Comparison of Denitrification in Two Riparian Soils

The factors controlling NO3removal in riparian buffer systems are poorly understood. We measured denitrification rates for two Coastal Plain, forested riparian zone soils: Kinston fine loamy sand (fine‐loamy, siliceous, acid, thermic Typic Fluvaquent) and Alapaha loamy sand (loamy, siliceous, thermic Arenic Plinthic Paleaquult). Kinston soils are more poorly drained and have higher organic matter than Alapaha soils. Surface soil and shallow aquifer samples were treated with solutions that contained chloramphenicol with either distilled water, NO3‐N, glucose‐C, or NO3plus glucose. Denitrification potentials (N2O production in the presence of acetylene) were significantly higher in Kinston soil for both depths. Surface samples from both soils showed significant responses to NO3additions but no response to C additions without NO3. Subsurface samples, taken from the top of the aquifer, showed no significant response to either NO3or C treatments for either soil. Both soils showed a high degree of stratification within the top 10 cm, with 88 and 68% of denitrification potential in the top 2 cm for Alapaha and Kinston soils, respectively. Denitrification rates in cores were much lower than in slurries but rates in cores with NO3or NO3‐plus‐glucose additions were significantly higher than unamended or C‐amended cores for the Kinston soil. Although both soils respond to NO3additions, Kinston soils are better able to reduce incoming NO3. These results indicate that denitrification in the shallow aquifer is a more important NO3removal mechanism at the Kinston site than at the Alapaha site.