| 1. |
- Dessirier, Benoît, 1987-
(författare)
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Numerical modeling of groundwater and air flow between compacted bentonite and fractured crystalline rock
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The geological repository for final storage of spent nuclear fuel, envisioned by the Swedish Nuclear Fuel and Management Company (SKB), relies on several barriers: copper canisters deposited in holes in the floor of underground tunnels in deep bedrock, embedded in a buffer of compacted bentonite. The initially unsaturated buffer would take up water from the surrounding rock mass and swell to seal any potential gap. This initial two-phase (gas and liquid) regime with two components (air and water) may impact the final density, swelling pressure and biogeochemical conditions in the buffer. A main objective of this work is to identify factors and mechanisms that govern deposition hole inflow and bentonite wetting under the prevailing two-phase flow conditions in sparsely fractured bedrock. For this purpose, we use the numerical code TOUGH2 to perform two-phase flow simulations, conditioned by a companion field experiment (the Bentonite Rock Interaction Experiment or BRIE) performed in a 417 m deep tunnel of the Äspö Hard Rock Laboratory in southeastern Sweden. The models predict a significant de-saturation of the rock wall, which was confirmed by field data. To predict the early buffer wetting rates and patterns, the position of local flowing fractures and estimates of local rock matrix permeability appear more important than the total open hole groundwater inflow. A global sensitivity analysis showed that the buffer wetting time and the persistence of unsaturated conditions over extended periods of time in the rock depend primarily on the local fracture positions, rock matrix permeability, ventilation conditions in the tunnel and pressure far in the rock. Dismantling photographs from BRIE were used to reconstruct a fine-scale snapshot of saturation at the bentonite/rock interface, showing tremendous spatial variability. The high level of heterogeneity in the rock generates complex two-phase flow phenomena (air trapping, dissolution), which need to be accounted for in buffer design and rock suitability criteria. In particular, results suggest that uncertainties regarding two-phase flow behavior are relatively high close to residual air saturation, which may also have important implications for other applications involving two-phase flows, such as geological storage of carbon dioxide.
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| 2. |
- Eriksson, Sofia, 1977-
(författare)
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Cross-scale perspectives on heterogeneity in Swedish boreal forests
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Maintaining species diversity, ecosystem functioning, and socioeconomic values requires continued ecosystem heterogeneity across scales. This thesis aims to bridge gaps between ecological theory, environmental goals, and practical application of sustainable forest management needed to maintain such heterogeneity. Included case studies of boreal Sweden concern three challenges in the cross-scale understanding of heterogeneity: matrix qualities and composition; acquiring and incorporating historical information; and interactions between forest composition and management. Paper I cover three large-scale forest companies in four boreal counties today, outlining available information on matrix qualities and composition from the companies. Papers II-III cover the village scale from 1720s–1850s–present in Dalarna County and papers IV-V the parish scale from 1860s–present in the same county. Geographic Information Systems were used to integrate historical maps with present data, perform spatiotemporal analyses, and extract data for statistical testing in primarily generalized linear models. For the practical realization of sustainable forest management, the results indicate a need for further monitoring across scales to understand matrix composition, especially in relation to small voluntary reservations in a larger spatiotemporal perspective. Historical material can provide information on temporal connectivity and spatial separation between the past and present forest composition from analysis of change trajectories respectively interacting variables. This thesis suggests that models of forest dynamics are more relevant for local implementation of sustainable forest management efforts if including interactions between forest dynamics and ownership as an approximate driver of local change.
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| 3. |
- Finné, Martin, 1981-
(författare)
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Climate in the eastern Mediterranean during the Holocene and beyond – A Peloponnesian perspective
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contributes increased knowledge about climate variability during the late Quaternary in the eastern Mediterranean. Results from a paleoclimate review reveal that regional wetter conditions from 6000 to 5400 years BP were replaced by a less wet period from 5400 to 4600 years BP and to fully arid conditions around 4600 years BP. The data available, however, show that there is not enough evidence to support the notion of a widespread climate event with rapidly drying conditions in the region around 4200 years ago. The review further highlights the lack of paleoclimate data from the archaeologically rich Peloponnese Peninsula. This gap is addressed in this thesis by the provision of new paleoclimate records from the Peloponnese. One stalagmite from Kapsia Cave and two stalagmites from Glyfada Cave were dated and analyzed for stable oxygen (δ18O) and carbon (δ13C) isotopes. The Glyfada record covers a period from ~78 ka to ~37 ka and shows that the climate in this region responded rapidly to changes in temperatures over Greenland. During Greenland stadial (interstadial) conditions colder (warmer) and drier (wetter) conditions are reflected by depleted (enriched) δ13C-values in the speleothems. The Kapsia record covers a period from ~2900 to ~1100 years BP. A comparison between the modern stalagmite top isotopes and meteorological data shows that a main control on stalagmite δ18O is wet season precipitation amount. The δ18O record from Kapsia indicates cyclical humidity changes of close to 500 years, with rapid shifts toward wetter conditions followed by slowly developing aridity. Superimposed on this signal is a centennial signal of precipitation variability. A second speleothem from Kapsia with multiple horizons of fine sediments from past flood events intercalated with the calcite is used to develop a new, quick and non-destructive method for tracing flood events in speleothems by analyzing a thick section with an XRF core scanner.
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| 4. |
- Granit, Jakob, 1966-
(författare)
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The Collective Action Dilemma in Managing Transboundary Freshwaters : An Analysis of an Outcome-Driven Framework
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is recognised by society that freshwater resources play a major role in economic development and in maintaining life supporting ecosystems services. Transboundary river basins cover about 45% of the earth’s land surface and their governance is therefore of critical importance. Transboundary freshwater resources are considered a common-pool resource. Collective action is therefore needed in order to supply both public and private goods from these resources but is yet in short supply. This thesis intends to analyse a complementary framework to the common Integrated Water Resources Management (IWRM) approach with the objective of enhancing investments in collective action to address this dilemma. Results indicate that transboundary water resources management in itself can be identified as a regional public good. The results also indicate that IWRM has been promoted as a standard management concept; often without first having identified and agreed the objectives of the intended multiple uses of water. Outcomes related to IWRM at the transboundary scale are therefore difficult to identify and evidence points towards continued water quality degradation at a global scale and development opportunities not achieved. Two different tools for how to assess the generation of benefits from cooperation are presented in this thesis including an institutional assessment framework adapted to transboundary institutions. Together these steps make up an outcome-driven approach that clarifies the value of water in all management and development stages. Through such an outcome-driven approach, water issues can provide the incentives necessary in order to identify cooperative paths and thus become important factors in negotiations to establish effective regional governance regimes. This would take the broader political, economic and geographical context into consideration thus supporting a process towards more integration of interests between countries.
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| 5. |
- Gribenski, Natacha, 1986-
(författare)
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Comparison of dating methods for paleoglacial reconstruction in Central Asia
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Reconstruction of former Central Asian glaciers extents can provide valuable information about past atmospheric circulation variations. These extents, often marked by terminal moraines, need to be chronologically constrained. Cosmogenic nuclide exposure (CNE) dating is widely used to directly date moraines. In addition, there is increasing interest on using optically stimulated luminescence (OSL) techniques for dating glacial landforms. This thesis focuses on the methodological aspects of directly dating glacial landforms to perform paleoglacial reconstructions in Central Asia, with an emphasis on OSL dating.For OSL dating of sediments from glacial settings, it is important to measure the luminescence signal at the single grain scale, because the sediments are likely affected by partial bleaching due to short light exposure during glacial or glaciofluvial transport. The use of an Electron Multiplying Charges Coupled Device (EMCCD)-based imaging system for single grain OSL measurements would offer larger flexibility in light stimulation and sediment type, compared to the current Single Grain Risø reader. An automated image processing procedure has been developed to compensate for sample carrier displacement over repeated measurements and for attributing pixels to each grain for signal integration when using this imaging system. However, significant cross talk contamination, demonstrated by laboratory and simulation experiments, prohibits accurate single grain luminescence measurements. Preliminary experiments using a basic image processing algorithm show good potential for software correction solutions.Paleoglacial reconstructions conducted in the Altai Mountains, Central Asia, using both CNE and OSL dating demonstrate that luminescence measurements of glaciofluvial sediments performed at the multi-grain scale result in large age overestimates, and that single grain measurements allow for more accurate dating of glacial landforms. However, uncertainties remain that are related to the model used for extracting equivalent doses for well-bleached grains and to fading corrections when using feldspar minerals. The timing of glaciation can be inferred from scattered CNE moraine boulder ages if most of the ages are concentrated within a few thousand years, with only few ages clearly older or younger. Overall, combining CNE and OSL techniques for dating a glacial landform is a powerful approach for producing robust glacial chronologies, despite uncertainties inherent to each technique.Paleoglacial reconstructions from the Altai Mountains indicate Marine Isotope Stage (MIS) 2 and MIS 4/late MIS 5 local Last Glacial Maximums. In Central Asia, in addition to a regional MIS 2 glaciation, previous studies indicate a period of major glacial advances during MIS 3 that is out of phase with global ice volume records. However, most MIS 3 glacial chronologies from Central Asia are based on too few or too heavily scattered CNE data sets, or on OSL or Electron Spin Resonance (ESR) ages for which partial bleaching has not been properly investigated. Hence, at this stage, chronological evidence is insufficient to demonstrate a regional MIS 3 glaciation in Central Asia.Surge-related glacial features identified in the Russian Altai also highlight the importance of conducting detailed geomorphology and sedimentology studies to understand former ice dynamics, which is essential for inferring appropriate paleoclimate information from paleoglacial reconstructions.
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| 6. |
- Higgins, Lindsey, 1985-
(författare)
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Linking lake variability, climate, and human activity in Basotu, Tanzania
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Paleoenvironmental investigations establish important baseline knowledge of the natural variability of lake systems, to better understand human impacts on the landscape, and the effects of climate change on water resources. By combining long-term environmental history with investigations into modern land use patterns and climatological events, a wider perspective can be reached that has practical applications in water governance. This thesis presents a case study of Lake Basotu (4.37°S, 35.07°E), a crater lake in the Hanang district of north-central Tanzania, which acts as an important source of freshwater for local people. A three-meter long sediment core from an interior crater of Lake Basotu was investigated using proxy records (diatoms, magnetic parameters, and carbon content) and radiometric dating (14C and 210Pb). The Lake Basotu record was then compared to other sediment-based reconstructions from East Africa and records of historical famines to better place it into the timeline and understanding of regional climate dynamics. This work was extended into modern times (1973–2015) by examining lake extent variations in the Landsat satellite archive. Shoreline boundaries for dry-season images were delineated and lake extent was calculated using GIS techniques. This remote sensing record was compared to climatological patterns, meteorological records, and the history of land-use changes in the surrounding district. As a whole, the Lake Basotu record indicates that major fluctuations in lake level are not abnormal; however, human influence has likely increased the lake’s sensitivity to climatic fluctuations. The timing of historical famines in East Africa were linked to periods of shallow lake conditions in Basotu, and the duration of the most extreme lake level changes correlate to a reversal in the 14C age-depth model. Recent variations in lake extent are likely connected to a mechanized wheat farming program implemented in the district as a foreign aid project in the early 1960s. To support the work done in Basotu, a preliminary investigation of sediment from the nearby Lake Babati was undertaken. Sediment from the two lakes indicates that their geographical location may be in a transition zone towards dryer conditions to the south during the Little Ice Age in East Africa. The results of this thesis support that Lake Basotu is an important location for understanding the potential impacts of climate change and human activity on water resources in this region.
