Subsurface peat decomposition, through CO2 production, was analyzed in laboratory and field experiments in a bog, poor fen, and beaver pond margin at Mer Bleue, Ottawa. Intact core samples in 10 cm depth intervals from 5--45 cm below the surface of each site were incubated in the laboratory. Treatments involved aerobic and anaerobic conditions at 4 and 14°C. Field measurements of CO2 flux were made by a static chamber technique. / Incubation results indicate modelled CO2 surface fluxes differ amongst wetlands. Aerobic CO2 modelled surface fluxes at 4°C were 2.3, 3.1 and 4.2 g CO2 m-2 d-1 for the bog, the beaver pond margin, and the poor fen, respectively. On average, aerobic production rates from peat cores with field moisture conditions were 11.7 times larger than anaerobic production rates. A mean Q10 of 2.3 defined the role of temperature. Differences among the peat samples were related to degree of decomposition, and differences among the sites were related to trophic status and nutrient availability. / A model of CO2 production was constructed and validated against field fluxes of CO2. The model provides a good prediction (r 2 = 0.72) of subsurface peat decomposition. The results suggest that warmer peat temperatures and lowered water tables, as predicted by climate change scenarios, will increase surface CO2 fluxes due to peat decomposition.

Daily net ecosystem CO$ sb2$ exchange (NEE) was monitored at several peatland communities in a mid-boreal headwater bog at the Experimental Lakes Area (Kenora, ON., Canada) throughout the 1995-96 growing seasons. Transparent and opaque chamber systems were used to measure NEE and dark respiration at replicate plots in which the vascular vegetation was either clipped or unclipped. CO$ sb2$ fixation and emission fluxes were estimated from NEE measurements and were compared within and among the peatland communities. Communities that supported shrubby, xerophytic vegetation fixed CO$ sb2$ at rates that ranged from, on average, 0.194 to 0.365 mg CO$ sb2$ m$ sp{-2}$ s$ sp{-1}$. These rates did not vary significantly on a daily to weekly timescale, and were comparable in magnitude to the wetter, sedge-dominated communities. CO$ sb2$ emissions varied within and among communities across the sampling season. Rates were, on average, from 0.0568 to 0.109 mg CO$ sb2$ m$ sp{-2}$ s$ sp{-1}$, and the variation was associated with differences in ground temperature and water table. Comparisons of CO$ sb2$ emissions from clipped and unclipped plots allowed an estimation of the contribution of vascular respiration to total CO$ sb2$ emissions. Contributions ranged from 25 to over 80%, depending on the community and season that the measurements were taken. Strong associations between vascular respiration and ground temperature were observed. Daily NEE had little variability between communities and throughout the sampling season. This was attributed to parallel variations for the CO$ sb2$ fixation and emission fluxes. Researchers should quantify the actual fluxes for vascular root respiration, as it possibly controlled a large part of the NEE variability within and between sites.

No description available.

No description available.

To further the understanding of respiration processes of northern peatlands, the relative importance of each type of belowground respiration was determined at Mer Bleue, a northern peatland located near Ottawa, Ontario, from June to November, 2003. Direct measurements of total, soil organic matter (SOM) and root respiration were made, with rhizosphere respiration determined by residual. Although an aboveground source, determination of live Sphagnum respiration was also attempted in the field. To identify changes in CO2 fluxes with environmental conditions, peat temperature and water table levels were monitored throughout the study period. / SOM respiration was higher than hypothesized at 63% while root and rhizosphere respiration were lower than hypothesized at 21% and 16%, respectively, of total belowground respiration. As the field experiment for determining live Sphagnum respiration was unsuccessful, it was determined by calculation to be 18% of total respiration, slightly higher than hypothesized. Opposite of hypothesized, air temperatures, peat temperatures and water table levels generally had weak and insignificant relationships when linearly regressed with total respiration.

No description available.

Carbon dioxide (CO2) and methane (CH4) fluxes from the soil surface, and concentrations within the soil profile, were measured between June 1998 and Sept. 1999 at four adjacent forest plantations and an old field in Nepean, Ontario. The objectives of this study were to quantify seasonal CO2 and CH4 fluxes from the soil surface and within the soil profile to determine the effect of soil moisture and temperature, and forest age and species on the exchange, and establish a chronosequence of organic carbon accumulation in the forest plantations and the old field soils. / Dynamic and static chamber techniques were used to measure surface fluxes of CO2 and CH4, respectively, and soil gas concentrations were sampled with probes. In the old field and forest plantations, surface soil CO2 flux ranged from 2.9 to 27 g CO2 m-2 d-1 and 2.0 to 39 g CO2 m -2 d-1 respectively. Significant differences due to age and species of plantation were observed. Seasonal variations in CO2 efflux from the soil surface and within the soil profile were related to variation in soil temperature and moisture. Uptake of CH4 was observed at all sites and there was no significant differences in flux due to vegetation type or age. Maximum rate of CH4 consumption was 6.3 mg CH4 m-2 d-1. Methane uptake was positively related to soil moisture conditions. / The carbon content of the soil increased in all sites following the establishment of vegetation on sandy parent material. Carbon content was greatest in the upper soil profile. Rates of carbon accumulation ranged from 109 to 426 g m-2 y-1. Soil carbon increased with increasing age of plantation during the first 30 years following the establishment of vegetation on parent material, but declined as the forest plantation matured.

No description available.

No description available.

Wetlands exchange significant amounts of carbon dioxide (CO2) and methane (CH4)---two major greenhouse gases (GHG), and thus have significant impacts on the Earth's climate. In this study, fluxes of CO2 and CH4 were measured in a cattail-dominated marsh in Eastern Ontario, Canada. Eddy covariance measurements of net ecosystem CO2 exchange (NEE) revealed that the marsh was an annual sink of 264 g C m-2, and that growing season net CO2 fluxes were strongly correlated with vegetation biomass and leaf area index. Fluxes of CH4 were measured from water, soil and plants using closed chambers and resulted in a net annual area-weighted emission from the marsh of 206 g C m-2. Consequently, the net (CO2 + CH4) annual carbon (C) balance of this wetland corresponded to a sink of 58 g C m-2. A simple radiative forcing model based on the marsh CO 2 and CH4 emission patterns suggests that, despite the net carbon uptake, this wetland is contributing to atmospheric warming because of the large CH4 efflux. Future potential climate impacts of this marsh were evaluated using different emission scenarios that could result in response to climatic or environmental changes. Overall, short-term impacts are driven by CH4 emission rate, while the CO2 flux determines the impacts on longer time horizons. Uncertainties in predicting future wetland GHG balance arise from uncertain feedbacks and responses. Future alterations of the marsh GHG emission and uptake patterns resulting from land use or climatic changes could lead to a shift in the marsh C balance, showing the importance of wetland ecosystems in national and global C budgets and GHG-related political decisions.