| 1. |
- Dimberg, Peter H., 1985-
(författare)
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Predictions Within and Across Aquatic Systems using Statistical Methods and Models
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aquatic ecosystems are an essential source for life and, in many regions, are exploited to a degree which deteriorates their ecological status. Today, more than 50 % of the European lakes suffer from an ecological status which is unsatisfactory. Many of these lakes require abatement actions to improve their status, and mathematical models have a great potential to predict and evaluate different abatement actions and their outcome. Several statistical methods and models exist which can be used for these purposes; however, many of the models are not constructed using a sufficient amount or quality of data, are too complex to be used by most managers, or are too site specific. Therefore, the main aim of this thesis was to present different statistical methods and models which are easy to use by managers, are general, and provide insights for the development of similar methods and models.To reach the main aim of the thesis several different statistical and modelling procedures were investigated and applied, such as genetic programming (GP), multiple regression, Markov Chains, and finally, well-used criteria for the r2 and p-value for the development of a method to determine temporal-trends. The statistical methods and models were mainly based on the variables chlorophyll-a (chl-a) and total phosphorus (TP) concentrations, but some methods and models can be directly transferred to other variables.The main findings in this thesis were that multiple regressions overcome the performance of GP to predict summer chl-a concentrations and that multiple regressions can be used to generally describe the chl-a seasonality with TP summer concentrations and the latitude as independent variables. Also, it is possible to calculate probabilities, using Markov Chains, of exceeding certain chl-a concentrations in future months. Results showed that deep water concentrations were in general closely related to the surface water concentrations along with morphometric parameters; these independent variables can therefore be used in mass-balance models to estimate the mass in deep waters. A new statistical method was derived and applied to confirm whether variables have changed over time or not for cases where other traditional methods have failed. Finally, it is concluded that the statistical methods and models developed in this thesis will increase the understanding for predictions within and across aquatic systems.
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| 2. |
- Rullander, Gabriella, 1992-
(författare)
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Microplastic Mitigation in Urban Stormwater : Assessing Horizontal-Flow Filters of Bark, Biochar and Sand as Remediation Strategies
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Urban stormwater has been suggested as a significant vector through which microplastics (MPs) reach aquatic environments. Currently, only a small fraction of stormwater in Sweden undergoes any form of treatment. Therefore, a considerable portion of the runoff reaches and pollutes recipients with microplastics, which have demonstrated adverse effects on aquatic life. In recent years, there has been a growing interest in the decentralized treatment of stormwater, shifting the treatment of stormwater upstream and close to the runoff source through filtration-based techniques. Filtration-units can be incorporated into urban environments prone to high runoff coefficients– such as roads, parking lots, and other paved surfaces. At present, there is an opportunity to also shape decentralized treatments towards sustainable and environmentally positive approaches, by utilizing forestry by-products as filter media. Due to the promising characteristics of large specific surface areas and high porosity, the carbon-rich bark and biochar materials have been suggested as potential filter media. This thesis aims to evaluate MP pollution in urban environments, with the city of Uppsala as a case study and parking lots as sampling sites. Then, the thesis assesses the current capabilities of removing MPs in traditional sand media, followed by an evaluation of the potential of bark and biochar, as filter media for removing MPs in stormwater.Road dust and spiderwebs were sampled from parking lots in Uppsala City, to assess the ground-based and airborne MP pollution. A wide range of MP types were identified, such as polyurethane (PU), polypropylene (PP), polyester (PET), Acrylic (PMMA), polyethylene (PE), polystyrene (PS), polyamide (PA), and cellulose acetate. The PU was especially dominant in the indoor parking and PET fibers were commonly found to be airborne. Overall, the road dust and spiderwebs contained 5.78–4951 and 2500–505000 MPs/g, respectively. Horizontal-flow filters of 25, 50, and 100 cm were established to evaluate the removal efficacy of MPs using sand, bark and biochar as filtration media. The filters were introduced to a heterogeneous mix of MPs, including PET and PP fibers, spherical PA, PE and PS, and fragmented PP, representative of the polymer types identified in Uppsala city. The analysis revealed a substantial removal, >97%, of individual MPs for all filter media, achieving an overall MP retention exceeding 99%. The high removal was achieved even with filter lengths of 25 cm, with a slight increased removal with increased filter length. This thesis has proved that MPs are present in a multitude of surfaces in the urban environment, including air, and showed that sand, bark, and biochar should be considered as potential media for filtration-based remedies to improve MP mitigation in urban stormwater.
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| 3. |
- Åhlgren, Kristina, 1976-
(författare)
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Environmental impact of alum shale mining in Kvarntorp, Närke, Sweden
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to scarcity of imported liquid fuel during World War II, alum shale was mined for oil production in the Kvarntorp area 1942-1966. The shale contains both organic matter (kerogen) and elevated concentrations of trace elements such as molybdenum, nickel, uranium and vanadium. Today there are several pit lakes in the area and a 100-meter-high waste deposit, Kvarntorpshögen, consisting mostly of crushed and burned shale but also some unburned crushed shale and lime waste.The aim of this study was to get a better understanding of the environmental impact of alum shale mining with focus on trace metal release. During the production era, the surroundings were highly affected by both sulphur rich flue gas emissions and bad water quality in downstream waters. The former mining activities show impact also today, with higher concentrations in downstream water than upstream the area. Analyses and leaching tests of solid samples have shown pyrite weathering in shale and unburned shale waste with release of for example nickel and uranium.Analyses of groundwater in eleven wells around the deposit show ongoing leaching of both shale waste generating a circumneutral leachate and unprocessed shale leading to acidic leachates.All pit lakes in contact with alum shale waste or the shale horizon show elevated sulphate concentrations indicating pyrite weathering, although only one is still acidic today. Also Norrtorpssjön was acidic until a pH rise due to adjacent dumping of alkaline waste. The pH increase was followed by a decrease in aluminium, cobalt, magnesium and nickel.Surface water analysis show that the waste deposit is estimated to contribute with less than a fifth of the mass transport whereas the western pit lakes contribute with the largest part.