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| 7. |
- Johansson, Emma, 1979-
(författare)
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The influence of climate and permafrost on catchment hydrology
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The cycling of water in the landscape is influenced by climate change on different time scales and in different directions regarding warming or cooling trends. Along with a changing climate, also the landscape and subsurface conditions, such as permafrost extent, may change in a long-term perspective. Permafrost and hydrology are intimately connected but the interactions between them are poorly understood, and the hydrological response to climate change is complex. The first part of this thesis investigates the effects of different drivers of future changes in hydrological flow and water storage components in the present day temperate Forsmark catchment in Sweden. The role of taliks and their influence on the exchange of deep and shallow groundwater in permafrost environments are also studied. This is done by a simulation sequence where the site is exposed to the landscape, climate and permafrost changes expected from site-specific numerical modeling. In the second part of this thesis, present day periglacial hydrological processes are studied in the Two Boat Lake catchment in western Greenland by field and model investigations of the site. The presence of a through talik below the Two Boat Lake, and data from a deep bedrock borehole into the talik, enable studies of the hydrological interactions between the lake and the talik. The spatial and temporal variability of the different water balance components of the catchment are quantified and the interactions between the surface water and the supra- and sub-permafrost groundwater are analyzed.The results show that the investigated changes in climate and permafrost influence hydrology more than the investigated landscape changes. Under permafrost conditions, the general direction of the exchange between deep and shallow groundwater may change relative to unfrozen conditions. The simulation studies of Forsmark show that the relative topography between taliks governs the recharging and discharging conditions, which is consistent with results from Two Boat Lake. The lake is located at high altitude relative to other taliks and hydraulic measurements indicate recharging conditions. The talik recharge is small compared to other water balance components and does not influence the lake level, which instead is found to be controlled by evapotranspiration and water inflow from the active layer. This is concluded from numerical simulations that take into account and combine evapotranspiration with other surface and subsurface hydrological processes. This thesis highlights the need to integrate surface and subsurface process modelling in order to quantitatively understand and represent the dynamics and complexity of hydrological interactions in periglacial catchments.
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| 8. |
- Lindgren, Jessica, 1971-
(författare)
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Small remnant habitats : Important structures in fragmented landscapes
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The world-wide intensification of agriculture has led to a decline in species richness due to land use change, isolation, and fragmentation of natural and semi-natural habitats in agricultural and forestry landscapes. As a consequence, there is a current landscape management focus on the importance of green infrastructure to mitigate biodiversity decline and preserve ecosystem functions e.g. pollination services and pest control. Even though intensification in agriculture has been ongoing for several hundreds of years, remnant habitats from earlier management practices may still be remaining with a surprisingly high plant richness. Preserving these habitats could help conserving plant species richness in agricultural landscapes, as well as other organisms that are dependent on plants for food and shelter.In this thesis I focus on two small remnant habitats; midfield islets and borders between managed forest and crop field in southeastern Sweden. In the past, both habitats were included in the grazing system and therefore often still have remnant population of grassland specialist species left today. I have used these two remnant habitats as model habitats to investigate the effect of landscape factors and local factors on species richness of plants, flower morphologies and plants with fleshy fruits. Additively, I analysed the effect of surrounding landscape and local openness on the functions; pollination success, biological pest control of aphids and seed predation on midfield islets.One of my studies showed that spatial distribution and size of the habitat affected plant species richness. Larger habitat size and higher connectivity between habitats increased species richness of plants in the habitats. Openness of the habitats was shown to be an important factor to increase species richness and richness of flower morphologies, both on midfield islets and in forest borders. Even though midfield islets had the highest species and morphology richness, both habitat types are needed for habitat complementary as forest borders have more plants with fleshy fruits and a higher richness of plant species that flowers in spring/early summer. It was also shown that a more complex forest border, not just with gaps in the canopy, but also with high variation in tree stem sizes increases plant species richness in the field layer. The conclusion is that by managing small remnant habitats to remain or become more semi-open and complex in their structure, would increase species richness of plants, grassland specialist species, and flower morphologies. It would also increase some ecosystem functions as seed predation and biologic pest control of aphids are more effective close to trees. If both midfield islets and forest borders would be managed to be semi-open, the area and connectivity of semi-open habitat would increase in the agricultural landscape, which may also improve pollination success as the connectivity between populations has a possibility to increase. Grassland specialist species are clearly abundant in the small remnant habitats. As the decline of semi-natural grasslands is causing a decline in grassland specialists’ species, not only plants, I recommend that small remnant habitats are included in conservation and management plans and strategies to improve habitat availability and connectivity for grassland species in agricultural landscapes.
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| 9. |
- Mercer, Andrew, 1972-
(författare)
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Studies in Glacier Mass Balance : Measurement and its errors
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The study of the surface mass balance of valley glaciers has a long history but one that is dogged by uncertainty and errors, and uncertainty about those errors. These problems are acknowledged by the glaciological community and have been examined and formalised in several publications. The latest of these stems from a workshop organised by the World Glacier Monitoring Service, the results of which are presented in the first paper of this thesis. The paper examines two common methods and some of their associated errors, with the aim of unifying them and providing more robust data sets. New methodologies, such as ground penetrating radar (GPR), are used in the second paper herein to provide richer and alternative data sources for approaching measurement problems related to snow depth and, to some degree, snow density. The third paper is concerned with both technical survey issues and glaciological definitions when surveys of glacier surfaces are performed for use in mass balance calculation. Many of these issues are common to remote sensing methods and ground based surveys but the paper attempts to make this commonality more explicit. Whilst the first three papers concern themselves with the act of measurement and calculation the fourth paper considers errors brought about by logistical constraints restricting the timing of surveys. Such errors are technically avoidable to a large degree but inevitable in practice. In the case presented here the error is one of unobserved accumulation, falling late in the season, after the last survey. By modelling expected ablation from minimal data, such as temperature, and comparing this with measured mass balance an estimate of unobserved accumulation is made.Also contained in this work is an assessment of glacier front surveys, specifically those performed by the Tarfala Research Station. Such surveys are assumed to act as a monitor of glacier response to climate change and are assumed to be a large scale proxy of mass balance but the resolution of the response as well as the resolution of survey methods indicates that the frequency of such surveys should be reduced and that remote sensing methods may be more effective.Common to all glaciological field surveys is the relative sparsity of data rendering error analysis and many statistical methods ineffective but new technologies such as Lidar, Global Navigation Satellite System, GPR and remote sensing indicate a way forward and the potential for future work to deliver detailed and reliable data.
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| 10. |
- Nguyen, Thanh Tam, 1981-
(författare)
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Pesticide use in rice farming and its impacts on climbing perch (Anabas testudineus) in the Mekong Delta of Vietnam
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The intensification of agricultural production in the Mekong Delta has faced serious challenges with respect to increased use of agrochemicals and especially pesticides. The indiscriminate use of pesticide could potentially impact on the long-term food production, environmental and human health in the delta. The aim of this thesis was to investigate the negative side effects of the current use of pesticides on climbing perch (Anabas testudineus) in rice fields using brain acetylcholinesterase (hereafter referred to as AChE) activity as a biomarker. The empirical work, on which this thesis is based, includes structured questionnaires, laboratory and field experiments. First, a field survey using questionnaires was carried out to gain a better understanding of the current state of rice farming systems, the use of pesticides and attitude to pest management strategies among rice and rice-fish farmers, as well as to provide basic information for the set-up of the laboratory and field experiments. Secondly, laboratory studies were conducted to clarify if the selected insecticides applied alone and in mixtures caused negative side effects on climbing perch fingerlings. Thirdly, further toxicity studies were carried out, under rice field conditions, to further investigate the toxicity effects of the insecticides, applied alone, in mixtures and under sequential applications, on climbing perch fingerlings.The results showed that although there were a more selective use of pesticides and an increased awareness among farmers of the negative side effects of pesticides in 2007 as compared to 1999, the current use of pesticide in the Mekong Delta still cause many problems to the environment and human health. Chlorpyrifos ethyl (hereafter referred to as CPF) was found to cause a significant and more prolonged inhibition on the brain AChE activity in climbing perch than fenobucarb (hereafter referred to as F). The inhibition by the mixture of CPF and F were significantly higher than the inhibition by only F, but less prolonged and significant lower than the inhibition by only CPF. The results suggest that the combined effect from a mixture of F and CPF can create both additive effects initially and later antagonistic effects.CPF and F applied at concentrations used by farmers, either as separate doses, in a mixture or in sequential doses, decreased the brain AChE activity, growth and survival rates in climbing perch. The results demonstrate that brain AChE activity in climbing perch is a relevant biomarker for monitoring of exposure to, and sub-lethal impacts from organophosphates and carbamates under tropical conditions. The result also shows that 2-PAM re-activate the brain AChE activity, and can be used as an alternative method to assess the AChE inhibition level in organisms recently exposed to OP’s, in situation where it may be difficult to find unexposed individuals as controls.In conclusion, this thesis shows that the current use of pesticides in the Mekong Delta has a negative effect on climbing perch living in rice fields. It indicates that a sustained long-term food production in the Mekong Delta must be based on ecological principles, taking advantages of ecosystem biodiversity and productivity, and not through intensified use of pesticides.
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| 11. |
- Plikk, Anna, 1982-
(författare)
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The Eemian Interglacial at Sokli, northern Finland : A multi-proxy environmental and climatic reconstruction based on a 9 m long lacustrine sediment sequence
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the fundamentals of the Earth’s climate system during the Quaternary Period (the past ca 2.6 million years) is of imminent interest in light of the reported recent climatic changes. The Eemian Interglacial (ca 129,000-116,000 years ago) is the last period before the present interglacial (the Holocene, the last ca 11,700 years) when temperatures were as warm as or warmer than today and may serve as an analogue to future climatic warming. The Eemian is a relatively well-studied period, but many aspects of the interglacial climatic dynamics still remain unresolved. One reason for this is the chronological uncertainties of many records from this time period; another is the relatively uneven distribution of palaeoarchives. Especially from high latitude areas, terrestrial records from the Eemian are few due to the impact of glacial erosion during the Weichselian Glacial (ca 116,000-11,700 years ago).This thesis is based on data from Sokli, N Finland, where cold-based conditions of the Weichselian ice sheets and non-typical bedrock conditions have allowed preservation of an unusually thick Eemian lacustrine deposit in stratigraphic sequence with overlying Weichselian and Holocene deposits. The main purpose of this thesis is to contribute to the knowledge of climate variability in Fennoscandia and the North Atlantic region during the Eemian, and it involves a qualitative multi-proxy reconstruction of the Eemian lake and its development as well as a quantitative reconstruction of the regional Eemian July temperature evolution using subfossil chironomids. Attention is paid also to the identification and characterization of short-term climatic events in the Sokli record.The main contribution of this study is to increase the spatial coverage of Eemian palaeoclimatological data. Specific results include the description of the lake development, identifying phases where non-climatic variables likely affect the quantitative chironomid-based temperature reconstruction, as well as qualitative and quantitative reconstructions of climatic features such as changes in seasonality and temperature. Five major lake phases are distinguished. A glaciolacustrine phase is followed by an early Eemian lake phase characterized by short mixing periods and rising nutrient levels. The following early mid-Eemian lake phase is characterized by a prolonged open water season and high productivity and possibly corresponds to the Eemian climatic optimum. The late mid-Eemian lake phase is characterized by infilling and eutrophic conditions while the late Eemian lake phase reflects shallow, dynamic and cooling conditions.The qualitative study suggests a shift from a higher seasonality in the early Eemian towards more oceanic conditions during the mid-Eemian, while chironomid-inferred July temperatures indicate that near present-day temperatures prevailed at Sokli already from the beginning of the interglacial and that optimum temperatures were only moderately (ca + 1°C) higher than at present. These results suggest that the climatic development at Sokli followed that of central Europe during the Eemian. Two events characterized by colder and more arid conditions are identified, and can be tentatively correlated to meltwater events registered in marine records from the Nordic seas and subpolar north Atlantic, possibly reflecting the effect that meltwater pulses and related disruptions in the thermohaline circulation had on adjacent continental areas.
