Simultaneous determination of nitrous oxide and ammonia for measurement of in-situ fluxes from natural ecosystems by gas chromatography with headspace autosampler and electron capture detection
Anthropogenic disturbance of the soil nitrogen cycle by changes in nitrogen and carbon availability influences the production of N2O and NH 3 emissions to the atmosphere affecting the environment and human health. This dissertation presents a new method for automated gas chromatographic analysis of N2O and NH3 and quantifies fluxes from a salt marsh and tropical rain forest. The automated system used single column gas chromatograhic separation on HayeSep Q and electron capture detection. Air (N2+O 2), N2O and NH3 are separated with retention times of 0.9, 1.7 and 2.15 minutes respectively. Samples were stored in headspace autosampler vials until analysis. The precision was 3--7% RSD for standards of N2O with a LOD of 0.001 ppmv and 3--12% RSD for standards of NH3 with a LOD of 0.002 ppmv. Nitrogen dynamics of an oil contaminated salt marsh (Spartina alterniflora) were examined to assess the effects of three bioremediation strategies: air purging, nitrate addition and full fertilizer addition. Compared to values reported in uncontaminated marshes N2O fluxes were lower by a factor of 7, and NH3 fluxes were slightly higher. This suggests that the petroleum had an inhibitory affect on denitrification but not mineralization. Extractable NO3- levels were 2--5 fold lower than those reported in the literature and NH4+ levels were 3 to 80 fold higher. The higher NH4+ levels suggest that oil contamination might inhibit nitrification and as a result could explain the reduced levels of NO3- and N2O flux. Hurricanes in the Caribbean can cause short term disturbances in trace gas flux, litter fall and plant structure in forests. The hurricane appears to have increased the N2O flux four fold, and caused a 40% increase in NO3- soil concentration while the NH4+ soil concentration is lower by two fold than previous levels (1995--97). N2O flux and NO3- concentrations returned to previous levels after 27 months, but not NH4+ concentrations. A correlation between NH3 and N2O flux suggests that the increased "litter pulse" from deforestation results in increased N availability in the soil and thus an increase in N 2O flux.
Chemistry, Analytical, Biogeochemistry, Environmental Sciences
Networked Digital Library of Theses and Dissertations