Rapid increases in air temperature in Arctic and subarctic regions are driving significant changes to surface water. These changes and their impacts are not well understood in sensitive high Arctic ecosystems. This thesis explores changes in surface water in the high Arctic pond complexes of western Banks Island, Northwest Territories, and examines the impacts of this change on vegetation communities. Landsat imagery (1985-2015) was used to detect trends in surface water, moisture, and vegetation productivity, aerial imagery change detection (1958 and 2014) quantified shifts in the size and distribution of waterbodies, and field sampling investigated factors contributing to observed changes. The impact of expanding lesser snow goose populations on observed changes in surface water was investigated using the aerial imagery change detection of 2409 waterbodies and an information theoretic model selection approach, while their impact on vegetation was assessed using data from field surveys. Our analyses show that the pond complexes of western Banks Island are drying, having lost 7.9% of the surface water that existed in 1985. This loss of surface water disproportionately occurred in smaller sized waterbodies, indicating that climate is the main driver. Model selection showed that intensive occupation of lesser snow geese was associated with more extensive drying and draining of waterbodies and suggests this intensive habitat use may reduce the resilience of pond complexes to climate warming. Evidence from field surveys suggests that snow goose foraging is also contributing to patches of declining vegetation productivity within drying wetland areas. Diminishing and degrading high Arctic pond complexes are likely to alter permafrost thaw and greenhouse gas emissions, as well as the habitat quality of these ecosystems. Additional studies focused the mechanisms of surface water loss, the direct impacts of wetland drying on vegetation, and the contributions of snow geese to these processes, are necessary to better understand the changes occurring on Banks Island. / Graduate

Although water stress is an important selective force in many environments, it is not commonly considered to be of particular importance in tundra areas. Even t hough large portions of tundra may have an abundance of water, other more exposed areas may become quite dry. This microsite variability with respect to moisture stress was reflected in soil water potential measurements obtained from an alpine tundra area on Niwot Ridge in Colorado. Even though soil water potentials were consistently above -5 bars in a relatively low lying Deschampsia meadow, soil water potentials from an exposed fellfield area were often as low as -15 bars. Since moisture stress affects a number of important physiological processes in plants and since moisture stress may develop in at least some tundra areas, this study was undertaken to determine whether the sensitivity of plant physiological processes to water stress may be one important contributing factor in determining the microsite distribution of different tundra species. The alpine tundra species examined in this study were Deschampsia caespitosa which is typically found in wet meadow habitats and Geum rossii, a species which ranges from wet meadow to exposed fellfield habitats. The arctic tundra species investigated were Dupontia fischeri which is restricted mainly to wet meadow areas and Carex aquatilis, a species ranging from wet meadows to drier, more exposed areas. For both the arctic and al pine tundra species, though the photosynthetic capacities of the tundra species restricted mainly to wet meadow areas were higher under conditions of low moisture stress, the wider ranging tundra species were able to maintain greater photosynthetic capacity as soil moisture stress increased. Although the depression of photosynthesis with water stress in these tundra species could be partially attributed to reduced stomatal aperture, with decreased soil water potential most of the decline of photosynthesis was due to a greater non-stomatal or residual resistance, indicating a direct impact of water stress on the photosynthetic apparatus. Dark respiration did not increase with enhanced water stress. Thus, although photorespiration may have increased, increased mitochondrial respiration is unlikely involved in the depression of net photosynthesis. The wet site species typically exhibited higher photosynthesis/transpiration ratios for photosynthesis at low soil moisture stress levels; however, as soil moisture stress increased, the wider ranging species generally maintained higher photosynthesis/transpiration ratios. At high soil water potentials stomata of the species restricted typically to wet meadow tundra areas did not appear to undergo a closing response until the bulk leaf water potential decreased; however, reduced stomatal aperture of the tundra species with a wider distribution was noted before leaf water potential dropped. Although the stomatal mechanism of wet site tundra species exhibited lower degrees of occlusion at high soil water potentials, for the more widely distributed tundra species, Carex and especially Geum, stomatal closure was less pronounced as soil water potential decreased. The ability of Geumto maintain a low liquid phase water transfer resistance from the soil to the leaves as well as to experience relatively small reductions in turgor pressure as moisture stress increased may be important factors in maintaining a favorable leaf water balance over a rather broad range of soil moisture regimes. Differences in turgor pressure response with respect to moisture stress may be associated with differences in cell wall elasticity. Calculations of cell wall elasticity suggest that the wider ranging species have more elastic cell walls as compared with the more rigid, inelastic cell walls in the wet site tundra species. The results of this study show that tundra plants have different gas exchange sensitivities and water relation responses with respect to moisture stress and suggest that these at tributes may be important contributing factors in determining the local distribution of these species.