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| 12. |
- Seguinot, Julien, 1987-
(författare)
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Numerical modelling of the Cordilleran ice sheet
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctoral dissertation presents a study of the glacial history of the North American Cordillera using numerical ice sheet modelling calibrated against field evidence. This area, characterized by the steep topography of several mountain ranges separated by large inter-montane depressions, was once covered by a large-scale ice mass: the former Cordilleran ice sheet. Because of the irregular topography on which the ice sheet formed, geological studies have often had only local or regional relevance, thus leaving the Cordilleran ice sheet least understood among Pleistocene ice sheets in terms of its extent, volume, and dynamics.Here, I present numerical simulations that allow quantitative reconstructions of the former ice sheet evolution based on approximated physics of glacier flow. These simulations show that the geometry of the Last Glacial Maximum Cordilleran ice sheet was largely controlled by sharp contrasts in regional temperature, precipitation, and daily temperature variability associated with the presence of mountain ranges.However, this maximum stage appears short-lived and out of balance with contemporaneous climate. During most of the simulated last glacial cycle, the North American Cordillera is characterized by an intermediate state of glaciation including isolated glaciers and ice caps covering major mountain ranges, the largest of which is located over the Skeena Mountains. The numerically modelled Cordilleran ice sheet appears in constant imbalance with evolving climate conditions, while the complexity of this transient response transcends that encapsulated in two-dimensional, conceptual models of ice sheet growth and decay.This thesis demonstrates the potential of numerical ice sheet modelling to inform on ice sheet history and former climate conditions over a glacial cycle, given that ice sheet models can be calibrated against field constraints.
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| 13. |
- Shala, Shyhrete, 1982-
(författare)
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Palaeoenvironmental changes in the northern boreal zone of Finland: local versus regional drivers
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multiple proxies derived from the Lake Loitsana sediment sequence (NE Finland) are employed to determine the timing of deglaciation, characterise an early Holocene proglacial lake stage and reconstruct Holocene lake development. Local-scale processes causing shifts in biological assemblages are identified and the most likely Holocene mean July air temperature (Tjul) development is assessed. The study area was deglaciated shortly prior to 10 700 cal. a BP. The sediment record reflects four local events; the presence of a glacial lake, glacial lake drainage and formation of Lake Loitsana, changes in fluvial input due to progressive wetland expansion, and gradual lake infilling. The results suggest that local events have driven changes in biological assemblages through various processes, and that biotic proxies reflect changes in environmental parameters in a highly individual manner. Furthermore, biological assemblages can themselves act as important drivers, influencing the composition of other assemblages. It is suggested that future studies should consider macrophyte abundance and food-web interactions as equally important factors when assessing changes in biological assemblages. Quantitative Tjul reconstructions based on biotic proxies display contrasting trends. While Tjul reconstructions based on pollen found in the Loitsana sequence display relatively low early Holocene values, plant macrofossil and chironomid data reflect warm summer conditions also during the early Holocene, i.e. at the peak of summer insolation. The early Holocene Tjul recorded by terrestrial pollen are affected by local factors possibly combined with a delayed response of the terrestrial ecosystem compared to the aquatic one. This study emphasises the importance of using multiple proxies in palaeoenvironmental studies and shows that local factors have a potential to drive changes in biological assemblages that can affect transfer-function based temperature reconstructions.
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| 14. |
- Sjöberg, Ylva, 1982-
(författare)
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Linking water and permafrost dynamics
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 15. |
- Thorslund, Josefin, 1988-
(författare)
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Hydrological spreading of metal pollution and wetlands as nature-based solutions
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The quality of the Earth’s water resources have deteriorated due to human impacts. A key scientific challenge is to understand, quantify and predict the water-borne spreading of pollutants at relevant scales for freshwater management and water quality restoration programs. However, understanding the natural processes controlling large-scale hydrological transport of pollutants may be masked by river regulation schemes (in the form of dams and reservoirs), which are common in many large rivers. The main objective of this thesis is to increase the current knowledge regarding large-scale spreading of metals in hydrological systems. This objective is addressed through studying net impacts of mining (a main contributor to global metal pollution) on the spreading of metals in water systems and through investigating the mitigation opportunities of wetlands across the landscape. The main study region of this thesis is the Lake Baikal basin of Russia and Mongolia, which includes the large unregulated Selenga River and its delta-wetland areas. In addition, a set of global wetland sites are also studied. A multi-method approach is used in the four studies of this thesis. The methods include field-measurements, data synthesis, metal mass flow and water flow-path quantifications, as well as geochemical modelling. Results show that mining in the upstream part of the Lake Baikal basin is a significant contributor to riverine mass flows of several metals. The mass flows increased by an order of magnitude over the mining site. The observed speciation between dissolved (more bioavailable) and suspended (less bioavailable) phases could be well predicted for some metals (Fe, V, Pb and Zn) using a geochemical equilibrium model. However, the model failed to reproduce the speciation of other metals (Cr, Cu, Mn and Mo). In these cases, non-equilibrium processes may need to be considered, and adsorption databases may need to be developed, in order to make dependable predictions. Results also suggest that the concentration of dissolved organic carbon, which exhibits seasonal variability and long-term increasing trends due to climate change effects in the Arctic, can have a large impact on metal pollution transport. Further, observations showed that individual wetlands of the Selenga River delta locally retained between 77-99 % of incoming metal loads. However, a systematic analysis of current knowledge showed that large-scale net effects can differ considerably from the functions observed at individual wetlands on smaller scales. Along large-scale flow-paths, through which wetlands are connected with each other as well as with the larger landscape, key processes which can considerably contribute to such scale differences in function may occur. A survey of the current wetland research showed that relatively few studies have considered the larger scales at which key pollutant pressures and water quality changes take place. This thesis highlights the need for more research on large-scale wetland systems, which can aid in evaluating net pollution effects at landscape scales. This in turn can facilitate evaluations of how and when wetland systems may function as large-scale nature-based solutions.
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| 16. |
- Verrot, Lucile, 1988-
(författare)
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Modeling long-term variability and change of soil moisture and groundwater level - from catchment to global scale
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The water stored in and flowing through the subsurface is fundamental for sustaining human activities and needs, feeding water and its constituents to surface water bodies and supporting the functioning of their ecosystems. Quantifying the changes that affect the subsurface water is crucial for our understanding of its dynamics and changes driven by climate change and other changes in the landscape, such as in land-use and water-use. It is inherently difficult to directly measure soil moisture and groundwater levels over large spatial scales and long times. Models are therefore needed to capture the soil moisture and groundwater level dynamics over such large spatiotemporal scales.This thesis develops a modeling framework that allows for long-term catchment-scale screening of soil moisture and groundwater level changes. The novelty in this development resides in an explicit link drawn between catchment-scale hydroclimatic and soil hydraulics conditions, using observed runoff data as an approximation of soil water flux and accounting for the effects of snow storage-melting dynamics on that flux. Both past and future relative changes can be assessed by use of this modeling framework, with future change projections based on common climate model outputs. By direct model-observation comparison, the thesis shows that the developed modeling framework can reproduce the temporal variability of large-scale changes in soil water storage, as obtained from the GRACE satellite product, for most of 25 large study catchments around the world. Also compared with locally measured soil water content and groundwater level in 10 U.S. catchments, the modeling approach can reasonably well reproduce relative seasonal fluctuations around long-term average values.The developed modeling framework is further used to project soil moisture changes due to expected future climate change for 81 catchments around the world. The future soil moisture changes depend on the considered radiative forcing scenario (RCP) but are overall large for the occurrence frequency of dry and wet events and the inter-annual variability of seasonal soil moisture. These changes tend to be higher for the dry events and the dry season, respectively, than for the corresponding wet quantities, indicating increased drought risk for some parts of the world.
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| 17. |
- Weiss, Niels, 1984-
(författare)
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Permafrost carbon in a changing Arctic : On periglacial landscape dynamics, organic matter characteristics, and the stability of a globally significant carbon pool
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic matter (OM) in arctic permafrost ground contains about twice as much carbon (C) as is currently present in the atmosphere. Climate change is particularly strong in the Arctic, and could cause a considerable part of the OM in permafrost to thaw out, decompose, and be released as greenhouse gases; further enhancing global warming. The exact size of the northern circumpolar C pool remains unclear, and processes that control decomposition and mineralization rates are even more uncertain. Superimposed on the long-term release of C through microbial decomposition of OM in the gradually deepening active layer, is the rapid release of currently sequestered OM through geomorphological processes. This thesis considers the quantity, quality, and availability of permafrost C, and explores interactions and common controls.To better understand the potential effects of thawing permafrost, it is vital to: i) obtain more accurate size and distribution estimates of permafrost C stocks, and develop methods to accurately and efficiently implement these in models, ii) identify OM characteristics that control decomposition, specifically for permafrost material, and iii) determine and quantify key geomorphological processes that cause large amounts of OM to become available for rapid decomposition.Detailed C quantifications are valuable to increase our fundamental understanding of permafrost soil processes and C sequestration, but including high levels of heterogeneity in models is challenging. Simple upscaling tools based on e.g. elevation parameters (Paper I) can help to bridge the gap between detailed field studies and global C models.Permafrost OM quality is controlled by different factors than those commonly observed in temperate soils (without permafrost). We observed an unexpected (significant) correlation in upper permafrost samples, where material that is generally considered more recalcitrant showed the highest CO2 production rates per g C, indicating high lability (Paper II). In ancient Pleistocene permafrost, labile samples related significantly to OM that was enriched in decomposed microbial remains, whereas less-decomposed plant material was more stable (Paper III). Investigation of multiple incubation datasets revealed that the unusual relationship between %C and CO2 production occurred in contrasting field sites throughout the Arctic, indicating important permafrost-specific controls over OM quality (Paper IV). We discuss several possible explanations for the observed high lability of permafrost OM, such as a pool of labile dissolved organic C in the upper permafrost, or increased lability caused by past decomposition. In order to conclusively identify causal relationships, and to answer the question whether or not the same mechanisms control OM quality in different environments, further investigation of permafrost-specific OM quality is required.Geomorphology plays a key role in C reworking and OM decomposition. Vast amounts of OM can be released abruptly (e.g. in thaw slumps and thermokarst lakes, Paper II), resulting in C turnover that will likely outweigh decomposition through gradual active layer deepening. Climate change could enhance this rapid release of C, and changes in surface hydrology and increased fire activity are expected to become the largest contributors to C loss from permafrost regions. Together with C quantity and quality, availability through gradual and abrupt processes must be parameterized and included in models in order to accurately assess the potential permafrost C climate feedback.
