Date of Award
Program or Major
Doctor of Philosophy
Patrick M Crill
This thesis examines the environmental controls on the biogeochemical cycling of the radiatively active trace gas CH$\sb4$ within boreal and arctic wetlands. Net CH$\sb4$ flux along peatland hydrologic gradients were examined to determine the effects of temperature and water table on CH$\sb4$ emissions. The level of the water table acts as a switch between CH$\sb4$ production and oxidation with small water level changes producing large changes in flux balance. Soil temperature determined whether CH$\sb4$ production potential was realized within sufficiently moist environments. A selective inhibitor technique was developed for directly measuring CH$\sb4$ oxidation in wetland soils. CH$\sb4$ oxidation was found to occur in all environments regardless of soil moisture. Wet sites were found to have the greatest CH$\sb4$ oxidation rates, with 20-70% of gross CH$\sb4$ production being consumed prior to emission. Oxidation within specific sites was found to consume a relatively constant fraction of CH$\sb4$ despite emissions varying over 3 orders of magnitude, suggesting that methanotrophic activity is dependent upon CH$\sb4$ source strength. Field and core studies within drier sites suggest a similar pattern, with the dominance of oxidation within dry sites arising from the lack of a significant CH$\sb4$ source. Conversion of a relatively dry site dominated by CH$\sb4$ oxidation to a moderate CH$\sb4$ source at the time of a rising water table agrees well with the stimulation of CH$\sb4$ production and oxidation observed within a dry bog site following a rain event. Both suggest that dry CH$\sb4$ sink environments can be converted to CH$\sb4$ sources with a sufficient increase in soil moisture. Changes in nutrient status have only indirect effects on CH$\sb4$ oxidation via changes in overall CH$\sb4$ supply. Significant feedbacks of CH$\sb4$ emissions to changes in environmental moisture should be expected, with effects of temperature moderating the magnitude of these changes.
Moosavi, Sadredin Cyrus, "Controls on CH(4) emissions from boreal and arctic wetlands" (1998). Doctoral Dissertations. 2027.