Over the past millennia, complex terrestrial ecosystems have evolved in the Arctic. However, the stability of these unique ecosystems is in jeopardy because of climate changes. Due to the fact that Arctic soils store great amounts of carbon (C) in soil organic matter (SOM), any change that may occur in SOM with climate changes may substantially affect many aspects of Arctic ecosystems such as vegetation, animals, and humans. On a more global perspective, any change in Arctic SOM has the potential of modifying the overall world climate by affecting the global greenhouse gas (GHG) budget. A better understanding of the soil factors that affect soil N and C cycling at the landscape scale, such as moisture, temperature, and SOM characteristics, is necessary to produce better models. The overall objective of this study was to characterize the properties of SOM in Arctic soils and their influence on soil N and C cycling dynamics � including GHG emissions � at the landscape scale. This study was conducted in three distinct Arctic ecosystems: Sub-Arctic (Churchill, MB), Low-Arctic (Daring Lake, NWT), and High-Arctic (Truelove, NU). For each site, the sampling locations were evenly divided into five landform units: 1) upper slope (Up), 2) back slope (Back), and 3) lower slope (Low) for catena sites, and 4) hummock (Hum) and 5) wedges of hummock (W) for hummocky sites (i.e., hummock in Churchill and ice-wedge polygons in Truelove). All sites were sampled at the end of their growing season (from 2 to 3 weeks before plant senescence). The characteristics of SOM were assessed using three methods: 1) density fractionation to separate the uncomplexed light fraction (LF) from heavy fraction (HF) of SOM (LF < 1.55 g mL-1 < HF), 2) solid-state CPMAS 13C nuclear magnetic resonance (NMR) spectroscopy that determined the relative proportions of carbonyl-C (CbyC), alkyl-C (AC), aromatic-C (AroC), o-alkyl-C (OAC), and carbohydrates-C (CC), and 3) water-extractable organic matter (WEOM) that estimated SOM diluted in soil solution. Soil gross N mineralization was measured in situ using 15N dilution technique. Soil GHG emissions [nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2)] were measured in situ using a multicomponent Fourier transform infrared gas analyzer coupled with an automated dark chamber. The first study showed that organic surface soils, which had more than 17% soil organic C (SOC) by weight, contained relatively more labile SOM than mineral surface soils (< 17% SOC). For example, OAC:AroC ratios of the organic soils ranged from 25 to 75% greater compared to mineral soils. At Churchill, Daring Lake, and Truelove, 53, 73, and 20% of the C and N was included in the LF, respectively. All results show that the organic soils of Sub- and Low-Arctic ecosystems sampled for this study contain more fresh and un-decomposed plant residues than High-Arctic organic soils. The second study showed that both topography and ecosystems had a significant impact on gross N mineralization and CO2 emission rates. For example, at Churchill, gross N mineralization increased about 6-fold from upper slope to lower slope areas. Similarly, at Daring Lake, CO2 emissions increase about 5-fold from upper slope to lower slope areas. Topography and ecosystems had a very limited impact on soil N2O and CH4 emissions most likely because net emissions were extremely low. The third study showed that soil moisture, SOM quantity, and labile SOM parameters such as OAC:AroC and water-soluble organic carbon (WSOC) positively influenced gross N mineralization, N2O, and CO2 emissions, whereas the relative proportion of AroC negatively influenced gross N mineralization, N2O, and CO2 emissions. Relationships between SOM characteristics and CH4 emissions were not significant. This study showed that Up and Back areas tended to store relatively more recalcitrant SOM (AroC) than Low, Hum, and W areas, suggesting less fresh plant input on these landform units. Assessing SOM qualities with the ability of the soils to mineralize N (i.e., gross N mineralization) and release GHG at the landscape scale and across the Arctic represents a great advance in the understanding of these complex and unique ecosystems. Lower proportion of fresh and labile SOM found on Up and some Back landform units compared to Low and hummocky sites suggest that plants have more difficulties establishing and growing on these landform units (e.g., Up and Back) that experience harsh climates. Therefore, generalizations of the climate change impacts on soil N and C cycling processes throughout Arctic landscapes and ecosystems are less certain if topography is not considered. These results are particularly important because they can be used to produce better models that evaluate SOM stocks and dynamics under several climate scenarios and across Arctic landscapes and ecosystems.

