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.

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Nitrogen and sulfur deposition and water table level fluctuations have the potential to influence the C biogeochemistry in peatlands. Processes in peatland mesocosms were examined under steady state and dynamic conditions at different rates of N and S deposition, and water table levels. Net turnover rates were calculated from diffusive-advective mass-balances of pore water constituents. The limitations of the approach were tested with tracer experiments, which showed that diffusive-advective transport adequately described the flow of dissolved substances in peat columns. Incubation experiments quantified potential CO2, CH4, DOC, H2S and Fe 2+ production rates. / The vegetation assimilated most of the deposited nitrogen and sulfate when water table levels were high. Lowered water table levels resulted in seepage of sulfate to the water table, reduced the rates of photosynthesis, and increased the soil respiration rates. The potential for sulfate reduction was fairly large, despite small in situ sulfate concentrations, and the CO2 production could not be fully accounted for by known processes. Potential rates of sulfate reduction were large both in samples taken from the field site and from the controlled experiments. SO42- addition resulted partly in stimulation, partly in reduction of potential CH4 production rates suggesting that the relationship between sulfate reduction and methanogenesis is not exclusively competitive. / Changes of the water table level had in situ effects on CO2 and CH4 production rates not explainable by a distinction in aerobic/anaerobic conditions. Anaerobic in situ rates at greater depths were much lower when the water table was at the surface of the mesocosms than when it was at greater depths. This might have been due to in situ accumulation of CO2 and CH 4 in the deeper peat, which lowers the energy gain of anaerobic C mineralization. Flooding and draining of peat soil resulted in a delayed onset of CH 4 production, in increased anaerobic CO2 production and decreased CH4 production rates, and in the decoupling of gas exchange from production rates. These results document that fluctuations of environmental variables on short time scales have an impact on rates of C turnover in peat soils, and also limit the predictability of fluxes by statistical models.

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Research for a dissolved nitrogen budget was conducted at Mer Bleue bog near Ottawa, ON, from May 20, 2003 to May 21, 2004. Mer Bleue is located within an area experiencing the highest levels of atmospheric nitrogen deposition in North America, although these levels are only low to moderate compared to those in Europe. Continuous measurements of precipitation, evapotranspiration, bog water table level and outflow water depth were used in conjunction with discrete measurements of precipitation and outflow to determine the hydrologic budget. Water samples were taken from precipitation collectors, piezometers at various depths and locations throughout the bog, and an outflow point in order to gauge changes and patterns in chemical concentrations at various points throughout the bog. The nature of the bog morphology and landscape allowed for collection of water samples from a single outflow point. / Chemical analysis combined with the water budget revealed that the majority of the dissolved nitrogen is entering the bog as NO3-N and NH 4-N (inorganic nitrogen), and leaving the bog as dissolved organic nitrogen (DON). Export of nitrogen was generally low relative to the input, and was only a very small fraction of the huge amount of nitrogen stored in the bog. Bog porewater concentrations were dominated by DON and did not show spatial patterns in relation to the bog edge. When comparing the annual accretion of nitrogen at the bog to the long-term storage numbers, it was apparent that there is a missing source of nitrogen. From the literature and patterns in the bog, it appears that this missing input at Mer Bleue is likely due to a combination of previously unmeasured nitrogen fixation and more diverse usage of DON by bog vegetation.

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.

Methane (CH$ sb4$) fluxes were measured in a range of peatland sites by a static chamber method in two regions of northern Canada, the Clay Belt of boreal Ontario and the Labrador Trough of subarctic Quebec. In both regions, seasonal mean water table position was the best predictor of mean CH$ sb4$ flux when microtopography was included in the analysis (r$ sp2$ = 0.73; p $<$ 0.01). The regression coefficients (slopes) were similar in both regions, suggesting a similar functional relationship between water table position and CH$ sb4$ flux; but the constants (intercepts) were different, implying a regional difference in climate or other biogeochemical factors. Broad-scale wetland classifications that do not account for microtopography and regional differences are inadequate for predicting CH$ sb4$ flux. / Vegetation and a suite of environmental variables in both regions were analyzed with multivariate statistics. Canonical correspondence analysis (CCA) showed that hydrology (water table position) explains most of the variability in bryophyte distribution, with chemistry (pore-water pH, Ca, Mg) as the second most important factor. The relative importance of the variables is reversed for vascular species in the Clay Belt; variables correlating with bryophyte and vascular species distribution are more similar in the Labrador Trough. Hydrology and chemistry are independent variables in both regions. CH$ sb4$ flux correlated strongly with hydrology in both regions, but not with chemistry. / Because of the strong correlation between bryophytes and CH$ sb4$ flux in the CCA analyses, a predictive model was developed using weighted averaging (WA) calibration. Optimum CH$ sb4$ flux values are highest for carpet/pool species and lowest for hummock species. No overlap in WA tolerances occurs between hummock and pool species, suggesting species at either end of the moisture gradient are the best predictors of CH$ sb4$ flux. Although the model works best within and not among regions, it has potential application in remote sensing of bryophytes for regional CH$ sb4$ budgets, paleoenvironmental reconstructions of CH$ sb4$ flux, and biological monitoring of future changes in CH$ sb4$ flux from climate-induced changes in peatland hydrology.

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