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| 18. |
- Ampel, Linda, 1979-
(författare)
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Dansgaard-Oeschger cycles and Heinrich events in western Europe - A diatom perspective
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The last glacial period was characterised by several abrupt climatic shifts referred to as Dansgaard-Oeschger (DO) cycles and Heinrich events. These shifts were most frequent between 60,000 and 20,000 years before present coinciding with Marine Isotope Stages (MIS) 3 and 2. DO cycles and Heinrich events have been most thoroughly investigated in marine and ice core records while their impact on terrestrial environments is less well known. The high-resolution, multi-proxy investigation of a long sediment sequence, obtained from the former lake at Les Echets in France, aims at filling this gap and allows determining the impact of these climatic events on the lake and its catchment. The site and its surroundings experienced distinct shifts in lake organic productivity and catchment conditions as a consequence of DO climate variability and Heinrich events. The detailed analysis of the fossil diatom record shows distinct changes in diatom productivity, diversity and community composition, which are most likely due to variations in the length of lake ice cover, thermal stratification regimes and catchment conditions during a DO cycle. The distinct reduction in lake organic productivity and particularly low concentrations of diatom valves during intervals corresponding to Heinrich events suggest that these cold and arid phases had the most severe impact on the paleolake at Les Echets. The results of this thesis provide new insight into the impact of abrupt climate change on lacustrine ecosystems and show the potential of high-resolution and multi-proxy studies in paleoenvironmental research.
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| 19. |
- Andersson, Sofia, 1975-
(författare)
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Late Holocene humidity variability in central Sweden
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to reconstruct humidity variability in central Sweden during the late Holocene. A multi-proxy approach was used to infer humidity changes as recorded in a lake and a mire. Age-models were constructed based on radiocarbon dating and the Askja-1875 tephra. Stable isotopes (δ18O and δ13C) on Chara spp encrustations and Pisidium spp mollusc shells and carbon content were analysed in the lake record, whereas peat stratigraphy, humification, testate amoebae assemblages, C/N ratio and stable isotopes (δ13C and δ15N) were analysed in the mire record. Stable isotopes (δ2H and δ18O) on lake water showed that Lake Blektjärnen responded to changes in the balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate during which evaporation and atmospheric equilibration likely enrich lake water in 18O and 13C, respectively, and vice versa for a low E/I ratio. The relatively high Chara δ18O and δ13C values between ca 4400 and 4000 cal yr BP thus suggest relatively dry and likely warm conditions, whereas depleted values suggest wetter and probably cooler conditions between ca 4000 and 3000 cal yr BP. Again, drier and probably warmer conditions were inferred from the relatively enriched δ18O values between ca 2500 and 1000 cal yr BP, and depleted δ18O values were recorded between ca 1000 and 50 cal yr BP indicating wetter and likely cooler conditions. The results from the mire mainly indicated vegetation succession, however, the changes inferred at ca 2600 and 1000 cal yr BP could have been triggered by climate change. This study shows that the proxies responded sensitively to humidity changes in the investigated archives allowing for reconstruction of climate change in central Sweden during late Holocene.
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| 20. |
- Berntsson, Annika, 1979-
(författare)
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The sensitivity of Swedish alpine lakes to hydro-climatic changes during the Late Holocene
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis objective is to use lake sediments to investigate the relationships between chironomids, as proxy for temperature, and δ18O and minerogenic in-wash, as precipitation proxies, in northern Sweden during the Late Holocene. Three lakes along a N–S transect in the Scandes were studied using biological, geochemical and physical sediment properties, together with numerical methods. Emphasis was put on changes in hydrological and erosional regimes and the configurations of lake catchments in an attempt to avoid misinterpretation of the climate signals. Mean July air temperatures were inferred from the chironomid composition in sediment records covering the last 5000 yrs in Vindelfjällen Mountains in Mid Lapland and the last 1000 yrs in Jämtland. The temperature reconstructions underwent significance tests, suggesting reliable results for the Vindelfjällen reconstruction but not the Jämtland reconstruction. Data from XRF core scanning and grain size variations, interpreted together with catchment geomorphology, suggested periods with increased fluvial erosion. A major flood event occurred at the Vindelfjällen site c. 2800 cal. yr BP. Furthermore, this record indicates stream flow and wetland surface erosion during the last 1200 yrs. Seasonal variations in the amount of precipitation, reflecting changes in atmospheric circulation during the last 1000 yrs, were reconstructed based on δ18O in diatoms from one lake in Jämtland and one in northern Lapland. Relatively higher summer precipitation was inferred between AD 1000 and 1080, AD 1300 and 1440, and during the early 19th century as a result of a positive Arctic Oscillation mode. Changes in chironomid composition in the Jämtland lake were concurrent with shifts in δ18Odiatom suggesting indirect responses to circulation changes. Changes in precipitation are suggested to be an important factor that may cause the spatially variable results among chironomid-based July air temperature reconstructions in Scandinavia.
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| 21. |
- Darracq, Amelie
(författare)
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Long-term development, modeling and management of nutrient loading to inland and coastal waters
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Environmental and water system protection and restoration require accurate knowledge and quantification of waterborne pollutant transport, retention-release and transformation processes taking place in the subsurface, river, lake and sea water systems, and at the interfaces between these systems. This thesis investigates the importance of spatial model resolution for such quantification and the possible long-term nutrient load development under different human perturbations and nutrient source management scenarios in the Swedish Norrström drainage basin, based on simulations with the GIS-based dynamic nutrient transport-attenuation model POLFLOW. The results indicate substantial nutrient load contributions from the subsurface water system (soil water and groundwater) to surface waters, which may largely control present and future nutrient mass loads from drainage basins to downstream inland and coastal waters. This role of the subsurface water system needs to be acknowledged, in conjunction with the effects of expected climate change and population and lifestyle developments, for achieving successful and sustained decreases in nutrient loading to inland and coastal waters. The results point also towards a need for downstream nutrient load control and abatement measures, to complement nutrient source reduction programs. The results further indicate the importance of the chosen spatial model resolution and account for subgrid variability for the accuracy of the necessary coupled transport and attenuation modeling of nutrient spreading in, and export from, river networks to coastal systems. Failure to correctly conceptualize and accurately account for the physical transport processes and their subgrid variability in this modeling may also yield systematic misinterpretation of the biogeochemical processes and process rates. Further, this may have important practical implications for the necessary abatement effectiveness and efficiency of nutrient and other waterborne pollutant loading to inland and coastal waters worldwide.
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| 22. |
- De Angelis, Hernán, 1974-
(författare)
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Palaeo-ice streams in the north-eastern Laurentide Ice Sheet
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a palaeoglaciological study aimed to determine the location, geometry and temporal evolution of palaeo-ice streams of the north-easternmost Laurentide Ice Sheet. The work was accomplished through the geomorphological interpretation of satellite imagery over 3.19 x 106 km2 of the Canadian Arctic, using a glaciological inversion scheme. Ice streams were active in this region during most of the time between the Last Glacial Maximum and the last deglaciation. A web of ice streams and inter-ice stream areas existed. Three major ice stream networks are identified: the M'Clintock Channel, Gulf of Boothia – Lancaster Sound and Hudson Strait. The M'Clintock Channel bears the most complex landform record, comprising three generations of palaeo-ice streams. Their location was weakly controlled by the subglacial topography and their geometry was determined by frozen-bed portions of the ice sheet, thus providing evidence for pure ice streams in the Laurentide Ice Sheet. In contrast, the more pronounced relief of the Gulf of Boothia – Lancaster Sound corridor supported topographically controlled ice streams. The landform record on emerged land along Hudson Strait is insufficient to support the existence of ice streams. It is therefore proposed that ice streams were constrained within the deep parts of the strait while flanked by cold-based zones on the margins. Small transient ice streams on Baffin and Prince of Wales islands drained local remnant ice caps during the collapse of the ice sheet. Analysis of the controls on the location and flow of palaeo-ice streams suggests that the interaction between the subglacial topography and thermal state of the substrate plays a more fundamental role than the geology. It is concluded that the behaviour of ice streams cannot be explained in terms of environmental controls alone, but the complex dynamics of ice stream shear margins and onset zones must be considered.
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| 23. |
- de Woul, Mattias, 1972-
(författare)
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Response of glaciers to climate change : Mass balance sensitivity, sea level rise and runoff
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this study is to enhance our understanding of the response of glaciers to climate change. Global sea level is affected by changes in glacier ice volume, and melt-water from glaciers is a principal water source in many regions. This study applies glacier mass balance modelling, with varying complexity and spatial resolution, ranging from individual glaciers to regional and global assessments of glacier mass losses. Glaciers located in maritime environments generally show considerably higher mass balance sensitivities than those in continental settings. On average, an assumed increase in annual precipitation of +10% tends to offset the effect of an annual temperature change of +1 K, by roughly 20%. Two case studies, at Storglaciären, Sweden, and Hofsjökull, Iceland, involve model results of future mass balance change and glacier melt induced changes in runoff. Applying a temperature and precipitation scenario for Iceland in 2050 results in increased total runoff from Hofsjökull by roughly one third, and results emphasize the role of the firn layer in delaying water flow through glaciers, yielding a redistribution of discharge within the year. Based on a global gridded data set of glacierized area, the sea level equivalent from all mountain glaciers and ice caps outside the ice sheets in Greenland and Antarctica during 1961–2004, caused by changes in temperature and precipitation, is estimated to be 0.58±0.34 mm a–1. The mountain glaciers and ice caps around Antarctica alone contribute almost 40% of the global estimate, and hence their contribution is considerably larger than previously assumed.
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| 24. |
- Ebert, Karin, 1976-
(författare)
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Cenozoic landscape evolution in northern Sweden : Geomorphological interpretation within a GIS-framework
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The large-scale bedrock landscape in northern Sweden has a complex evolution history of planation, uplift, transgression, burial, weathering, and erosion. The aim of this thesis is to examine the long-term development of the area. Terms for base-level surfaces in the area are defined. A combination of GIS-analyses of digital elevation models and field work is used to explore landform characteristics and formation. Inselbergs east of the northern Scandes in northern Sweden are used as a basis for describing landscape development. In total, 794 inselbergs are identified in the study area. The inselbergs are classified according to their degree of glacial erosion. The Parkajoki area, with low glacially modified inselbergs, tors, boulder fields and saprolites, has been shown to have largely escaped Quaternary glacial erosion and is taken as a type area to describe the late-Neogene landscape development prior to glaciation. The removal of Neogene saprolite mantles at the inselberg feet in areas of glacial erosion increased inselberg relief during the Quaternary by 10-20 m. For landscape evolution further back in time, beyond the Neogene, the hypsography of the study areas shows at least two palaeosurface generations in the northern Scandes and at least four palaeosurface generations on the inselberg plains. The distribution of inselbergs in relation to palaeosurface generations in the same elevation intervals suggests land uplift with a tilt towards the SE-ESE. Eocene marine diatom findings at 260 m a.s.l. in Finland, 200 km east of the study area, indicate a pre-Eocene age of the inselberg plains above this elevation. The development of today’s inselberg plains likely started in the late Mesozoic, with a sub-Mesozic etch surface that was subjected to land uplift at the late Mesozoic-Paleocene transition during breakup of the Atlantic. The great antiquity of the northern Swedish bedrock landscape stands as an analogy for shield areas in for example Australia and Africa.
