Because of its toxic nature mercury is a threat to both wildlife and human health, and thus, it is an element of concern in the environment. Currently much of the mercury emitted to the atmosphere is derived from anthropogenic sources – both direct emissions and re-emission of already deposited anthropogenic mercury. Following deposition mercury is affected by a long array of processes, and this thesis has focused on trying to increase our knowledge on the net retention of mercury in lake sediments and peatlands. This information is vital in order to understand how mercury behaves in the environment and where mercury is at risk of becoming a problem. Knowledge about the retention of mercury is also important when using lake sediments and peat records as environmental archives over past mercury deposition. By using varved, annually laminated, sediments I have determined that lake sediments are reliable archives for inorganic mercury, but not for methylmercury. A study of the spatial distribution of mercury in a whole-lake basin shows that inorganic- and methylmercury are controlled by different sediment properties. Inorganic mercury is controlled by combination of fine-grained mineral matter and organic matter concentrations, whereas methylmercury is controlled by water depth and sulfur concentration. This study also shows that especially methylmercury have a very heterogeneous spatial distribution across the lake basin, something that might be of large importance when using lake sediments to calculate whole-lake burdens of mercury. In a study regarding the effects of vegetation on the net retention of mercury in a peatland I showed that there are considerable differences in both plant- and peat-mercury concentrations depending on vegetation type. This might have implications for the use of peat records as archives over atmospheric mercury deposition. Finally I have used a combination of a peat and a lake sediment record to study how past and recent climatic changes affects the stability of a peatland currently underlain by permafrost. Here we are able to show that destabilization of peatlands, as a result of permafrost melt, can cause a significant release of organically bound mercury from the mire to the surrounding aquatic environment. Considering the currently warming climate there is a risk of sub-arctic peatlands turning into mercury sources, which might be important to recognize when assessing current mercury pollution pathways.

Two peat cores from two mires with different characteristics, but both containingpermafrost features and located in the eastern part of the Tavvavuoma mire complex innorthernmost Sweden, were analysed for macrofossils and geochemical properties. Local vegetationsequences and changes in geochemical properties of peat were used to reconstruct development ofthe studied mires during the Holocene. The study includes measurements of water/ice content, bulkdensity, loss-on-ignition and C/N ratio. Radiocarbon dates for peatland inception and permafrostaggradation are available. The main purpose of the study is to verify permafrost history in thepeatlands. The results of the macrofossil analysis and values of C/N ratio indicate nutrient poor tointermediate fen environments in both studied mires until recently. Signs of permafrost upheavalwhich caused formation of xerophilic peat can be proved only since late 1950’s. The study resultscorroborate with other studies from Northern Fennoscandia and infer peatland initiation soon afterthe deglaciation of the area and permafrost-free conditions throughout entire Holocene untilrecently.

The oxidation of sulfide minerals in mine waste rock has the potential to generate acidity and contribute sulfate, metals and other trace constituents to drainage. The rate and extent to which this process occurs are dependent upon climactic conditions and the overall hydrologic, geochemical and physical properties of the waste rock. A laboratory and field-based study is currently being conducted at the Diavik Diamond Mine in the Northwest Territories, Canada, which is investigating the evolution of waste rock exposed to subaerial conditions in the continuous permafrost region. Over the course of the mine life, Diavik is expected to generate a stock pile up to 120 Mt of low-sulfide waste-rock composed primarily of granite and granite pegmatite with smaller amounts of biotite schist which occurs as xenoliths, and trace contributions from diabase dykes. Waste rock is segregated based on sulfur content into Type I (< 0.04 wt % S), Type II (0.04-0.08 wt % S) and Type III (> 0.08 wt % S) rock. The Diavik Waste Rock Research Project includes four 2 m by 2 m lysimeter experiments, two each constructed with Type I and Type III waste rock. Also constructed were two well-instrumented, 15 m high test scale waste-rock piles, one composed of Type I and one composed of Type III uncovered waste rock, and one covered test pile based on a reclamation concept which consists of a Type III waste rock core, a 1.5 m glacial till layer, and a 3 m layer of Type I waste rock. In addition, instrumentation was installed in four locations of the operational waste-rock stockpile. The geochemical differences between the Type I and Type III lysimeters and test piles is discussed to compare the non-acid generating Type I waste rock with the potentially acid-generating Type III. The effluent from the Covered test pile retained the character of the Type III waste-rock core over the course of observation producing slightly acidic drainage, possibly due to a zone of unfrozen till on the crest as a result of heat trace within the test pile. Observations from the geochemistry of the Type III waste rock will also be compared to mineralogical analysis from Type III samples collected during installation of instruments in the full scale waste-rock stockpile. Due to the low concentration of sulfide minerals, advanced techniques such as SEM and synchrotron-based analyses were employed for in-depth characterization of initial sulfide-oxidation products. SEM images and elemental mapping reveal development of reaction rims on many pyrrhotite grains, but lower instances of weathering of pyrite. Distinct zonation of weathering trends between depths within the stockpile was also absent. These observations indicate that the waste rock is in the early weathering stages may not yet be affected by the formation of permafrost. These observations act as a baseline for future studies. Correlations between the mineralogical and geochemical analyses, in addition to future monitoring and continuation of these studies, will assist in understanding the evolution of waste rock stored in a permafrost environment.

