Most undisturbed peatlands sequester carbon, and rising levels of atmospheric nitrogen deposition may have the potential to destabilize this function, possibly resulting in an increased release of carbon dioxide into the atmosphere.  It is therefore of vital importance to investigate further the link between atmospheric nitrogen deposition and carbon dynamics in exposed ecosystems such as peatlands. The work described in this thesis aimed to elucidate the impact of increasing nitrogen on aspects of carbon turnover in peatlands.  Using a long-term field-based experiment, I tested the effects of 4 years of ammonium and nitrate addition (8, 24 and 56 kg N ha^-1 y^-1) on the fate of newly photosynthesised carbon by plants and the turnover of labile and recalcitrant carbon.  A second set of experiments undertaken in the laboratory assessed the use of plant wax analysis as potential biomarkers of past changes in vegetation and carbon status in peat. Overall, this work has shown that the form of nitrogen (ammonium versus nitrate) is a crucial component of atmospheric pollution and must be taken into consideration when investigating or predicting effects of reactive nitrogen on peatlands.  In addition, nitrogen addition affected the fate of newly synthesised carbon differently in <i>Eriophorum vaginatum </i>and <i>Calluna vulgaris, </i>revealing the importance of considering plant traits when investigating environmental changes in terrestrial ecosystems.  Furthermore, it has led to the development of an investigative tool for further exploration of the historical effects of atmospheric nitrogen deposition on vegetation an carbon content in peatlands.

Les premiers essais agricoles dans les terres basses de la Guyane française commencent dès 1763 sur les côtes de Kourou. Ce fut le début d’une entreprise qui, sous la forme de dents de scie, va marquer l’économie de cette colonie française de l’Amérique du sud jusqu’à nos jours. Les terres noyées de la Guyane française, sont toutes localisées sur la bande côtière et correspondent à des zones humides (tourbières, mangroves, marais). Au début de la colonisation, en 1604 précisément, les Français se sont établis sur l’île de Cayenne, et ont occupés les terres hautes, situées plus à l’intérieur du continent. L’agriculture de ces terres a débuté à la même période, selon le modèle d’agriculture sur brûlis développé par les autochtones. Ce modèle traditionnel convenait à la production des denrées alimentaires pour des petits groupes. Néanmoins, au bout d’un siècle, leur rendement ne satisfaisait plus au commerce de la colonie. L’épuisement ou la faible productivité de ces terres hautes à la fin du XVIIIeme siècle, a ainsi occasionné une ruée ver les terres basses. Le développement de ces terres noyées avait déjà été entrepris par les Hollandais (Guyane hollandaise), mais ces zones humides rebutaient encore les Colons-Planteurs en Guyane française. Dès l’arrivée de V. Malouet (nouvel intendant de la colonie) vers 1778, les techniques d’assèchement et de construction de polders se développent en Guyane française sous la direction de l’ingénieur J. S. Guisan. Ce dernier essaya de faire des terres noyées, la réponse aux problèmes agricoles de la Guyane française. Mais, les différents évènements socio-politiques qui touchèrent la France à cette époque (Révolution française, abolition de l’esclavage, activités aurifères), mirent fin dès 1848 à cette entreprise. Certaines contraintes climatiques doivent également être considérées. Un siècle plus tard, vers 1950 avec le lancement du plan vert, les rizières de Mana témoignent encore de l’importance de la culture des terres basses en Guyane française. / The first agricultural trials in the lowlands of French Guyana started in AD 1763 on Kourou coasts. It was the beginning of an initiative that will mark the economy of this French colony of South America until today. The flooded lands of French Guyana are all located on the coastal strip. This area is composed of wetlands (peatlands, mangrove and swamps). At the beginning of colonisation, in AD 1604 exactly, French people established themselves on the Cayenne Island and on the uplands (mainland). The cultivation of these uplands started at the same time, adopting the slash-and-burn agriculture developed by autochthonous people. More, this agricultural model was butter suited to foodstuffs production for small groups. However, early in the century, their performance no longer satisfied trade of the colony. Depletion or low production of these uplands at the end of the XVIIIth century, caused a rush to the lowlands. The development of these low lands has already been undertaken by the Dutch (Dutch Guyana), but these wetlands were still rejected by the Colon-planters in the French Guyana. As soon as V. Malouet arrived (new intendant of the colony) ca. AD 1778, the techniques of dewatering and polder construction developed in the French Guyana under the supervision of the engineer J. S. Guisan. He tried to manage the flooded lands as an answer to agricultural problems of the French Guyana. But, several socio-political events occurred in France at this period (the French Revolution, the abolition of slavery, the gold-bearing activity) put a stop to this process in AD 1848. Climate control should also be considered. One century later, around AD 1950, Mana rice fields still testify of the importance of cultivation of lowland of French Guyana, in particular thanks to the launch of the green plan.Keys words: French Guyana