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| 25. |
- Fu, Ping, 1982-
(författare)
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Paleoglaciology of Shaluli Shan, southeastern Tibetan Plateau
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Reconstructing the paleoglaciation of the Tibetan Plateau is critical to understanding linkages between regional climate changes and global climate changes. This work focuses on the paleoglaciology of the Shaluli Shan Mountain area in the southeastern Tibetan Plateau. Multiple approaches, including geomorphological mapping, field assessment, cosmogenic nuclide exposure dating, and numerical glacier modeling are employed to reconstruct the extent, timing, erosion patterns, basal thermal regime, and ice dynamic of past glaciation of the Shaluli Shan. Detailed geomorphological mapping and analysis provide evidence for multiple past glaciations involving valley glaciers and small ice fields in the high mountains and ice caps on low-relief plateaus at intermediate elevations. Ice cap glaciation on the low-relief Haizishan Plateau produced glacial landforms in a zonal pattern, suggesting that the Haizishan paleo-ice cap had a complex basal thermal regime. 10Be exposure ages for glacial erratics and till depth profiles constrain three major glaciations in the Shaluli Shan: pre global Last Glacial Maximum (gLGM) (with minimum ages at 102.3 ± 10.0 – 183.6 ± 17.0 ka), gLGM (21.6 ± 2.0 ka), and Late Glacial (13.0 ± 1.2 – 17.1 ± 1.6 ka) . Extensive glacier expansion in the Shaluli Shan during Marine Isotope Stage (MIS) 6 and gLGM, and the lack of evidence of glaciation during MIS 4 and 3, suggests that the extent and timing of glaciations in the southeastern Tibetan Plateau are synchronized with northern Hemisphere climate changes. The glacial erosion depth constraints based on 10Be and 26Al concentrations in bedrock, glacial erratics, and till depth profiles indicate a complex glacial erosion pattern during the gLGM and Late Glacial, consistent with the hypothesis of complex basal thermal regime of Haizishan paleo-ice cap. Numerical model simulations of a Haizishan ice cap also predict a complex basal thermal regime and indicate high sensitivity of the ice cap to past temperature.
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| 26. |
- Gessesse Dessie, , 1963-
(författare)
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Forest decline in South Central Ethiopia : Extent, history and process
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study presents the extent, history and process of forest decline in Awassa watershed, south central Ethiopia. By combining different data sources such as satellite images, social surveys and historical documents, forest decline is described quantitatively and qualitatively and the main causes behind this process are identified. Forest decline in the study area is interpreted as the result of a combination of socio-political changes, economic activities, population growth, cultural patterns and agricultural developments while local conflicts over resources also play an important role. The findings of this study reveal forest decline to be a continuous process associated with spatial fragmentation and location specific losses. The recent increase in production of the cash crop khat has made a significant impact on the forest through several mechanisms: it relocates the agricultural/forest frontier; it causes intrusion and permanent settlement within forests; and fragments remaining forest. The analysis of human-spatial boundaries indicates unsystematic management of the natural forests by several administrative units. As a result, multiple claims have been made on the forests simultaneously as weak control and accountability conditions have negatively affected forest management. The main conclusions are as follows: Forest decline in the study area has a long history, spanning at least one century. The causes are identifiable as both temporally spaced individual events as well as chains of events. These interact with each other at different levels and scales as well as with the geographical properties of the study area. Land users’ rationale in weighing the advantages between keeping and replacing the forest is affected by economic gain, market conditions and transport facilities. Multiple claims to the forest land and weak accountability contribute to inefficient management, which accelerates forest decline.
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| 27. |
- Goodfellow, Bradley W., 1971-
(författare)
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Relict non-glacial surfaces and autochthonous blockfields in the northern Swedish mountains
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Relict non-glacial surfaces occur in many formerly glaciated landscapes, where they represent areas that have escaped significant glacial modification. Frequently distinguished by blockfield mantles, relict non-glacial surfaces are important archives of long-term weathering and landscape evolution processes. The aim of this thesis is to examine the distribution, weathering, ages, and formation of relict non-glacial surfaces in the northern Swedish mountains. Mapping of surfaces from aerial photographs and analysis in a GIS revealed five types of relict non-glacial surfaces that reflect differences in surface process types or rates according to elevation, gradient, and bedrock lithology. Clast characteristics and fine matrix granulometry, chemistry, and mineralogy reveal minimal chemical weathering of the blockfields. Terrestrial cosmogenic nuclides were measured in quartz samples from two blockfield-mantled summits and a numerical ice sheet model was applied to account for periods of surface burial beneath ice sheets and nuclide production rate changes attributable to glacial isostasy. Total surface histories for each summit are almost certainly, but not unequivocally, confined to the Quaternary. Maximum modelled erosion rates are as low as 4.0 mm/kyr, which is likely to be near the low extreme for relict non-glacial surfaces in this landscape. The blockfields of the northern Swedish mountains are Quaternary features formed through subsurface physical weathering processes. While there is no need to appeal to Neogene chemical weathering to explain blockfield origins, these surfaces have remained continuously regolith-mantled and non-glacial since their inception. Polygenetic surface histories are therefore indicated, where the large-scale surface morphologies are potentially older than their regolith mantles.
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| 28. |
- Grudd, Håkan, 1958-
(författare)
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Tree Rings as Sensitive Proxies of Past Climate Change
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the boreal forests of the Northern Hemisphere, time series of tree-ring width (TRW) and maximum density in the latewood (MXD) are highly correlated to local instrumental summer-temperature data and are thus widely used as proxies in high-resolution climate reconstructions. Hence, much of our present knowledge about climatic variability in the last millennium is based on tree-rings. However, many tree-ring records have a lack of data in the most recent decades, which severely hampers our ability to place the recent temperature increase in a longer-timescale perspective of natural variability.The main objective of this thesis is to update and extend the Torneträsk TRW and MXD records in northern Sweden. Local instrumental climate-data is used to calibrate the new tree-ring records. The results show that TRW is mainly forced by temperature in the early growing season (June/July) while MXD has a wider response window (June – August) and has a higher correlation to temperature. Two reconstructions of summer temperature are made for (i) the last 7,400 years based on TRW, and (ii) the last 1,500 years based on a combination of TRW and MXD. The reconstructions show natural variability on timescales from years to several centuries. The 20th century does not stand out as a notably warm period in the long timescale perspective. A medieval period from AD 900 – 1100 is markedly warmer than the 20th century.The environmental impact from a large explosive volcanic eruption in 1628/1627 BC is analysed in the tree rings of 14C-dated bog pines in south-central Sweden and in absolutely-dated subfossil pines from Torneträsk. The results show evidence of an impact in the southern site at approximately this time but no detectable impact in the North. Subfossil trees of Fitzroya cupressoides in southern Chile were 14C-dated to approx. 50,000 years BP and amalgamated into a 1,229-year TRW chronology. This tree-ring record is the oldest in the world. The variability in this Last-glacial chronology is similar to the variability in present-day living trees of the same species. These results suggest that the growth–forcing mechanisms 50,000 years ago were similar to those at present.
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| 29. |
- Hannerz, Fredrik, 1977-
(författare)
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Making water information relevant on local to global scale – the role of Information Systems for Integrated Water Management
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Relevant information is essential for finding solutions in Integrated Water Management (IWM). Complex water systems and a need for increasing integration of sectors, actors and scales in IWM require new methods for developing and managing such information. This thesis investigates the role of information within the IWM process, as well as the main challenges for development of representative, accessibleand harmonized information. Results show how information needs and the information production process for IWM may be systematized, and indicate a large potential for information system development for IWM. However, in order to reach the full potential, today’s limited and heterogeneous water information needs to become more comprehensive, transparent, interoperable, dynamic, scalable and openly accessible. Large pressures on water systems are found in coastal catchment areas that are unmonitored across the local to the global scale, indicating a large importance of these areas for nutrient and pollutant loading. The globally accessible runoff data from catchment areas that are rich in pressures from population, agriculture and general economic activity further exhibit a rapidly declining trend during recent years. Major water system changes may therefore pass unnoticed if analyzed on the basis of openly accessible runoff global data. Furthermore, large discrepancies are found between land cover databases, which may result in major uncertainties in quantification of water and evapotranspiration flows. Identified information challenges may be relatively easily overcome by making better use of available information, while other challenges such as development of consistent baselines of core data and a possible re-prioritization of water-environmental monitoring programs may be both difficult and costly.
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| 30. |
- Heyman, Jakob, 1979-
(författare)
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Palaeoglaciology of the northeastern Tibetan Plateau
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study concerns the palaeoglaciation of the northeastern Tibetan Plateau, with emphasis on the Bayan Har Shan (Shan = Mountain) in the headwaters of Huang He (Yellow River). To reconstruct past glacier development multiple techniques, including remote sensing, field investigations, cosmogenic exposure dating, and numerical modelling have been employed. Analysis of the large-scale geomorphology indicates that glacial erosion has been dominant in the elevated mountain areas on the low-relief plateau, whereas fluvial erosion outpaces glacial erosion along the plateau margin. Landform and sediment records yield evidence for multiple local glaciations, restricted to the highest mountain areas, and a maximum glaciation beyond the mountain front. Absence of data supporting the former presence of proposed ice sheets, plateau-wide or regional, tentatively indicates that no ice sheet glaciation occurred on the northeastern Tibetan Plateau. Cosmogenic exposure dating of boulders, surface pebbles, and sediment sections in central Bayan Har Shan indicates that its record of past glaciations predates the global Last Glacial Maximum (LGM). Based on a world-wide analysis, yielding that wide age disparity within apparent exposure age datasets is most likely caused by post-glacial shielding processes, the Bayan Har Shan exposure ages constrain four periods of glaciation with minimum ages of 40-65 ka, 60-100 ka, 95-165 ka, and undetermined oldest stage. Similar to Bayan Har Shan, the plateau-wide distribution of boulders with pre-LGM exposure ages close to present-day glaciers shows that its LGM glaciers were generally not much larger than today. The results of a high resolution glacier model applied to nine regions across the plateau indicates that temperature depressions of 2-4 K are enough to expand glaciers beyond their global LGM extent, implying that during periods of Northern Hemisphere glaciation the Tibetan Plateau was not much colder than today or became exceedingly dry.
