Globally, peatlands are vulnerable to degradation via drainage, with consequences for ecosystem structure and function such as increased fire vulnerability, soil oxidation, and altered vegetation composition. Peatland function is largely dependent on hydrologic regimes and their influences on the accumulation and properties of peat soil. Therefore, an understanding of soil-hydrology interactions is needed to inform management in drained peatlands, including expansive systems such as the Great Dismal Swamp (GDS; Virginia and North Carolina, USA) where hydrologic restoration is underway. Two physically distinct soil layers have been observed at GDS, the upper layer thought to be a result of past drainage and the lower layer more representative of an undisturbed state. To understand the occurrence and consequences of these distinct layers, we integrated continuous water level data, peat profile characterization, and analyzed soil physical and hydraulic properties. The transition from upper to lower peat soil layers typically occurred at depths below contemporary water level observations, suggesting that the upper layer may be a result of historical drainage with limited recovery following hydrologic restoration. We also found distinct differences between the properties of the two layers, where upper layers had lower fiber and organic matter contents and higher bulk densities. Further, upper layers had higher proportions of macropores, resulting in an overall lower water retention capacity. These differences in layer properties suggest the upper layer is more susceptible to drying, increasing fire vulnerability, oxidation, and shifts in vegetation composition that do not support current management objectives. / Master of Science / Peatlands provide many valuable ecosystem services, including carbon storage, water quality maintenance, and habitat provision. However, peatlands have been subjected to centuries of drainage (i.e., lowered water levels) to support timber harvesting, land conversion, and other land use actions. Drainage and the resulting drier conditions can lead to soil carbon loss, increased fire vulnerability, and changes in vegetation communities. Additionally, peatland drainage has consequences for peat soil properties and their role in ecosystem services. In an effort to restore peatland ecosystem services, hydrologic restoration, usually in the form of water control structures, is often implemented to reduce drainage and reestablish historical water levels. To guide restoration practices, research is needed to understand how drained peat soils respond to such hydrologic management. In this study, we investigated peat soil profiles, current water level regimes, and soil properties at the Great Dismal Swamp (Virginia and North Carolina, USA), a drained peatland currently undergoing hydrologic restoration. We found a visibly distinct upper soil layer, which we suggest developed as a result of past drainage and with little recovery under restored, wetter conditions. We also found that this upper layer has altered soil properties and thus is more vulnerable to drying, with implications for ecosystem function such as fire vulnerability, carbon sequestration and vegetation composition. Together, our findings will help inform restoration and water level management at GDS and our understanding of drained peatlands more broadly.

Peatlands store nearly one third of the soil global carbon, and approximately 10% of the world's drinkable water on only 3% of the land surface. Peatlands store large amounts of carbon from the organic matter due to the reduced decomposition rates in the soil allowing the accumulation of new plant growth each year. Rising temperatures and increasing nutrient inputs from human activities can accelerate decomposition rates in the soil transforming peatlands from sinks to sources of carbon, and reducing their ability to regulate the local hydrological cycles. To identify how rising temperatures and increasing human originated disturbances have peatlands, I studied the current vegetation patterns and related them to elevation, temperature and disturbance environmental gradients, explored the recent history (last 200 years) of the peatland vegetation, and built models that described the past rates of gains by primary production and losses due to decomposition; finally I constructed a forecasting model to describe the dynamics of northern Andean peatlands. Past vegetation and historic production and decomposition rates were estimated from 210Pb chronologies. Results indicate a strong effect of the interaction between elevation and the intensity of human disturbance; superficial carbon stocks were negatively affected by human disturbances that at the same time favored the encroachment of upland vascular species. Elevation was an important gradient with lower peat accumulation rates at higher elevations, except when water from glacial meltdown was supplied in which case production reached extremely high values. Modeling of peatland dynamics indicated increasing decomposition rates in sites with high human disturbance, an effect that propagated towards the future in the form of net losses of carbon in the upper part of the peat column. Conversely, sites with low human disturbance or at high elevations but receiving water from glacial meltdown become larger carbon sinks. In conclusion, climate change is having a direct and measurable effect on the dynamics of northern Andean peat dynamics; however, the effects become less predictable when interactions with the climatic or human systems are included. The rate of peat degradation due to modifications in the environment indicates the urgency to better understand the northern Andean peatland ecosystems. In conclusion: high elevation peatlands in the Northern Andes are ecosystems that offer extremely important ecological services but that may have started an irreversible decline.