It is estimated that peatlands cover around 20% of Scotland’s land area. Scotland’s peatlands are important ecosystems in terms of the services they provide; carbon sequestration, water chemistry and flow regulation, biodiversity, as well as for the homes and livelihoods they offer to their inhabitants. Due to historical management practices over 70% of Scotland’s peatlands are damaged to some degree, and are now in need of restoration. The remaining peat bogs need to be conserved. Peatlands are complex landscapes that require good governance in order to be managed fairly and effectively. This thesis sets out to explore the issues surrounding peatland management and offer some recommendations. Workshops were carried out in Dumfries, The Cairngorms, Thurso and Shetland in order to explore how landowners and managers perceived peatlands and peatland restoration and the potential to fund restoration through the Peatland Code Payment for Ecosystem Services Scheme. The main findings were; there was confusion over the policy concerning peatlands, landowners and managers felt uncertain of the potential carbon benefits and methods to predict them, the Peatland Code focuses on carbon benefits and landowners and managers cared more about water and wildlife. These findings prompted a more in depth study of the objectives, priorities and values of landowners and managers through the use of qualitative interviews, and a policy analysis to clarify funding options and regulations and to identify potential barriers. Sixty-seven semi-structured interviews were carried out with landowners and managers from the four regions around Scotland. These were analysed in order to find common themes. Many of the interviewees had social and environmental aims for their land, as well as financial aims. There was a very strong sense of care and responsibility for the land, which was linked to heritage, legacy and identity. Communication was poor between different groups (landowners vs crofters, locals vs incomers, landowners and managers vs NGOs, Scientists, Politicians), fostering a sense of discord or antagonism. This lead to a lack of trust and a reluctance to engage with other groups, exacerbating communication issues. Poor communication means that the good environmental intensions of evident from the interviews did not always translate into action. Exceptions to this always involved face-to-face communication, site visits, and a long term relationship allowing the build-up of trust. Policy documents relating to peatlands were reviewed. Findings were presented at a workshop attended by peatland policy experts, in order to identify gaps or misconceptions, which were then addressed. Peatlands do not have their own policy area, but are mentioned in policy related to agriculture, forestry, fresh water and biodiversity. Peatlands are most often mentioned in terms of their carbon sequestration potential. They are poorly integrated in fresh water policy. This shows a mismatch between the interests of policy-makers, and the interests of practitioners, as identified in the workshops. Funding for peatland restoration is limited, restrictive in terms of activities that will be funded, and the application process is onerous. The regulations are poorly communicated leading many to fear they will be penalised for undertaking management that is beneficial to peatlands. There are few policies with the intention of building capacity through information provision or training. The uncertainty surrounding funding options for peatland restoration may discourage contractors from diversifying in this area, leading to a shortage of people with the skills necessary to carry out the work. In all three chapters there is a common thread that the various policies and schemes created in order to facilitate conservation and restoration of peatlands do not adequately harness the feelings of care and responsibility towards the environment that are present in the landowning and managing communities. This is due to poor communication and a misunderstanding of the various perspectives of groups in these areas, leading to sometimes obstructive policies which fall short of their ambitions.