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| 31. |
- Hugelius, Gustaf, 1980-
(författare)
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Quantity and quality of soil organic matter in permafrost terrain
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High latitude terrestrial ecosystems are considered key components in the global carbon (C) cycle and hold large reservoirs of soil organic carbon (SOC). Much of this is stored as soil organic matter (SOM) in permafrost soils and peat deposits and is vulnerable to remobilization under future global warming. While the large size and potential vulnerability of arctic SOM reservoirs is recognized, detailed knowledge on its landscape partitioning and quality is poor. This thesis describes total storage, landscape partitioning and lability of SOM stored in permafrost areas of Canada and Russia. Detailed studies of SOC partitioning highlight the importance of especially permafrost peatlands, but also of O-horizons in moist tundra soils and cryoturbated soil horizons. A general characterization of SOM in an area of discontinuous permafrost shows that >70% of the SOC in the landscape is stored in SOM with a low degree of decomposition. Projections of permafrost thaw predict that the amount of SOC stored in the active layer of permafrost soils in this area could double by the end of this century. A lateral expansion of current thermokarst lakes by 30 m would expose comparable amounts of SOC to degradation. The results from this thesis have demonstrated the value of high-resolution studies of SOC storage. It is found that peat plateaus, common in the sporadic and discontinuous permafrost zones, store large quantities of labile SOM and may be highly susceptible to permafrost degradation, especially thermokarst, under future climate warming. Large quantities of labile SOM is also stored in cryoturbated soil horizons which may be affected by active layer warming and deepening. The current upscaling methodology is statistically evaluated and recommendations are given for the design of future studies. To accurately predict responses of periglacial C pools to a warming climate detailed studies of SOC storage and partitioning in different periglacial landscapes are needed.
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| 32. |
- Hättestrand, Martina, 1968-
(författare)
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Vegetation and climate during Weichselian ice free intervals in northern Sweden : Interpretations from fossil and modern pollen records
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis the Weichselian history of northern Sweden is investigated, with emphasis on vegetation and climate during ice-free intervals. The main method used has been pollen analysis of sediments from pre-Late Weichselian landforms. To interpret fossil pollen assemblages, comparisons with modern pollen spectra were made. Modern pollen data were retrieved through monitoring of annual pollen deposition at seven sites in northern Sweden, from the boreal forest to above the present forest-line of birch. Eight years of pollen monitoring is described and put in a larger context through comparison with monitoring data from Iceland, Svalbard, Norway and Finland. A study of sediment cores from the Riipiharju esker shows evidence of two ice free phases during the Weichselian glacial; Tärendö I and Tärendö II. The Tärendö II ice free interval includes large climatic shifts, previously not recognized, from relatively warm conditions with Betula as the dominating pollen taxon to cold conditions with dominance of Artemisia and Gramineae and back to warmer conditions again. Correlation alternatives of the north Swedish ice free intervals Tärendö I and II are: 1/ Brörup (MIS 5c; c. 105-93 ka BP) and Odderade (MIS 5a; c. 85-74 ka BP), respectively, or 2/ Odderade and early Middle Weichselian time (MIS 3; c. 59-40 ka BP). Of these, alternative 2 is regarded as the most likely. Interstadial sediments deposited in a Veiki moraine plateau during downwasting of a pre-Late Weichselian ice sheet include only Betula dominant pollen spectra, showing that the climate during formation of the Veiki moraine was relatively warm. According to stratigraphical correlation there are three possible alternatives for Veiki moraine formation. Either it was formed during 1/ early Tärendö I, 2/ early Tärendö II, or 3/ late Tärendö II. Alternative 3 implies growth of an intermediate ice sheet reaching the eastern limit of Veiki moraine distribution during the cold phase of Tärendö II.
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| 33. |
- Ingvander, Susanne, 1979-
(författare)
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Snow particle size investigations using digital image analysis - implications for ground observations and remote sensing of snow
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the past century climate warming has caused rapid changes in the Cryosphere. This has increased the need to accurately monitor rates of change in snow and ice in remote or sparsely populated areas where environmental observing capacity is limited. Monitoring snow cover requires understanding of the snow pack and the snow surface attributes. Snow particle size is an important parameter for characterization of snow pack properties. The size and shape of the snow particles affects the snow/air-ratio which in turn affect how energy is reflected on the snow surface. This governs the snow pack energy balance by changing the albedo or backscattering properties of the snow. Both the albedo and the snow particle size can be quantified by remote sensing. However, the snow particle size estimated by remote sensing, also called the optically equivalent particle size, represents only an approximation of the true or physical particle size of snow. Thus, there is demand for methods that relate both parameters and help to improve the interpretation of remote sensing data of snow at higher spatial and temporal scales. To address this demand the aim of this dissertation thesis is to improve existing sampling methods of the physical snow particle size to retrieve high-resolution, spatial and temporal data sets for validation of remote sensing data. A field sampling method based on object-oriented analysis of digital images was developed that allows measurements of various snow particle size parameters such as length, width, area, specific surface area and shape. The method generates a continuous snow particle size distribution that supports the detailed statistical characterization of a large number of samples. The results show its possibility to compare data from different existing methods. The sampling method was applied in field sites in Antarctica and in northern Sweden, to characterize the spatial variability in the physical snow particle size and to estimate correlations between various remote sensing products and the observed physical snow particle size. The results of the presented studies show that more detailed measurements of snow particle size in the field at higher temporal and spatial scales can improve the interpretation of active and passive satellite retrieved data.
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| 34. |
- Johansson, A. Malin
(författare)
-
Remote sensing of supra-glacial lakes on the west Greenland Ice Sheet
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Greenland Ice Sheet is the largest ice sheet in the northern hemisphere. Ongoing melting of the ice sheet, resulting in increased mass loss relative to the longer term trend, has raised concerns about the stability of the ice sheet. Melt water generated at the surface is temporarily stored in supra-glacial lakes on the ice sheet. Connections between melt water generation, storage and ice sheet dynamics highlight the importance of the surface hydrological system.In this thesis different methods are used that improve our ability to observe the supra-glacial lake system on the west Greenland Ice Sheet. This region of the Greenland Ice Sheet has the most extensive supra-glacial hydrological system with a dense network of streams connecting lakes that can exceed several square kilometres in area. Synthetic Aperture Radar (SAR) and visible-near infrared (VNIR) images are used to explore the potential of different sensor systems for regular observations of the supra-glacial lakes. SAR imagery is found to be a useful complement to VNIR data. VNIR data from moderate resolution sensors are preferred as these provide high temporal resolution data, ameliorating problems with cloud cover.The dynamic nature of the lakes makes automated classification difficult and manual mapping has been widely used. Here a new method is proposed that improves on existing methods by automating the identification and classification of lakes, and by introducing a flexible system that can capture the full range of lake forms. Applying our new method we are better able to analyse the evolution of lakes over a number of melt seasons. We find that lakes initiate after approximately 40 positive degree days. Most lakes exist for less than 20 days before draining, or later in the season, and less often, freezing over. Using the automated method developed in this thesis lakes have been mapped in imagery from 2001–2010 at approximately five day intervals.
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| 35. |
- Johnsen, Timothy, 1971-
(författare)
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Late Quaternary ice sheet history and dynamics in central and southern Scandinavia
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent work suggests an emerging new paradigm for the Scandinavian ice sheet (SIS); one of a dynamically fluctuating ice sheet. This doctoral research project explicitly examines the history and dynamics of the SIS at four sites within Sweden and Norway, and provides results covering different time periods of glacial history. Two relatively new dating techniques are used to constrain the ice sheet history: the optically stimulated luminescence (OSL) dating technique and the terrestrial cosmogenic nuclide (TCN) exposure dating technique. OSL dating of interstadial sediments in central Sweden and central Norway indicate ice-free conditions during times when it was previously inferred the sites were occupied by the SIS. Specifically, the SIS was absent or restricted to the mountains for at least part of Marine Isotope Stage 3 around 52 to 36 kyr ago. Inland portions of Norway were ice-free during part of the Last Glacial Maximum around 25 to 20 kyr ago. Consistent TCN exposure ages of boulders from the Vimmerby moraine in southern Sweden, and their compatibility with previous estimates for the timing of deglaciation based on radiocarbon dating and varve chronology, indicate that the southern margin of the SIS was at the Vimmerby moraine ~14 kyr ago. In central Sweden, consistent TCN ages for boulders on the summit of Mt. Åreskutan and for the earlier deglaciated highest elevation moraine related to the SIS in Sweden agree with previous estimates for the timing of deglaciation around 10 ka ago. These results indicate rapid decay of the SIS during deglaciation. Unusually old radiocarbon ages of tree remains previously studied from Mt. Åreskutan are rejected on the basis of incompatibility with consistent TCN ages for deglaciation, and incompatibility with established paleoecological and paleoglaciological reconstructions. Altogether this research conducted in different areas, covering different time periods, and using comparative geochronological methods demonstrates that the SIS was highly dynamic and sensitive to environmental change.
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| 36. |
- Jonsell, Ulf, 1974-
(författare)
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Sulfur in polar ice and snow : Interpretations of past atmosphere and climate through glacial archives
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Snow contains information on the atmosphere it is deposited from. This information is stored in polar ice sheets (Antarctica and Greenland), which are unique geochronological archives of past climate and atmospheric composition. On time scales from annual to glacial cycles, this thesis deals with the signals of sulfur compounds in these archives. The objectives are to interpret the content and origin of sulfur aerosols in the atmosphere and their interactions with climate. By using sulfur isotopic signals, the sources of sulfate were apportioned from two shallow Antarctic ice cores covering the last 1200 years of deposition. Marine phytoplankton was shown to be the predominant source. A surprisingly stable sulfate flux signal over the last eight glacial cycles was obtained from the Antarctic EPICA Dome C ice core, which with a predominant marine biogenic sulfate origin implies that production of sulfur aerosols by phytoplankton neither forced nor was sensitive to glacial/interglacial shifts in climate. Methanesulfonate (MS-) originates solely from phytoplankton, but the record in Antarctic ice cores is biased by variations in atmospheric dust concentrations. In contrast to Antarctic conditions, enhanced dust concentrations on Greenland increase the deposition of sulfate but do not affect MS-. Thus, MS- remains in Greenlandic ice cores as a potential proxy record of marine biogenic sulfur aerosol production. Northern and central Greenland ice core signals of MS- displayed systematically different responses to climate variations during the last glacial period, possibly due to different portioning of air mass origin. Surface snow analyses indicate that sulfate on Greenland is at present mainly deposited as a salt in association with dust particles. On an Antarctic site where sulfate and possibly MS- are present as acids, their concentrations in the surface snow are suggested to be a result of a redeposition process altering the signals of the original snow fall.
