2 production increased with the addition of water, but increased approx 2 orders of magnitude (from 0.26 to an average of 23.5 mu L CO2/h/g) when 1.0 g/g yeast extract was added to the sediment samples. In these coastal sediments, temperature, depth, and addition of water influenced microbial activity, but the addition of 1.0 mu g/g yeast extract as a micronutrient rapidly increased the rate of CO2 production 2 orders of magnitude.