Denitrification and Nitrous Oxide Emissions In Riparian Buffers.

Riparian buffers are used extensively to protect water bodies from nitrogen pollution. Yet, there is relatively little information on the impact of these buffers on production of nitrous oxide (N₂O).  This presentation will discuss nitrous oxide production in riparian buffers of the southeastern Coastal Plain from three different aspects.  The first assessment was via denitrification enzyme activity (DEA) measured by the acetylene inhibition method.  Using this technique the soil C/N ratios >25 soil was found to be a controlling factor in nitrous oxide production.  The second assessment was via soil microbial composition. Molecular techniques were used to compare the composition of bacterial communities in four riparian buffers with different DEA values.  The clone libraries of 16S rDNA genes were constructed, and phylogenetic analyses were performed. A total of 350 clones from four sites, ranging from low to high DEA levels, were analyzed. The predominant bacterial divisions present in all four 16s rDNA libraries belonged to the alpha, beta, and gamma subdivisions of the phylum Proteobacteria. The phylum Acidobacteria was also well represented amongst all four sites. The third directly assessed nitrous oxide emission using a static chamber technique with a photoacoustic multi-gas analyzer.  Nitrous oxide emissions were assessed in the context of soil characteristics along with emissions of ammonia, carbon dioxide, and methane. Nitrous oxide emissions were only significant when the soil was spiked with nitrate.