The objective of this study was to determine the dominant biogeochemical controls on mercury partitioning in super-permafrost groundwater at Truelove Lowland, Devon Island, Nunavut. Mercury partitioning in snow, ephemeral standing water, and super-permafrost groundwater was investigated. <p>Results indicate that partitioning differs between matrices, and that particulate mercury is spatially and temporally dynamic in Truelove Lowland groundwater. Particulate mercury in groundwater was 73 % of total mercury, while snow had only 22 % particulate mercury. Particulate mercury in groundwater rose by over 20 % from Julian day 181 to 189, and decreased slightly on Julian day 191. No single geochemical parameter was a good predictor of particulate mercury concentrations. To expand upon the findings of the field study a laboratory microcosm study was conducted to determine whether certain biogeochemical processes influence mercury partitioning in super-permafrost groundwater. Particulate mercury in the dissimilatory iron reducing bacteria inhibited microcosm was 61 % of total mercury, approximately 18 % lower than in all other treatments. Iron (III) concentrations had a positive correlation with particulate mercury while chloride concentrations had a negative correlation with particulate mercury. Sulfate reducing bacteria were not found to influence mercury partitioning.

This thesis investigates the relationships between mercury (Hg) and stable isotope of carbon (δ13C) in marine pelagic zooplankton (Calanus spp., Themisto spp. and Euchaeta spp.) with water mass characteristics in the North Water Polynya (NOW) and in the Mackenzie shelf – Amundsen Gulf area. Two ship based sampling field expeditions were carried out in late summer of 2005 and 2006 in both regions on board the CCGS Amundsen. In the North Water (NOW) polynya, higher levels of water Hg, depleted δ18O, lower salinity and lower nitrate levels were measured at sampling locations near the Prince of Wales glacier (POW) on the eastern coast of Ellesmere Island in the Smith Sound area. These results suggest that the glacier may be a source of Hg to this region which, in turn, is responsible for the correspondingly high concentrations of THg and MMHg measured in Calanus spp. and Euchaeta spp. at the same locations. The Mackenzie shelf – Amundsen Gulf region was characterized by fresher surface water properties (low salinity and depleted δ18O) in the western part and was strongly linked to the influence of the Mackenzie River. Higher THg concentrations in zooplankton were associated with larger fractions of both meteoric water and sea-ice melt. These findings suggest that in the western Arctic, inorganic Hg uptake in zooplankton via-absorption near surface water was highly driven by freshwater inputs into the system. Based on the analysis of three main genus Calanus spp. (mostly adult females Calanus hyperboreus), Euchaeta spp. and Themisto spp. (mostly adult Themisto libellula), THg and MMHg concentrations were the highest in the carnivorous copepod Euchaeta spp. in the North Water polynya followed by the omnivorous hyperiid amphipod Themisto spp. The herbivorous copepod Calanus spp. had both the lowest THg and MMHg concentrations in the Eastern and the Western Arctic. In addition, the Western Arctic is the area in which each zooplankton genus had the most depleted carbon and the most enriched nitrogen. The highest concentrations of THg in Calanus spp., Euchaeta spp. and Themisto spp. were measured in the Western Arctic as well as the highest MMHg in Calanus spp. and Themisto spp. The highest %MMHg was calculated in the Archipelago for Themisto spp., in the Eastern Arctic for Euchaeta spp. and in the Western Arctic for Calanus spp. The relationships observed between THg, MMHg, %MMHg and δ13C in all three major zooplankton taxa and water mass properties were in agreement with what have been previously described in the literature. Our findings suggested that both Hg and δ13C can be used as tracers to help understand zooplankton vertical distribution, feeding ecology and ultimately to predict climate changes impact at lower trophic level in the pelagic food web. The implications for marine mammals foraging in these regions are also discussed. / October 2008

The arctic and subarctic regions of Canada are increasingly developing as integral, participating parts of the total Canadian and world scene. Basic to this development in the North are the human, natural physical, and designed or man- made environments. This study is concerned with one aspect of the designed environment: human settlements. On the basis of an evaluation of the existing settlement planning situation, an attempt is made to develop a skeletal, yet consistent, theory and methodology for settlement planning in the Mackenzie River Delta, Northwest Territories. The approach is from a comprehensive point of view, and includes social, economic and physical criteria directly in the planning process. A combined systems-factor analysis technique is experimentally developed as an aid to creativity in the planning process. Preliminary results indicate both an immediate practical use and a good potential for the further development of the approach as a panning tool.

