The CO2 flux of two peatlands in northern Alberta was examind during the 2004 growing season using eddy covariance measurements of net ecosystem exchange (NEE), chamber measurements of total ecosystem respiration, and empirical models driven by meteorological inputs. The two ecosystems, a poor fen and an extreme-rich fen, differed significantly in plant species composition, leaf area index, aboveground biomass and surface water chemistry. The mean diurnal pattern of NEE at the peak of the season was similar between the sites, however, the extreme-rich fen had a higher photosynthetic and respiratory capacity than the poor fen. Over the 6 month study, the poor fen was shown to accumulate between 2 to 3 times more carbon than the extreme-rich fen despite having a lower photosynthetic capacity. The evergreen nature of the poor fen site allowed for a longer season of net CO2 uptake than the deciduous species that dominated the extreme-rich fen. / xii, 126 leaves : ill. (some col.) ; 29 cm.

Carbon dioxide and methane fluxes were measured between May 2003 and August 2004 on vegetated surfaces and pools of three peatlands located in the La Grande Riviere watershed, James Bay lowland, Quebec, Canada. Gas flux measurements were made using static chambers on a variety of sites in the three peatlands, chosen to represent the different biotypes present, from hummocks with water table position 35 cm below the surface to pools 100 cm deep. / Average CH4 fluxes for the different biotypes on vegetated surfaces sampled during summer 2003 ranged from 3.5 to 197 mg m-2 d-1 while summer 2004 average floating chamber pool fluxes ranged between 6.2 and 3165 mg CH4 m-2 d -1. Mean daily CH4 fluxes on vegetated surface are strongly correlated (r2 > 0.75) with summer average water table depth, greater fluxes occurring where water table is close to the surface. The vegetated surface CH4 fluxes were also correlated with peat temperature as fluxes increase with increasing peat temperature during the summer. / Most net ecosystem productivity values calculated for the different biotypes in the three peatlands showed release of CO2 during both early and mid growing season periods. An annual budget calculated for the LG2 peatland showed that the peatland emitted CO2 to the atmosphere at a rate of 0.77 g m-2 d-1. The overall release of CO 2 may have been caused in part by dry conditions in the peatlands during summer 2003, due to high temperature and low precipitation.

Beaver ponds are important parts of peatland landscapes and have high fluxes of CO2 and CH4. This study was undertaken in Mer Bleue Bog, Ontario, to determine the response of a beaver pond to drainage (lowering by 25 cm) as a sink or source of carbon. Plant distribution was changed in response to a new water table gradient. Each vegetation community and the remaining beaver pond were sampled for fluxes of CO2 and CH4 from mid-April to end-November, 1999, one year after the water table was lowered. / A flow-through chamber system was used to measure CO2 flux from vegetated sites. Mean daily CO2 flux ranged from 0.4--1.6 g CO2-C M-2 (positive denoting uptake from the atmosphere). Variations in CO2 flux amongst the sites along the gradient could not be related to differences in plant species composition, peat temperature, or water table. The mean daily CO2 emission measured by a static floating chamber on the pond area was -24.1 g CO2-C m-2. / A closed chamber was used to measure CH4 on vegetated sites. Daily CH4 fluxes ranged from 1 to -159 mg CH4-C m-2, increasing from the beaver pond margin to the open water surface. The water table explained 83% of the seasonal average CH 4 flux variability and the vegetation added another 11%. The mean daily CH4 flux measured by a static floating chamber on the pond area was -54 mg CH4-C m-2. / The seasonal measurements were integrated into an areal estimate of CO 2 and CH4 flux for the beaver pond area prior to and after drainage. The beaver pond area sequestered 96 g m-2 before drainage (104 g CO2-C m-2 and -8 g CH 4-C m-2), and the same area more than doubled the uptake to 231 g m-2 after being drained (233 g CO 2-C m-2 and -3 g CH4-C m -2).

The exchange of carbon and water between a temperate peatland and the atmosphere was studied directly for the vascular plants; Chamaedaphne calyculata, Kalmia angustifolia, Vaccinium myrtilloides, and Maianthemum trifolium and indirectly for the bryophytes; Sphagnum rubellum and S. magellanicum. In vascular plants, carbon and water fluxes were well coupled (∼2.27 mumol CO 2 mmol-1 H2O) except in the post-deciduous period where temperature constrained water flux more than carbon flux. The seasonal cycle of Sphagnum water content was driven by water table depth; rain depth, rain frequency and atmospheric vapor pressure deficit. In 2000, these factors combined to cause primarily over saturation with regard to optimal net photosynthesis in Sphagnum. Carbon and water exchange at the community scale was also studied and related to the leaf level patterns observed. Few leaf level patterns were observable at the community scale although the effects of species composition and leaf area index were well represented in the community signal.

