| 1. |
|
|
| 2. |
- Andersson, Anna, 1990-
(författare)
-
Uncharted Waters : Non-target analysis of disinfection by-products in drinking water
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Disinfection by-products (DBPs) are potentially toxic compounds formed when drinking water is treated with disinfectants, such as chlorine or chloramine. A large proportion of the exposure to DBPs is still unknown and the health risks observed through epidemiological studies cannot be explained by DBPs known today. In this thesis, a part of the unknown DBP fraction is investigated, covering a wide range of non-volatile, chlorine/bromine-containing DBPs. The goals were to investigate how the compositions of these DBPs differ between water treatment plants, how their occurrence changes in the distribution system until reaching consumers and how new treatment techniques can reduce their formation and toxicity. To analyze unknown DBPs, a non-targeted approach adopting ultra-high-resolution mass spectrometry, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), was used, where the mass of molecules is measured with such accuracy that the elemental composition of individual DBPs can be calculated. A panel of bioassays was used to assess the combined toxic effects from these DBP mixtures. The results show that the formation of these DBPs to a large extent was specific to each water treatment plant and that local conditions influenced DBP formation, based on e.g., the abundance of organic material with certain chemical structures, bromide and disinfection procedure and agent (chlorine or chloramine). The DBPs were detected in both chlorinated and chloraminated water and in all tap water samples, demonstrating that they are part of human exposure. The number of DBP formulae decreased and the DBP composition changed between drinking water treatment and consumer taps, suggesting that DBP exposure to consumers is not necessarily resembling measurements at the treatment plants. Evaluation of new treatment techniques showed that suspended ion exchange and ozonation have potential to decrease the formation and toxic effects of DBPs and that the removal of organic matter can influence qualitative aspects of DBP formation, such as the proportions of chlorine-containing (less toxic) versus bromine-containing (more toxic) DBPs. Through increased knowledge about the role and relevance of non-volatile DBPs, this work can contribute to future monitoring and actions to reduce the health risks associated with DBPs in chlorinated or chloraminated drinking water.
|
|
| 3. |
|
|
| 4. |
- Rudberg, David, 1989-
(författare)
-
CO2 Emissions from Northern Lakes : Insights on regulation and spatiotemporal variability across contrasting lakes in Sweden
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lakes cover only ~2 % of the global land area, but their connections to the surrounding catchment make them important for the global carbon cycle. A considerable amount of the carbon input to lakes is emitted to the atmosphere as carbon dioxide (CO2) through diffusive flux. This CO2 flux varies with surface water CO2 concentrations (CwCO2) and the transfer velocity of CO2 across the thin boundary layer between surface water and atmosphere (k), which both in turn depend on physical, biological, and chemical factors that interplay with lake and catchment characteristics over various time scales. Comprehensive studies of these interlinkages across lake types are rare, and current assessments of lake CO2 emissions are therefore uncertain. In this thesis, the variability and regulation of lake CO2 fluxes across a latitudinal gradient in Sweden is investigated. The thesis explores how CwCO2 and k regulate lake CO2 fluxes and how spatiotemporal patterns of CO2 fluxes vary within and across lakes.Regulation of CO2 flux at shorter temporal scales (<1 week) was dominated by k. However, the contribution from CwCO2 increased over time making it the dominant factor for seasonal CO2 flux in some lakes. Furthermore, we show that ways of assessing k in lakes may lead to bias, possibly due to inadequate consideration of processes occurring at the upper surface layer of lakes. In the three lakes where daynight variability was studied, we found consistent patterns of higher fluxes of CO2 at daytime during periods where lakes were emitting CO2. Meanwhile, the period of lake water column turnover in autumn was crucial for both day-night variability and total lake CO2 fluxes. Based on the patterns above, we have made recommendations on improved study design for representative measurements of CO2 fluxes in lakes. In addition, we produced models for estimating CO2 flux from combinations of climatic data, satellite imagery and national lake inventory data, i.e., information that is relatively easily available and thus simplify extrapolation of flux estimates to other lakes. Patterns observed across our models suggest strong climate feedbacks, which may lead to increasing CO2 fluxes from lakes at northern latitudes along with precipitation and temperature increases there. Thus, results in this thesis urges forthcoming studies to better account for spatiotemporal variability to improve upon models that can be used for large-scale estimates and future predictions of lake CO2 fluxes.
|
|
| 5. |
- Rudberg, David, et al.