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| 37. |
- Jonsson, Christina E., 1965-
(författare)
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Holocene climate and atmospheric circulation changes in northern Fennoscandia : Interpretations from lacustrine oxygen isotope records
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates how variations in the oxygen isotopic composition of lake waters in northern Fennoscandia are recorded in lake sediment archives, especially diatoms, and how these variations can be used to infer past changes in climate and atmospheric circulation. Results from analyses of the oxygen isotopic composition of lake water samples (δ18Olakew) collected between 2001 and 2006 show that δ18O of northern Fennoscandian lakes is mainly controlled by the isotopic composition of the precipitation (δ18Op). Changes in local δ18Op depend on variations in ambient air temperature and changes in atmospheric circulation that lead to changes in moisture source, vapour transport efficiency, or winter to summer precipitation distribution. This study demonstrates that the amount of isotopic variation in lake water δ18O is determined by a combination of the original δ18Olakew, the amount and timing of the snowmelt, the amount of seasonally specific precipitation and groundwater, any evaporation effects, and lake water residence time. The fact that the same isotope shifts have been detected in various δ18Olakew proxies, derived from hydrologically different lakes, suggests that these records reflect regional atmospheric circulation changes. The results indicate that diatom biogenic silica isotope (δ18Odiatom) records can provide important information about changes in atmospheric circulation that can help explain temperature and precipitation changes during the Holocene. The reconstructed long-term Holocene decreasing δ18Op trend was likely forced by a shift from strong zonal westerly airflow (relatively high δ18Op) in the early Holocene to a more meridional flow pattern (relatively low δ18Op). The large δ18Olakew depletion recorded in the δ18O records around ca. 500 cal yr BP (AD 1450) may be due to a shift to more intense meridional airflow over northern Fennoscandia resulting in an increasing proportion of winter precipitation from the north or southeast. This climate shift probably marks the onset of the so-called Little Ice Age in this region.
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| 38. |
- Kaislahti Tillman, Päivi, 1958-
(författare)
-
Holocene climate and environmental change in high latitudes as recorded by stable isotopes in peat deposits
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, stable carbon and oxygen isotopes in α-cellulose isolated from Sphagnum fuscum moss remains were used as climate proxies. The main focus was to implement the methods in records from high latitude peatlands in the Northern Hemisphere (west-central Canada and north-eastern European Russia), reconstruct palaeoclimate of the studied regions during the Holocene, and evaluate the compatibility of results with other proxy records, especially tree-ring isotope time-series. The variation of stable carbon and oxygen isotope ratios (δ13C, δ18O) in different moss plant components was investigated and differences between untreated plants and α-cellulose extracts were evaluated. The impact of peat decay on the stable isotope proxies was studied by colorimetric and chemical (C/N) methods. Temperature reconstructions were developed based on the statistically significant relationship between δ13C and modern summer temperature records. Wet/dry periods were derived from a combination of δ18O records, macrofossil analysis, and a peat humification record in west-central Canada. A tentative reconstruction of snow depth in north-eastern European Russian tundra and northern taiga was based on δ18O records. The most promising result of the thesis is that stable carbon isotope variability in α-cellulose isolated from Sphagnum fuscum stems can be used to reconstruct and quantify palaeotemperatures several millennia back in time and to reveal both long-term and rapid climate shifts from peat archives.
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| 39. |
- Klintenberg, Patrik
(författare)
-
More Water, Less Grass? : An assessment of resource degradation and stakeholders’ perceptions of environmental change in Ombuga Grassland, Northern Namibia
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objectives of this thesis are to assess: to what degree have natural resources deteriorated in a grazing area in northern Namibia, how do perceptions of environmental change held by local stakeholders there, correspond to scientific assessments, and how do these relate to national estimates? Analysis of the process of developing national indicators for monitoring of land degradation concluded that specific indicators should be developed on national level, and in some instances even on local level as there are no universal causes of land degradation. According to farmers overgrazing and low rainfall since the early 1990s cause negative environmental changes in the study area, partly confirming findings from national monitoring. Results also suggest that: less grazing outside the study area, improved access, permanent water supply, and fencing of large areas, also contributed. Results show that improved water supply was the most important factor. Investigation of the influence of permanent water points on grazing resources showed that perennial grasses are replaced by less palatable annual grasses as far as 6 km from water points along a water pipeline. No significant grazing induced changes in grass composition were observed around privately owned wells. Private ownership seems to be a key factor preventing over-utilization of grazing resources around the latter. A remote sensing study using Landsat TM imagery identified bare ground, saltpans and grassland with a fair accuracy. Separation of woodland from shrubland and shrubland from grassland was less accurate using supervised classification. The results show that the soil adjusted vegetation index provides valuable information about variations of green biomass over time in semi-arid environments. However, it is suggested that satellite based investigations should be supported by thorough ground based assessment due to the influence of underlying soil in this environment.
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| 40. |
- Lind, Ewa, 1968-
(författare)
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Tephra horizons in the North Atlantic region during the Early Holocene
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Uncertainties about the rate and magnitude of future climate change have drawn attention to the climate variability following the Late Glacial-Early Holocene transition, c. 12-8 ka BP. Tephrochronology is a method that uses volcanic ash as isochrons in order to link, date and synchronise geological and palaeoclimatic records which could provide a better understanding of short rapid climate shifts but also the timing of these.The main purpose of this thesis was to improve and refine the Late Younger Dryas-Early Holocene (c. 12-8 ka BP) tephrochronological framework with focus on dating and identification of new and previously known tephra horizons in the North Atlantic region. A special emphasis was to identify tephra horizons contemporary to short rapid climate events that occurred during the period; the Preboreal Oscillation (c. 11.3 ka BP), the Erdalen events (c. 10.0-9.8 ka BP), the 9.3 ka BP and the 8.2 ka BP events. Additional purposes have been to evaluate the potential of XRF ITRAX core-scanning to identify tephra in lake sediments but also as a tool in palaeoclimate studies.The potential of tephrochronology for linking climate archives across the North Atlantic region is a main outcome in this thesis. Specific results include five new tephra horizons; four identified on the Faroe Islands and one in Central Norway. Two previously known tephras, the Hässeldalen and Askja-S tephras, were identified on the Faroe Islands for the first time and at new locations in Sweden which confirmed their widespread distribution in NW Europe. Several of these tephras have the potential to become marker horizons for some of the short rapid climate events which occurred during the Late Younger Dryas-Early Holocene but their importance is yet to be determined. Further results show that the XRF core scanner can be used successfully to identify high concentrations of basaltic tephra but also to identify palaeoclimatic events in lake sediments.
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| 41. |
- Margold, Martin, 1981-
(författare)
-
Retreat pattern and dynamics of glaciers and ice sheets: reconstructions based on meltwater features
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glaciers and ice sheets covered extensive areas in the Northern Hemisphere during the last glacial period. Subsequently to the Last Glacial Maximum (LGM), they retreated rapidly and, except for Greenland and some other ice caps and glaciers, they vanished after the last glacial termination. This thesis examines the dynamics of deglacial environments by analysing the glacial geomorphological record with focus on the landforms created by glacial meltwater. The aims are (i) to evaluate the data available for mapping glacial meltwater features at the regional scale, and (ii) to demonstrate the potential of such features for regional ice retreat reconstructions in high-relief landscapes. Meltwater landforms such as ice-marginal meltwater channels, eskers, deltas and fossil glacial lake shorelines are used to infer former ice surface slope directions and successive positions of retreating ice margins. Evaluated high-resolution satellite imagery and digital elevation models reveal their potential to replace aerial photographs as the primary data for mapping glacial meltwater landforms. Following a methods study, reconstructions of the deglacial dynamics are carried out for central Transbaikalia, Siberia, Russia, and for the Cordilleran Ice Sheet (CIS) in central British Columbia, Canada, using regional geomorphological mapping surveys. Mapped glacial landforms in central Transbaikalia show evidence of a significant glaciation that possibly extended beyond the high mountain areas. Large glacial lakes were formed as advancing glaciers blocked rivers, and of these, Glacial Lake Vitim was the most prominent. Deglacial dynamics of the CIS reveals that the ice divide shifted to the Coast Mountains in north-central British Columbia and the eastern ice margin retreated towards the ice divide in late glacial time. This thesis demonstrates the potential to reconstruct ice retreat patterns and deglacial dynamics at regional scales by interpretation of the meltwater landform record.
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| 42. |
- Mazi, Aikaterini, 1969-
(författare)
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Seawater intrusion risks and controls for safe use of coastal groundwater under multiple change pressures
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the era of intense pressures on water resources, the loss of groundwater by increased seawater intrusion (SWI), driven by climate, sea level and landscape changes, may be critical for many people living in commonly populous coastal regions. Analytical solutions have been derived here for interface flow in coastal aquifers, which allow for simple quantification of SWI under extended conditions from previously available such solutions and are suitable for first-order regional vulnerability assessment and mapping of the implications of climate- and landscape-driven change scenarios and related comparisons across various coastal world regions. Specifically, the derived solutions can account for the hydraulically significant aquifer bed slope in quantifying the toe location of a fresh-seawater sharp interface in the present assessments of vulnerability and safe exploitation of regional coastal groundwater. Results show high nonlinearity of SWI responses to hydro-climatic and groundwater pumping changes on the landside and sea level rise on the marine side, implying thresholds, or tipping points, which, if crossed, may lead abruptly to major SWI of the aquifer. Critical limits of coastal groundwater change and exploitation have been identified and quantified in direct relation to prevailing local-regional conditions and stresses, defining a safe operating space for the human use of coastal groundwater. Generally, to control SWI, coastal aquifer management should focus on adequate fresh groundwater discharge to the sea, rather than on maintaining a certain hydraulic head at some aquifer location. First-order vulnerability assessments for regional Mediterranean aquifers of the Nile Delta Aquifer, the Israel Coastal Aquifer and the Cyprus Akrotiri Aquifer show that in particular the first is seriously threatened by advancing seawater. Safe operating spaces determined for the latter two show that the current pumping schemes are not sustainable under declining recharge.
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| 43. |
- Mård Karlsson, Johanna, 1979-
(författare)
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Arctic Water System Change and its Interactions with Permafrost and Ecosystem Changes
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate change and various changes in the landscape itself, such as permafrost thaw, may trigger and mediate substantial changes in the inland water system of the Arctic. Many climate change responses in the Arctic landscape and ecosystems are then related to alterations in the hydrological system. The nature of all these change interactions is not well understood. This thesis aims to improve our understanding of changes in the Arctic inland water system and their interactions with permafrost and ecosystem changes. Investigation of the spatial coverage of systematic hydrological monitoring data and observation data for hydro-climatically related ecosystem shifts, such as large-scale lake-area change, shows that this overlap is small. Yet some monitoring hotspot areas exist, where such data overlap and can be used to improve our understanding of linked hydrological, permafrost and ecosystem changes in the Arctic under climate change. Analysis of lake-change patterns in such hotspot areas indicates permafrost thaw as a main change driver/mediator of some change patterns. However, clear indication of basin-wide influence of permafrost thaw on hydrological discharge dynamics was only found in two relatively small out of total six investigated permafrost basins of different scales. Further, both permafrost and non-permafrost basins exhibit large-scale lake-area changes. A salient change pattern emerging across all investigated basins is an opposite direction of runoff change to that of precipitation change. This contrast is explainable by apparent evapotranspiration changes that may be due to observed changes in surface water (lake) area and associated water-storage changes. Patches of local lake-area change can thus add up to considerable large-scale effects on evapotranspiration and runoff changes. Overall, this thesis shows that linking water system change to permafrost and ecosystem changes is essential for advancing our understanding of Arctic environmental change.
