Abstract:
Urban ecosystems provide a range of ecosystem services such as temperature regulation and mitigating noise and air pollution and CO2 emissions. The soil of urban ecosystems are also potential sources and sinks of greenhouse gases (CO2, CH4, and N2O). In this thesis, I quantified the magnitude of soil CO2, CH4, N2O fluxes in urban forests and urban grasslands across seasons and sites and determined soil factors (soil temperature, soil moisture, bulk density, particle size distribution, biomass of organic layer and grass, soil carbon and nitrogen stocks, C: N ratio, and hydrogen ion concentration) influencing soil CO2, CH4, N2O fluxes. I hypothesized that soil CO2 and N2O fluxes are higher in urban grasslands than forests and that urban grassland have a lower CH4 uptake than urban forests. Further, I hypothesized that soil CO2 flux, CH4 uptake and N2O flux is mainly driven by soil temperature and soil moisture with the highest CO2 flux, CH4 uptake and N2O flux occurring at higher soil temperature. Soil greenhouse gases were sampled using static chambers followed by gas analysis using a cavity ring down spectrometer. Soil CO2 efflux was significantly lower in urban forests (median: 418.9 mg C m-2 h-1) than grasslands (median: 809.3 mg C m-2 h-1). Soil CH4 uptake was significantly higher in forests (median: -67.8 μg C m-2 hour-1) than in grasslands (median: -24.4 μg C m-2 hour-1) confirming my hypothesis. However, N2O efflux was significantly higher in forests (median: 9.4 μg N m-2 hour-1) than grasslands (median: 6.2 μg N m-2 hour-1). I did not find a significant relationship between greenhouse gas fluxes and soil temperature in urban forests and grasslands. In contrast, a significant relationship was found between soil moisture and all greenhouse gases in urban forests and grasslands. Further, CO2 flux, CH4 uptake and N2O flux in urban forests were significantly negatively correlated by hydrogen ion concentration. In urban grasslands, bulk density had a significant effect on soil CO2 flux and CH4 uptake. Soil C and N stocks and hydrogen ion concentration influenced N2O flux in urban grasslands suggesting a stronger influence of land-use management and anthropogenic disturbances on greenhouse gas fluxes in urban grasslands. Hence, for the purpose of reduction in greenhouse gas emissions, urban and soil ecosystems offer a potential opportunity but is highly depending on how the land is managed. Key words: carbon dioxide, methane, nitrous oxide, urban forests, urban grasslands, urbanization, soil characteristics