| 1. |
- Olajos, Fredrik, 1987-
(författare)
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Using environmental DNA to unravel aquatic ecosystem dynamics
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Human-induced climate change has led to unprecedented declines in Earth's biodiversity and significant habitat loss. Aquatic ecosystems areespecially at risk, facing pollution, overexploitation, and destruction. Consequently, monitoring biodiversity is critical. Traditional monitoring methods are often low in detection rates, time-consuming, invasive, and harmful to species, which hampers comprehensive biodiversity assessments. Environmental DNA (eDNA) offers a rapid alternative fortaxonomic identification, extracting genetic material from soil, sediments, or water without capturing living organisms, proving useful where traditional methods fall short. However, its integration into aquatic ecology is hampered by unresolved methodological issues.This thesis demonstrates how eDNA can help reconstruct fish colonization histories in lakes post-glacial retreat. I employed species-specific primers with digital droplet PCR and metagenomic shotgun sequencing on ancient DNA from Holocene lake sediments. My findings show the detectability of DNA from ancient fish populations. However, each method exhibited technical limitations that led to varying degrees offalse negatives and false positive results. Additionally, I examined how Northern pike (Esox Lucius) affects ecological speciation in Europeanwhitefish (Coregonus lavaretus), promoting a shift from insectivorous to piscivorous states, enhancing predator biodiversity and biomass. Dietan alyses of piscivorous birds through digital droplet PCR revealed that smaller whitefish support a larger, more diverse bird community. Finally, I compared two molecular techniques for quantifying bird diets from fecal DNA, finding that metabarcoding with a universal fish primer and digital droplet PCR yielded similar results. This research enhances ourunderstanding of the potential and limitations of molecular tools forspecies identification and aids the integration of eDNA into aquatic ecology.
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| 2. |
- Sjöström, Jenny, 1978-
(författare)
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Mid-Holocene mineral dust deposition in raised bogs in southern Sweden : Processes and links
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Atmospheric mineral dust is a key component of the climate system, which affects insolation, brings nutrients to marine and terrestrial ecosystems, and acts as a cloud condensation nuclei. To reconstruct past patterns in terrestrial dust deposition natural archives may be utilized, such as loess, dunes, lakes, and peat bogs. Bogs became an established dust archive in the early 2000s, and the number of studies has since increased. However, most studies use single records to represent dust deposition, meaning that we have limited understanding of regional paleodust dynamics or about the representativeness of single bog records. This thesis aims to address these uncertainties by comparing paleodust deposition between bogs located on a 65 km transect. The thesis includes a methodological development for organic matter removal from peat samples for XRD mineral analysis (Paper I) and two peat paleodust reconstruction studies (Paper II, III). The first paleodust reconstruction from Draftinge Mosse (mosse translates to bog in English), Småland, showed that four dust events (DE) were recorded during the ombrotrophic stage (Paper II). These results were compared to a previously conducted study on Store Mosse, 20 km northeast of Draftinge Mosse, which showed similar patterns in DE and peat accumulation rate (PAR), indicating that the events were at least regional in character. However, the magnitude of the DE differed, which was related to differences in the sizes of the two bogs. The second paleodust reconstruction, from (Davidsmosse) located c. 25 km from the west coast, recorded many more DE (14) compared to the more inland sites (Paper III). Two longer periods saw numerous DE, dominated by coarse particles: between 2800 and 2130 cal BP, and from 1000 towards 490 cal BP. These two periods occurred during regionally cold periods. Human activities also intensified during the latter period, possibly amplifying the DE. Most of these episodic events were not recorded at the inland sites, and the Davidsmosse record seemed to be more in line with previously constructed coastal paleostorm records. That the bog located closer to the coast recorded many more events compared to the inland sites suggests that the location of a bog will influence the aeolian events recorded. However, the DE observed at the inland sites were also recorded at Davidsmosse, indicating that the inland events might represent winds that were sustained over longer distance, or alternatively, that regionally dry conditions prevailed during these periods. The paleostorm records from south-western Sweden, including the new results from Davidsmosse presented here, suggest that storm intensities have varied during the last 3000 years, with increased storminess frequency coupled to colder episodes related to extended sea ice and a southward shift of storm tracks. When comparing DE and PAR at both sites studied here, a recurring pattern of increased accumulation rates were observed during a majority of DE, supporting the suggestion of previous studies that dust deposition may affect peat growth, and thus also peat carbon sequestration.Combining elemental data with XRD mineral analysis enabled anchoring of elemental inferences with mineral observations, allowed identification of authigenic minerals, and aided in source tracing. Despite the fact that local factors affect mineral deposition and PAR, this work has outlined some of the possible mechanisms behind these observations (e.g. distance to the coast, or bog size difference) which may be important for future peat paleodust studies to consider. For example, future studies should include grain size analysis (down-core, as well as across a bog surface); pollen analysis to further elaborate on human activities and vegetation cover; and further investigate differences in mass accumulation rates between bogs.