(författare)
-
Diel Variability of CO2 Emissions From Northern Lakes
- 2021
-
Ingår i: Journal of Geophysical Research - Biogeosciences. - Hoboken, United States : John Wiley & Sons. - 2169-8953 .- 2169-8961. ; 126:10
-
Tidskriftsartikel (refereegranskat)abstract
- Lakes are generally supersaturated in carbon dioxide (CO2) and emitters of CO2 to the atmosphere. However, estimates of CO2 flux ((Formula presented.)) from lakes are seldom based on direct flux measurements and usually do not account for nighttime emissions, yielding risk of biased assessments. Here, we present direct (Formula presented.) measurements from automated floating chambers collected every 2–3 hr and spanning 115 24 hr periods in three boreal lakes during summer stratification and before and after autumn mixing in the most eutrophic lake of these. We observed 40%–67% higher mean (Formula presented.) in daytime during periods of surface water CO2 supersaturation in all lakes. Day-night differences in wind speed were correlated with the day-night (Formula presented.) differences in the two larger lakes, but in the smallest and most wind-sheltered lake peaks of (Formula presented.) coincided with low-winds at night. During stratification in the eutrophic lake, CO2 was near equilibrium and diel variability of (Formula presented.) insignificant, but after autumn mixing (Formula presented.) was high with distinct diel variability making this lake a net CO2 source on an annual basis. We found that extrapolating daytime measurements to 24 hr periods overestimated (Formula presented.) by up to 30%, whereas extrapolating measurements from the stratified period to annual rates in the eutrophic lake underestimated (Formula presented.) by 86%. This shows the importance of accounting for diel and seasonal variability in lake CO2 emission estimates.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Šafarič, Luka, 1988-
(författare)
-
Anaerobic Digester Fluid Rheology and Process Efficiency : Interactions of Substrate Composition, Trace Element Availability, and Microbial Activity
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As the anthropogenic greenhouse gas emissions continue imposing stress on our environment, it is becoming increasingly important to identify and implement new renewable technologies. Biogas production through anaerobic digestion has a great potential, since it links waste treatment with extraction of renewable energy, enabling circular bio-economies that are vital for a sustainable future.For biogas to have an important role as a renewable energy carrier in society, the scale of its production will need to be increased substantially. New substrates need to be introduced along with raising organic loading rates of the reactors to increase the rate of biogas production. This contributes to challenges in maintaining process stability, thus increasing the risk for process disturbances, including problems that were not commonly encountered before. These difficulties may be particularly pronounced when a broad range of new, largely untested substrates are introduced, leading to an increased heterogeneity of organic material entering the reactors. In the case of currently the most common reactor type; the continuous stirred-tank biogas reactor (CSTBR); such problems may include shifts in rheology (i.e. fluid behaviour) of the anaerobic digester sludge. This may lead to increased energy consumption and decreased digester mixing efficiencies, which in turn may lead to inefficient biogas processes, ultimately decreasing the economic and environmental viability of biogas production. Much is still unknown regarding how rheology shifts happen in biogas reactors, particularly when it comes to what role the substrate plays in rheological dynamics, as compared to the microbial community during varying levels of biogas process stability.This thesis elucidates the interactions between substrate type, microbial community and its metabolic activity, and anaerobic sludge rheology. A number of sludge samples from mesophilic and thermophilic CSTBRs digesting a broad range of substrates was analysed for their rheology. The specific effects of individual substrate types on CSTBR sludge rheology and the resulting implications for stirring power requirements and mixing efficiency were investigated. In order to also asses to which extent the microbial metabolism affects rheology at different levels of process disturbance, an experiment with a trace-element-induced inhibition of specific metabolic pathways under mesophilic reactor conditions was performed. This was used to identify the sequence of different interactions that occur in the reactor after the process begins to fail, and to evaluate how these interactions link to changes in digester sludge rheology. Finally, a case study of a disturbed thermophilic anaerobic digestion process was performed, including the monitoring of the response of rheology in relation to process stability, which was