The sources, sinks, fluxes, spatial distributions, and temporal variations of dissolved organic carbon (DOC) in subarctic fen catchments as well as the temporal patterns of DOC in streams draining subarctic fen catchments in the region of Schefferville, Quebec were investigated. / In June to August sampling, DOC concentrations averaged 17 mg/L in peat water, 2-16 m/L in stream water, 49-56 mg/L in canopy throughfall, 14-19 mg/L in understory throughfall, 122-187 mg/L in stemflow, 25-39 mg/L in lichen and moss mat water, and 35-42 mg/L in soil A horizon water. / Precipitation and canopy and understory throughfall were all significant DOC sources with seasonal DOC fluxes to the forest floor of 0.1-0.4, 0.5-1.3, and 0.8-1.7 g DOC/m$ sp2$ of forest, respectively. The lichen and moss mats and the A soil horizon were also found to be DOC sources, whereas the B soil horizon was a DOC sink. The soil column was estimated to export 0.4-0.5 g DOC/m$ sp2$. Peat, also a DOC source, released 1.2-2.1 g DOC/m$ sp2$. / DOC concentrations in streams draining ten fen catchments were found to be positively correlated with the percentage of fen area in the catchments.

Energy availability and environmental issues are of growing concern; nations are striving to use energy more efficiently while at the same time decreasing the negative impacts on the environment. / The objectives of this study are to: (1) establish a supply price for ethanol derived from switchgrass, (2) establish an accounting budget for carbon dioxide during feedstock production and processing into ethanol, and (3) determine the cost/tonne of CO$ sb2$ using this strategy. / Total cost of production of the feedstock for cycles of 5, 10, 15, and 20 years are $357.06/ha ( $32.73/ODT), $337.81/ha ( $30.96/ODT), $331.52/ha ( $30.39/ODT), and $328.47/ha ( $30.11/ODT) respectively. Thus, the approximate cost of producing one litre of ethanol from switchgrass is $0.47/litre. / Overall, the switchgrass-ethanol system is a net carbon sink for all four cycles, and each hectare of swithgrass sequesters between 1.9 and 6.8 tonne of CO$ sb2$ per year. However, this process is not indefinite, and will stop once the soil organic matter reaches an equilibrium. / The current price for gas is $0.24/litre (excluding taxes and profit margins). According to the price differential existing between ethanol and gasoline and the CO$ sb2$ emissions difference between both systems, the cost of sequestering CO$ sb2$ ranges between $83/tonne and $129/tonne, with the adoption of this specific strategy. At the macro level, Quebec and Canada's total carbon dioxide emissions reached 70 million tonnes and 461 million tonnes respectively, in 1991. Thus, displacing fossil-based energy sources (gasoline) with a renewable energy source (ethanol from switchgrass) to reduce those emissions by 20 % by the year 2010, incurs a cost ranging between $1.16 billion and $1.8 billion for Quebec, and between $7.7 billion and $11.9 billion for Canada. (Abstract shortened by UMI.)

Carbon storage was compared between two perennial biomass energy systems, namely switchgrass (Panicum virgatum L.) and short-rotation willow Salix alba x glaffelteri L.) at 2 adjacent sites, and further compared with a corn cultivation, a 20-year-old abandoned field, and a mature hardwood forest, in southwestern Quebec. Aboveground carbon results indicated that switchgrass and corn had significantly greater carbon levels than willow at the less fertile site, but no significant differences were detected at the more fertile site. Root carbon results indicated that corn had significantly lower carbon levels than both perennial systems to a depth of 30 cm at both sites. However, switchgrass had significantly greater root carbon levels beyond 30 cm compared with willow and corn, and beyond 45 cm compared with the forest and abandoned field. These findings indicate that deep-rooted perennial grasses such as switchgrass have the potential to sequester carbon at deeper soil layers. Soil carbon results showed that at the more fertile site, willow was associated with significantly greater soil carbon levels than switchgrass. Moreover, both perennial crops had soil carbon levels that were greater than for corn, the abandoned field, and the forest. In contrast, at the less fertile site, no significant differences in soil carbon were detected between the various plant systems examined. The results of this study suggest that the perennial energy crops used, when grown on relatively fertile soils, have the potential to substantially increase soil carbon levels compared with conventional agricultural and/or forest systems. Consequently, when these crops are grown on less fertile soils, their added advantage of increasing carbon storage is lost.