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| 3. |
- Milan, Manuela, 1983-
(författare)
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Long-term development of subalpine lakes : effects of nutrients, climate and hydrological variability as assessed by biological and geochemical sediment proxies
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sediment records of two Italian subalpine lakes (Lake Garda and Lake Ledro) were analyzed in order to reconstruct their ecological evolution over the past several hundred years. A multi-proxy and multi-site approach was applied in order to disentangle the effects of local anthropogenic forcings, such as nutrients, and climate impacts on the two lakes and their catchments. Biological indicators (sub-fossil pigments, diatoms and Cladocera) were used to reconstruct changes in the aquatic food web and to define the lake reference conditions, while geochemical methods, i.e. wavelength-dispersive X-ray fluorescence spectroscopy (WD-XRF), were used to provide quantitative information on the different physical or chemical processes affecting both lake and catchment systems.Sub-fossil pigments and diatoms, together with their respective inferred TP values, suggested very stable oligotrophic conditions in both lakes until the 1960s. The period following was affected by nutrient enrichment, which led to a drastic shift in the phytoplanktonic community. The response of sub-fossil pigments and diatoms to major climatic anomalies such as the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA) were not pronounced, and the taxonomic composition remained relatively stable. On the contrary, these proxies showed an indirect response to climate variability since the beginning of the nutrient enrichment phase in the 1960s. In Lake Garda, the winter temperature regulates the water column mixing, which in its turn controls the degree of nutrient fertilization of the entire water column, and the related phytoplankton growth. In Lake Ledro a rapid reorganization of planktonic diatoms was observed only during the temperature recovery after the LIA, while recent temperature effects are masked by the prevailing nutrient effects. In Lake Garda, Cladocera remains responded in quantitative and qualitative terms to climatic changes, whereas in Lake Ledro they appeared to be mainly affected by variations in hydrological regimes, i.e. flood events. Cladocera remains corroborated the nutrient enrichment after the 1960s in both lakes as inferred by diatoms and pigments.In Lake Garda, the geochemical data showed a pronounced shift in elemental composition since the mid-1900s, when major elements and lithogenic tracers started to decrease, while some elements related to redox conditions and other (contaminant) trace elements increased. The general trends since the mid-1900s agree with the biological records. However, some differences recorded in the two different basins of Lake Garda reflected the effects of local conditions, both related to hydrology and sedimentation patterns. Lake Ledro showed higher short-term variability for most elements, even though some features were comparable to Lake Garda. The geochemical record of Lake Ledro revealed a major influence of human-induced lake-level fluctuations and catchment properties.This paleolimnological study allows us to place temporally restricted limnological surveys into a longer-term secular perspective, which is highly valuable for the definition of lake reference conditions. Because the restoration targets are usually based on the lake reference conditions, this study highlighted also the necessity to pay particular attention to the lake-specific sensitivity patterns. The multi-proxy and multi-site approach showed that the lake conditions of large and deep lakes in northern Italy, such as Lake Garda, are mainly driven by nutrient enrichment and/or climate change. In contrast, smaller lakes with larger catchment areas, such as Lake Ledro, are seemingly more impacted by conditions and processes occurring in the drainage basin.
