EVALUATING THE BIOGEOCHEMICAL FUNCTIONING OF A CONSTRUCTED FEN ON THE POST-MINING LANDSCAPE OF ATHABASCA OIL SANDS REGION, FORT MCMURRAY, ALBERTA, CANADA

Peatlands have a unique biogeochemical function, characterized by an imbalance between the rates of biomass accumulation and decomposition. These characteristics facilitate the ability of peatlands to support the sequestration of nutrients and carbon. In disturbed peatlands, these functions are compromised. Thus, reclamation targets amongst other key functions, the recovery of biogeochemical functioning. These functions could serve as a measure of recovery to conditions that are present in natural analogues. This thesis examines the recovery of microbially-mediated nutrient transformation processes in a fen peatland that was constructed on a post-mining landscape in the Athabasca oil sands region, Fort McMurray, Alberta. The major themes of this thesis examined (1) the concept of developing a functional-based approach for evaluating the functioning and trajectory of the constructed fen, (2) the impacts of donor-peat management practices on the resulting peat quality and the potential implications to the ecohydrological functioning of the constructed fen, (3) the evolution of above and below-ground nutrient transformation processes among different revegetation strategies in the constructed fen, and (4) the effect of revegetation and edaphic variables on the greenhouse gas (GHG) dynamics of the constructed fen. The concept of developing a functional-based approach for evaluating the functioning of a constructed fen was examined by synthesizing the dominant processes of peatland development. The interactions and feedback processes that underlie various peatland ecosystem functions and their quantifiable variables were identified through this synthesis. This also highlighted the sensitivity of microbially-mediated biogeochemical processes to a range of variability in other ecosystem processes. As an alternative to the bio-indicator approach, microbially-mediated biogeochemical processes present potential functional indicators of ecosystem function. The impact of donor-peat management practices on the ecohydrological functioning of the constructed fen was studied using cores extracted along transects in the donor fen before peat transfer, and after placement in the constructed fen. Relative to the properties of a reference fen, the donor-peat had a higher surface bulk density, and higher concentration of extractable nutrients. Transfer of peat to the constructed fen increased the near-surface bulk density, and decreased organic matter content and concentration of extractable nutrients. Evolution of above and below-ground nutrient transformation processes were assessed among different revegetation strategies, over the first two growing seasons post-construction. Revegetation facilitated both above-ground productivity and the cycling of below-ground nutrients. Supply of labile substrates in the re-vegetated plots increased microbial potential activity, which was reflected in higher rates of respiration, nutrient acquisition and productivity. Nutrient dynamics within the constructed fen suggest that phosphorus limitation could hamper the establishment of a diverse plant community, whereas the build-up of microbial biomass appears to be NO3- limited. Ammonification, nitrogen mineralization and phosphorus availability were identified as potential functional indicators of the fen’s recovery. Finally, the effects of revegetation strategies and environmental characteristics of the constructed fen on GHG dynamics were examined. Relative to a natural fen, significantly lower (p \u3c 0.001) fluxes of methane (CH4) were observed in the constructed fen. This correlated with higher bulk density, lower organic matter content, and higher pH and SO42- concentration. Revegetation did not stimulate CH4 production, but increased carbon dioxide (CO2) uptake and reduced the global warming potential (GWP) contribution of nitrous oxide (N2O) by 63CO2-e m-2 yr-1 relative to the non-vegetated control. These studies provide a novel insight into the concept of assessment of a constructed fen ecosystem through the evolution of biogeochemical functioning

Changes in nitrogen functional genes and microbial populations in soil profiles of a peatland under different burning regimes

