Abstract of PhD Thesis

Four years of observations of carbon dioxide fluxes, water and energy budgets, and vegetation patterns in an Irish Atlantic blanket bog

Matteo Sottocornola , University College Cork (2007)

Atlantic blanket bogs are peatlands that occur in maritime regions where precipitation is much greater than evapotranspiration. These ecosystems are rare but locally they are important for their role in carbon and water balance of regions and for their biodiversity value.

In this study we investigated CO2, energy and water exchange in a pristine Atlantic blanket bog at Glencar, South-western Ireland, over a four-year period (2002-2006). A field survey of the vegetation patterns in relation to the environmental variation was also performed, which indicated that the distribution of the plant species was mainly explained by the depth of the water table. The bryophyte distribution was secondarily controlled by pH while the distribution of vascular plants was explained by the peat depth. The analyses of the vegetation gradients from the peatland centre to its borders indicate the existence of a pattern of variation along the natural margins but not along the artificial borders. This suggests that conservation policies should also include small blanket bog areas and that the natural borders should also be protected because they are likely to be rich in biodiversity and to have different vegetation to that of the bog centre.

In addition, the vegetation survey identified the study site as typical of Atlantic blanket bogs in North-west Europe suggesting that the measured fluxes can be considered representative of this ecosystem in western Ireland. The CO2 uptake fluxes measured over the four years using an eddy covariance system ranged between –26.4 and –95.9 g C-CO2 m-2, showing a high interannual variability and values similar to boreal raised bogs, although both photosynthesis and respiration were lower. Over the four years, annual precipitation ranged from 2428 to 2742 mm yr-1 and evapotranspiration ranged from 357 to 406 mm yr-1. The stream discharge measured over one hydrological year was 1852 mm. The water balance was dominated by stream discharge while evapotranspiration was lower than in other peatland types, despite higher precipitation and water table. Evapotranspiration was limited by the low occurrence of both vascular plants and mosses, more than by the low vapour pressure deficit and cool summer air temperature.

A comparison between the four years suggests that the predicted climate change will probably increase winter evapotranspiration and cause an earlier start of the growing season. The expected decrease in summer precipitation may not radically affect the evapotranspiration pattern of the bog unless the frequency of summer rain events will diminish, causing the moss vegetation to become water-stressed. The ecosystem CO2 uptake will probably decrease if summer rainfall will reduce (as predicted). Since the carbon, water and energy cycles are closely interconnected, modification to any of these processes due to climate change will affect the other cycles and produce a vegetation change with complex feedbacks to the ecosystem functioning.

Should precipitation increase significantly, the water table will rise and so will methane emissions. Such climate change will ultimately change the vegetation community with feedbacks to the carbon, water and energy cycles.