Because of climate change and resource development there is an ongoing increase in the attention directed towards high latitude areas. Over the last years, warming in the Arctic has accelerated quickly. The warming climate can possibly lead to thawing of ground ice, which in turn leads to alterations of the cryosphere. This can have a huge influence on the terrestrial hydrology of the Arctic and, more specifically, on the presence and distribution of lakes in arctic regions since both are coupled to subsurface ice. In this thesis data from remote sensing were used to look at the change in the size distribution of lakes for the Nadym catchment in northern Russia. The aim was to find out if there has been an increase or decrease in the number of lakes in the area over the past years. Results suggest that there were 229 lakes less (representing a 4% decrease) in 2007–2009 compared to 1987, indicating that lakes are slowly disappearing. Also, the total lake surface area decreased with 5%. Almost half of the lakes that disappeared (49%) can be found among the smallest lakes ranging between 10–20 ha. In the entire catchment this size class was also found to be the class with by far the highest number of lakes.

The extent and dynamics of permafrost are tightly linked to the distribution and movement of water in arctic landscapes. As the Arctic warms more rapidly than the global average, profound changes are expected in both permafrost and hydrology; however, much is still not known about the interactions between these two systems. The aim of this thesis is to provide new knowledge on the links between permafrost and hydrology under varying environmental conditions and across different scales. The objectives are to (i) determine how permafrost distributions and patterns in morphology are linked to hydrology, (ii) determine how groundwater flow influences ground temperature dynamics in permafrost landscapes, and (iii) explore the mechanisms that link permafrost to groundwater and streamflow dynamics. A range of methods have been applied within the four studies (papers I-IV) comprising the thesis: geophysical (ground penetrating radar and electrical resistivity tomography) and GIS techniques for mapping and analyzing permafrost distributions and related morphology; numerical modeling of coupled heat and water fluxes for mechanistic understanding permafrost-hydrological links; and statistical analyses for detecting trends in streamflow associated with permafrost thaw. Combining these various methods here allows for, and may be considered a prerequisite for, novel insights to processes. The thesis also presents statistical analyses of field observations of ground temperatures, ground- and surface water levels, as well as lake and shore morphological variables. Discontinuous permafrost peatlands are heterogeneous environments regarding permafrost distributions and thickness which is manifested in surface systems such as lake geometries. In these environments, lateral groundwater fluxes, which are not considered in most permafrost models, can significantly influence ground temperature dynamics, especially during high groundwater gradient conditions. River discharge data provide a potential for monitoring catchment-scale changes in permafrost, as the magnitude and seasonality of groundwater fluxes feeding into streams are affected by the distribution of permafrost. This thesis highlights the need to understand water and permafrost as an integrated system with potential internal feedback processes. For example, permafrost thaw can lead to increases in groundwater discharge which in turn can lead to increased heat transfer through the ground, resulting in further acceleration of permafrost thaw rates. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.</p>

Active marine electromagnetic methods have proven to be a powerful tool to detect resistivity anomalies associated with gas hydrate. However, because the propagation of electromagnetic fields for these methods works in the diffusive regime the spatial resolution of the resistivity structure is limited. So far only bulk electrical properties have been estimated from measured data, although hydrate bearing layers are found to be highly heterogeneous. We computed response curves for synthetic one- and two-dimensional models to investigate the resolution capabilities for various measurement geometries with respect to resistive features. Electric dipole transmitters (TXs) are used as sources. In the marine case, the in-line electric dipole-dipole configuration has proven its capabilities to detect the shallow resistive gas-hydrate. Our model study demonstrates that both the depth to a resistive feature can be resolved nicely using data for multiple TX-RX offsets. However, resolving smaller features of the resistive zone, for example if the zone is split in separate resistive layers, is extremely difficult. The resolution of the target can be improved using electrical downhole transmitters. So far there have been no reports of the detection of permafrost gas hydrate deposits with surface electromagnetic methods. Our calculations show that a similar setup to that used in the marine case is capable of detecting gas hydrate on land. The resolution, however, is lower than for the marine case, because of the significantly greater depths to the target.

No description available.