modified by changing trace element concentrations. The use of artificial substrate without polymeric compounds in both cases allowed for an evaluation of effects of the microbial community and its metabolic products on rheology without including the effects of complex substrates.The results showed that substrate type has a large effect on how different process parameters correlate with fluid behaviour. This was particularly apparent in the case of total solids and total volatile solids, which correlated well with rheological parameters for samples from reactors digesting agricultural waste, sewage sludge, paper mill waste, or food waste, but not for mesophilic co-digesters. Among the different substrates investigated, food waste was generally observed to lead to the highest limit viscosities (i.e. apparent viscosities at high shear rates, where it becomes linear and constant) of the anaerobic sludge, while digestion of paper mill waste and thermophilic co-digestion led to some of the lowest. No fluid type could be clearly coupled to a specific substrate, but it could be observed that increased solids content could generally be associated with more complex, non-Newtonian rheological behaviour. The differences in fluid characteristics between reactors corresponded to large differences in modelled stirring power requirements and mixing efficiency. The results indicated that fluids with high values of rheological parameters, such as the consistency index (K) or yield stress (τ0), would likely require more power or an adapted stirring system to achieve complete mixing. The substrates generally contributed more to the rheology characteristics of the anaerobic sludge than microbial cells on their own. Trace element-induced process disturbance initially led to the inhibition of specific microbial groups among methanogenic archaea or their syntrophic partners, which later escalated to broader inhibition of many microbial groups due to the accumulation of fermentation products. This resulted in microbial cell washout with a corresponding decrease of the contribution of the cells to anaerobic sludge rheology. A recovery of the thermophilic anaerobic digestion process was possible after the supplementation of selenium and tungsten was increased, resulting in increased propionate turnover rates, growing cell densities, and higher viscosity. Major shifts in the methanogenic community were observed, corresponding to the level of process stability. It could be concluded based on these experiments that the specific effect of microbial cells and their activity on sludge rheology were linked to cell density, which corresponded to process stability.A conceptual scheme was developed based on the studies in this thesis, defining complex interactions between substrate, microbial metabolism, and anaerobic sludge rheology in biogas processes. The possible causes of rheology shifts are visualised and discussed.
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
- Schenk, Jonathan, 1992-, et al.
(författare)
-
Methane in Lakes : Variability in Stable Carbon Isotopic Composition and the Potential Importance of Groundwater Input
- 2021
-
Ingår i: Frontiers in Earth Science. - Lausanne, Switzerland : Frontiers Media S.A.. - 2296-6463. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Methane (CH4) is an important component of the carbon (C) cycling in lakes. CH4 production enables carbon in sediments to be either reintroduced to the food web via CH4 oxidation or emitted as a greenhouse gas making lakes one of the largest natural sources of atmospheric CH4. Large stable carbon isotopic fractionation during CH4 oxidation makes changes in 13C:12C ratio (δ13C) a powerful and widely used tool to determine the extent to which lake CH4 is oxidized, rather than emitted. This relies on correct δ13C values of original CH4 sources, the variability of which has rarely been investigated systematically in lakes. In this study, we measured δ13C in CH4 bubbles in littoral sediments and in CH4 dissolved in the anoxic hypolimnion of six boreal lakes with different characteristics. The results indicate that δ13C of CH4 sources is consistently higher (less 13C depletion) in littoral sediments than in deep waters across boreal and subarctic lakes. Variability in organic matter substrates across depths is a potential explanation. In one of the studied lakes available data from nearby soils showed correspondence between δ13C-CH4 in groundwater and deep lake water, and input from the catchment of CH4 via groundwater exceeded atmospheric CH4 emissions tenfold over a period of 1 month. It indicates that lateral hydrological transport of CH4 can explain the observed δ13C-CH4 patterns and be important for lake CH4 cycling. Our results have important consequences for modelling and process assessments relative to lake CH4 using δ13C, including for CH4 oxidation, which is a key regulator of lake CH4 emissions.
|
|
| 12. |
|
|
| 13. |
- Andersson, Anna, et al.
