PARENT SESSION
Organized Oral Session 21: Implications of disturbance on boreal peatland carbon cycling: From sites to to landscape-scale carbon budgets
Organizer(s): RK Wieder, KD Scott, and DH Vitt
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 511a, Level 5, Palais des congrès de Montréal
Seven years of eddy covariance measurements of carbon fluxes at Mer Bleue: Insights into interannual variation at an ombrotrophic bog.
Humphreys, Elyn*,1, Lafleur, Peter1, Roulet, Nigel2, Moore, Tim2, 1 Trent University, Peterborough, ON, Canada2 McGill University, Montreal, QC, Canada
ABSTRACT- Over the past 8400 years, the Mer Bleue bog, a 2800 ha low shrub ombrotrophic bog east of Ottawa Ontario, has accumulated roughly 4 Mt of carbon (C) with a maximum peat depth of 6 m. Long-term C accumulation in peatland ecosystems such as Mer Bleue results from a small imbalance between C uptake through photosynthesis and C loss through decomposition and respiration. However, current and future changes in climate have the potential to alter the C balance of these ecosystems. Continuous eddy covariance measurements of the net ecosystem exchange of carbon dioxide (NEE) since June 1998 are used to assess the contemporary C exchange of the Mer Bleue bog and its response to interannual variations in weather. Annual mean temperature has varied by 2.5 °C, while precipitation has varied by 185 mm but neither variable has fallen outside the range of conditions observed in this region during the previous 30 years. During this time, the bog has been either C neutral or a net C sink with NEE varying from 0 to −112 g C m-2 y-1 with a mean of −39 ± 17 g C m-2 y-1 (± SE), where negative values indicate C uptake by the ecosystem. During the winter months, C loss is significant but relatively conservative and accounts for as much as 100% of the C taken up during the growing season. Consequently, interannual variations in NEE are driven largely by variations in the NEE during the growing season but particularly in late summer. This is in contrast to many other northern ecosystems, including a subarctic fen, where annual NEE has been found to vary in response to spring temperatures. At Mer Bleue, there is a strong link between hydrology and NEE; late summer drought negatively impacts the photosynthetic capacity of both vascular and non-vascular species. Somewhat surprisingly, little correlation has been found between soil moisture and ecosystem respiration. When the loss of C through methane emissions and the export of DOC is accounted for (about 10 g C m-2 y-1), the bog was a small net source of C during drought years. These results suggest that this bog could become an annual C source with greater drought induced by warmer summer temperatures and further reductions in rainfall.
Key words: peatland, carbon dioxide exchange, interannual variability