Mer Bleue (Fig. 1) was the eastern peatland within the Canadian Carbon Program (http://www.fluxnet-canada.ca) and an eddy covariance tower operated by Elyn Humphreys (Carleton University) and Peter Lafleur (Trent University) has measured CO2 exchange since 1998 providing an assessment of the seasonal and interannual variability and the influence of changes in climate and water table. Combination of CO2 exchange, CH4 flux and DOC export over 6 years provides an estimate of the interannual variability of the overall C flux in this system. The publications and theses of our Mer Bleue are listed at this link (Mer Bleue Publications and theses:).
Fig. 1. The Mer Bleue peatland in fall and the eddy covariance tower.
My work at Mer Bleue has involved studies of plant biomass and production and rates of decomposition of litter and peat, and CO2 and CH4 exchange from chambers covering the range of vegetation types from bog to beaver pond. Recent work involves the effect of beaver pond drainage at Mer Bleue on vegetation and CO2 and CH4 fluxes.
To evaluate the effect of nutrients on the bog, Jill Bubier (Mount Holyoke College) and I are conducting a long-term (18-year +) fertilization with N, P and K, and determining plant and CO2 flux response (Fig. 2). Added nutrients enhance shrub growth and shade out mosses, changing the ecosystem structure and CO2 exchange. The ecosystem converts from a sink to a source of CO2. Although there is an increased N concentration in shrub leaves and Sphagnum mosses in the fertilized plots, there is a weak response in leaf photosynthesis suggesting that N uptake is stored rather than being in a form enhancing photosynthesis. PhD student Meng Wang has observed that nutrient content in foliar tissues varies by species and treatment, with evidence of differential homeostasis between shrubs and mosses and that nutrient resorption during senescence of shrub leaves is affected by the fertilization and varies among elements. Ecological stoichiometry suggests that the vegetation at Mer Bleue is mainly co-limited by N and P and analysis of peat cores suggests that N is buried along with C but there are mechanisms which keep the P recycling close to the surface. PhD student Tanja Zivkovic is establishing rates on N2 fixation at Mer Bleue, with moisture content and N:P ratio primary controls.
Fig. 2 The experimental fertilization plots at Mer Bleue.
Litter decomposition and ecological stoichiometry
Rates of litter decomposition in litter-bags over 5 or more years have been measured at a range of peatlands sites, in Canada, in New Zealand (Fig. 3) and North Carolina (Fig. 4) and this allows establishment of the range of controls (litter characteristics and environmental) on decomposition rate.
Fig. 3. Peatlands for litter decomposition studies, North Island, New Zealand.
Fig. 4. The pocosin peatlands, coastal North Carolina, used for litter decomposition studies, in collaboration with Duke University (Dr. Curt Richardson).
Near Rivière du Loup (QC) and Shippagan (NB), we have examined the effect of drainage and harvesting of peat moss on the C cycle and whether vegetation restoration practices can bring back the peat to C cycling function similar to that before the peat was disturbed (Fig. 5). The conclusion is that it may take several decades for this to occur. A life-cycle analysis of C in the peat harvesting industry showed the importance what happens to the peat after it has been marketed, and we are now examining end-user fate of the C in peat moss.
Fig. 5. Peatland restoration in eastern Quebec and New Brunswick.
Detection of graves
To aid in the detection of clandestine graves, Moshe Dalva and I have examined patterns of CO2, CH4 and N2O gas concentration in pore air and emission to the atmosphere in soils in an animal graveyard of Parc Safari Africain and at experimental pig graves at the National Research Council near Ottawa. Although CH4 was useful at Parc Safari because the soils were wet, in the dry soil at the pig graves N2O provided the best evidence for buried cadavers, and lasted for several years.
Dissolved organic carbon (DOC) in forests
DOC plays an important role in the biogeochemistry of many ecosystems, and we have examined controls on rates of DOC production and consumption and fluxes in upland forests and peatlands supported by BIOCAP and NSERC.
Soil carbon and land-use change
There is strong evidence in changes in soil organic carbon associated with changes in land use. In 2001 in Sardinilla, Panama, a large old pasture was converted to a native tree plantation by Catherine Potvin (Biology, McGill) in collaboration with the Smithsonian Tropical Research Institute (Fig. 6). We established the soil organic carbon content of the pasture soils and resampled in 2011 and showed that the land-use change reduced the soil organic carbon mass in the surface layers. Carbon-13 allows an identification of the source of soil organic matter – pasture or trees. This loss, then, partially compensates for the increased carbon in plant biomass from pasture to plantation, and the site was resampled in 2017.
Fig. 6. The old pasture at Sardinilla, Panama, in 2001 and part of the native tree plantation, 2011.
Department of Geography
Last updated 21/11/2011