Date of Award

Spring 1998

Project Type

Dissertation

Program or Major

Earth Sciences

Degree Name

Doctor of Philosophy

First Advisor

Patrick M Crill

Abstract

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.

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