Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Geography & Environmental Studies

Program Name/Specialization

Environmental Science

Faculty/School

Faculty of Arts

First Advisor

William L. (Bill) Quinton

Advisor Role

Assists in organization and formulation of research goals and objectives, guidance in planning and implementation of field programs and results interpretation.

Abstract

Permafrost is ground that remains at or below 0°C for at least two consecutive years (PIWP, 2012). In the continuous permafrost zone its thickness may exceed 300 m, in lower latitudes, permafrost thickness is progressively decreasing, its occurrence becomes discontinuous and eventually sporadic (PIWP, 2012). At the southern fringe of permafrost in northwestern Canada, just about few meters. In subarctic peatlands permafrost is one of the main elements governing the hydrological processes. Being very thin and with temperature just fractions of the degree below 0oC, it is very vulnerable to any changes in soil temperature and water content. Permafrost in peatlands is found exclusively under peat plateaus, which are elevated 1-2 m over fens and bogs that do not contain perennially frozen ground. In this environment the peat plateaus act as natural frozen dams between such water bodies as fens and bogs. If the surface of a peat plateau is disturbed naturally, as by forest fires, or artificially, as by human activity, the function of the peat plateau as a frozen dam is diminished with the permafrost thaw. The effects of ground surface disturbance propagates through the water, ice, soil and vegetation components of peatland ecosystems (Woo, 2011). Permafrost degradation can occur from the top due to the changes in ground surface conditions, from the sides by heat conduction and convection from the surrounding permafrost free terrains and from the bottom due to the geothermal heat flux. The combination of two or more of these scenarios can lead to rapid permafrost thaw and its complete disappearance.While climate warming is the main natural cause of permafrost degradation in the zones of discontinuous permafrost, economic development of natural resources resulting in considerable ground surface disturbance can also lead to permafrost thaw. Vegetation has a profound effect on the energy balance at ground level. For example, in winter time trees intercept large amounts of snow, creating conditions for deeper freezing of the soil. In summer time tree crowns create a shade and as a result, the amount of short wave radiation, which reaches the ground level decreases, thereby decreasing soil temperature. Peatlands are widespread in regions of permafrost. Peat has physical properties that are different from the physical properties of mineral soil. Undisturbed, it contains a large amount of air and has very low thermal conductivity, thus heat does not penetrate into the deeper soil layers in the summer. Conversely, in winter wet frozen peat has a high thermal conductivity. Consequentially, peat freezing in winter prevails over thawing in summer, creating favorable conditions for permafrost generation.Vegetation removal and peat layer compaction are the most common and usually unavoidable types of environmental damage. This creates an imbalance in the thermal regime of the active layer as well as of permafrost. The process of permafrost degradation can develop so rapidly that within a few years the landscape can be completely transformed. The cutting of seismic lines is one of the most widespread forms of surface disturbance in the northern ecosystem. Compared to modern practices, the seismic explorations of the 20th century were less concerned with environmental impact. As a result of the former relaxed regulations, the magnitude of negative effects of seismic geophysical activities in subarctic environment is hard to overestimate. The wide10-15 m seismic lines bulldozed through boreal forest and peatlands caused soil waterlogging and shifting of the water drainage patterns. Soil contamination and erosion are also the direct outcome of the seismic exploration of the past century. The disappearance of permafrost from below the seismic lines leads to surface subsidence and changes to the balance between mass and heat fluxes. The observations show that seismic lines often convey water over their surfaces and as a result are able to connect previously hydrologically isolated landscape elements such as fens and bogs, at the same time collecting drainage water from the adjacent undisturbed peat plateaus.Knowledge of permafrost distribution below the linear disturbances helps understand the hydrological role of such disturbances in the low Arctic wetland ecological complex.The thesis consists of two manuscripts which examine the effects of linear disturbances in a Scotty Creek basin through a combination of visual observations, instrumentation measurements, GPR surveys and thermal modeling. The main subject of the study is the analysis of hydrological effects of seismic lines and development of tools and methods, which can be used for quantitative and qualitative evaluation of permafrost degradation and talik development in the area of discontinuous permafrost. The first Manuscript focuses on the development of conceptual model of permafrost degradation under the seismic line based on the field data collected during the 2012-2013 summer and winter research seasons. The manuscript also presents the analysis of active layer and talik temperatures at various locations of the examined seismic line as well as the interpretation of the GPR data.Based on the conceptual model described in the first manuscript, we developed a mathematical model of the active layer and permafrost thaw which is described in the second manuscript. This model allows us to make a prediction of when the examined seismic line becomes free of permafrost free. We also demonstrated that seismic lines create a permanent link between previously disconnected hydrological units.A brief summary of the main research findings explaining how linear disturbances of peat plateaus contribute to permafrost degradation concludes the thesis. Furthermore, the final chapter identifies gaps in the existing body of scientific knowledge on the subject of permafrost degradation and presents recommendations on potential areas for future research.

Convocation Year

2017

Convocation Season

Spring

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Hydrology Commons

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