| 1. |
- Fischer, Sandra
(författare)
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Waterborne pollution from mining in cold climates : Potential catchment-scale immobilization of substances by microbial sulfate reduction (MSR)
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Waterborne pollution from mining is impacting groundwater and surface water resources in many regions of the world. Main problems include acidification and high levels of dissolved toxic metals that adversely affect humans and ecosystems. Over the past millennium, mineral extraction has left behind vast amounts of waste rock, tailings and exposed rocks across landscapes that, in contact with air and water, risk generating acid mine drainage (AMD). In comparison with large-scale mining sites, the impacts of the numerous abandoned small-scale mines have received limited attention in the scientific literature, in particular in the Arctic region. Furthermore, whereas the immobilization and retardation of toxic substances through sorption and (chemical) precipitation have been relatively well investigated, less is known about the potential impact of microbial processes on the large-scale transport and retardation of AMD. Main objectives of this thesis are to improve the understanding of contributions from abandoned small mines to the waterborne mining pollution, and to determine how the spreading of AMD via ground- and surface water may be mitigated on catchment scales by microbial sulfate reduction (MSR), which is a process that transforms sulfate into sulfide and facilitates metal precipitation from the aqueous solution. Multiple field measurement campaigns were conducted in Arctic Fennoscandia to evaluate the water quality downstream of mining sites, and a data-driven sulfur isotopic fractionation and mixing scheme was developed to quantify field-scale MSR. Results showed that small abandoned mines could contribute disproportionately to downstream water pollution, as compared with larger mines. Copper mass flows in a stream passing the abandoned Nautanen mines (northern Sweden) was for instance found to be 450 kg/year one century after mine closure. Furthermore, across five study areas (both mining-impacted and reference catchments) spanning geographically from southern Sweden to the Kola Peninsula (Russia), MSR was quantified as the percent reduction in sulfate concentration, showing within-catchment MSR magnitudes of 0 to 79%, between-catchment magnitudes of 2 to 28%, and a catchment-average of 13%. The overall magnitude of catchment-scale MSR was found to correspond relatively well with the presence of landscape elements that provided favorable conditions for sulfate-reducing microorganisms (SRM), such as forest providing organic material and wetland/lakes providing anoxic conditions which are both needed for the SRM. MSR has previously been neglected in freshwater systems due to assumed unsuitable conditions, however the results from this thesis have shown, for the first time, that MSR can in fact be wide-spread across landscapes. This opens the possibility of utilizing MSR as a nature-based solution for AMD by further enhancing favorable conditions for SRM. Moreover, MSR has not been accounted for in quantifications of large-scale pyrite weathering, which in presence of wide-spread MSR may be underestimated. This can have consequences for the global sulfur cycle as well as the carbon cycle, e.g., since pyrite weathering contributes with CO2-releases to the ocean-atmosphere system.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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
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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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