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

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Climate change is expected to have significant and uncertain impacts on methane (CH4) emissions from northern peatlands. Biogeochemical models can extrapolate site-specificCH(4) measurements to larger scales and predict responses of CH4 emissions to environmental changes. However, these models include considerable uncertainties and limitations in representing CH4 production, consumption, and transport processes. To improve predictions of CH4 transformations, we incorporated acetate and stable carbon (C) isotopic dynamics associated with CH4 cycling into a biogeochemistry model, DNDC. By including these new features, DNDC explicitly simulates acetate dynamics and the relative contribution of acetotrophic and hydro-genotrophic methanogenesis (AM and HM) to CH4 production, and predicts the C isotopic signature (delta C-13) in soil C pools and emitted gases. When tested against biogeochemical and microbial community observations at two sites in a zone of thawing permafrost in a subarctic peatland in Sweden, the new formulation substantially improved agreement with CH4 production pathways and delta C-13 in emitted CH4 (delta C-13-CH4), a measure of the integrated effects of microbial production and consumption, and of physical transport. We also investigated the sensitivity of simulated delta C-13-CH4 to C isotopic composition of substrates and, to fractionation factors for CH4 production (alpha(AM) and alpha(HM)), CH4 oxidation (alpha(MO)), and plant-mediated CH4 transport (alpha(TP)). The sensitivity analysis indicated that the delta C-13-CH4 is highly sensitive to the factors associated with microbial metabolism (alpha(AM), alpha(HM), and alpha(MO)). The model framework simulating stable C isotopic dynamics provides a robust basis for better constraining and testing microbial mechanisms in predicting CH4 cycling in peatlands.

Wetland reclamation efforts in the Athabasca Oil Sands Region seek to restore important ecosystem services that were lost consequent of disturbance from oil sands mining development in northern Alberta, Canada. Constructed on the Syncrude Canada Ltd. mineral surface lease, the Sandhill Watershed is the first attempt to engineer a landscape capable of supporting a self-sustaining wetland above a backfilled open-pit mine. In the chapters below, through characterization of porewater chemistry patterns, plant community structure, physical characteristics of soil and nutrient availability the overall performance of the wetland area (the Sandhill Wetland) is evaluated. Further, observations at the reclaimed site are compared to 12 reference wetlands (10 fens and 2 marshes) to evaluate the type of wetland to which the Sandhill Wetland is most analogous. After six growing seasons, although water table position management has occurred annually, the Sandhill Wetland exhibits many attributes similar to those of the natural sites monitored. In terms of porewater chemistry, the dominant anions and cations present in near-surface water (bicarbonate, sulfate, chloride, sodium, calcium, and magnesium) have increased annually since the first growing season. If trends continue, the chemical conditions at the reclamation site could be analogous to saline fens in about 7-8 years based on projections for increasing sodium and chloride concentrations. The Sandhill Wetland currently exhibits porewater chemistry attributes most similar to saline fens and slightly brackish marshes. Total plant cover across the reclaimed wetland was quite high averaging 95% in the sixth growing season. Using multivariate approaches (NMDS), results show that plant community structure across high and intermediate water table position areas are most comparable to marshes, with Typha latifolia and Carex aquatilis exhibiting the highest cover. Across the periphery of the site, where water table position is several centimeters below the soil surface, plant communities are quite dissimilar from the reference sites and dominated by the grass Calamagrostis canadensis. While sodium-tolerant species are present at the site, albeit at low abundance, it is unclear whether long-term exposure to sodium-dominated porewaters currently present at the Sandhill Wetland will affect performance of wetland plants that established under low-sodium conditions. In terms of soil characteristics, clear differences were apparent, namely, for soil bulk density patterns. Bulk density observations across all areas at the Sandhill Wetland were higher than the reference sites and total soil carbon concentrations were also low. These observations were expected, and as the Sandhill Wetland matures, I predict annual production and (or) deposition of plant litter/ roots and increased biological activity will restore near-surface soil properties in the wetland area, thereby increasing TC concentrations and reducing soil compaction. For functional processes, using plant root simulator (PRS) probe ion exchange membranes, results demonstrate nutrient supply across the Sandhill Wetland was most similar to the moderate-rich and saline fens except for sulfur supply, which was considerably elevated. Based on PRS probe and porewater observations, the Sandhill Wetland is not a eutrophic system in the sixth growing season, and supply for most nutrients are within the ranges of natural systems. However, effects from local atmospheric nitrogen deposition (reported up to 12 kg N ha-1 yr-1) could alter structure and function over subsequent growing seasons. Currently, ecosystem health and functionality of the belowground environment appears to be adequately restored at the reclamation site. Lastly, as no officially recognized protocols exist for evaluating performance of recently reclaimed wetlands constructed above open-pit mines, using the Sandhill Wetland as a test site I propose a framework for evaluating reclamation site performance. Although the proposed evaluation protocol does not rely on multivariate techniques, the performance evaluation results support the previous findings (that were based on multivariate analysis) that a marsh-like analogue is the most realistic reclamation outcome for the reclaimed Sandhill Wetland. While the reclamation has been highly successful in terms of creating a wetland that has persisted, future monitoring of water chemistry and plant community structure should continue at the Sandhill Wetland, to capture important successional changes that may occur as the site matures.

