Measuring the carbon budget of a sedge fen in Canada's Southern Arctic
Arctic environments are currently experiencing climate warming. The fate of the carbon stored in soils that are often saturated and/or frozen in these regions is uncertain. Also uncertain are the rates of current carbon dioxide uptake as growing seasons lengthen and summer temperatures increase. To assess the response of the current carbon budget of an arctic sedge fen to interannual variations in growing season weather in the Daring Lake area (64deg52' N, 111deg34' W), we measured ecosystem-scale fluxes of carbon dioxide over three years (eddy covariance technique) and small plot-scale fluxes of methane (chamber technique). We then compared the contemporary carbon exchange with the apparent carbon accumulation for the past 2000 years obtained from carbon density and age-depth profile of a peat core.
The importance of water table in controlling dissolved carbon dynamics along a fen successional gradient
Peatlands are important to global carbon (C) sequestration and surface water acid-base status. Fens are minerotrophic peatlands whose structure changes over time. Younger fens are nutrient-rich and dominated by grasses and sedges, whereas older fens are nutrient-poor and dominated by Sphagnum mosses, shrubs, and trees. This study examined how dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) changed along the fen gradient from rich to poor during the snow-free periods of 2005, 2006 (DOC only) and 2007 from piezometers at 25, 50 and 100 cm depths and suction lysimeters at 25 cm depth. Dissolved C concentrations varied with water table. DIC concentrations increased with increasing water table (poor < intermediate < rich) and increased with precipitation (2005 < 2007), and were related to rates of calcite dissolution, soil respiration, and their mixing in the peat profile. DOC concentrations decreased with increasing water table depth (rich < intermediate < poor) and were related to plant productivity, microbial decomposition, and porewater ionic strength. At high water tables in the rich fen, DOC concentrations were low due to low productivity and decomposition and high ionic strength. At low water tables in the poor fen, DOC concentrations were high and poorly humified due to high productivity/decomposition and low ionic strength. At moderately low and variable water tables in the intermediate fen, DOC concentrations were moderate because productivity and decomposition was offset by high ionic strength from sulfur (S) oxidation and cation exchange. Climate conditions affected fen DOC differently, with drier conditions having no effect on concentrations in the rich fen, an inhibitory effect on concentrations in the intermediate due to increased S oxidation and ionic strength, and a stimulatory effect on concentrations in the poor fen due to enhanced production and/or decomposition. This work highlights the need to consider both biological and chemical processes that control dissolved C dynamics in peatlands.
Examining Gas Flux Interactions in Wetland-Dominated Permafrost Terrain
Northern boreal wetland complexes have been identified as substantial reservoirs for greenhouse gases and play a crucial role in both regional and global carbon budgets. These reservoirs are not only responding to shifts in atmospheric temperatures, but are also under additional pressure from increasing permafrost degradation. This study examines the carbon (CO2) respiration and net ecosystem exchange (NEE) of a high boreal wetland during the 2008 spring melt season, located near Fort Simpson (61o18'N, 121o 18'W), Northwest Territories. Gas flux was monitored daily with a dynamic closed-system chamber at nine sites in order to characterize and compare the gas flux gradients for three terrain types typical of the lower Liard River valley: channel fens, ombrotrophic flat bogs and peat plateaus. Each terrain site shows a clear pattern of increasing respiration rate during the transition period from snowmelt to senescence; however significant variation in this rate of change between terrain types is apparent. In order to determine how the fluxes change for each terrain during a period of active layer growth in relation to each other, controlling environmental variables (soil moisture, air temperature, relative humidity, and photosynthetic active radiation) were measured to derive any significant relationships. Additionally, the spatial variability of parameters such as soil moisture, snow and frost table depth, water table depth, and plant communities were investigated. This provides information on the gas flux characteristics for specific terrain features with implications for predicting the future regional flux for this area as a sink or source for carbon.
Water budget of a Quebec North-boreal minerotrophic peatland
A significant percentage of the northern Quebec boreal region consists of minerotrophic peatland. Their impact on large-scale watersheds, used for hydroelectric production, is important, especially in relation to climate change. During the last decades, a subtle increase in the surface of ponds at the expense of terrestrial compartments has been observed. To better understand the impacts of this development, a multidisciplinary study to perform a complete integrated analysis of the water balance was launched in summer 2008 on the Abeille peatland (54° 06'52" N, 72° 30'01"W), a minerotrophic peatland with an open-water surface. While all features of the water balance will be considered (precipitation, evapotranspiration, runoff, storage and error), some will be studied in greater depth. Notably, evapotranspiration and storage changes will be considered, since, they are particularly difficult to measure in peatland ecosystems. Indirect methods for estimating actual evapotranspiration are often used. One method is to use a semi-empirical formula to estimate potential evapotranspiration. The main problem with this method is that a relationship between potential and actual evapotranspiration must be established and this is a highly variable process for peat ecosystems. To establish a relationship appropriate to our study site, different methods of direct measurement of the actual evapotranspiration will be used (lysimeters, turbulence flow, daily fluctuations of storage, etc.) and compared. A dense network of wells has been installed to enable monitoring of changes in storage and subsurface runoff. A high accuracy topographic survey will be executed to assess the total water content of the site. A device for measuring the variation of peat surface elevation will also be established. Preliminary results are showing complex dynamic behaviors of water migration through the site, therefore opening the way to new questions and hypotheses to clarify in the coming years.