Abstract:
This research aims to firstly quantify soil greenhouse gas (GHG; carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)), fluxes from trial riparian zones. Riparian trials have been set up by The University of Canterbury in conjunction with the Canterbury Waterway Rehabilitation Experiment (CAREX) project. My second aim was to determine the dissolved GHG concentrations over a gradient of nitrate in streams. Physiochemical characteristics of the soil and water were quantified to determine the environmental determinants of GHG emissions. Terrestrial GHGs were collected using static chambers and dissolved GHGs were collected using headspace equilibrium method. Gas samples were analysed using cavity ring down spectroscopy. Riparian soil gas fluxes ranged from: soil CO2 flux, 0.1 to 234.9 mg C m-2 hour-1; soil CH4 flux, -44.2 to 145.7 μg C m-2 hour-1; soil N2O flux, -0.4 to 140.8 μg N m-2 hour-1. Dissolved gases ranged from: CO2, 0.0 to 10.8 mg C L-1; CH4, 22.8 to 1433.8 μg C L-1; N2O, 0.3 to 10.9 μg N L-1. This study tries to shed light on the understanding of environmental drivers of soil gas fluxes and highlights the complexities in understanding fluxes. Vegetation variables drove soil CO2 and CH4 fluxes and soil respiration was found to be predominantly autotrophic. Soil characteristics influenced soil N2O flux. This is the first study that I am aware of that looks at soil GHG fluxes of riparian zones in New Zealand. In aquatic systems nitrate was positively correlated to dissolved CO2 and N2O, while negatively to CH4. Correlations between GHGs differed between terrestrial and aquatic systems due to the availability of organic matter creating competition between anaerobic bacteria. This research provides additional information regarding the production of GHGs and mechanisms for their production in differing riparian management techniques.