Microbes in peatlands provide key ecosystem services and are essential for their role in biogeochemical cycling. Prescribed burning is a common aspect of peatland management but the practice has been criticized for being ecologically damaging due to its effect on the biological, chemical and physical properties of the soil. It is poorly understood how burning affects soil N cycling and previous studies have focused predominantly on the topsoil whilst giving less attention to changes with soil depth. This study investigated the changes of microbial abundance (bacterial 16S rRNA and fungal 18S rRNA) and the abundance of N-cycle functional genes involved in archaeal and bacterial ammonia oxidation (amoA-AOA and amoA-AOB), denitrification (nirK and nirS), N fixation (nifH) and organic N decomposition (chiA) in soil profiles across three burn treatments on a managed peatland landscape (a ‘non-burn’ since 1954 control, 20 years burn interval, and 10 years burn interval). Our results indicate the abundance of bacterial 16S rRNA and fungal 18 s rRNA was affected by burn treatment, soil depth and their interaction and were greater in the non-burn control plots. The abundances of amoA-AOA, amoA-AOB, and nifH were significantly higher in the topsoil of the non-burn control plots while the abundance of nirK was higher in plots subject to short rotation and long rotation burn regimes but also decreased significantly with soil depth. The abundance of nirS was not affected by burn treatment or soil depth. ChiA abundance was affected by burn treatment, soil depth and their interaction. N-cycle functional gene abundance responded differently to environmental factors associated with prescribed burning and varied with soil depth. These findings suggest that the practice of burning affects microbial N turnover potential and provides an important insight into the soil N-cycling potential of peatlands under different burning regimes

Bacterial and Fungal Communities in a Degraded Ombrotrophic Peatland Undergoing Natural and Managed Re-Vegetation

The UK hosts 15–19% of global upland ombrotrophic (rain fed) peatlands that are estimated to store 3.2 billion tonnes of carbon and represent a critical upland habitat with regard to biodiversity and ecosystem services provision. Net production is dependent on an imbalance between growth of peat-forming Sphagnum mosses and microbial decomposition by microorganisms that are limited by cold, acidic, and anaerobic conditions. In the Southern Pennines, land-use change, drainage, and over 200 years of anthropogenic N and heavy metal deposition have contributed to severe peatland degradation manifested as a loss of vegetation leaving bare peat susceptible to erosion and deep gullying. A restoration programme designed to regain peat hydrology, stability and functionality has involved re-vegetation through nurse grass, dwarf shrub and Sphagnum re-introduction. Our aim was to characterise bacterial and fungal communities, via high-throughput rRNA gene sequencing, in the surface acrotelm/mesotelm of degraded bare peat, long-term stable vegetated peat, and natural and managed restorations. Compared to long-term vegetated areas the bare peat microbiome had significantly higher levels of oligotrophic marker phyla (Acidobacteria, Verrucomicrobia, TM6) and lower Bacteroidetes and Actinobacteria, together with much higher ligninolytic Basidiomycota. Fewer distinct microbial sequences and significantly fewer cultivable microbes were detected in bare peat compared to other areas. Microbial community structure was linked to restoration activity and correlated with soil edaphic variables (e.g. moisture and heavy metals). Although rapid community changes were evident following restoration activity, restored bare peat did not approach a similar microbial community structure to non-eroded areas even after 25 years, which may be related to the stabilisation of historic deposited heavy metals pollution in long-term stable areas. These primary findings are discussed in relation to bare peat oligotrophy, re-vegetation recalcitrance, rhizosphere-microbe-soil interactions, C, N and P cycling, trajectory of restoration, and ecosystem service implications for peatland restoration

Microbial communities and biogeochemical functioning across peatlands in the Athabasca Oil Sands region of Canada: Implications for reclamation and management

Peatlands play an important role in global biogeochemical cycles and are essential for multiple ecosystem functions. Understanding the environmental drivers of microbial functioning and community structure can provide insights to enable effective and evidence-based management. However, it remains largely unknown how microbial diversity contributes to the functioning of belowground processes. Addressing this gap in knowledge will provide a better understanding of microbial-mediated processes in peatlands that are undergoing restoration or reclamation. This study assessed the changes in microbial community diversity and structure as well as soil function by measuring microbial respiration on a range of substrates from three natural fen types found in the Athabasca Oil Sands region of Alberta, Canada (a poor fen, a hypersaline fen, and a tree-rich fen) and a nearby constructed fen undergoing reclamation following open pit mining. Overall, substrate induced respiration was significantly higher in the constructed fen. Alpha diversity of fungi and prokaryotes was highest in the tree-rich fen, and the composition of microbial communities was significantly different between fens. Both fungal and prokaryotic communities were strongly related to pore water pH and temperature, with plant richness also contributing to the shape of fungal communities. In summary, microbial community structure reflects the underlying differences in soil condition across different fens but plays essential roles in the ecological functions of soil. These findings provide a new outlook for the management of peatlands undergoing post-mining reclamation. Future research on peatland reclamation should consider the dynamic interaction between communities and ecosystem functionality, for which this study forms a useful baseline