(författare)
-
Evaluating gas chromatography with a halogen-specific detector for the determination of disinfection by-products in drinking water
- 2019
-
Ingår i: Environmental Science and Pollution Research. - : Springer Berlin/Heidelberg. - 0944-1344 .- 1614-7499. ; 26, s. 7305-7314
-
Tidskriftsartikel (refereegranskat)abstract
- The occurrence of disinfection by-products (DBPs) in drinking water has become an issue of concern during the past decades. The DBPs pose health risks and are suspected to cause various cancer forms, be genotoxic and have negative developmental effects. The vast chemical diversity of DBPs makes comprehensive monitoring challenging. Only few of the DBPs are regulated and included in analytical protocols. In this study, a method for simultaneous measurement of 20 DBPs from five different structural classes (both regulated and non-regulated) was investigated and further developed for 11 DBPs using solid phase extraction and gas chromatography coupled with a halogen specific detector (XSD). The XSD was highly selective towards halogenated DBPs, providing chromatograms with little noise. The method allowed detection down to 0.05 µg/L and showed promising results for the simultaneous determination of a range of neutral DBP classes. Compounds from two classes of emerging DBPs, more cytotoxic than the “traditional” regulated DBPs, were successfully determined using this method. However, haloacetic acids (HAAs) should be analyzed separately as some HAA methyl esters may degrade giving false positives of trihalomethanes (THMs). The method was tested on real water samples from two municipal waterworks where the target DBP concentrations were found below the regulatory limits of Sweden.
|
|
| 14. |
- Andersson, Anna, et al.
(författare)
-
Waterworks-specific composition of drinking water disinfection by-products
- 2019
-
Ingår i: Environmental Science. - Cambridge : Royal Society of Chemistry. - 2053-1400 .- 2053-1419. ; :5, s. 861-872
-
Tidskriftsartikel (refereegranskat)abstract
- Reactions between chemical disinfectants and natural organic matter (NOM) upon drinking water treatment result in formation of potentially harmful disinfection by-products (DBPs). The diversity of DBPs formed is high and a large portion remains unknown. Previous studies have shown that non-volatile DBPs are important, as much of the total toxicity from DBPs has been related to this fraction. To further understand the composition and variation of DBPs associated with this fraction, non-target analysis with ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was employed to detect DBPs at four Swedish waterworks using different types of raw water and treatments. Samples were collected five times covering a full year. A common group of DBPs formed at all four waterworks was detected, suggesting a similar pool of DBP precursors in all raw waters that might be related to phenolic moieties. However, the largest proportion (64–92%) of the assigned chlorinated and brominated molecular formulae were unique, i.e. were solely found in one of the four waterworks. In contrast, the compositional variations of NOM in the raw waters and samples collected prior to chemical disinfection were rather limited.This indicated that waterworks-specific DBPs presumably originated from matrix effects at the point of disinfection, primarily explained by differences in bromide levels, disinfectants (chlorine versus chloramine) and different relative abundances of isomers among the NOM compositions studied. The large variation of observed DBPs in the toxicologically relevant non-volatile fraction indicates that non-targeted monitoring strategies might be valuable to ensure relevant DBP monitoring in the future.
|
|
| 15. |
- Ashiq, Muhammad Jamshaid, 1987-
(författare)
-
The occurrence of disinfection by-products in four Swedish drinking waterworks
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Disinfection by-products (DBPs) are unwanted, potentially toxic compounds formed when drinking water is disinfected with chemical disinfectants such as chlorine or chloramine. The levels of DBPs produced depends on parameters, such as levels of natural organic matter (NOM) and the nature and concentration of chemical disinfectant used. In this thesis, the effects of two different types of chemical disinfectants, chlorine and chloramine, are investigated in terms of levels of DBP production. The goal was to investigate if chlorine disinfection produces similar levels and types of DBPs as in case of chloramination.Within the thesis work was also tested a method based on a gas chromatograph coupled with halogen selective detector (GC-XSD) to determine the known DBPs in the drinking water.The results show that the formation of DBPs at chlorine or chloramine disinfection were similar. Still, chloramine is preferably used because it produces less legally regulated DBPs.The GC-XSD worked well for the determination of DBPs in drinking water. Since XSD is very selective and specific towards halogens and easy to operate, therefore this setup not only a potential tool for routine DBPs monitoring at drinking water facilities, but it could also be used for the determination of unknow halogenated compounds.Through increased knowledge in the formation of DBPs and their determination with GC-XSD can contribute to the development of better methods to quantify known and identify unknow halogenated organic compounds in treated drinking water and reduce public exposure to potentially toxic halogenated organic compounds.