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Peatland ecosystems are important as natural climate regulators for their capacity to store carbon over long-time scales. Carbon cycling in peatlands in the boreal ecozone of Canada has been more widely studied than the boreal shield of Ontario, where peat depths are thinner and peatlands spatially smaller. The reliance on fill and spill hydrologic connectivity makes the water table dynamics of peatlands in Ontario’s Eastern Georgian Bay (EGB) region of the Ontario shield ecozone sensitive to rain and drought periods. The drying of wetlands in the EGB region decreases moss productivity and increases the ecosystem’s vulnerability to wildfire through an increase in the water table depth. In an effort to understand how peatlands respond to interannual climate variability and wildfire, we examined the role of regional climate patterns on growing season CO2 exchange from an Ontario shield peatland and completed a post-wildfire assessment of CO2 exchange patterns in a recently burned peatland for the first and second year post-wildfire. Using the eddy covariance technique, we analyzed 5-years of growing season CO2 exchange data from 2016 to 2020 from an unburned peatland and 2-years of growing season CO2 exchange data from a burned peatland (2019-2020) in EGB. Plot-scale CO2 exchange measurements were also completed within the burned peatland jointly with abiotic variables and vegetation community surveys. Water table depth was identified as an important variable to explain total summer CO2 uptake (GPP) and net ecosystem exchange (NEE), where years of considerable rainfall maintained a water table near the peat surface and perpetuated high vegetation productivity. Summer total ecosystem respiration (ER) was greatly influenced by preceding winter and spring air temperature, with warmer winter air temperatures leading to summers of increased total ER. Warmer winter air temperatures also initiated water flow across the landscape, thus reviving plant and microbial activity following snow cover. These findings have important implications for the function of these shallow Ontario shield peatlands in a warming climate, where decreased water availability with projected increased temperatures and evapotranspiration leaves peatlands at risk of a net loss of C over the summer with lower water table. In the burned landscape, there was lower GPP in the summer (2019) compared to the wet summer of 2020, however the burned landscape continued to act as a net CO2 sink for the summer season of both years. The rapid recovery of vegetation across the wildfire-disturbed landscape has important implications for the function of these peatlands over time, with the ability for continued carbon uptake and reinstating peat accumulation processes. / Thesis / Master of Science (MSc)

<p>Disturbed peatlands may undergo a dramatic alteration in ecohydrological conditions, potentially limiting the recolonisation of peat-forming species like <em>Sphagnum</em>. A poor fen was experimentally drained in 1984, both the drained and undrained portion of the peatland burned in 2001, providing an unique opportunity to examine the ecohydrological response to ‘double disturbance’.</p> <p>The undrained site<em> </em>was characterized by a healthy recovery of<em> </em>peatland microform <em>Sphagnum</em> species, low soil water pressure (Ψ), high volumetric soil moisture (θ) content and high and stable water table position. However, the drained site showed no recolonization of <em>Sphagnum</em> with <em>Brome</em> grasses representing the dominant surface cover nine years post-wildfire.</p> <p>While the study period was generally wet and as such Ψ did not exceed thresholds limiting <em>Sphagnum</em> growth (≥ -100 mb) during the study period, a series of ecohydrological influences were found to be operating, limiting <em>Sphagnum</em> recolonisation at the drained site. The physical peat structure following drainage and wildfire has been considerably altered, changing the moisture retention and water storage properties of the peat, largely through substantive increases in bulk density (ρ_b). Moreover, specific yield (<em>Sy</em>) has also decreased the drained peat having become more humified, increasing unstable water table fluctuations. As such, this has lowered the resilience to drought. Only smaller decreases in θ are required to reach Ψ ≥ -100 mb at the drained and impose ecophysiological stress on <em>Sphagnum</em> growth. Dense canopy cover (<em>Betula</em> and <em>Sali</em>x) has limited available radiation at the surface to recolonisation, shading out the surface, further limiting <em>Sphagnum</em> recolonisation.</p> / Master of Science (MSc)

<p>The objective of this thesis is to examine the changes to peatland ecohydrological processes as a result of wildfire disturbance in forested ombrotrophic peatlands of the Boreal Plains. The hydrology and atmospheric exchanges of energy and water were examined at two peatlands in northern Alberta: one recently burned and the other approximately 75 years since fire.</p> <p>Wildfire resulted in little change in net radiation flux to the peatland during the snow-free period. A decrease in the net radiation flux during the late winter was caused by the loss of the tree canopy and the increase in albedo during winter. While summer albedo largely returned to pre-fire values within two years after fire, the amount of solar radiation reaching the burned peat surface increased by nearly 50%. As a result, surface evaporation increased by an amount only marginally greater than the loss of transpiration. The net result on the water balance was a modest increase in water losses during the course of the summer, resulting in a lower water table. Water table decline per unit of evaporation was higher due to a decrease in specific yield, likely from a combination of post-fire peat compression and the combustion of high specific yield surface peat during wildfire. The combination of lower water table and enhanced evaporation cause greater pore-water pressures after fire, particularly in hummocks. The hydrological regime of hollows was not significantly altered by wildfire, despite the larger depth of burn in the hollows.</p> / Doctor of Philosophy (PhD)