Fire refugia, defined as unburned, functionally intact patches of habitat within a fire footprint, play an important role in post-fire recovery and landscape resilience to fires. Increased fire activity in the Canadian boreal forest due to climate change highlights the need to properly identify and manage wildfire refugia to protect the natural resilience of boreal ecosystems. While previous fire refugia research has focused on western Canada, we present the first characterization of fire refugia, with a focus on peatland fire refugia, in Ontario. We use remotely sensed multispectral imagery and stereo-derived DEM data from the 2018 Parry Sound 33 wildfire in the Ontario Boreal Shield to determine the primary drivers of fire refugia formation on this landscape, and to develop a model to predict the occurrence of potential fire refugia based on these drivers. We found that the Normalized Difference Moisture Index (NDMI) and the Topographic Position Index (TPI, 200m radius neighbourhood) had the strongest control on wildfire refugia probability in the model, with a combined relative influence of 63.8%. Additionally, wildfire refugia tended to form in peat-filled depressions, valleys, and forested areas within the study area, whereas drier, open rock barrens were most susceptible to fire. Overall, the model had a high predictive accuracy, with a cross-validated AUC of 0.88, and a sensitivity of 81.2%. We conclude that local scale topography and simple flow accumulation models can act as a powerful tool in predicting fire refugia occurrence in this landscape. In the second part of this study, we examined the in-situ indicators of peatland fire refugia occurrence. We conducted vegetation surveys at eight peatland fire refugia and eight reference sites representative of the range of wetland types found on this landscape. We found that the peatland fire refugia had a significantly different understorey vegetation composition when compared to the reference sites. Environmental factors within the peatland fire refugia which significantly influenced this separation included median peat depth, pH, and specific conductance (SpC); where peatland fire refugia were deeper and had a lower pH and SpC when compared to the reference sites. While no vascular indicator species were identified within the peatland fire refugia, there were two bryophyte indicator species: Sphagnum rubellum and Sphagnum magellanicum which were significantly associated with the peatland fire refugia. We conclude that understorey vegetation composition, indicator species presence, peat depth, pH and SpC could be useful when distinguishing peatlands with a high refugia probability, however, further research is needed to understand how this may vary geographically and in response to top-down controls, such as fire weather. Overall, the preliminary characterization of fire refugia in the Ontario Boreal Shield will provide a basis for the identification and mapping of fire refugia within this ecozone for applications in conservation, restoration, and fire and land management. / Thesis / Master of Science (MSc) / Areas which remain unburned, or burn at a low severity during a wildfire, are referred to as fire refugia by scientists and conservationists for their role in providing habitat to plants and animals following a fire and promoting the regeneration of the burned landscape. Here, we use modelling and field survey methods to examine the biological and physical controls of fire refugia occurrence in an Ontario Boreal Shield landscape. We find that large, deep peatlands and wetlands in bedrock depressions on this landscape are more likely to act as fire refugia, and that confirmed peatland fire refugia have distinct vegetation communities and more stable water tables when compared to other peatlands and wetlands on this landscape. These insights into fire refugia occurrence in the Ontario Boreal Shield will assist in the detection of potential refugia for the targeting of conservation and management strategies to help protect these ecologically important areas.

This study analyzes tree, soil, and microtopographic patterns present within the Cranberry Glades, a bog wetland complex located in the mountains of West Virginia. The Cranberry Glades are comprised of four open bog meadows, which provide unique habitat to several rare and endangered plant species. However, these meadows are filling in with trees and alder. This research is a study on the factors that may be involved in the processes and patterns influencing tree encroachment into the bog meadows across the open meadow – bog forest ecotone. To determine the patterns of infilling and the potential relationships among the trees, microtopography, and soil conditions, I collected and analyzed data on each of these factors within nine belt transects located across the ecotone. I gathered tree data on the following: location within transect, species, diameter at breast height or diameter at ground level, height class, associated microtopography, and growing conditions on 1,389 trees. Soil samples were gathered across the ecotone and analyzed for percent moisture, pH, and various nutrients and metals. I assessed historical aerial photographs to gain a temporal history on the patterns of infilling. The results indicate that trees decrease in density across the ecotone towards the peatland interior, and that trees are likely to be growing on hummock features and within tree islands. Soil properties resulted in mixed conclusions. The aerial photograph assessment revealed that trees and alders have been steadily encroaching into the open peatlands for at least the past 52 years. The finding of this research lend to increased knowledge on southern peatlands, wetland succession, and the Cranberry Glades Botanical Area. / Master of Science

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.

