| 1. |
- Münzner, Karla, 1989-
(author)
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Causes and consequences of Gonyostomum semen blooms
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Aquatic ecosystems provide essential ecosystem services, but are also highly vulnerable to global change. Climate change, eutrophication and browning, for example, collectively drive the increase of harmful algal blooms in freshwaters. While cyanobacterial blooms have been intensively studied, blooms caused by other algal species have received far less attention.The aim of my thesis was to increase our understanding of the causes and consequences of the freshwater raphidophyte Gonyostomum semen (Ehrenberg) Diesing, which forms high biomass blooms in lakes all over the world. I used laboratory experiments, field studies and lake monitoring data to investigate how G. semen growth is affected by environmental factors related to water color, and how G. semen blooms affect carbon cycling in lakes.High iron concentration (>200 µg L-1) was found to be a requirement for G. semen growth, but not for bloom formation. Rather, increase in dissolved organic carbon (DOC) concentration may drive bloom formation, possibly by a combination of providing additional nutrients to lakes as DOC is imported from terrestrial sources, and by reducing light availability for other competing phytoplankton species. Gonyostomum semen can possibly avoid light limitation and form blooms over a wide range of DOC concentration (8 – 20 mg L-1) due to its diel vertical migration and special pigment composition, although there likely exists a DOC threshold at which also G. semen growth becomes light limited.By fixing CO2 through photosynthesis, G. semen did considerably reduce the partial pressure of CO2 (pCO2) in the studied lakes. Furthermore, the relationship between pCO2 and G. semen became stronger with decreasing DOC concentration, suggesting that reduction in pCO2 caused by G. semen is highest in moderately colored lakes (8 – 12 mg DOC L-1). This resulted in temporary reduction in CO2 emission to the atmosphere during summer, though it is unlikely that it changes annual carbon emissions. Organic matter (OM) generated by G. semen was transported to the sediments, though this did not appear to affect carbon burial rates. However, G. semen increased the fraction of autochthonous OM that sank to the sediment, which may result in altered CO2 and methane (CH4) production on a short-term basis.In summary, G. semen growth is dependent on sufficient iron concentrations, while bloom formation is likely controlled by DOC. Blooms temporarily affect in-lake carbon dynamics through increased rates of CO2 fixation via photosynthesis, transport of autochthonous OM to the sediment and subsequent changes in CO2 and CH4 production. Thus, G. semen may contribute to changes in ecosystem functioning in lakes experiencing browning.
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| 2. |
- Logue, Jürg Brendan
(author)
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Factors influencing the biogeography of bacteria in fresh waters - a metacommunity approach
- 2010
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Doctoral thesis (other academic/artistic)abstract
- One of ecology’s primary goals is to comprehend biodiversity and its patterns of distribution over space and time. Since microorganisms play a pivotal role in key ecological processes, the diversity of microbial communities may have important implications for the stability and functioning of Earth’s ecosystems. Thus, it is of utmost importance to develop a theoretical foundation but also a conceptual understanding for the mechanisms that generate and maintain microbial diversity. The aim of this thesis is to investigate to what extent local freshwater bacterioplankton diversity, i.e. richness and community composition, is structured by local environmental interactions and/or regional processes. The key objective is to identify ecological linkages between lake bacterioplankton and bacterial communities in connected streams and the surrounding terrestrial landscape, thereby applying a metacommunity approach. To do so, I studied several natural lake bacterioplankton assemblies within different regions of Sweden and assessed both local environmental properties and regional parameters (e.g. dispersal, landscape position). The genetic composition of freshwater bacterioplankton diversity was determined by means of terminal-restriction fragment length polymorphism or 454 pyrosequencing. From the review on the biogeography of bacterioplankton in inland waters it became clear that microbial diversity and its spatial distribution are governed by a complex interplay of both local and regional drivers. In one case, freshwater bacterioplankton communities were structured by local environmental conditions rather than by regional dispersal processes. These local environmental conditions seemed to be equally important in controlling both the total bacterioplankton community and its active fraction. In a study of bacterioplankton communities from five different regions, locally abundant aquatic bacteria were shown to be also regionally widespread, a pattern predicted by neutral theory. Yet, this degree of similarity decreased with increasing environmental heterogeneity. In another study, bacterioplankton richness was controlled mostly by nutrient content, indicating that productivity exerted influence on bacterioplankton richness. However, landscape position and productivity covaried, suggesting that the landscape dictates environmental properties, which then directly structure local bacterioplankton richness. Finally, a review synthesising results from empirical metacommunity approaches and comparing these to theory showed that yet a gap between empirics and theory exists. To conclude, local bacterioplankton diversity appeared to be mainly structured by local environmental properties. However, signatures of neutral processes driving local bacterioplankton community assembly were also recorded.
