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.

No description available.

No description available.

Biogeochemical carbon dynamics govern the ability of peatlands to storecarbon. The processes controlling the balance between the photosyntheticuptake of C02 and respiration of C02 and CH4 back to the atmosphere remainunclear. A process-based ecosystem biogeochemical study, encompassing tracegas flux measurements, laboratory chemical analyses and field analyses, wasundertaken in order to better understand the carbon dynamics of borealCanadian peatlands.

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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No description available.

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.