Impending natural resources development and concern about the effects of climate change have spurred increased efforts to study and monitor aquatic habitats in the Mackenzie River system. As part of Environment Canada’s attempt to survey the system in advance of the construction of the Mackenzie Gas Pipeline, benthic macroinvertebrates were sampled at 50 streams spanning the geographical range of the Mackenzie system in the Northwest Territories, Canada, to assess spatial patterns in diversity and assemblage structure and the environmental factors driving them. Replicated, quantitative D-net samples were collected during the late summer of 2005 through 2008, mostly at crossings of the proposed pipeline route. 373 macroinvertebrate taxa were recorded, mainly aquatic insects, which were identified to the genus or species levels; other groups were identified to higher taxonomic levels. Ephemeroptera and Plecoptera diversity declined along a latitudinal gradient, while Trichoptera diversity declined in the middle of the latitudinal range and rose towards the far north. Chironomidae (Diptera) increased in diversity and abundance towards the far north, becoming dominant in the northern sub-arctic forest and lowland tundra of the Mackenzie Delta. Diversity, measured as the average generic richness per stream, correlated with a composite environmental variable representing stream size, but not much else; spatial trends in local generic richness were only apparent in the far north of the study area. Regional diversity was assessed using rarefaction curves and showed a clear decrease from south to north across the study area for most taxa; the major exception was the chironomid subfamilies Orthocladiinae and Chironomini, the former being diverse throughout the study area and the latter increasing in diversity on the tundra. Odonata, Hemiptera and Coleoptera were well-represented in the south of the study area, but decreased sharply in diversity and abundance in the north; another common order, Megaloptera, was entirely absent from the study area, as were crayfish. Community composition varied along a latitudinal gradient, with some species restricted to northern latitudes and many more species restricted to the southern areas. Composition varied by region, as did the environmental factors that control it. Streams in the north of the system are connected to hundreds of small lakes and tend to freeze in the winter, which increases habitat stability; assemblages in this region were characterized by relatively large chironomids that are usually associated with lentic habitats and by a lack of taxa that are intolerant to freezing. Substrate was the main factor explaining differences in assemblage composition in this region. Just to the south, alluvial streams are more common and permafrost is continuous with very shallow active layers, iv which likely results in intense discharge peaks and ice scour in the spring and flashy summer hydrographs. Invertebrates in this region were mainly short-lived, small sized orthoclads, baetids and chloroperlids; the annual disturbance regime seems likely to be an important factor shaping community composition in this region. Many streams in this region received input from saline springs, resulting in perennial flow, and these streams harboured several taxa that were absent or rare in other streams at similar latitudes, including several stoneflies (e.g. Pteronarcys, Sweltsa); the presence of flow during the winter was found to be a major factor affecting community composition in this region, which surrounded the town of Norman Wells, NT. Nutrient dynamics appeared to be important in structuring benthic assemblages in the southern portion of the study region, with highnutrient streams supporting a diverse fauna which included many taxa that were absent in the north, while communities in low-nutrient streams were more similar to the northern alluvial stream fauna. There was no spatial distinction between low- and high-nutrient streams in the southern region, and the difference may be due to the local conditions of permafrost, which is patchy and discontinuous in the region. Evidence that winter ice and permafrost conditions are important drivers of benthic invertebrate diversity and community composition in the Mackenzie system, along with the latitudinal gradients which are consistent with a temperature/climate gradient, raises the possibility that benthic assemblages may be useful as indicators of effects of global climate change on freshwater habitats in the Canadian north. More immediately, construction of the Mackenzie Gas Pipeline may affect stream habitat due to sedimentation, and plans for the operation of the pipeline have raised concerns about potential effects on permafrost conditions. Implications for development of a biomonitoring program utilizing benthic invertebrates and their potential as indicators of climate change are discussed.