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Bastviken, David, 1971-
(författare)
-
Anoxic degradation of organic matter in lakes : implications for carbon cycling and aquatic food webs
- 2002
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Considerable evidence from laboratory studies and marine environments suggests that degradation of organic matter (OM) is restricted under anoxic conditions compared to when molecular oxygen (O2) is present. However, other studies contradict this view since they found similar OM degradation rates and bacterial growth rates under both oxic and anoxic conditions in aquatic environments. Studies from freshwater environments are rare, and have been primarily based on bacterial production estimates. Anoxic degradation of OM in lakes is commonly considered to be slow and of little importance for overall lake food webs compared to oxic degradation. The present thesis and the work it is based on challenge this view. First, the performance of a commonly used method to measure bacterial production was tested in both oxic and anoxic lake water. Then, the oxic and anoxic potentials of bacterial growth and OM mineralization were compared in lake water and sediment. In addition, I assessed the potential of carbon transfer from methane (CH4; i.e. an end-product of anoxic degradation) to pelagic food webs. Three methods for measuring water column methane oxidation were evaluated. Then, the potential transport of methane carbon into the microbial community via methane oxidation, and further -up the food web- into the zooplankton community was estimated. Results indicate 1) that OM degradation and bacterial growth may be similar in oxic and anoxic lake environments, 2) that OM characteristics may be more important for the mineralization than the O2 regime per se in the short term (daysweeks), and 3) that methane can be a significant source of carbon and energy for pelagic food webs. This suggests that the anoxic carbon metabolism may be extensive and potentially important for pelagic organisms in many lakes.
|
|
| 19. |
|
|
| 20. |
- Bastviken, David, Professor, 1971-, et al.
(författare)
-
Measuring greenhouse gas fluxes : what methods do we have versus what methods do we need?
- 2022
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Appropriate methods to measure greenhouse gas (GHG) fluxes are critical for our ability to detect fluxes, understand regulation, make adequate priorities for climate change mitigation efforts, and verify that these efforts are effective. Ideally, we need reliable, accessible, and affordable measurements at relevant scales. We surveyed present GHG flux measurement methods, identified from an analysis of >11000 scientific publications and a questionnaire to sector professionals and analysed method pros and cons versus needs for novel methodology. While existing methods are well-suited for addressing certain questions, this presentation presents fundamental limitations relative to GHG flux measurement needs for verifiable and transparent action to mitigate many types of emissions. Cost and non-academic accessibility are key aspects, along with fundamental measurement performance. These method limitations contribute to the difficulties in verifying GHG mitigation efforts for transparency and accountability under the Paris agreement. Resolving this mismatch between method capacity and societal needs is urgently needed for effective climate mitigation. This type of methodological mismatch is common but seems to get high priority in other knowledge domains. The obvious need to prioritize development of accurate diagnosis methods for effective treatments in healthcare is one example. This presentation provides guidance regarding the need to prioritize the development of novel GHG flux measurement methods.
|
|
| 21. |
- Bastviken, David, 1971-
(författare)
-
Methane
- 2009. - 1
-
Ingår i: Encyclopedia of Inland Waters. - Oxford : Elsevier. - 9780120884629 - 0120884623 ; , s. 783-805
-
Bokkapitel (refereegranskat)abstract
- Inland aquatic habitats occur world-wide at all scales from marshes, swamps and temporary puddles, to ponds, lakes and inland seas; from streams and creeks to rolling rivers. Vital for biological diversity, ecosystem function and as resources for human life, commerce and leisure, inland waters are a vital component of life on Earth. The Encyclopedia of Inland Waters describes and explains all the basic features of the subject, from water chemistry and physics, to the biology of aquatic creatures and the complex function and balance of aquatic ecosystems of varying size and complexity. Used and abused as an essential resource, it is vital that we understand and manage them as much as we appreciate and enjoy them. This extraordinary reference brings together the very best research to provide the basic and advanced information necessary for scientists to understand these ecosystems - and for water resource managers and consultants to manage and protect them for future generations. . Encyclopedic reference to Limnology - a key core subject in ecology taught as a specialist course in universities . Over 240 topic related articles cover the field . Gene Likens is a renowned limnologist and conservationist, Emeritus Director of the Institute of Ecosystems Research, elected member of the American Philosophical Society and recipient of the 2001 National Medal of Science . Subject Section Editors and authors include the very best research workers in the field
|
|
| 22. |
- Bastviken, David, 1971-, et al.