In Arctic tundra soils pH serves as an important parameter related to several biotic parameters such as, plant and microbial community composition, biodiversity, nutrient dynamics and productivity. Both abiotic and biotic factors, for instance, base saturation (BS) and plant nutrient uptake may exert a control on soil pH, while it is still unclear to what extent different factors can explain soil pH across different tundra vegetation types. The aim of this study was to investigate to what extent different abiotic and biotic factors influence soil pH in the humus layer across different tundra vegetation types. To do so, eight different tundra vegetation types of which four were underlaid by permafrost (Arctic Alaska) and four with no permafrost (Arctic Sweden) were studied in detail with regard to different properties affecting soil pH. I found that BS was the main factor controlling soil pH across the different vegetation types regardless if the soil was underlain by permafrost or not. Factors, such as, ionic strength or soil water content could not explain any overall pH variation and did only significantly affect the heath soils. Further, the uptake of the most abundant base cations (Ca2+, Mg2+ and K+) from meadow and heath vegetation revealed a high difference between plant functional groups within the same vegetation types. The higher dominance of slow growing woody species in heath vegetation which had a lower uptake corresponded with a lower BC content (especially (Ca2+), pH and BS in the humus soil relative the meadow meanwhile the content of K+ was more than three times higher in heath. Overall, this study suggests that the degree of neutralization (base saturation) regulates pH either via the influence of bedrock and hydrogeochemistry and/or via plant traits that affects the uptake and turnover of base cations.

<p>High-latitude watersheds have been regarded as a carbon sink with soil carbon accumulating at low temperature. This sink is now believed to turn into a source, acting as positive feedback to climate warming. However, thawing permafrost soils would allow more water to percolate down to deeper soil layers where some of the carbon could be “consumed” in weathering and exported as bicarbonate to the sea. Using a hydrological mixing model showed that this could counterbalance the predicted positive feedback resulting from thawing soils.</p><p>Vegetation-covered riparian zones in headwater areas appear to have a significant role for the dissolved constituent fluxes. Higher concentrations of weathering products are found in taiga and tundra rivers with larger areas of forest and peat cover in the watershed. These landscape elements can thus be regarded as “hot spots” of river loading with dissolved constituents.</p><p>Comparing a regulated and an unregulated river tested the hypothesis that damming leads to a depletion of major elements also in oligotrophic river systems as a consequence of changes in landscape elements. A loss of upper soils and vegetation through inundation prevents the contact of surface waters with vegetated soil, and consequently reduces weathering fluxes. The hypothesis that the lower fluxes of dissolved silica (DSi) in the regulated river could also be explained by biological uptake was then tested using a model, and budget calculations indicate a significant reduction as a result of regulation. About 10% of this reduction can be attributed to the flooding of the fluvial corridor and the rest to diatom blooms in the reservoirs. A more detailed study of landscape elements for the headwaters of the river Luleälven showed that only 3% of the surface area has been inundated by reservoirs but ca. 37% of the deciduous forest. Such a significant loss of hot spots may indeed explain the observed lower DSi fluxes in the regulated watersheds of northern Sweden.</p>