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| 3. |
- Groeneveld, Marloes M.
(author)
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Adsorption of dissolved organic matter in aquatic ecosystems : Effects on composition and reactivity
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Inland waters receive organic matter from terrestrial ecosystems and in situ production. In transit from land to the ocean, dissolved organic carbon (DOC) may be mineralised to inorganic forms (CO2 and CH4) by microbial degradation and photodegradation. It may also transition from dissolved into particulate phase, and be transferred to the sediment and buried. One way in which this can happen is by adsorption of dissolved organic matter (DOM) to mineral particles. This process is rarely studied in inland waters, since suspended particles are often in short supply. However, there are scenarios under which high particle concentrations occur, and in those cases, adsorption may have a substantial effect on DOM composition and reactivity. The overall aim of this thesis was to investigate the potential for DOM adsorption to inorganic particles and the resulting effect on DOM composition, as well as its biological reactivity. Three studies within this thesis focus on different types of surfaces waters in the boreal landscape of Sweden, and one study focuses on coastal moorland streams in the United Kingdom. Adsorption experiments were conducted under controlled laboratory conditions using batch experiments. DOM quality was studied based on bulk optical properties, and composition was examined by high resolution mass spectrometry. Adsorption experiments using a commercially available reference clay (containing substantial amounts of aluminium and iron oxides) as the adsorbent show a widespread potential for DOM in inland water to adsorb to mineral particles. The extent of DOM adsorption in the experiments was regulated by two factors: 1) DOM composition, since compounds with a terrestrial signature were selectively adsorbed, and 2) water chemistry, as adsorption was impaired by pH>7 and higher concentrations of base cations. These general patterns were observed across surface waters with contrasting DOC concentrations, DOM composition and water chemistry parameters, and across spatial and temporal scales. In contrast, adsorption to suspended sediment derived from a glacial stream resulted in the removal of ‘protein-like’ DOM that is produced in situ, rather than terrestrially derived DOM. Hence, the mineralogy of particles may determine which DOM fraction is adsorbed. Experiments examining microbial degradation indicated that the effect of adsorption on the bioavailability of the remaining DOM depends on which DOM fraction is removed by the different adsorbents. This thesis shows that adsorption to mineral particles in aquatic ecosystems is a highly relevant biogeochemical process that has the potential to alter DOM composition and thereby affect its biological reactivity.
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| 4. |
- Mostovaya, Alina, 1985-
(author)
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Dissolved organic matter in lakes : Chemical diversity and continuum of reactivity
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Dissolved organic matter (DOM) is the largest pool of organic carbon in aquatic systems and an important component of the global carbon cycle. Large amounts of DOM are decomposed within lakes, resulting in fluxes of CO2 and CH4 to the atmosphere. Therefore, there is a considerable interest in understanding the controls of DOM decomposition in freshwaters. There is evidence that in lakes intrinsic controls related to DOM composition are of primary importance, yet our knowledge about molecular drivers of DOM degradation is limited. This thesis addresses the link between chemical composition and reactivity of lake DOM by applying an experimental approach, molecular-level DOM characterization, and kinetic modeling of DOM decay.The first study shows that photoinduced transformations and partial removal of colored aromatic components of DOM have profound effects on DOM degradation kinetics, mediated by the shifts in the relative share of rapidly and slowly degrading DOM fractions. Two following studies estimate exponential decay coefficients for each individual molecular formula identified within bulk DOM. A continuous distribution of exponential decay coefficients is found within bulk DOM, which directly corroborates the central and previously empirically untested assumption behind the reactivity continuum model of DOM decay. Further, individual decay rates are evaluated in connection to specific molecular properties. On average, highly unsaturated and phenolic compounds appear to be more persistent than compounds with higher aromatic content (plant polyphenols and polycondensed aromatics), and aliphatic compounds demonstrate the highest decay rates. The reactivity of aromatics additionally increases with increasing nominal oxidation state of carbon. Molecular analysis further indicates that increasing reactivity of DOM after UV exposure is caused by disintegration of supramolecular complexes. Study IV shows that changes in relative proportion of terrestrial versus algal DOM control degradability of DOM through seasons. Under ice, when algal-derived DOM is maximally depleted, DOM degradation potential converges to similarly low levels, regardless of lake type (productive or humic), and bacterial respiration primarily relies on terrestrial carbon. This suggests a general pattern of baseline metabolism across boreal lakes. I conclude that DOM is a dynamic reactivity continuum and a tight link exists between DOM behavior and compositional properties.