Reliable determinations of ecosystem scale fluxes of net carbon (C) and greenhouse gases for northern peatland ecosystems are of great value to determine the impact of soil warming and altered precipitation on emissions. Additionally, few studies have been performed which measure the C fluxes, particularly methane flux (FCH4), during the spring melt and fall freeze up periods, therefore making it difficult to provide adequate annual C estimates from northern peatland ecosystems. This study aimed to determine ecosystem scale FCH4 from a eutrophic Subarctic fen at Churchill, Manitoba (58°45'N 94°4'W), to understand (a) seasonal trends over two consecutive growing seasons,(b) if over-winter stored CH4 was released as a pulse during the spring-melt period, and (c) soil temperature - FCH4 relations for modelling FCH4 over the spring-melt period. An ecosystem scale methane (CH4) and carbon dioxide (CO2) flux measurement system using the eddy covariance (EC) technique was used from late-June to mid-October of 2008 and early-June to late-September of 2009, with focus on the spring-melt period of late-May to mid-July of 2009. The EC flux measurement system consisted of a closed-path RMT-200 Fast Methane Analyzer (Los Gatos Research Inc.) along with a LI-7500 open-path CO2/H2O gas analyzer (LI-COR Biosci.) and a CSAT3 3-dimensional sonic anemometer (Campbell Sci.). The system was powered by a combination of wind, solar, and gas electric generation. The EC flux measurement system provided seasonal FCH4 values of 0 – 90 nmol CH4 m-2 s-1, similar to previous studies in Subarctic and Arctic peatlands which incorporated the EC technique. A melt period CH4 emission burst was not observed, rather a gradual increase in emission over the spring period. Modelled FCH4 using a temperature-response curve relationship with soil temperature at 5 cm depth over the spring-melt period (May 30 – July 19, 2009) showed the fen to be a net source of CH4, of 1.4 mmol m-2 CO2 equivalent.

Roads and highways in cold regions are negatively affected by settlement of embankments in areas of degraded or degrading permafrost, particularly in areas with mean annual temperatures close to 0°C where permafrost is locally discontinuous. Climate warming and human activities can lead to increases in the temperature of permafrost and to thawing. In regions of discontinuous permafrost, thawing may produce thickening of the active layer, large settlements and non-recoverable shear deformations. These can cause potentially dangerous trafficability issues. The research program involved a test site on Provincial Road PR391, about 18 km northwest of Thompson, Manitoba. The foundation material of PR391 is currently classified as “degraded (thawed) permafrost”. The purpose of this research was to investigate and understand the performance of highway embankments on thawed permafrost. The research involved field instrumentation and data collection, laboratory testing, thermal modelling and frost heave predictions. The results of the field instrumentation and data collection show net heat flow into the ground, as well as development of cyclic seasonal gradients of total head. This is believed to be a significant original contribution to understanding the effects of climate change on highway infrastructure. The results also show that displacements observed at the PR391 embankment are a combination of consolidation and shearing strain of the foundation material. Most studies of embankments concentrate on vertical settlements. This research shows that horizontal movements are also present, a contribution that helps explain the mechanism of lateral spreading. The results of the laboratory testing show that the mechanical and shearing properties of the soil collected from the PR391 embankment are not significantly affected by differences in temperature once water in the soil has actually thawed. The results of the thermal modelling show reasonable trends in simulated ground temperatures compared with the data obtained from the thermistors underneath the embankment. The frost heave prediction of PR391 shows that in situ frost heave characteristics can be estimated by applying the Segregation Potential (SP) frost heave method in field conditions. This provides a valuable field study to the limited number of such studies of Segregation Potential, which are normally done under laboratory conditions.

There is a growing need to improve the understanding of the behaviour of infrastructure in permafrost regions. Permafrost affects nearly half of the land surface in Canada, especially in the north. Further development of natural resources in northern Canada will provide socio-economic benefits to the region and its residents. Linear infrastructure, such as highways, is an important part of that development. The integrity of infrastructure in northern regions is negatively impacted by thawing and degradation of the underlying permafrost initiated by changes in both air and ground temperatures. Subsequent deformations due to settlement and lateral spreading can lead to potentially hazardous driving on highways. The author’s research focused on a section of highway embankment on Provincial Road (PR) 391 located 18 km north of Thompson, Manitoba. The purpose of the research was to further understanding of the thermal and deformation behaviour of an embankment subjected to degrading permafrost conditions. The author’s research consisted of laboratory testing, instrumentation installation, data monitoring, and numerical modelling. Laboratory tests on four-inch (101.6 mm) diameter Shelby tube samples characterized the soil at the site. Data were collected remotely via satellite, and included ground temperatures, pore water pressures, and displacements both laterally and vertically. Ground temperatures indicated a frost bulb, a region of frozen ground, under the embankment. Thermal models using TEMP/W simulated the current ground thermal regime and projections of future thermal behaviour of the embankment. Deformation numerical models using SIGMA/W incorporated changes in the size of the frost bulb over a freeze-thaw cycle to simulate the deformation behaviour of the embankment. The numerical models were compared with the collected data.