Net ecosystem exchange of CO$ sb2$ (NEE) and CH$ sb4$ flux were measured at five sites within a boreal peatland near Thompson, Manitoba, from June through September, 1994. Sites were chosen to represent the different plant communities present along a productivity gradient where the water table was at or near the peat surface. Methane emissions, water table depth, and peat temperature were measured on weekly basis, while the relationship between photosynthetically active radiation (PAR) and net ecosystem exchange of CO$ sb2$ was determined three times during the field season, and then used to develop net ecosystem production (NEP) models at each site. Porewater methane was sampled for $ rm delta sp{13}C/ sp{12}C$ isotopic analysis once a month. / Among the sites, after PAR, light CO$ sb2$ flux was primarily controlled by sedge biomass and water table position, while dark CO$ sb2$ flux was controlled by peat temperature. From early June to late August, the five sites consumed approximately 1 to 2 g $ rm CO sb2$-C m$ rm sp{-2}d sp{-1}$. Seasonal CH$ sb4$ fluxes ranged between 16 and 456 mg $ rm CH sb4 m sp{-2}d sp{-1}$, and were higher than fluxes measured at other boreal sites in the same latitude. Seasonal average NEP was a good predictor of seasonal CH$ sb4$ fluxes from the sites (r$ sp2$ = 0.50), providing a model which estimates CH$ sb4$ flux based on site productivity alone. Stable carbon isotope analysis indicates root exudates that stimulate methanogenesis are an important control on this relationship, as is a high water table, particularly in its influence on the depth of the CH$ sb4$ oxidizing layer in the peat. These results suggest NEP measurements have the potential to be used in remote sensing applications to estimate CH$ sb4$ flux from wetlands, but that their use may be restricted to inundated sites.

Atmospheric inversion has recently become an important tool in estimating CO2 sinks and sources albeit that the existing inversion results are often uncertain and differ considerably in terms of the spatiotemporal variations of the inverted carbon flux. More measurements combined with terrestrial ecosystem information are expected to improve the estimates of global surface carbon fluxes which are used to understand the relationships between variabilities of the terrestrial carbon cycle and anomalies of climatic factors. Inversions using more observations have often been hampered by the intense diurnal variations of CO2 concentrations at continental sites. Diurnal variations of the surface flux are included with atmospheric boundary dynamics in order to improve the atmospheric inversion accuracy. Modeling experiments conducted in this study show that inverse estimates of the carbon flux are more sensitive to the variation of the atmospheric boundary layer dynamics than to the diurnal variation in the surface flux. It is however generally better to consider both diurnal variations in the inversion than to consider only either of them. Forest carbon dynamics is closely related to stand age. This useful terrestrial ecosystem information has been used as an additional constraint to the atmospheric inversion. The inverse estimates with this constraint over North America exhibit an improved correlation with carbon sink estimates derived from eddy-covariance measurements and remotely-sensed data, indicating that the use of age information can improve the accuracy of atmospheric inversions. Terrestrial carbon uptake is found mainly in northern land, and a strong flux density is revealed in southeastern North America in an improved multi-year inversion from 2002 to 2007. The global interannual variability of the flux is dominated by terrestrial ecosystems. The interannual variabilities of regional terrestrial carbon cycles could be mostly explained by monthly anomalies of climatic conditions or short-time extreme meteorological events. Monthly anomalies of the inverted fluxes have been further analyzed against the monthly anomalies of temperature and precipitation to quantitatively assess the responses of the global terrestrial carbon cycle to climatic variabilities and to determine the dominant mechanisms controlling the variations of terrestrial carbon exchange.