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| 4. |
- Ninnes, Sofia, 1984-
(författare)
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Molecular analysis of lake-sediment organic matter : long-term dynamics and environmental implications in boreal lakes
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lake sediment organic matter is material composed of residues from plants, algae, animals, fungi and bacteria. Its molecular composition is dependent on the sources as well as secondary biotic and abiotic transformations, which combined generates a highly complex matrix. Considering that organic matter plays a key role in carbon and nitrogen cycle, and its composition affects many different biogeochemical reactions, paleolimnologic studies have payed proportionately little attention to the organic matter composition compared with the other sediment fractions, even though organic matter makes up 20–60 % of the dry sediment mass in boreal and subarctic lakes. This thesis therefore primarily aims to explore and evaluate two methods; pyrolysis-gas chromatography/mass spectrometry (Pyrolysis-GC/MS) and diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS) for characterisation of bulk organic matter at the molecular level, both which have been extensively used for soils and peat and which balances the need for cost and time-effective analysis and for analytical detail.With pyrolysis-GC/MS the organic matter composition and long-term dynamics in two neighbouring boreal lakes is explored and compared with the conventional bulk carbon and nitrogen contents and their stable isotopes. Both pyrolysis data and conventional data capture the timing of organic matter compositional changes, but only pyrolysis provides detailed information on how the composition changes, which allows for a deeper understanding of the processes behind the changes. The same two lakes are also analysed with DRIFTS and with this approach information on the major organic compound groups aromatics, lignin, aliphatics, proteins and polysaccharides is extracted. In combination with the rapid analysis time and low cost, DRIFTS emerges as a very useful tool for rapid yet informative organic matter analysis. DRIFTS is then evaluated as a stand-alone tool for sediment characterisation in four mountain lakes. The four lakes all have different sediment composition and as a result of the multi-fraction information obtained with DRIFTS compositional differences can be related and explained in terms of their individual lake and landscape settings. The importance of landscape setting is further highlighted in the synthesis of the long-term dynamics of lake-water quality in seven lakes where development trajectories and responses to different types of disturbances are connected to the extent of peatlands within the lake catchments. This thesis demonstrates the advantages of two different approaches for more detailed lake sediment organic matter characterisation and advances our understanding of the molecular organic matter composition in boreal lakes over the Holocene, and how landscape setting affects both the organic matter composition and the sensitivity of lakes to disturbance.
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| 5. |
- Chawchai, Sakonvan, 1984-
(författare)
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Paleoenvironmental and paleoclimatic changes in northeast Thailand during the Holocene
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The long-term climatic and environmental history of Southeast Asia is still fragmentary. This thesis therefore aims at studying lake sediment/peat sequences using a multi-proxy approach to reconstruct the environmental history and the impact of past changes in monsoon variability and intensity on lake ecosystems in Thailand. The study focuses on two lakes located in northeast Thailand: the larger Lake Kumphawapi and the smaller Lake Pa Kho.The comparison of multiple sediment sequences and their proxies from Kumphawapi suggests a strengthening of the summer monsoon between c. 10,000 and 7000 cal yr BP. Parts of the lake had been transformed into a wetland/peatland by c. 7000 cal yr BP, while the deeper part of the basin still contained areas of shallow water until c. 6600 cal yr BP. This gradual lowering of the lake level can point to a weakening of the summer monsoon. Paleoenvironmental information for the time interval between 6200 and 1800 cal yr BP is limited due to a several thousand-year long hiatus. This new investigation demonstrates that arguments using the phytolith and pollen record of Lake Kumphawapi to support claims of early rice agriculture in the region or an early start of the Bronze Age are not valid, because these were based upon the assumption of continuous deposition. The lithostratigraphy and multi-proxy reconstructions for Pa Kho support a strengthened summer monsoon between 2120-1580 cal yr BP, 1150-980 cal yr BP, and after 500 cal yr BP; and a weakening of the summer monsoon between 1580-1150 cal yr BP and between 650-500 cal yr BP. The increase in run-off and higher nutrient supply after AD 1700 can be linked to agricultural intensification in the region. Conclusively, the Holocene records from northeast Thailand add important paleoclimatic information for Southeast Asia and allow discussing past monsoon variability and movements of the Intertropical Convergence Zone in greater detail.