The arctic and subarctic regions of Canada are increasingly developing as integral, participating parts of the total Canadian and world scene. Basic to this development in the North are the human, natural physical, and designed or man- made environments. This study is concerned with one aspect of the designed environment: human settlements. On the basis of an evaluation of the existing settlement planning situation, an attempt is made to develop a skeletal, yet consistent, theory and methodology for settlement planning in the Mackenzie River Delta, Northwest Territories. The approach is from a comprehensive point of view, and includes social, economic and physical criteria directly in the planning process. A combined systems-factor analysis technique is experimentally developed as an aid to creativity in the planning process. Preliminary results indicate both an immediate practical use and a good potential for the further development of the approach as a panning tool.

Impending natural resources development and concern about the effects of climate change have spurred increased efforts to study and monitor aquatic habitats in the Mackenzie River system. As part of Environment Canada’s attempt to survey the system in advance of the construction of the Mackenzie Gas Pipeline, benthic macroinvertebrates were sampled at 50 streams spanning the geographical range of the Mackenzie system in the Northwest Territories, Canada, to assess spatial patterns in diversity and assemblage structure and the environmental factors driving them. Replicated, quantitative D-net samples were collected during the late summer of 2005 through 2008, mostly at crossings of the proposed pipeline route. 373 macroinvertebrate taxa were recorded, mainly aquatic insects, which were identified to the genus or species levels; other groups were identified to higher taxonomic levels. Ephemeroptera and Plecoptera diversity declined along a latitudinal gradient, while Trichoptera diversity declined in the middle of the latitudinal range and rose towards the far north. Chironomidae (Diptera) increased in diversity and abundance towards the far north, becoming dominant in the northern sub-arctic forest and lowland tundra of the Mackenzie Delta. Diversity, measured as the average generic richness per stream, correlated with a composite environmental variable representing stream size, but not much else; spatial trends in local generic richness were only apparent in the far north of the study area. Regional diversity was assessed using rarefaction curves and showed a clear decrease from south to north across the study area for most taxa; the major exception was the chironomid subfamilies Orthocladiinae and Chironomini, the former being diverse throughout the study area and the latter increasing in diversity on the tundra. Odonata, Hemiptera and Coleoptera were well-represented in the south of the study area, but decreased sharply in diversity and abundance in the north; another common order, Megaloptera, was entirely absent from the study area, as were crayfish. Community composition varied along a latitudinal gradient, with some species restricted to northern latitudes and many more species restricted to the southern areas. Composition varied by region, as did the environmental factors that control it. Streams in the north of the system are connected to hundreds of small lakes and tend to freeze in the winter, which increases habitat stability; assemblages in this region were characterized by relatively large chironomids that are usually associated with lentic habitats and by a lack of taxa that are intolerant to freezing. Substrate was the main factor explaining differences in assemblage composition in this region. Just to the south, alluvial streams are more common and permafrost is continuous with very shallow active layers, iv which likely results in intense discharge peaks and ice scour in the spring and flashy summer hydrographs. Invertebrates in this region were mainly short-lived, small sized orthoclads, baetids and chloroperlids; the annual disturbance regime seems likely to be an important factor shaping community composition in this region. Many streams in this region received input from saline springs, resulting in perennial flow, and these streams harboured several taxa that were absent or rare in other streams at similar latitudes, including several stoneflies (e.g. Pteronarcys, Sweltsa); the presence of flow during the winter was found to be a major factor affecting community composition in this region, which surrounded the town of Norman Wells, NT. Nutrient dynamics appeared to be important in structuring benthic assemblages in the southern portion of the study region, with highnutrient streams supporting a diverse fauna which included many taxa that were absent in the north, while communities in low-nutrient streams were more similar to the northern alluvial stream fauna. There was no spatial distinction between low- and high-nutrient streams in the southern region, and the difference may be due to the local conditions of permafrost, which is patchy and discontinuous in the region. Evidence that winter ice and permafrost conditions are important drivers of benthic invertebrate diversity and community composition in the Mackenzie system, along with the latitudinal gradients which are consistent with a temperature/climate gradient, raises the possibility that benthic assemblages may be useful as indicators of effects of global climate change on freshwater habitats in the Canadian north. More immediately, construction of the Mackenzie Gas Pipeline may affect stream habitat due to sedimentation, and plans for the operation of the pipeline have raised concerns about potential effects on permafrost conditions. Implications for development of a biomonitoring program utilizing benthic invertebrates and their potential as indicators of climate change are discussed.