(författare)
-
Methane as a source of carbon and energy for lake pelagic food webs
- 2003
-
Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 84:4, s. 969-981
-
Tidskriftsartikel (refereegranskat)abstract
- Water-column methane oxidation can represent a substantial carbon transformation pathway in lakes, and circumstantial evidence indicates that methane may be a potentially important source of carbon for pelagic food webs. We estimated methanotrophic bacterial production (MBP), methanotrophic bacterial growth efficiency (MBGE), heterotrophic bacterial production (HBP), primary production (PP), and the relative contribution of methanotrophic bacteria to overall bacterial biomass in three very different lakes during summer and winter. In addition, we measured stable carbon isotope ratios in particulate organic matter (POM), surface sediments, zooplankton, and methane. MBP corresponded to 0.3-7% of the organic C production by primary producers, and 0.5-17% of HBP during summer. During winter, MBP was 3-120% of HBP. MBP generally dominated the heterotrophic bacterial production at greater depths. Methanotrophic biomass was 3-11% of total bacterial biomass on a depth-integrated basis. Zooplankton were generally more depleted in 13C than POM. If phytoplankton d13C signatures were -35 to -30ë, such as the POM signals, observed zooplankton signatures could be explained by a fraction of 5-15% methanotrophic bacteria in their diet. The results indicate that methanotrophic bacteria can provide a significant food source for zooplankton, and that methane oxidation represents a potentially important benthic-pelagic carbon and energy link in many lakes, particularly during winter.
|
|
| 23. |
|
|
| 24. |
- Bastviken, David, 1971-, et al.
(författare)
-
Similar bacterial growth on dissolved organic matter in anoxic and oxic lake water
- 2001
-
Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 24:1, s. 41-49
-
Tidskriftsartikel (refereegranskat)abstract
- Anoxic metabolism yields less energy per unit substrate utilized than oxic respiration. In addition, substrate availability is believed to be reduced under anoxic conditions since oxygenases cannot be used. Consequently, it is generally assumed that bacteria grow slower in anoxic environments than in oxic environments. The results of the present study challenge this view. We compared the growth of bacterial assemblages under carbon-limited conditions in lake water under anoxic and oxic conditions. Bioassay experiments were performed with water from 3 lakes differin9 in nutrient concentrations and organic matter content. Amon9 bacteria usin9 the same source of organic matter, median anoxic growth rates were 84 to 110% of oxic growth rates. The total biomass yield durin9 the experiments did not differ between anoxic and oxic treatments. We suggest that anoxic bacterial growth was regulated by substrate availability rather than by metabolic energy yield and that availability of organic matter under anoxic conditions was equal to or even greater than that in oxic treatments. This implies that anoxic decomposition rates may actually have been faster than oxic rates.
|
|
| 25. |
- Bastviken, David, 1971-, et al.
(författare)
-
Simultaneous measurements of organic carbon mineralization and bacterial production in oxic and anoxic lake sediments
- 2003
-
Ingår i: Microbial Ecology. - : Springer Science and Business Media LLC. - 0095-3628 .- 1432-184X. ; 46:1, s. 73-82
-
Tidskriftsartikel (refereegranskat)abstract
- Based on work in marine sediments it can be hypothesized that (i) overall OM mineralization depends on the enzymatic capacity and is largely independent from the energy yield, (ii) similar oxic and anoxic rates are expected for fresh OM, while oxic rates should be faster for old OM that is partially degraded or adsorbed to particles, and (iii) that the thermodynamic energy yield does not regulate mineralization, but primarily determines the energy fraction allocated to bacterial production (BP). We addressed these hypotheses by simultaneous measurements of mineralization rates (MR) and BP in sediments from a eutrophic lake, along with MR measurements in sediments of a dystrophic lake. Anoxic MR were 44 and 78% of oxic MR in the eutrophic and dystrophic lake, respectively, which was always higher than expected given the theoretical energy yields. The BP:MR ratio was 0.94 and 0.24 in the oxic and anoxic treatments, respectively, in accordance with the expected energy yields. Thus, the results support all three hypotheses above. We also critically discuss BP measurements in sediments and suggest that bacterial growth efficiency values from simultaneous MR and BP measurements can be used to evaluate the reliability of BP estimates.
|
|
| 26. |
- Bastviken, David T. E., 1971-, et al.