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| 6. |
- Meyer-Jacob, Carsten, 1984-
(författare)
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Infrared spectroscopy as a tool to reconstruct past lake-ecosystem changes : Method development and application in lake-sediment studies
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Natural archives such as lake sediments allow us to assess contemporary ecosystem responses to climate and environmental changes in a long-term context beyond the few decades to at most few centuries covered by monitoring or historical data. To achieve a comprehensive view of the changes preserved in sediment records, multi-proxy studies – ideally in high resolution – are necessary. However, this combination of including a range of analyses and high resolution constrains the amount of material available for analyses and increases the analytical costs. Infrared spectroscopic methods are a cost-efficient alternative to conventional methods because they offer a) a simple sample pre-treatment, b) a rapid measurement time, c) the non- or minimal consumption of sample material, and d) the potential to extract quantitative and qualitative information about organic and inorganic sediment components from a single measurement.The main objective of this doctoral thesis was twofold. The first part was to further explore the potential of Fourier transform infrared (FTIR) and visible-near infrared (VNIR) spectroscopy in paleolimnological studies as a) an alternative tool to conventional methods for quantifying biogenic silica (bSi) – a common proxy of paleoproductivity in lakes – in sediments and b) as a tool to infer past lake-water total organic carbon (TOC) levels from sediments. In a methodological study, I developed an independent application of FTIR spectroscopy and PLS modeling for determining bSi in sediments by using synthetic sediment mixtures with known bSi content. In contrast to previous models, this model is independent from conventional wet-chemical techniques, which had thus far been used as the calibration reference, and their inherent measurement uncertainties. The second part of the research was to apply these techniques as part of three multi-proxy studies aiming to a) improve our understanding of long-term element cycling in boreal and arctic landscapes in response to climatic and environmental changes, and b) to assess ongoing changes, particularly in lake-water TOC, on a centennial to millennial time scale.In the first applied study, high-resolution FTIR measurements of the 318-m long sediment record of Lake El’gygytgyn provided a detailed insight into long-term climate variability in the Siberian Arctic over the past 3.6 million years. Highest bSi accumulation occurred during the warm middle Pliocene (3.6-3.3 Ma), followed by a gradual but variable decline, which reflects the first onset of glacial periods and then the finally full establishment of glacial–interglacial cycles during the Quaternary. The second applied study investigated the sediment record of Torneträsk in subarctic northern Sweden also in relation to climate change, but only over the recent post-glacial period (~10 ka). By comparing responses to past climatic and environmental forcings that were recorded in this large-lake system with those recorded in small lakes from its catchment, I determined the significance and magnitude of larger-scale changes across the study region. Three different types of response were identified over the Holocene: i) a gradual response to the early landscape development following deglaciation (~10000-5300 cal yr BP); ii) an abrupt but delayed response following climate cooling during the late Holocene, which occurred c. 1300 cal yr BP – about 1000-2000 years later than in smaller lakes from the area; and iii) an immediate response to the ongoing climate change during the past century. The rapid, recent response in a previously rather insensitive lake-ecosystem emphasizes the unprecedented scale of ongoing climate change in northern Fennoscandia. In the third applied study, VNIR-inferred lake-water TOC concentrations from lakes across central Sweden showed that the ongoing, observed increase in surface water TOC in this region was in fact preceded by a long-term decline beginning already AD 1450-1600. These dynamics coincided with early human land use activities in the form of widespread summer forest grazing and farming that ceased over the past century. The results of this study show the strong impact of past human activities on past as well as ongoing TOC levels in surface waters, which has thus far been underestimated. The research in this thesis demonstrates that infrared spectroscopic methods can be an essential component in high-resolution, multi-proxy studies of past environmental and climate changes.