The objective of this study was to determine the dominant biogeochemical controls on mercury partitioning in super-permafrost groundwater at Truelove Lowland, Devon Island, Nunavut. Mercury partitioning in snow, ephemeral standing water, and super-permafrost groundwater was investigated. <p>Results indicate that partitioning differs between matrices, and that particulate mercury is spatially and temporally dynamic in Truelove Lowland groundwater. Particulate mercury in groundwater was 73 % of total mercury, while snow had only 22 % particulate mercury. Particulate mercury in groundwater rose by over 20 % from Julian day 181 to 189, and decreased slightly on Julian day 191. No single geochemical parameter was a good predictor of particulate mercury concentrations. To expand upon the findings of the field study a laboratory microcosm study was conducted to determine whether certain biogeochemical processes influence mercury partitioning in super-permafrost groundwater. Particulate mercury in the dissimilatory iron reducing bacteria inhibited microcosm was 61 % of total mercury, approximately 18 % lower than in all other treatments. Iron (III) concentrations had a positive correlation with particulate mercury while chloride concentrations had a negative correlation with particulate mercury. Sulfate reducing bacteria were not found to influence mercury partitioning.

Over the past millennia, complex terrestrial ecosystems have evolved in the Arctic. However, the stability of these unique ecosystems is in jeopardy because of climate changes. Due to the fact that Arctic soils store great amounts of carbon (C) in soil organic matter (SOM), any change that may occur in SOM with climate changes may substantially affect many aspects of Arctic ecosystems such as vegetation, animals, and humans. On a more global perspective, any change in Arctic SOM has the potential of modifying the overall world climate by affecting the global greenhouse gas (GHG) budget. A better understanding of the soil factors that affect soil N and C cycling at the landscape scale, such as moisture, temperature, and SOM characteristics, is necessary to produce better models. The overall objective of this study was to characterize the properties of SOM in Arctic soils and their influence on soil N and C cycling dynamics � including GHG emissions � at the landscape scale. This study was conducted in three distinct Arctic ecosystems: Sub-Arctic (Churchill, MB), Low-Arctic (Daring Lake, NWT), and High-Arctic (Truelove, NU). For each site, the sampling locations were evenly divided into five landform units: 1) upper slope (Up), 2) back slope (Back), and 3) lower slope (Low) for catena sites, and 4) hummock (Hum) and 5) wedges of hummock (W) for hummocky sites (i.e., hummock in Churchill and ice-wedge polygons in Truelove). All sites were sampled at the end of their growing season (from 2 to 3 weeks before plant senescence). The characteristics of SOM were assessed using three methods: 1) density fractionation to separate the uncomplexed light fraction (LF) from heavy fraction (HF) of SOM (LF < 1.55 g mL-1 < HF), 2) solid-state CPMAS 13C nuclear magnetic resonance (NMR) spectroscopy that determined the relative proportions of carbonyl-C (CbyC), alkyl-C (AC), aromatic-C (AroC), o-alkyl-C (OAC), and carbohydrates-C (CC), and 3) water-extractable organic matter (WEOM) that estimated SOM diluted in soil solution. Soil gross N mineralization was measured in situ using 15N dilution technique. Soil GHG emissions [nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2)] were measured in situ using a multicomponent Fourier transform infrared gas analyzer coupled with an automated dark chamber. The first study showed that organic surface soils, which had more than 17% soil organic C (SOC) by weight, contained relatively more labile SOM than mineral surface soils (< 17% SOC). For example, OAC:AroC ratios of the organic soils ranged from 25 to 75% greater compared to mineral soils. At Churchill, Daring Lake, and Truelove, 53, 73, and 20% of the C and N was included in the LF, respectively. All results show that the organic soils of Sub- and Low-Arctic ecosystems sampled for this study contain more fresh and un-decomposed plant residues than High-Arctic organic soils. The second study showed that both topography and ecosystems