POTENTIAL DENITRIFICATION RATES IN DEEP SEDIMENTS FROM THE SOUTHEASTERN COASTAL-PLAIN

Measurements of potential dentrification, by the acetylene block technique, and CO2 production were made in sediment samples from cores taken to a depth of 185 m on Parris Island, SC. A significant denitrification potential in sediments overlying the Floridan aquifer and in the Floridan aquifer itself was found. Denitrification rates in subsurface sediments (5-185 m) amended with 1 mM NO3- averaged 1.7 .+-. 1.8 nmol of N2O g-1 (.+-. SD), whereas samples of organic rich surface soils gave mean rates from 117 .+-. 71 to 173 .+-. 39 nmol of N2O g-1 d-1. Depth-integrated rates indicate that potential denitrification in a 150-m column of subsurface sediment, excluding the surface layer, is 253 mmol of N2O m-2 d-1. The surface layer has a potential rate of 74 mmol of N2O m-2 d-1. Denitrification rate was apparently limited by NO3- concentration in assays with 1 mM NO3-. CO2 and N2O production showed parallel trends with depth; mean surface CO2 production was from 104 .+-. 29 to 1034 .+-. 307 nmol of CO2 g-1 d-1 and was greater than subsurface rates. The latter averaged 21 .+-. 18 nmol of CO2 g-1 d-1 between 5- and 185-m depth.