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| 5. |
- Patriarca, Claudia, 1986-
(author)
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Characterisation of natural dissolved organic matter with liquid chromatography and high resolution mass spectrometry
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Dissolved organic matter (DOM) is one of the most heterogeneous and complex mixture on Earth. DOM plays a crucial role in biogeochemical processes on the global scale and it is essential to sustain and regulate the biological processes in aquatic ecosystems. DOM originates from a multitude of biological, physical and chemical transformations, leading to its phenomenal chemical diversity. In order to understand and predict its effect on the global carbon cycle, an intimate characterization at molecular level is necessary. The investigation of the extraordinary complexity of the DOM mixture represents a compelling challenge for analytical chemistry. The focus of this thesis was the development of methods for the characterization of DOM in natural waters. High resolution mass spectrometry (HRMS), was combined with high pressure liquid chromatography (HPLC) and electrospray ionization (ESI), to investigate the chemical diversity of DOM. The first study demonstrated that cutting-edge techniques (such as the Fourier-transform ion cyclotron resonance mass spectrometer - FTICR-MS), are not indispensable to disclose essential information on the DOM molecular composition, in fact the Orbitrap mass analyser is a suitable alternative for the analysis of complex natural mixtures. In the second study, the potential benefits offered by the online coupling of HPLC and HRMS instruments were explored, revealing significant advantages in terms of analysis time, achievable information and versatility of the method. The advantages of online separation were further confirmed in the third study, focused on the characterization of autochthonous labile DOM. Chromatographically resolved profiles emerged from the bulk-DOM, allowing the monitoring of labile autochthonous components in presence of heterotrophic bacteria. Despite the advantages achieved by the application of online separation, a strong limiting factor in DOM characterization is the ESI source, suitable only for the analysis of the DOM fraction susceptible to ionization. In the last study, the extent of the DOM material prone to ionization was estimated, revealing the occurrence of an extensive portion of the material resistant to routinely employed ESI approach. The full characterization of DOM is still an open challenge and the combination of multiple techniques is fundamental to unravel is extreme intricacy.
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| 6. |
- von Wachenfeldt, Eddie, 1975-
(author)
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Flocculation of Allochthonous Dissolved Organic Matter – a Significant Pathway of Sedimentation and Carbon Burial in Lakes
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Inland waters receive substantial amounts of organic carbon from adjacent watersheds. Only about half of the carbon exported from inland waters reaches the oceans, while the remainder is lost en route. This thesis identifies flocculation as an important and significant fate of carbon in the boreal landscape. Flocculation reallocates organic carbon from the dissolved state into particles which are prone to settle. Thus, flocculation relocates organic carbon from the water column to the sediment.The dissolved organic carbon (DOC), mainly originating from terrestrial sources, in a set of Swedish lakes was found to determine the extent of sedimentation of particulate organic carbon. A major fraction of the settling particles were of allochthonous origin. This implies that allochthonous DOC was the precursor of the settling matter in these lakes. The gross sedimentation was of the same magnitude as the evasion of carbon dioxide to the atmosphere.Sunlight, especially in the photosynthetically active region, stimulated flocculation of DOC. The effect of light appeared to involve a direct photochemical reaction. Iron was involved in the flocculation but it could not be unravelled whether the iron catalyzes the flocculation or just co-precipitates with the settling matter. Microbial activity was identified as the main regulator of the flocculation rates. Accordingly, alteration of temperature, oxygen concentration and pH did not affect flocculation only indirectly, via their effects on microbial metabolism.A comparison of fluorescence characteristics of organic matter collected in sediment trap and in the sediment surface layer revealed that autochthonous organic carbon was preferentially lost in the sediments while allochthonous matter increased. The recalcitrant nature of the flocculated matter could favour sequestration of this matter in the lake sediment. Hence, the lakes will act as sinks of organic carbon due to a slower mineralization of the flocculated matter in the sediments.
