Wetlands are considered critically important in the delivery of ecosystem services such as water quality improvement, flood protection, and conservation of native biodiversity. A common measure of the effectiveness of these ecosystem services is denitrification, an anaerobic microbial process that converts nitrate (NO3-), a common water pollutant, into dinitrogen (N2) gas. In addition to oxygen, denitrification is controlled by the amount of carbon available (a denitrifying bacterial energy source) in the soil and NO3-. My objectives were to determine how different types of sites (agricultural, natural wetland, and restored wetland) cycle nitrogen using denitrification methods.
Potential denitrification rates were determined using denitrification enzyme assays (DEAs) with and without the addition of acetylene gas, which was added to prevent the last step in the denitrification cycle. Other soil characteristics were also measured to compare their relationship to the denitrification potential of each site type: extractable organic carbon (EOC), NO3-, and percent moisture (H2O).
DEA rates were directly related to H2O, so rates were notably higher during the rainier times of the year. There was no relationship detected between DEA rate and EOC or DEA rate and NO3-, although EOC and NO3- showed a positive correlation to one another. This positive relationship is consistent with what others have found, and theory would predict. Studies have shown the higher the NO3-, generally the lower the N2O reduction activity because there is ample NO3- to accept electrons so there are not as many electrons “left over” to reduce N2O. By decreasing the levels of NO3- in the soil, it may be possible to reduce levels of N2O production, thereby decreasing its potent effect as a greenhouse gas.