Peat soils store a large fraction of the global soil carbon (C) pool and comprise 95% of wetland C stocks. They also have the capability to produce and release significant amounts of greenhouse gasses (CO2, CH4) into the atmosphere. Most studies of wetland soil C and gas flux dynamics have been done in expansive peatlands in northern boreal and subarctic biomes. However, wetlands in temperate and tropical climates are vastly understudied despite accounting for more than 20% of the global peatland C stock and storing large amounts of biogenic gasses Although studies investigating greenhouse gas dynamics from peatlands have increased during the last decade, the spatial and temporal distribution of these gases still remains highly uncertain, mainly due to the limitations in terms of spatial and temporal resolution and invasive nature of most methods traditionally used. This thesis combines a series of field and laboratory studies at several sites in the Greater Everglades as examples to show the potential of hydrogeophysical methods to better understand: 1) the belowground C distribution and overall contribution to the global C stocks of certain wetlands (Chapter 2); and 2) the spatial and temporal variability in both C accumulation and releases from peat soil monoliths from several wetland sites in the Greater Everglades (Chapter 3 and 4). To estimate belowground C in the field, I used a combination of indirect non-invasive geophysical methods (GPR), aerial imagery, and direct measurements (coring) to estimate the contribution of subtropical depressional wetlands to the total C stock of pine flatwoods landscape at the Disney Wilderness Preserve (DWP, Orlando, FL). Three-dimensional (3D) GPR surveys were used to define the thickness of stratigraphic layers from the wetland surface to the mineral soil interface within depressional wetlands. Depth-profile cores in conjunction with C core analysis were utilized to visually confirm depths of each interface and estimate changes in soil C content with depth and were ultimately used to estimate total peat volume and C stock for each depressional wetland. Aerial photographs were used to develop a relationship between surface area and total wetland C stock, that were applied to estimate total landscape C stock of all depressional wetlands throughout the entire preserve. Additionally, low-frequency GPR surveys were conducted to image the stratigraphy underneath the peat basin of depressional wetlands to depict lithological controls on the formational processes of depressional wetlands at the DWP. Spatial and temporal variability in biogenic greenhouse gas (i.e. methane and carbon dioxide) production and release were investigated at the laboratory scale. Two 38 liter (0.5 m x 0.23 m x 0.3 m) peat monoliths from two different wetland ecosystems in central Florida (sawgrass peatland and a wet prairie) were compared in order to understand whether changes in matrix properties influence gas dynamics in a controlled environment (i.e. constant temperature). Gas content variability (i.e. build-up and release) within the peat matrix was estimated using a series of high frequency (1.2 GHz) GPR transects along each sample about three times a week. An array of gas traps (eight per sample) fitted with time-lapse cameras were also used in order to constrain GPR measurements and capture gas releases at 15-minute intervals. Gas chromatography was performed on gas samples extracted from the traps to determine CH4 and CO2 content. Also, at the lab scale, temporal variability in biogenic gas accumulation and release was investigated in a large 0.073 m3 peat monolith from the Blue Cypress Preserve in central Florida. An autonomous rail system was constructed in order to estimate gas content variability (i.e. build-up and release) within the peat matrix using a series of continuous GPR transects along the sample. This system ran virtually nonstop using high frequency (1.2 GHz) antennas. GPR measurements were again constrained with an array of gas traps (6) fitted with time-lapse cameras and gas chromatography. The aim of this study is to better constrain temporal scale, and better understand the heterogeneous nature (both in time and space) of gas releases from peat soils. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Global warming, associated with elevated levels of greenhouse gases is expected to alter hydrologic regimes, permafrost extent and vegetation composition in the Hudson Bay Lowlands (HBL). Greenhouse gas (respiration, CH4 and N2O; GHG) emissions and soil gas concentrations were determined over the growing seasons of 2005 and 2006 from numerous habitats within three dominate ecosystems within the HBL, a polygonized-peat plateau, northern fringe boreal forest and palsa fen, near Churchill, Manitoba. Nitrous oxide emissions and soil concentrations were near zero however, a trend for very slight production of N2O was observed at dry aerobic sample positions while very slight consumption occurred at very wet sample locations. “Hot-spots” of intense CH4 emissions and soil concentrations occurred in the sedge-dominated areas of high moisture and plant productivity, whereas areas of low moisture and plant productivity resulted in slight CH4 consumption. Of all the ecosystems studied, the palsa fen had the greatest CH4 production, with carbon losses from CH4 occurring at rates of approximately 50 g C m-2 during the growing season. A peat plateau ecosystem site was also used to compare GHG emissions using a similar vegetation type (Cladina stellaris) and under differing soil conditions. Based on the results, slight gradients in soil conditions such as moisture content, peat accumulation and active layer depths altered respiration emissions but did not significantly affect CH4 and N2O fluxes. The differences in GHG emissions were not as great as those between different plant community types, which suggest plant community types could be used to predict GHG emissions in similar environments. / October 2007

Northern peatlands are large repositories of carbon and little is known about the effect the microbial community has on carbon mineralization rates, and there is concern that a loss of microbial diversity due to environmental change may lead to reduced ecosystem functioning. Microbial communities vary among peatland types and abiotic variables such as temperature and pH have a large influence on carbon dioxide production, but distinguishing between abiotic controls and the role of microbial community structure has proved challenging. Microbial activity and community composition was characterized in three peatlands within the James Bay Lowlands, Ontario. Similar dominant microbial taxa were observed at all three peatlands despite differences in nutrient content and substrate quality and geographic location. In contrast, microbial activity differed among the sites, indicating that it is influenced by the quality of the peat substrate and the presence of microbial inhibitors. A series of reciprocal field and laboratory transplant experiments were conducted at a rich and poor fen near White River, Ontario to more explicitly distinguish between the abiotic and microbial controls on carbon mineralization. The effect of transplantation differed between the laboratory and field studies and when viewed individually could lead to different interpretations of the effect of substrate change. Surprisingly, intensive sampling within both fens was unable to reveal a difference between the rich and poor fen microbial community due to high within site temporal and spatial variation. Thus studies with small sampling effort will have a very incomplete understanding of microbial community structure and thus microbial ecology. A reciprocal sterilization transplant experiment was also conducted to examine how different microbial communities adapted to various peat substrates influenced C-mineralization patterns. Post-inoculation/incubation bacterial communities across peatlands converged towards a similar community structure, suggesting that abiotic variables are the dominant control on peatland microbial activity and community composition. The studies presented in this thesis collectively show that across a broad range of temperate and sub-arctic peatland types dominant members of the microbial community are generally similar, and decomposition rates can be predicted by broader controlling environmental factors rather than temporal niche or distributional constraints of the microbial community.

A hydrological modelling effort using MODFLOW was undertaken in order to determine the relative importance of some of the factors influencing hydraulic gradient reversals in peatlands. Model domains were of two types, large raised bog type (LRBT) and kettle bog type (KBT), and were made to undergo various levels of meteorological forcing (water deficit). Substrate, too, was varied in order to determine its importance on reversals. Domain-wide reversals were successfully simulated in LRBT systems, but not in KBT systems. Although simulated flow patterns matched field-observed patterns, both pre- and post-drought, simulated reversals occurred more quickly than in the field. This may be due to insufficiently distributed parameters, such as hydraulic conductivity. Reversals were easily terminated by simulating non-drought conditions. In the LRBT system, reversal duration decreased, and time-to-reversal increased, with a decrease in drought severity. Increasing drought severity in KBT systems had the opposite effect on the duration of semi-reversed flow patterns, suggesting a possibly different/additional mechanism for flow reversals in KBT systems. Hydraulic conductivity had an appreciable effect on flow reversal evolution, though neither changing porosity, nor differences in catotelm layering had a great effect.

