Abstract of PhD Thesis

Carbon Gas Fluxes in an Irish lowland blanket bog

Anna Laine (2006) - University College Cork

Peatlands have accumulated a significant amount of carbon (C) since the last ice age. Currently pristine peatlands affect the atmospheric concentration of greenhouse gases by being a small sink of carbon dioxide (CO2) and a source of methane (CH4). However, large spatial variation has been observed in the flux rates within and between peatlands, which is linked to water level and vegetation characteristics. In this study, CO2 and CH4 exchange was studied in a lowland blanket bog. Fluxes were measured in four different vegetation communities along a water level gradient, namely hummocks, high lawns, low lawns and hollows. Lawns were the most common vegetation community in the bog. During the study period the bog acted as a moderate C sink. The net ecosystem CO2 exchange varied between the vegetation communities in the order hummock > high lawn > low lawn > hollow and the CH4 flux varied in the order hollow > low lawn > high lawn > hummock. The spatial variation in fluxes was primarily controlled by the water level. The seasonal dynamics in the gas fluxes followed the changes in temperature and vegetation cover. Flux rates were lowest, but still noteworthy, during winter and highest during the second half of the summer. The peatland C balance is sensitive to changes in hydrological conditions; therefore it is projected that climate change will affect peatlands via changes in water level. The water level was raised and lowered experimentally, following which, gas fluxes were monitored during one year. Water level drawdown increased ecosystem respiration and gross photosynthesis and decreased the CH4 flux in all vegetation communities. When the water level was raised, the ecosystem respiration and gross photosynthesis decreased and the CH4 flux increased. Low lawns were an exception, insofar that their gross photosynthesis increased after water level was raised.