<p>This thesis presents results from several studies that have focused on the carbon and nutrient dynamics in soils at the forest – tundra ecotone in Fennoscandia. The main objectives of the study were: (i) to investigate the links between the physical environment, above-ground vegetation communities, soil carbon storage, nutrient status and the chemical composition of the soil organic matter (SOM), and (ii) to quantify trace gas fluxes (methane and carbon dioxide) between mesic soils and the atmosphere. Four main field areas spanning an 8 degree latitudinal gradient were established at the ecotone in 1998 and studied for four years. In addition to the natural gradients we also established a warming treatment. Decomposition rates (i.e. carbon dioxide efflux and litter decomposition) were higher at our forest sites. This was linked principally to the more favourable physical environment at the forest sites, rather than to SOM quality, despite some indications of higher SOM quality at forest sites based upon conventional chemical analysis and ¹³C NMR techniques. Tundra soils stored large amounts of potentially labile carbon that could readily be accessed by microorganisms when transferred to a forest environment. The interrelation between increased soil temperature and reduced soil moisture content is likely to moderate the response of decomposition rates to increased temperatures. Generally, these mesic soils showed net methane uptake from the atmosphere, which was enhanced by the warming treatment. No differences between forest or tundra soils could be detected.</p><p>The major conclusions presented here are that (1) soil carbon storage is likely to be reduced if mountain birch forest replaces tundra heath and (2), methane uptake in mesic soils in the Fennoscandian mountains represents a negative feedback to further environmental change in a warmer climate.</p>

This thesis presents results from several studies that have focused on the carbon and nutrient dynamics in soils at the forest – tundra ecotone in Fennoscandia. The main objectives of the study were: (i) to investigate the links between the physical environment, above-ground vegetation communities, soil carbon storage, nutrient status and the chemical composition of the soil organic matter (SOM), and (ii) to quantify trace gas fluxes (methane and carbon dioxide) between mesic soils and the atmosphere. Four main field areas spanning an 8 degree latitudinal gradient were established at the ecotone in 1998 and studied for four years. In addition to the natural gradients we also established a warming treatment. Decomposition rates (i.e. carbon dioxide efflux and litter decomposition) were higher at our forest sites. This was linked principally to the more favourable physical environment at the forest sites, rather than to SOM quality, despite some indications of higher SOM quality at forest sites based upon conventional chemical analysis and 13C NMR techniques. Tundra soils stored large amounts of potentially labile carbon that could readily be accessed by microorganisms when transferred to a forest environment. The interrelation between increased soil temperature and reduced soil moisture content is likely to moderate the response of decomposition rates to increased temperatures. Generally, these mesic soils showed net methane uptake from the atmosphere, which was enhanced by the warming treatment. No differences between forest or tundra soils could be detected. The major conclusions presented here are that (1) soil carbon storage is likely to be reduced if mountain birch forest replaces tundra heath and (2), methane uptake in mesic soils in the Fennoscandian mountains represents a negative feedback to further environmental change in a warmer climate.

High-latitude watersheds have been regarded as a carbon sink with soil carbon accumulating at low temperature. This sink is now believed to turn into a source, acting as positive feedback to climate warming. However, thawing permafrost soils would allow more water to percolate down to deeper soil layers where some of the carbon could be “consumed” in weathering and exported as bicarbonate to the sea. Using a hydrological mixing model showed that this could counterbalance the predicted positive feedback resulting from thawing soils. Vegetation-covered riparian zones in headwater areas appear to have a significant role for the dissolved constituent fluxes. Higher concentrations of weathering products are found in taiga and tundra rivers with larger areas of forest and peat cover in the watershed. These landscape elements can thus be regarded as “hot spots” of river loading with dissolved constituents. Comparing a regulated and an unregulated river tested the hypothesis that damming leads to a depletion of major elements also in oligotrophic river systems as a consequence of changes in landscape elements. A loss of upper soils and vegetation through inundation prevents the contact of surface waters with vegetated soil, and consequently reduces weathering fluxes. The hypothesis that the lower fluxes of dissolved silica (DSi) in the regulated river could also be explained by biological uptake was then tested using a model, and budget calculations indicate a significant reduction as a result of regulation. About 10% of this reduction can be attributed to the flooding of the fluvial corridor and the rest to diatom blooms in the reservoirs. A more detailed study of landscape elements for the headwaters of the river Luleälven showed that only 3% of the surface area has been inundated by reservoirs but ca. 37% of the deciduous forest. Such a significant loss of hot spots may indeed explain the observed lower DSi fluxes in the regulated watersheds of northern Sweden.