Peatlands provide a variety of ecosystem services including carbon sequestration, nutrient cycling and increased biodiversity, and are thus an important Canadian natural resource. Mountain peatlands, including those in the foothill region of the Canadian Rockies are particularly important due to their proximity to headwater streams which supply the Prairie Provinces with water. Yet, distribution of peatlands in the Canadian Rocky Mountains is unknown. There is also a lack of understanding of the form of these peatlands and the processes influencing them. The purpose of this research is to improve our understanding of Canadian mountain peatlands in terms of their abundance, distribution and subsurface form. Specific objectives are to: determine the distribution of beaver impacted wetlands in the study area; quantify the proportion of these which are peatlands; determine the impact beaver have on one hydrological variable, the area of open water and; describe the stratigraphy of peatlands with beaver at their surface. Beaver impacted wetland distribution was assessed through manual analysis of georeferenced aerial photographs. Combining these data with an existing GIS layer provided the basis of a wetland inventory of the region, allowing wetlands to be separately inventoried by physiographic location (Mountain and Foothills) and jurisdiction (Alberta Parks, Municipal Districts, Improvement Districts and First Nations Reserve). Approximately 75% of wetlands are located in the Foothills and Municipal District areas. Beaver impact is evident in 30% of the 529 wetlands inventoried, with the highest number in protected areas. Area of open water on wetlands, as assessed by manual analysis of aerial photographs, indicated that beaver impacted sites have on average approximately ten times more open surface water area than non- beaver impacted sites. In total, 81 wetlands were ground-truthed of which 77% were peat-forming wetlands or peatlands. Ground penetrating radar surveys and soil coring performed at 9 peatlands with beaver activity at their surface showed structural differences from those peatlands for which ecosystem services are described in the literature in that they are stratigraphically complex. Little is known about the factors affecting how this form develops, and this requires further study. The distribution of peatlands in the study area highlights them as important landscape units, and that in order to best manage them, further research is required into the various influences on their hydrological and ecological function.

Northern peatlands are large repositories of carbon and little is known about the effect the microbial community has on carbon mineralization rates, and there is concern that a loss of microbial diversity due to environmental change may lead to reduced ecosystem functioning. Microbial communities vary among peatland types and abiotic variables such as temperature and pH have a large influence on carbon dioxide production, but distinguishing between abiotic controls and the role of microbial community structure has proved challenging. Microbial activity and community composition was characterized in three peatlands within the James Bay Lowlands, Ontario. Similar dominant microbial taxa were observed at all three peatlands despite differences in nutrient content and substrate quality and geographic location. In contrast, microbial activity differed among the sites, indicating that it is influenced by the quality of the peat substrate and the presence of microbial inhibitors. A series of reciprocal field and laboratory transplant experiments were conducted at a rich and poor fen near White River, Ontario to more explicitly distinguish between the abiotic and microbial controls on carbon mineralization. The effect of transplantation differed between the laboratory and field studies and when viewed individually could lead to different interpretations of the effect of substrate change. Surprisingly, intensive sampling within both fens was unable to reveal a difference between the rich and poor fen microbial community due to high within site temporal and spatial variation. Thus studies with small sampling effort will have a very incomplete understanding of microbial community structure and thus microbial ecology. A reciprocal sterilization transplant experiment was also conducted to examine how different microbial communities adapted to various peat substrates influenced C-mineralization patterns. Post-inoculation/incubation bacterial communities across peatlands converged towards a similar community structure, suggesting that abiotic variables are the dominant control on peatland microbial activity and community composition. The studies presented in this thesis collectively show that across a broad range of temperate and sub-arctic peatland types dominant members of the microbial community are generally similar, and decomposition rates can be predicted by broader controlling environmental factors rather than temporal niche or distributional constraints of the microbial community.

Subsurface peat decomposition, through CO2 production, was analyzed in laboratory and field experiments in a bog, poor fen, and beaver pond margin at Mer Bleue, Ottawa. Intact core samples in 10 cm depth intervals from 5--45 cm below the surface of each site were incubated in the laboratory. Treatments involved aerobic and anaerobic conditions at 4 and 14°C. Field measurements of CO2 flux were made by a static chamber technique. / Incubation results indicate modelled CO2 surface fluxes differ amongst wetlands. Aerobic CO2 modelled surface fluxes at 4°C were 2.3, 3.1 and 4.2 g CO2 m-2 d-1 for the bog, the beaver pond margin, and the poor fen, respectively. On average, aerobic production rates from peat cores with field moisture conditions were 11.7 times larger than anaerobic production rates. A mean Q10 of 2.3 defined the role of temperature. Differences among the peat samples were related to degree of decomposition, and differences among the sites were related to trophic status and nutrient availability. / A model of CO2 production was constructed and validated against field fluxes of CO2. The model provides a good prediction (r 2 = 0.72) of subsurface peat decomposition. The results suggest that warmer peat temperatures and lowered water tables, as predicted by climate change scenarios, will increase surface CO2 fluxes due to peat decomposition.