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| 7. |
- Myrstener, Erik, 1986-
(författare)
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Lake sedimentary archives of medieval mining and smelting in Sweden : tracking environmental changes from site to landscape
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- While the environmental impact of the industrial age is massive, including climate change, pollution, microplastics and habitat loss, our influence reaches further back than many recognize. In Sweden, an early and important activity with large potential impact was the mining and smelting of iron, copper and silver ores over the last ~800 years. This occurred in a mineral rich region called Bergslagen, where thousands of smelters and forges and tens of thousands of mines produced the metal riches central to the growth of both local and national economies.In this thesis, I and collaborators present data from >30 lakes in Bergslagen and its surroundings with the aim to identify and track both the metallurgical activities themselves and the environmental impacts associated with this early agricultural-metallurgical society. The results indicate that the metallurgical activities can be traced using multiproxy sediment analyses including charcoal particles from the blast furnace and other metallurgical activities at the sites, metals from the ores (Pb, Zn, Cu, Hg) and indicators of erosion associated with activity at the site or damming and rechanneling of streams. We show a widespread pattern of a spread of mining and smelting throughout Bergslagen from ~1250 CE, including activities at Moshyttan close to Nora, Gammalkroppa close to Filipstad, a hitherto unknown blast furnace close to Norberg, the copper mines in Falun and the mine and smelters at Gladhammar. A notable exception to this medieval pattern is evidence from Garpenberg of copper mining already from the 4thcentury BCE. This widespread, medieval expansion of metallurgy occurred during a time of few written sources, and indicates that this was a period of technological proliferation in Sweden.The environmental effects of these activities were wide-ranging. Pollen-inferred vegetation reconstructions (using REVEALS) indicate a minor decline in forest cover (~10–15%) starting in the 12th and 13th centuries when the first metallurgical activities were established. The loss of forest accelerated from the 16th century, likely driven by the greatly increasing metal production at this time which required substantial amounts of charcoal. No site was totally deforested, however, and inferred forest cover is between 40 and 60% at all sites associated with metallurgy, indicating that the documented efforts to produce a sustainable yield of charcoal were largely successful. The remaining forests were likely substantially changed as historical documents and maps indicate an intensive short-rotation (~60 years) forestry was common in the region, and cadastral maps from the late 17th century indicate extensiveforest areas were ‘young’. The area of cultivated land and open land plants benefitted by grazing (e.g. Poaceae) also increased indicating an expanded agriculture from the 12th century and especially from the 16th century.The expanded land use and forestry coincided with a decreasing spectrally-inferred lake-water total organic carbon (LW-TOC) in all studied lakes, in line with other studies, contributing to the notion that the current increase in LW-TOC observed in contemporary environmental monitoring has an underlying historical component. The decrease in LW-TOC indicated for the lakes was generally ~25% during the early land use and metallurgy but lowest values (~50% of background concentrations) were generally reached in the early–mid 20th century concurrent with increasing industrial acid deposition, which is an important driver of terrestrial carbon export. Many lakes also experienced an increase in pH (0.3–0.5 units) associated with the land use and metallurgy, but the effects are similar to the ‘cultural alkalization’ commonly observed in lakes outside of Bergslagen. One important exception is the lakes surrounding Falun where previous research had shown that the massive mining and smelting of sulfide ores contributed to a decrease in pH of ~0.5 in many near-by lakes prior to modern industrial acid deposition.Taken together, the most important environmental effects of the medieval and early modern mining and metallurgy were driven by the host of supporting activities that produced charcoal and food for the mines, smelters and workers at the sites. The changes in forest composition and water quality have implications for our understanding of reference conditions and the long history of human impacts even in this small corner of Europe.
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