Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Dr. Irena Creed

Abstract

The release of greenhouse gases into the atmosphere is becoming an increasingly important problem due to the overwhelming evidence of the relationship between rising greenhouse gas concentrations and increased global temperatures. It is important that we gain a better understanding of the processes controlling the release of N2O, a powerful greenhouse gas. Topographic influences on soil temperature, moisture, reduction-oxidation (redox) potential, dissolved organic carbon, and nitrate conditions, which in turn influence N2O release, were investigated in a natural temperate forest ecosystem in Ontario, Canada. Wetland positions were observed to have the conditions most suited for N2O production (redox potential between +100 and -100 mV). More N2O was released during the summer from the inner (IW) and outer (OW) wetland positions than from lowland and upland topographic positions. Significant positive relationships between N2O efflux and precipitation events in both the IW and OW were observed, suggesting that precipitation creates conditions that promote bursts of N2O release. In addition, substantial biogeochemical activities were observed during the non-growing season under a snow-pack, including denitrification, which can produce N2O. It is important that we gain a better understanding of the processes controlling the release of N2O during the non-growing season. Fluxes of N2 were estimated using the acetylene inhibition technique from wetland positions that had the optimal redox conditions. Adding N2 and N2O fluxes to catchment N export not only reduced the discrepancy in N export observed among catchments but also between N inputs and outputs. During summer months, rainfall events can be used to predict N2O fluxes from the wetland positions within catchments in temperate forests and the IW position had greater potential of reducing N2O to N2 compared to the OW and the lowland and upland areas. Failing to account for winter denitrification products may lead to underestimation of annual N losses.

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