Four continuous high-resolution peat records for the Holocene have been reconstructed across a ~300km transect from Shebster in Caithness to Yell in the Shetland Isles. These records describe the nature and extent of North Atlantic climate changes inferred from indicators of storminess and minerogenic aeolian dust, and are supported by radiogenic isotope analysis, tephrochronology and radiocarbon dating. The environmental changes at all four sites displays a significant degree of synchrony in response to changes in the position of the polar front jet (PFJ) stream and the phase of the North Atlantic Oscillation (NAO). Bromine concentrations in the peat, derived from sea spray, are used to reconstruct storm frequency and storm intensity, and mire surface wetness is used as an indicator of longer-term climate shifts. The results suggest a strong link between positive phases of the NAO and storminess. Subtle differences between the bromine concentrations and the mire surface wetness suggest that high intensity but perhaps less frequent periods of storminess are not necessarily associated with a wetter climate. Atmospheric minerogenic dust concentrations are used to reconstruct large-scale climate changes across the wider North Atlantic region. The results suggest a sympathy between dust activity and periods of glacial advance and a negative index of the NAO. Radiogenic isotope analysis suggests that the smallest particles may originate from Iceland.

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No description available.

Les tourbières ont accumulé des quantités importantes de matière organique (tourbe) depuis le début de l’Holocène. La tourbe séquestre des quantités de carbone (C), d’azote (N) et de phosphore (P) substantielles à l’échelle globale. Cependant, très peu d’études ont estimé les stocks de ces nutriments à l’échelle régionale. De plus, les estimations actuelles sont souvent obtenues sans considérer la variabilité des profondeurs de tourbe et les variables biophysiques et physiques qui dictent la capacité de stockage en nutriments. Ce mémoire vise à estimer les stocks en C, N et P des tourbières d’une région du sud du Québec en modélisant les variations de profondeurs de tourbe et en identifiant quelles variables biophysiques et physiques expliquent la capacité de stockage en nutriments des différents types de tourbières. Le sondage manuel des sites d’études a révélé des différences significatives de profondeurs de tourbe entre les types de tourbières. La profondeur moyenne de tourbe obtenue pour les tourbières ombrotrophes était de 4,4 m alors que celles des tourbières minérotrophes et forestières étaient respectivement de 2,3 et 2,0 m. Les profondeurs ont été modélisées par interpolation spatiale pour chaque bassin d’accumulation de tourbe. La relation entre la superficie des tourbières et les stocks en C était significativement différente entre les tourbières ombrotrophes et les tourbières minérotrophes et forestières. Aucune variable étudiée ne permettait de discriminer les stocks en N et P selon le type de tourbière. Les stocks en C, N et P de la tourbe ont été extrapolés pour la région en utilisant la superficie des tourbières et estimés à 5,65 Tg C, 230,5 Gg N et 21,8 Gg P. Mes travaux ont démontré que l’hétérogénéité du bassin d’accumulation et les caractéristiques de surface influencent les stocks en C, N et P contenus dans la tourbe. / Peatlands have accumulated important amounts of organic matter since the beginning of the Holocene. This organic matter accumulation is described as peat, that globally stores large amounts of carbon (C), nitrogen (N), and phosphorus (P). Regional estimations of C and nutrients stocks have seldom been quantified. Moreover, peat depth variability and biophysical and physical variables are often not included in actual peat C, N, and P pool size estimations. The goal of this thesis is to provide an estimation of peat C, N, and P pool sizes for a regional county of southern Quebec by modeling peat depth variations and by using biophysical and physical variables to discriminated peat C, N, and P storage among peatland types. Manual peat depth probing showed significant differences in peat depth among peatland types. Mean peat depth of bogs was 4.4 m, while fens and forested peatlands mean peat depths were of 2.3 and 2.0 m, respectively. Modeling of peat accumulation basin by spatial interpolation took these peat depth variations into account, among peatland types. The relationship between peatland area and peat C stocks was statistically different between bogs and fens, and bogs and forested peatlands. Peat N and P content among peatland types were not discriminated by the biophysical and physical variables considered in this study. Peat C, N, and P stocks were extrapolated within the study region using peatland area and estimated at 5.65 Tg C, 230.5 Gg N et 21.8 Gg P. This study has shown that peat accumulation basin heterogeneity and peatland geometric shape influenced peat C, N, and P stocks at the regional scale.

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No description available.