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| 7. |
- Bohman, Irene, 1960-
(author)
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Coarse detritus in oligotrophic lake littoral zones : utilization by intervertebrates and contribution to carbon flow
- 2005
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Doctoral thesis (other academic/artistic)abstract
- Syftet med denna avhandling är att öka förståelsen av hur grovt organiskt material, sk grovdetritus, tex löv och makrofytrester, bryts ner i sjöars strandzoner. Motivet bakom intresset för detta är att små näringsfattiga sjöar i skogsrika områden ofta är beroende av tillförsel av energi utifrån och att nedbrytningen av grovdetritus är relativt lite undersökt i sjöar. Utifrån tillförd detritus, i löst och partikulär form kan utgöra extra energikälla för sjöekosystem, men bara om några organismer kan tillgodogöra sig detta organiska material. I sötvatten kan sådana organismer vara bakterier, svampar och ryggradslösa djur. Under nedbrytningsförloppet produceras en mängd mellanprodukter som kan användas av andra konsumenter tex fisk. På så sätt återcirkuleras energi och näring från detritus utan fullständig nedbrytning. Vidare har det föreslagits att hög biodiversitet kan resultera i hög ekosystemfunktion, t ex effektiv nedbryning. Därför kan studier av både samhällen och enskilda arter av nedbrytare öka förståelsen av förändringar i hela ekosystemets funktion. Inom ramen för avhandlingen har jag studerat vilka arter som deltar i nedbrytningen av grovdetritus och vilka möjliga vägar för det fortsatta nyttjandet av detta material som finns. Jag har särskilt betonat det säsongsmässiga mönstret för omsättningen av grovdetritus och för tillgängligheten av mellanprodukter. Resultaten visar att både mikroorganismer och ryggradslösa djur successivt processar tillgängligt grovt organiskt material under hela året. Viktminskningsmönstret över året hos löv och makrofytrester är nära kopplat till förekomst och tillväxt hos olika arter av nedbrytande ryggradslösa djur, sk fragmenterare. Av de vanligaste förekommande tio arterna fragmenterare, var nio nattsländelarver. Därför drar jag slutsatsen att dessa arter av nattsländelarver spelar en avgörande roll för omsättningen av grovdetritus i sjöstränder i sydöstra Sverige. Samtidigt visar resultaten att sötvattengråsuggan spelar mindre roll för nedbrytningen av grovdetritus än förväntat. Denna art föredrar andra födoämnen åtminstone under våren och undviker de grunda bottnarna där grovdetritus finns under vintern. I laboratorieexperiment har jag visat att nedbrytning av löv i närvaro av fragmenterare huvudsakligen ger upphov till två olika produkter: löst organiskt material och finpartikulära rester. Därmed har jag visat att fragmenterare kan omsätta grovdetritus snabbare än mikroorganismer. Slutsatsen blir att mikroorganismernas kvantitativa bidrag till nedbrytning av grov grovdetritus är beroende av mängden fragmenterare. Jag har också visat att olika kombinationer detritussorter och fragmenterararter kan påverka när olika nedbryningsprodukter blir tillgängliga för andra organismer. Sammanfatningsvis har jag visat att grovdetritus är en attraktiv födoresurs för ryggradslösa djur i näringsfattiga sjöars strandzoner, precis som i små bäckar. Dessutom visar jag att de arter av fragmenterare som är speciella för sjöar, tillsammans omsätter tillgängligt grovdetritus i ett finskaligt tidsmönster över året. Detta mönster har utvecklats genom anpassning till trädens lövfällning och nedvissningen av vattenväxter som sker på hösten i vårt klimat. Jag vill också betona att ökade kunskaper om nedbrytning av grovdetritus krävs för att kunna förutsäga effekter av olika störningar i dessa ekosystem. Slutligen rekommenderar jag att nedbrytningshastigheten för grovdetritus testas som mått på ekosystemfunktion också i sjöar.
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| 8. |
- Chaguaceda, Fernando, et al.
(author)
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Supportive data for "Short-term apparent mutualism drives responses of aquatic prey to increasing productivity", Chaguaceda et al.