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| 4. |
- Gleisner, Magdalena, 1972-
(författare)
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Quantification of mineral weathering rates in sulfidic mine tailings under water-saturated conditions
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tailings are a fine-grained waste product produced during the metal recovery process. Tailings consist mostly of different silicates but also sulfides (e.g. pyrite), since 100 % metal recovery is not possible. Freshly processed tailings are deposited in large impoundments. If the mine tailings in the impoundments are exposed to water and oxygen, the sulfides will oxidize and release acidity and metals such as Fe, Cu, Zn, and Pb. The sulfide mineral oxidation reactions are catalyzed by sulfur and iron oxidizing bacteria (principally Acidithiobacillus ferrooxidans) that oxidize ferrous iron to ferric iron, which then oxidizes pyrite. When the leachate produced by this process discharges from the impoundment, it is called acid mine drainage, which may lead to the pollution of adjacent streams and lakes.The intention with this thesis is to investigate and quantify mineral weathering processes and element release rates occurring in water-saturated and soil-covered sulfidic mine tailings. The study was performed in different batch and column experiments in room temperature and in the laboratory. The batch experiments were conducted for ca. three months and investigated: a) microbial and abiotic sulfide oxidation in freshly processed tailings under oxic conditions at pH 2-3 and pH 8, b) microbial oxidation of pure pyrite grains at pH 2-3 under different oxygen concentrations ranging from anoxic to oxic conditions. The column experiments, consisting of unoxidized tailings in water-saturated columns, were conducted for up to three years. In these experiments, an oxygen-saturated solution was continually pumped into the column inlet, and investigated: a) differences in oxidation rates between tailings of two different grain sizes, b) factors affecting element discharge rates, acid neutralization, and sulfide oxidation, c) the effect of ions released in a soil cover on release rates in the tailings.Sulfide oxidation processes within the batch experiments were limited by surface kinetics. The microbial oxidation of pure pyrite at atmospheric conditions produced the most rapid rate, while the microbial oxidation of pure pyrite at anoxic conditions was slower by 1.8 orders of magnitude. Microbial and abiotic oxidation of pyrite in freshly-processed tailings resulted in pyrite oxidation rates that were intermediate between these two extremes. The results from the microbial experiments with pure pyrite indicated a positive correlation between the concentration of dissolved oxygen, ferric iron and bacterial cells (at a total cell concentration > 106 cells/mL and a dissolved oxygen concentration ≥ 13.2 µM), which implies an interdependence of these factors. The results from these batch experiments support the indirect mechanism for microbial oxidation by the ferric oxidation pathway. Pyrite oxidation rates estimated from the batch experiments may be comparable with oxidation rates in the unsaturated zone and at the groundwater table in a tailings impoundment.Acid neutralization reactions in the column experiments resulted in the release of base cations to the column leachate. Calcite was the most important neutralizing mineral despite that it was only present in minor amounts in the tailings. It was confirmed that acidity forced the calcite dissolution. Element release rates in the column experiments were controlled by the availability of dissolved oxygen, which was a function of the water flow rate into the column. These column experiments also showed that the results are comparable with results from field studies, justifying the use of column experiments to study processes within tailings impoundments.
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| 5. |
- Karlsson, Ulrika, 1976-
(författare)
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Environmental levels of thallium : influence of redox properties and anthropogenic sources
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thallium is a highly toxic element that humans are exposed to mainly by consumption of drinking water and vegetables grown in soil with high thallium content but also through inhalation of particles in the air. Thallium is also present in fossil fuels, alloys, and in electronic utilities. The increasing use of the element and emissions from notably energy production has lead to a higher load on the surface of the Earth. This study aims at increasing the knowledge about the behaviour of thallium in aquatic environments. Focus has been on the redox chemistry of thallium in relation to its mobility, which is of great importance because Tl(I) and Tl(III) have very different properties in this respect. The relationship between Tl(I) and Tl(III) in surface waters from contaminated and uncontaminated environments was examined by ion chromatography connected on line to ICP-MS (inductively coupled plasma mass spectrometry). It was found in controlled systems that even though Tl(III) is thermodynamically unstable under fresh water conditions Tl(I) was oxidised in the presence of light and iron(III). This was also confirmed in field studies. When lake water samples were exposed to light, Tl(I) was oxidised and thallium was lost from the solution. The most likely explanation for this was adsorption of thallium to particle surfaces. The concentration of thallium in Swedish lakes and soil were measured. In unpolluted lakes the concentration ranges between 4.5-12 ng/l, the sediment concentration was 0.07-1.46 mg/kg. The anthropogenic load was found to have increased since the end of the Second World War although concentrations above background were found since the early industrialisation. In contaminated areas the concentration in soil ranges from 0.64-88 mg/kg, high concentrations were found in systems with alum shale and in soil exposed to runoff from a lead and zinc enrichment plant. The mobilisation of thallium from solid phases in contaminated areas was dependent on pH and about 50% of the leachable content was mobilised already at pH 5-6. Once it had been released to water it was highly mobile. These conditions suggest that in a large part of the Swedish environment a high mobility of thallium can be expected.
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