<p>Northern boreal peatlands represent a globally significant carbon pool that are at risk of drying through land-use change and projected future climate change. The current ecohydrological conceptualization of peatland response to persistent water table (WT) drawdown is largely based on short-term manipulation experiments, but where the long-term response may be mediated by vegetation and microtopography dynamics. The objective of this thesis is to examine the changes to peatland evapotranspiration, soil physical properties, and moisture stress in response to a long-term WT manipulation. The energy balance, hydrology, vegetation, and soil properties were examined at three adjacent peatland sites in the southern sub-boreal region which were subjected to WT manipulations on the order of ±10 cm at two treatment sites (WET, and DRY) compared to the reference site (INT) as a result of berm construction in the 1950s.</p> <p>Sites with an increasing depth to WT were found to have greater microtopographic variation and proportion of the surface covered by raised hummocks. While total abundance of the major plant functional groups was altered, species composition and dominant species of vascular and non-vascular species within microforms was unaltered. Changes in vegetation and microtopography lead to differences in albedo, surface roughness, and surface moisture variability. However, total ET was only significantly different at the WET site. Transpiration losses accounted for the majority of ET, where LAI best explained differences in total ET between sites. Surface moisture availability did not appear to be limiting on moss evaporation, where lab results showed similar moisture retention capacity between microforms and sites, and where low surface bulk density was shown to be a strong controlling factor. Modelling results further suggested that, despite dry surface conditions, surface moisture availability for evaporation was often not limited based on several different parameterizations of peat hydraulic structure with depth.</p> / Doctor of Philosophy (PhD)

<p>Organic soil depth of burn in Canadian boreal peatlands cited in the literature generally ranges from 0.05 to 0.10 m despite fire manager reports that suggest higher burn severity (> 0.50 cm) may exist on the landscape. It was hypothesized that hydrogeological setting imposes different landscape patterns of peat bulk density and moisture content leading to greater variability in organic soil burn severity across the landscape than previously thought. To examine this, depth of burn was measured in three peatlands located along a hydrogeological and topographic gradient that were affected by the May 2011 Utikuma Complex forest fire (SWF-057, ~90,000 ha) in Canada’s Western Boreal Plain. The results demonstrate that peatland margins, due to fluctuating water tables, burned significantly deeper (0.25 ± 0.01 m) than the middle (0.06 ± 0.01 m) of peatlands. Additionally, in a coarse textured glaciofluvial outwash, a bog with ephemeral groundwater connections had the greatest depth of burn (0.51 ± 0.02 m) and a low-lying flow-through bog had the lowest burn severity (0.07 ± 0.03 m). An expansive peatland in the lacustrine clay plain showed an intermediate depth of burn (0.16 ± 0.01 m). To further investigate the role of groundwater connectivity in the outwash, GWC and smouldering energy dynamics were modelled at several unburned peatlands across a topographic gradient. It was shown that the peatland with the most groundwater connectivity showed the lowest vulnerability, while the ephemerally perched peatland was the most vulnerable. The peatland at the highest topographic position and least groundwater connection showed intermediate vulnerability. This research indicates that groundwater connectivity and subsequent influence on water table fluctuations in peatland margins can have a dominant control on soil carbon combustion, it is therefore suggested that a hydrogeological ‘template’ be used to identify deep burning ‘hotspots’ on the landscape a priori, so as to increase the efficacy of wildfire mitigation strategies.</p> / Master of Science (MSc)