Atmospheric inversion has recently become an important tool in estimating CO2 sinks and sources albeit that the existing inversion results are often uncertain and differ considerably in terms of the spatiotemporal variations of the inverted carbon flux. More measurements combined with terrestrial ecosystem information are expected to improve the estimates of global surface carbon fluxes which are used to understand the relationships between variabilities of the terrestrial carbon cycle and anomalies of climatic factors. Inversions using more observations have often been hampered by the intense diurnal variations of CO2 concentrations at continental sites. Diurnal variations of the surface flux are included with atmospheric boundary dynamics in order to improve the atmospheric inversion accuracy. Modeling experiments conducted in this study show that inverse estimates of the carbon flux are more sensitive to the variation of the atmospheric boundary layer dynamics than to the diurnal variation in the surface flux. It is however generally better to consider both diurnal variations in the inversion than to consider only either of them. Forest carbon dynamics is closely related to stand age. This useful terrestrial ecosystem information has been used as an additional constraint to the atmospheric inversion. The inverse estimates with this constraint over North America exhibit an improved correlation with carbon sink estimates derived from eddy-covariance measurements and remotely-sensed data, indicating that the use of age information can improve the accuracy of atmospheric inversions. Terrestrial carbon uptake is found mainly in northern land, and a strong flux density is revealed in southeastern North America in an improved multi-year inversion from 2002 to 2007. The global interannual variability of the flux is dominated by terrestrial ecosystems. The interannual variabilities of regional terrestrial carbon cycles could be mostly explained by monthly anomalies of climatic conditions or short-time extreme meteorological events. Monthly anomalies of the inverted fluxes have been further analyzed against the monthly anomalies of temperature and precipitation to quantitatively assess the responses of the global terrestrial carbon cycle to climatic variabilities and to determine the dominant mechanisms controlling the variations of terrestrial carbon exchange.

Current estimates of terrestrial carbon (C) fluxes overlook explicit hydrological controls. In this research project, a spatially explicit hydro-ecological model, BEPS-TerrainLab V2.0 was further developed to improve our understanding of the non-linearities associated with various hydro-ecological processes. A modeling study was conducted in a humid boreal ecosystem in north central Quebec, Canada. The sizes and nature of various ecosystem-C-pools were comprehensively reconstructed under a climate change and disturbance scenario prior to simulation in order to ensure realistic biogeochemical modeling. Further, several ecosystem processes were simulated and validated using field measurements for two years. A sensitivity analysis was also performed. After gaining confidence in the model’s ability to simulate various hydrologically controlled ecophysiological and biogeochemical processes and having understood that topographically driven sub-surface baseflow is the main process determining the soil moisture regime in humid boreal ecosystem, its influence on ecophysiological and biogeochemical processes were investigated. Three modeling scenarios were designed that represent strategies that are currently used in ecological models to represent hydrological controls. These scenarios were: 1) Explicit, where realistic lateral water routing was considered 2) Implicit, where calculations were based on a bucket-modeling approach 3) NoFlow, where the lateral sub-surface flow was turned off in the model. In general, the Implicit scenario overestimated GPP, ET and NEP, as opposed to the Explicit scenario. The NoFlow scenario underestimated GPP and ET but overestimated NEP. The key processes controlling the differences were due to the combined effects of variations in plant physiology, photosynthesis, heterotrophic respiration, autotrophic respiration and nitrogen mineralization; all of which occurred simultaneously in different directions, at different rates, affecting the spatio-temporal distribution of terrestrial C-sources or sinks (NEP). From these results it was clear that lateral water flow does play a significant role in the net terrestrial C distribution and it was discovered that non-explicit forms of hydrological representations underestimate the sizes of terrestrial C-sources rather than C-sinks. The scientific implication of this work demonstrates that regional or global scale terrestrial C estimates could have significant errors if proper hydrological constraints are not considered for modeling ecological processes due to large topographic variations of the Earth’s surface.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.