The severity of stratospheric ozone depletion in the temperate and polar latitudes has raised concerns about the sensitivity of terrestrial vegetation and ecosystems to solar ultraviolet (UV-B) radiation. This dissertation examined the responses of plants and microbes to solar UV-B for 3 years in Tierra de! Fuego, Argentina (55° S). This region is under the influence of the Antarctic "ozone hole" during the austral spring. Additionally, a quantitative review of the UV-B literature was conducted using a set of statistical techniques known as meta-analysis. For the field studies in Tierra de! Fuego, plots were established in a Sphagnum moss peatland and a Carexsedge fen during the spring of 1996. These plots received either near-ambient solar UV-B (90% of ambient) or reduced UV-B (20% of ambient) using specially designed plastic films. At the end of the first field season, no effects of the solar UV-B treatments were apparent on the growth and pigmentation of the plant species in either community The height growth of the moss Sphagnum mageffanicum was less under near-ambient solar UV-B than reduced UV-B during the second and third growing seasons. In contrast, volumetric density of the moss was greater under nearambient UV-B. The growth of the vascular plants did not respond to the solar UV-B treatments even after 3 years although UV-B-absorbing compounds were greater under near-ambient UV-B in some species. Populations of testate amoebae (i.e., shelled amoebae) inhabiting S. magellanicum had greater numbers under near-ambient UV-B than reduced UV-B throughout the 3 years. This response may be an indirect effect of solar UV-B mediated by the direct effect of UV-Bon S. mageffanicum height growth. Fungi on the leaf surfaces of the tree Nothojagus antarctica appeared to be directly inhibited by solar UV-B. The quantitative literature review of plant field studies simulating stratospheric ozone depletion assessed the effects of elevated UV-B on 10 plant response variables from papers published between 1976 and mid-1999. Modest significant inhibitions of leaf area, aboveground biomass, and plant height were apparent due to increased UV-B using meta-analysis. An increase in UV-B-absorbing compounds appears to be the most robust general response to increased UV-B radiation.

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Peatlands cover approximately 2-3% of the world’s land area yet represent approximately a third of the worlds estimated total soil carbon pool. They therefore play an important role in regulating global atmospheric CO2 and CH4 concentrations, and even minor changes in their ability to store carbon could potentially have significant effects on global climate change. Much previous research has focussed primarily on land-atmosphere fluxes. Where aquatic fluxes have been considered, they are often in isolation from the rest of the catchment and usually focus on downstream losses, ignoring evasion (degassing) from the water surface. However, as peatland streams have been repeatedly shown to be highly supersaturated in both CO2 and CH4 with respect to the atmosphere, they potentially represent an important pathway for catchment GHG losses. This study aimed to a) create a complete GHG and carbon budget for Auchencorth Moss catchment, Scotland, linking both terrestrial and aquatic fluxes, and b) understand what controls and drives individual fluxes within this budget. This understanding was further developed by a short study of C exchange at the peat-aquatic interface at Mer Bleue peatland, Canada. Significant variability in soil-atmosphere fluxes of both CH4 and N2O emissions was evident at Auchencorth Moss; coefficients of variation across 21 field chambers were 300% and 410% for CH4 and N2O, respectively. Both in situ chamber measurements and a separate mesocosm study illustrated the importance of vegetation in controlling CH4 emissions. In contrast to many previous studies, CH4 emissions were lower and uptake greater where aerenchymous vegetation was present. Water table depth was also an important driver of variability in CH4 emissions, although the effect was only evident during either periods of extreme drawdown or when the water table was consistently near or above the peat surface. Significant pulses in both CH4 and N2O emissions were observed in response to fluctuations in water table depth. Despite the variability in CH4 and N2O emissions and the uncertainty in up-scaled estimates, their contribution to the total GHG and carbon budgets was minor. Concentrations of dissolved CO2 in peatland drainage waters ranged from a mean of 2.88 ± 0.09 mg C L-1 in the Black Burn, Scotland, to a mean of 7.64 ± 0.80 mg C L-1 in water draining Mer Bleue, Canada. Using non-dispersive infra-red (NDIR) CO2 sensors with a 10-minute measurement frequency, significant temporal variability was observed in aquatic CO2 concentrations at the 2 contrasting field sites. However, the drivers of this variability differed significantly. At Mer Bleue, Canada, biological activity in the water column led to clear diurnal cycles, whereas in the Black Burn draining Auchencorth Moss, dilution due to discharge was the primary driver. The NDIR sensor data also showed differences in soil-stream connectivity both between the sites (connectivity was weak at Mer Bleue) and across the range of conditions measured at Auchencorth Moss i.e. connectivity increased during periods of stormflow. Compiling the results from both the terrestrial and aquatic systems at Auchencorth Moss indicated that the catchment was functioning as a net sink for GHGs (382 kg CO2-eq ha-1 yr-1) and a net source of carbon (143 kg C ha-1 yr-1). The greatest flux of GHGs was via net ecosystem exchange (NEE). Terrestrial emissions of CH4 and N2O combined returned only ~5% of CO2-equivalents captured by NEE to the atmosphere, whereas evasion of CO2, CH4 and N2O from the stream surface returned ~40%. The budgets clearly show the importance of aquatic fluxes at Auchencorth Moss and highlight the potential for significant error in source/sink strength calculations if they are omitted. Furthermore, the process based understanding of soil-stream connectivity suggests the aquatic flux pathway may play an increasingly important role in the source-sink function of peatlands under future management and climate change scenarios.