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| 44. |
- Norström, Elin, 1972-
(författare)
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Late Quaternary climate and environmental change in the summer rainfall region of South Africa : A study using trees and wetland peat cores as natural archives
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contributes with information on past climate and environmental changes in South Africa’s summer rainfall region. The study is based on multi-proxy analyses on wetland peat cores and analyses of stable isotope composition (δ13C, δ18O) and wood anatomy in cross sections from subtropical trees (Breonadia salicina). The peat archive covers the last 16 ka (ka; 1000 cal yrs BP) and was analysed in terms of fossil pollen, charcoal, diatoms, phytoliths and stable isotope composition. The peat record infers relatively wet climate conditions at c. 13.7-12.8 ka, 10.5-9.5 ka and 2.5-0.5 ka, and drier conditions at c. 16-13.7 ka, 12.8-10.5 ka and during mid-Holocene. Tentatively, cooler late Pleistocene temperatures shifted towards warmer after c. 9.5 ka. The study of B. salicina demonstrates the paleo-climatic value of subtropical trees despite absence of annual tree rings. An age model was constructed from radiocarbon dating and calibration by wiggle matching. δ13C in B. salicina shows a co-variation with annual rainfall amounts, suggesting that it may be considered a regional climate-proxy. δ18O is mainly influenced by local factors, but acts as a useful complement when interpreting δ13C. Together with other regional, high-resolution records, the 600 year long δ13C-record suggests dry climate conditions in northern South Africa during the 1700s and mid-1500s AD. Inferred climate and environmental changes are suggested being a response to expansion, contraction and latitudinal shifts of the tropical, subtropical and mid-latitude atmospheric circulation cells. An observed inverse humidity pattern between southern and equatorial Africa suggests that ENSO-like teleconnections may be a possible forcing mechanism in a decadal to centennial time perspective.
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| 45. |
- Olli, Gull, 1935-
(författare)
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Waterborne sediment and pollutant transport into lakes and accumulation in lake sediments
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The general objective of this thesis is to contribute to the knowledge of the transport of sediments and pollutants from catchments to downstream water recipient systems and their accumulation in these systems, such as lakes and lake sediments. One part of the thesis studies the importance of drainage reach morphology and water flow for the phosphorous (P) transport and retention in the reaches, and the main controlling processes of the P retention in the reach sediments. The second part of the thesis investigates and describes the environmental history of sediment, P and metal transport into and accumulation in the sediments of bay Karlskärsviken, a typical near-shore zone in Lake Mälaren, west of Stockholm, Sweden. The thesis generally shows that the investigated P and metal loads (except for lead) into the near-shore zones of Lake Mälaren have increased over the last 30-40 years and, in spite of environmental regulation, not yet started to decrease. The thesis further shows that the P retention rate in drainage reaches depends on the reach depth and water flow, where shallow reaches retain P faster than deeper ones. A decrease of reach depth and/or water flow, e.g., by allowing ditches to meander and/or become overgrown with vegetation, may therefore decrease the P and possibly also other nutrient and pollutant loading into the recipient waters.
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| 46. |
- Persson, Klas, 1979-
(författare)
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Quantifying pollutant spreading and the risk of water pollution in hydrological catchments : A solute travel time-based scenario approach
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research presented in the thesis develops an approach for the estimation and mapping of pollutant spreading in catchments and the associated uncertainty and risk of pollution. The first step in the approach is the quantification and mapping of statistical and geographical distributions of advective solute travel times from pollutant input locations to downstream recipients. In the second step the travel time distributions are used to quantify and map the spreading of specific pollutants and the related risk of water pollution. In both steps, random variability of transport properties and processes is accounted for within a probabilistic framework, while different scenarios are used to account for statistically unquantifiable uncertainty about system characteristics, processes and future developments. This scenario approach enables a transparent analysis of uncertainty effects that is relatively easy to interpret. It also helps identify conservative assumptions and pollutant situations for which further investigations are most needed in order to reduce the uncertainty. The results for different investigated scenarios can further be used to assess the total risk to exceed given water quality standards downstream of pollutant sources. Specific thesis results show that underestimation of pollutant transport variability, and in particular of those transport pathways with much shorter than average travel times, may lead to substantial underestimation of pollutant spreading in catchment areas. By contrast, variations in pollutant attenuation rate generally lead to lower estimated spreading than do constant attenuation conditions. A scenario of constant attenuation rate and high travel time variability, with a large fraction of relatively short travel times, therefore appears to be a reasonable conservative scenario to use when information is lacking for more precise determination of actual transport and attenuation conditions.
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| 47. |
- Ryner, Maria, 1967-
(författare)
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Past environmental and climate changes in northern Tanzania : Vegetation and lake level variability in Empakaai Crater
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents palaeoenvironmental data from equatorial Africa covering two important time intervals; i) the warming period forming the Pleistocene/Holocene transition and ii) the last millennium. The Empakaai Crater, in northern Tanzania contains a lake from where sediment cores, spanning two time-slices 14.8-9.3 ka and 800-2000 AD, have been studied. Palaeoecological and palaeohydrological reconstruction is based on a multitude of proxies from the sediments, representing both catchment environment and the lakes aquatic ecosystem response. Between 14.8 and 10 ka the catchment vegetation and lake hydrology responded to both regional climate changes and local environment, but with different amplitude and frequency, reflecting temporal and spatial lags between the two systems. However, at c 10 ka both lake conditions and catchment vegetation showed drastic changes towards drier conditions. The record covering the last millennium reveals environmental changes related to climate and human activities. The catchment’s vegetation was affected by frequent fires, most probably human induced, while near shore vegetation responded to lake level fluctuation associated with rainfall variability. About 15 km from Empakaai Crater is an extensive abandoned irrigation system, the Engaruka complex, which was in active use between c 1400 AD and 1840 AD. By comparing a number of social and environmental factors potentially influencing the societal development at Engaruka it is shown that wet climate conditions have had positive effects on the societal development but also that dry climate conditions were not always disastrous to the society. The resemblance of the pollen taxa present is strong between the two time slices and pollen representing catchment conditions respond in similar manner in both records. The lake conditions are however very different between the two periods Thus the lake responds to both long and short term changes of variable amplitude, while the catchment vegetation seems to responds to high amplitude, low frequency changes.
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| 48. |
- Sannel, A. Britta K., 1968-
(författare)
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Temporal and spatial dynamics in subarctic peat plateaus and thermokarst lakes
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Permafrost peatlands are widespread at high northern latitudes and are important soil organic carbon reservoirs. A future warming in these areas, as suggested by global climate models, can cause thawing and increased ground subsidence (thermokarst), resulting in changes in surface hydrology and ecosystem functioning. The aim of this thesis is to increase our knowledge of temporal and spatial dynamics in subarctic peat plateaus with interspersed thermokarst lakes in order to better understand how these ecosystems respond to climate change. Detailed plant macrofossil and carbon/nitrogen ratio analyses of two peat plateaus located in the continuous and northern discontinuous permafrost zones in west-central Canada show that permafrost conditions have been stable since permafrost developed around 5600–4500 cal yr BP. Peat plateaus act as carbon sinks over time. The lack of wet phases since the plateaus formed, despite several local fires, suggests that this type of peatlands have been negligible as methane sources throughout most of their history, representing a negative net radiative forcing on climate. Thermokarst lakes are common features in peat plateaus across the northern permafrost region. A time-series analysis of aerial photographs and high resolution satellite images in three peat plateau/thermokarst lake complexes along a climatic and permafrost gradient shows that where the mean annual air temperature (MAAT) is below -5ºC and ground temperatures are -2ºC or colder, only minor changes in thermokarst lake extent have occurred from the mid 1970s until the mid 2000s. During the same time interval extensive lake drainage and new lake formation has taken place where the MAAT is ca -3ºC and the ground temperature is close to 0ºC. In a future progressively warmer and wetter climate, permafrost degradation can cause significant impacts on landscape pattern and greenhouse gas exchange also in the vast peat plateaus presently experiencing stable permafrost conditions.
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| 49. |
- Shibuo, Yoshihiro, 1976-
(författare)
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Modelling water and solute flows at land-sea and land-atmosphere interfaces under data limitations
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water and vapour flows from land to sea and the atmosphere are important for water resources, coastal ecosystems and climate. This thesis investigates possible methods for modelling these flows under often encountered unmonitored hydrological conditions and data limitations. Two contrasting types of drainage basin and associated data limitation/availability cases are considered: the Swedish unmonitored near-coastal catchment areas Forsmark and Simpevarp, for which detailed spatial but not much temporal variability data is available; and the much larger Aral Sea Drainage Basin (ASDB), for which spatial hydrological information is limited, while there is relatively well-known temporal change occurring in the Aral Sea itself and in the land and water use of the region over the last 50 years.The hydrologic modelling for the Forsmark and Simpevarp catchment areas showed that the relatively large focused stream flows, and the mean values and total sums of the diffuse small stream-groundwater flow fields in between the large stream flows from land to sea are largely constrained by the catchment hydrological balances and relatively robust and certain to estimate. The ASDB hydrologic modelling indicated an evapotranspiration return flow to the atmosphere from the irrigation water input on irrigated land that is much higher than previous estimates in atmospheric modelling, implying possible considerably larger than previously estimated non-local water and climate effects of the world’s irrigated areas. The more detailed groundwater-seawater dynamics modelling carried out for the coastal parts of the ASDB showed that regional topography and bathymetry largely influence coastal water fluxes during sea level lowering, with the Aral Sea shrinkage decreasing the seawater intrusion risk into the coastal groundwater considerably more for steeper than for flatter coastal topography parts of the region.
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| 50. |
- Sundqvist, Hanna S., 1972-
(författare)
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Speleothems as environmental recorders : A study of Holocene speleothems and their growth environments in Sweden
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main aim of this thesis was to contribute with detailed information of regional environmental change during the Holocene through studies of speleothems and their growth environments from two caves, Korallgrottan and Labyrintgrottan in northwestern Sweden, and a cellar vault in Uppsala. This was done through studies of stable isotopes and luminescence properties in the speleothems in combination with a detailed monitoring study in Korallgrottan.The monitoring study suggests that stalagmites fed by stalactites with slow and stable drip rates from deep inside the cave may be suitable as palaeoclimate archives. Similarities between oxygen isotope signals of contemporary samples from Labyrintgrottan and Korallgrottan emphasize the potential of speleothems from Labyrintgrottan to also provide high resolution regional palaeoclimate information.Except for a number of cold events stalagmite δ18O records from northern Scandinavia indicate that temperatures were warmer than today between 9500 and 6000 years ago. During this period the interval between 7800 and 6000 years ago seems to have been the warmest. The area above Labyrintgrottan was most likely covered by much denser vegetation than today at the time of stalagmite growth (9500-7500 years ago) and was, unlike today, probably situated below the local tree-limit between 9000 and 8000 years ago. The δ18O record of a stalagmite from Korallgrottan covering the last 4000 years agrees with the concept of a warmer period, the so called Medieval Warm Period, centred around AD1000 and a colder period, the so called Little Ice Age, somewhere between AD1000 and today.Studies of luminescence properties in fast growing speleothems from Uppsala indicate that the variations in luminescence intensity are annual and that the annual lamiae of the luminescent record represent a flush of organic material.
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