- 2020
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Other publicationabstract
- This dataset contains both biological variables (phytoplankton, periphyton, zooplankton, Chironomidae emergence) and physico-chemical variables (temperature, dissolved oxygen, pH, turbidity) of an aquatic mesocosm experiment that gradually manipulated nutrient additions (10 nutrient steps, 20 – 1000 µg L -1 total P (TP) and 0.45 – 11.3 mg L -1 total N (TN)) and also manipulated the presence or absence of generalist fish (Crucian carp, Carassius carassius), making a total of 10*2=20 mesocosms.Crucian carp feed both on benthic prey (Chironomidae) and on pelagic prey (Cladocera). Based on that, this experiment aimed to test the indirect interactions between Chironomidae and Cladocera prey due to shared predation, and how these interactions changed in response to nutrient additions through changes in benthic and pelagic food-web pathways. In the dataset there are five different sheets:Sheet number 1 shows the summary values of all the variables after the fish were added. Most variables are shown as mean values over a 7-week experimental period (after fish addition). The other sheets show the time-series of food-web variables (Phytoplankton Chla, periphyton biomass, Chironomidae emergence and Cladocera abundance), where the week refers to week relative to fish addition (week 0 is the first week after fish addition).
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| 9. |
- Eiler, Alexander, 1976-
(author)
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The Niches of Bacterial Populations in Productive Waters : Examples from Coastal Waters and Four Eutrophic Lakes
- 2006
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Doctoral thesis (other academic/artistic)abstract
- Recent research in microbial ecology has focused on how aquatic bacterial communities are assembled. Only a few of these studies follow a “Gleasonian” approach where the roles of single bacterial populations are in focus. In this thesis, novel molecular tools were used to describe the distribution and evolutionary relationships of microbes in productive aquatic environments. Many new phylogenetic groups of bacteria were identified, likely representing bacterial populations restricted to productive freshwaters. I also addressed the dynamics and functional role of individual bacterial populations in eutrophic lakes and brackish environments with a focus on either biogeochemically significant or potentially pathogenic representatives. Flavobacteria blooms were observed, on occasions characterized by high heterotrophic production. In addition to high temporal dynamics microbial community composition and function differed on the spatial scale, as exemplified by free-living and Cyanobacteria-associated habitats. At the community scale, microbial processes, such as biomass production and substrate uptake could be predicted from the presence and absence of individual bacterial populations. I also studied the niches of potentially pathogenic Vibrio populations in various coastal waters. Using a novel culture-independent method, a V. cholerae population was detected along the entire Swedish coastline. Results from an environmental survey and a laboratory mesocosm experiment reveal that phytoplankton-derived dissolved organic matter enhance the growth of V. cholerae and other Vibrio spp. and hence create a largely overlooked niche for these heterotrophic bacteria. This thesis and future work on the role of individual bacterial populations will facilitate predictions of biogeochemical cycles and the distribution of bacteria in the context of global climate change and local eutrophication.
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| 10. |
- Gudasz, Cristian, 1973-
(author)
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Boreal Lake Sediments as Sources and Sinks of Carbon
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Inland waters process large amounts of organic carbon, contributing to CO2 and CH4 emissions, as well as storing organic carbon (OC) over geological timescales. Recently, it has been shown that the magnitude of these processes is of global significance. It is therefore important to understand what regulates OC cycling in inland waters and how is that affected by climate change. This thesis investigates the constraints on microbial processing of sediment OC, as a key factor of the carbon cycling in boreal lakes. Sediment bacterial metabolism was primarily controlled by temperature but also regulated by OC quality/origin. Temperature sensitivity of sediment OC mineralization was similar in contrasting lakes and over long-term. Allochthonous OC had a strong constraining effect on sediment bacterial metabolism and biomass, with increasingly allochthonous sediments supporting decreasing bacterial metabolism and biomass. The bacterial biomass followed the same pattern as bacterial activity and was largely regulated by similar factors. The rapid turnover of bacterial biomass as well as the positive correlation between sediment mineralization and bacterial biomass suggest a limited effect of bacterial grazing. Regardless of the OC source, the sediment microbial community was more similar within season than within lakes. A comparison of data from numerous soils as well as sediments on the temperature response of OC mineralization showed higher temperature sensitivity of the sediment mineralization. Furthermore, the low rates of areal OC mineralization in sediments compared to soils suggest that lakes sediments are hotspots of OC sequestration. Increased sediment mineralization due to increase in temperature in epilimnetic sediments can significantly reduce OC burial in boreal lakes. An increase of temperature, as predicted for Northern latitudes, under different climate warming scenarios by the end of the twenty-first century, resulted in 4–27% decrease in lake sediment OC burial for the entire boreal zone.
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