<p> Natural peatlands are an important component of the global carbon cycle representing a net long-term sink of atmospheric carbon dioxide (CO2). The natural carbon storage function of these ecosystems can be severely impacted due to peatland drainage and peat extraction leading to large and persistent sources of atmospheric CO2 following peat extraction abandonment. Moreover, the cutover peatland has a low and variable water table position and high soil-water tension at the surface which creates harsh ecological and microclimatic conditions for vegetation reestablishment, particularly peat-forming Sphagnum moss. Standard restoration techniques aim to restore the peatland to a carbon accumulating system through various water management techniques to improve hydrological conditions and by reintroducing Sphagnum at the surface. However, restoring the hydrology of peatlands can be expensive due to the cost of implementing the various restoration techniques. The goal of this study is to examine a new extraction-restoration technique where the acrotelm is preserved and replaced on the cutover surface. More specifically, this thesis examines the effects of an acrotelm transplant experiment on the hydrology (i.e. water table, soil moisture and soil-water tension) and peatland-atmosphere CO2 exchange at a cutover peatland.</p> <p> The experimental acrotelm restoration technique maintained both high water table and moisture conditions providing sufficient water at the surface for Sphagnum moss. Furthermore, the high moisture conditions and low soil-water tensions compared to an adjacent natural site were maintained well above the measured critical Sphagnum threshold of 33% (-100 mb) VMC further providing favourable conditions for Sphagnum moss survival and growth.</p> <p> Peat respiration at the experimental restored acrotelm (110.5 g C m-2) was considerably lower than the natural peatland (144.8 and 203.7 g C m-2). However, gross ecosystem production (GEP) at the experimental site (-54.0 and -34.4 g C m-2) was significantly reduced compared to the natural site (-179.2 and -162.0 g C m-2). Consequently this resulted in a shift towards a net source of CO2 to the atmosphere over the season at the experimental site (78.5 and 56.5 g C m-2) and a sink of CO2 at the natural site (-17.6 and -22.8 g C m-2).</p> <p> Light response curves indicated that maximum GEP was considerably lower at the experimental site; however it is likely that the percentage of living and dead vegetation at the plots post restoration had a large control on this lower productivity as plots with more living vegetation had higher overall productivity (GEP). Despite wetter conditions at the experimental site, large diurnal variations in moisture (~30%) were observed suggesting disturbance to the peat structure. Although soil-water retention analysis and physical peat properties indicated that no apparent structural change in peat structure occurred, it is theorized that a change in volume in the capitula may enhance the wetting and drying cycles in moisture. Lateral expansion/contraction within the peat matrix may occur due to spaces (gaps/fissures) left between the replaced acrotelm blocks from the extraction-restoration process promoting large changes in moisture which consequently can affect the gas exchange process at the surface. Large changes in peat and capitual moisture have been shown to affect productivity leading to variable GEP and enhanced respiration, making it important to limit the moisture variability at the surface from a carbon cycling perspective. Therefore it is likely that a combination of both physiological health of the vegetation and wetting/drying cycles contributed to lower GEP, suggesting the importance of limiting disturbance at the surface during the extraction and restoration process.</p> <p> The new extraction-restoration technique has potential to return a peatland to both near-natural hydrological conditions and towards a net sink of atmospheric CO2. The replaced acrotelm on the cutover surface aided in maintaining adequate moisture conditions thereby provided adequate conditions for Sphagnum survival and reestablishment. However, the ability of the system to remain a net sink of CO2 as like the natural site was not observed post-disturbance due to differences in productivity. Nevertheless, the experimental site did maintain limited productivity post-extraction indicating that the carbon dynamics of the system was maintained due to this acrotelm restoration process potentially returning the ecosystem towards a natural sink of atmospheric CO2 over a longer period time.</p> / Thesis / Master of Science (MSc)

ABSTRACT The effects of restoration on dissolved organic carbon (DOC) dynamics were examined at the Boi~-des-Bel peatland. This study included both laboratory measurements of DOC production by different peatland vegetative components and field measurements of DOC dynamics within a recently restored, a cutover and a natural peatland. Shrub and herbaceous plant material were found to be the most significant producers of DOC in the short term. Moss, peat and straw samples had a high potential to release DOC ;;ontinuously under warm, moist and aerobic conditions. On a short timescale, all components have the potential to release the three dissolved organic matter (DOM) fractions examined with humic acid (HA) most prominently being produced by shrubs and herbaceous plants and hydrophilic (HPI) and hydrophobic (HPO) fractions by mosses, peat and straw. Comparison of growing season results over three study years at the restored and cutover site indicated that DOC concentrations increased after restoration while DOC export decreased due to lowered runoff caused by the blockage of drainage ditches. Compared to the natural peatland, both the restored and the cutover site had a more humic DOM character. No difference could be found between the character of DOM released from the restored and cutover sites. The most active layer of DOM production was the top 75 em where the water iii table fluctuated during the season. Water storage units such as pools and ditches also play an important role in DOM export from the site. Spring snowmelt was found to be the most significant DOC export event of the study season in 2001, when export values were significantly larger than those measured during the growing season. Solubility of the different DOM fractions was the main controlling factor on the DOM character seen at the outflows. Storm events contributed significantly to the summer DOC output. DOC dynamics were affected by antecedent moisture conditions and differences emerged between the restored and cutover site during this period. The results of this study emphasize the importance of managing water table fluctuations and the restoration (reestablishment) of Sphagnum species in order to improve the retention of DOM within cutover peatlands. / Thesis / Master of Science (MS)