The consortia of microorganisms responsible for the hydrolysis of cellulose in situ are at present poorly characterized. Nonetheless, the importance of these communities is underscored by their capacity for converting biomass to greenhouse gases such as carbon dioxide and methane. The metabolic capacities of these organisms is particularly alarming considering the volume of biomass that is projected to re-enter the carbon cycle in Arctic tundra soil environments as a result of a warming climate. Novel cold-adapted cellulase enzymes also present enormous opportunities for a broad range of industries. DNA stable-isotope probing (DNA-SIP) is a powerful tool for linking the phylogenetic identity and function of cellulolytic microorganisms by the incorporation of isotopically labelled substrate into nucleic acids. By providing 13C-enriched glucose and cellulose to soil microcosms, it was possible to characterize the communities of microorganisms involved in the metabolism of these substrates in an Arctic tundra soil sample from Resolute Bay, Canada. A protocol for generating 13C-enriched cellulose was developed as part of this thesis, and a visual DNA-SIP protocol was generated to demonstrate the experimental outline. Denaturing gradient gel electrophoresis (DGGE) and 16S rRNA clone libraries were used to visualize changes in community structure and to identify prevalent, active phylotypes in the SIP incubations. Notably, predominant phylotypes changed over time and clustered based on substrate metabolism. Labelled nucleic acids identified by sequenced DGGE bands and 16S rRNA gene clone libraries provided converging evidence indicating the predominance of Clostridium and Sporolactobacillus in the 13C-glucose microcosms, and Betaproteobacteria, Bacteroidetes, and Gammaproteobacteria in the 13C-cellulose microcosms. Active populations consuming glucose and cellulose were distinct based on principle coordinate analysis of “light” and “heavy” DNA. A large portion of the recovered sequences possessed no close matches in the GenBank database, reflecting the paucity of data on these communities of microorganisms.

The application of natural tundra wetlands for municipal wastewater treatment is an option to meet upcoming federal wastewater systems effluent regulations for Canada’s Far North. A treatment performance assessment with physical, hydraulic and biogeochemical contextual data was conducted on the wetland treatment area of Coral Harbour, Nunavut. A modified Tanks-In-Series model was used to model treatment kinetics. The study showed seasonal variability in treatment performance and hydraulic characteristics. A decrease in vegetation diversity and deposition of organic detritus was observed in high effluent loading areas. Effective reduction in effluent concentrations was observed. Dilution from watershed contributions accounted for much of the reductions observed. The importance of the determination of the hydraulic residence time, field delineation of the wetted area, and delineation of the watershed was demonstrated. First order rate coefficients determined suggested that the selection of the lowest percentiles from literature of southern treatment wetlands is conservative in this case.

Cape Bounty, Melville Island is a partially vegetated High Arctic landscape with three main plant communities: polar semi-desert (47% of the study area), mesic tundra (31%) , and wet sedge meadows (7%). The objective of this research was to relate biophysical measurements of soil, vegetation, and CO2 exchange rates in each vegetation type to high resolution satellite data from IKONOS-2, extending plot level measurements to a landscape scale. Field data was collected through six weeks of the 2008 growing season. Two IKONOS images were acquired, one on July 4th and the other on August 2nd. Two products were generated from the satellite data: a land-cover classification and the Normalized Difference Vegetation Index (NDVI). The three vegetation types were found to have distinct soil and vegetation characteristics. Only the wet sedge meadows were a net sink for CO2; soil respiration tended to exceed photosynthesis in the sparsely vegetated mesic tundra and polar semi-desert. Scaling up the plot measurements by vegetation type area suggested that Cape Bounty was a small net carbon source (0.34 ± 0.47 g C m-2 day-1) in the summer of 2008. NDVI was strongly correlated with percent vegetation cover, vegetation volume, soil moisture, and moderately with soil nitrogen, biomass, and leaf area index (LAI). Photosynthesis and respiration of CO2 both positively correlated with NDVI, most strongly when averaged over the season. NDVI increased over time in every vegetation type, but this change was not reflected in any significant measured changes in vegetation or CO2 flux rates. A simple spatial model was developed to estimate Net Ecosystem Exchange (NEE) at every pixel on the satellite images based on NDVI, temperature and incoming solar radiation. It was found that the rate of photosynthesis per unit NDVI was higher early in the growing season. The model estimated a mean flux to the atmosphere of 0.21 g C m-2 day-1 at the time of image acquisition on July 4th, and -0.07 g C m-2 day-1 (a net C sink) on August 2nd. The greatest uncertainty in the relationship between NDVI and CO2 flux was associated with the polar semi-desert class. / Thesis (Master, Geography) -- Queen's University, 2011-12-28 23:27:34.824