had a significant impact on gross N mineralization and CO2 emission rates. For example, at Churchill, gross N mineralization increased about 6-fold from upper slope to lower slope areas. Similarly, at Daring Lake, CO2 emissions increase about 5-fold from upper slope to lower slope areas. Topography and ecosystems had a very limited impact on soil N2O and CH4 emissions most likely because net emissions were extremely low. The third study showed that soil moisture, SOM quantity, and labile SOM parameters such as OAC:AroC and water-soluble organic carbon (WSOC) positively influenced gross N mineralization, N2O, and CO2 emissions, whereas the relative proportion of AroC negatively influenced gross N mineralization, N2O, and CO2 emissions. Relationships between SOM characteristics and CH4 emissions were not significant. This study showed that Up and Back areas tended to store relatively more recalcitrant SOM (AroC) than Low, Hum, and W areas, suggesting less fresh plant input on these landform units. Assessing SOM qualities with the ability of the soils to mineralize N (i.e., gross N mineralization) and release GHG at the landscape scale and across the Arctic represents a great advance in the understanding of these complex and unique ecosystems. Lower proportion of fresh and labile SOM found on Up and some Back landform units compared to Low and hummocky sites suggest that plants have more difficulties establishing and growing on these landform units (e.g., Up and Back) that experience harsh climates. Therefore, generalizations of the climate change impacts on soil N and C cycling processes throughout Arctic landscapes and ecosystems are less certain if topography is not considered. These results are particularly important because they can be used to produce better models that evaluate SOM stocks and dynamics under several climate scenarios and across Arctic landscapes and ecosystems.

Ecosystem degradation in Iceland has been severe since man arrived 1100 years ago. Birch woodlands cover has declined from 25% of the land area, to only 1%. The deforestation is considered to be the initial stage in the land degradation process, followed by surface destabilization, and later erosion. The objective of this study was to quantify and evaluate factors that contribute to the early stages of land degradation in Icelandic ecosystems. Specific objectives were to improve our understanding of how livestock grazing might initiate early degradation stages, elucidate field-based landscape metrics useful for characterizing degradation stages, and to determine if landscape metrics obtained from remote sensing data can be used to detect landscape structure changes and identify degraded and at risk rangelands in real time over extensive and remote areas. A State-and-Transition conceptual model was constructed for the experimental area to identify potential key processes in the degradation sequence, and to formalize research questions. Experimental plots were established in five plant community types representing a space-for-time degradation sequence. Birch seedling (Betula pubescens Ehrh.) growth and survival was reduced with repeated clipping treatment applied to simulate browsing, but the amount of decline varied with plant community type. This suggests that continuous grazing may contribute to deforestation, as regeneration will be reduced over time. Intense grazing treatments, simulating both grazing and trampling, increased surface instability and soil loss compared to grazing only or control, suggesting that intense grazing may contribute to surface destabilization and therefore to land degradation. Erosion appeared to be active in the most intense treatments, also within the woodlands. The data indicate that the woodlands may have lower resilience than the other plant communities as treatment effects appeared quicker there. The woodlands may thus be particularly vulnerable to intense grazing. The landscape metrics used to quantify changes in landscape surface properties over a 51 year period yielded inconclusive results, either because of data limitations or because of non-detectable erosion activity. The results do generally support the proposed S&T model for the experimental area. It is concluded that grazing may contribute to woodland decline, and intensify degradation processes.