(författare)
-
Experimental measurements of zebra mussel (Dreissena polymorpha) impacts on phytoplankton community composition
- 1998
-
Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 39:2, s. 375-386
-
Tidskriftsartikel (refereegranskat)abstract
- 1. To investigate direct effects of zebra mussel (Dreissena polymorpha) feeding activities on phytoplankton community composition, short-term microcosm experiments were performed in natural water with complex phytoplankton communities. Both gross effects (without resuspension of mussel excretions) and net effects (with resuspension) were studied. 2. Gross clearance rates were not selective; essentially all taxa were removed at similar rates ranging from 24 to 63 mt mussel(-1) h(-1). Net clearance rates were highly selective; different plankton taxa were removed at very different rates, ranging from 12 to 83% of the gross rates, leading to consistent changes in the phytoplankton community composition. Thus, although zebra mussels can cause most phytoplankton to decline, there is considerable variation among taxa in either pre-digestive selection or post-digestive survival. 3. The direct, short-term effects of zebra mussels on phytoplankton community composition are consistent with some of the major changes observed in the Hudson River since establishment of zebra mussels. 4. We show, with simple calculations, how zebra mussel filtration rate, its selective efficiency on various taxa, and phytoplankton growth rates interact to produce changes in the phytoplankton composition.
|
|
| 27. |
- Bastviken, David, 1971-, et al.
(författare)
-
Temperature sensitivity indicates enzyme controlled chlorination of soil organic matter
- 2009
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:10, s. 3569-3573
-
Tidskriftsartikel (refereegranskat)abstract
- Old assumptions that chloride is inert and that most chlorinated organic matter in soils is anthropogenic have been challenged by findings of naturally formed organochlorines. Such natural chlorination has been recognized for several decades, but there are still very few measurements of chlorination rates or estimates of the quantitative importance of terrestrial chlorine transformations. While much is known about the formation of specific compounds, bulk chlorination remains poorly understood in terms of mechanisms and effects of environmental factors. We quantified bulk chlorination rates in coniferous forest soil using 36Cl-chloride in tracer experiments at different temperatures and with and without molecular oxygen (O2). Chlorination was enhanced by the presence of O2 and had a temperature optimum at 20 °C. Minimum rates were found at high temperatures (50 °C) or under anoxic conditions. The results indicate (1) that most of the chlorination between 4 and 40 °C was biotic and driven by O2 dependent enzymes, and (2) that there is also slower background chlorination occurring under anoxic conditions at 20 °C and under oxic conditions at 50 °C. Hence, while oxic and biotic chlorination clearly dominated, chlorination by other processes including possible abiotic reactions was also detected.
|
|
| 28. |
- Bengtson, Per, et al.
(författare)
-
Possible role of reactive chlorine in microbial antagonism and organic matter chlorination in terrestrial environments
- 2009
-
Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 11:6, s. 1330-1339
-
Forskningsöversikt (refereegranskat)abstract
- Several studies have demonstrated that extensive formation of organically bound chlorine occurs both in soil and in decaying plant material. Previous studies suggest that enzymatic formation of reactive chlorine outside cells is a major source. However, the ecological role of microbial-induced extracellular chlorination processes remains unclear. In the present paper, we assess whether or not the literature supports the hypothesis that extracellular chlorination is involved in direct antagonism against competitors for the same resources. Our review shows that it is by no means rare that biotic processes create conditions that render biocidal concentrations of reactive chlorine compounds, which suggest that extracellular production of reactive chlorine may have an important role in antagonistic microbial interactions. To test the validity, we searched the UniprotPK database for microorganisms that are known to produce haloperoxidases. It appeared that many of the identified haloperoxidases from terrestrial environments are originating from organisms that are associated with living plants or decomposing plant material. The results of the in silico screening were supported by various field and laboratory studies on natural chlorination. Hence, the ability to produce reactive chlorine seems to be especially common in environments that are known for antibiotic-mediated competition for resources (interference competition). Yet, the ability to produce haloperoxidases is also recorded, for example, for plant endosymbionts and parasites, and there is little or no empirical evidence that suggests that these organisms are antagonistic.
|
|
| 29. |
- Carpenter, Stephen R., et al.
(författare)
-
Ecosystem subsidies : Terrestrial support of aquatic food webs from C-13 addition to contrasting lakes
- 2005
-
Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 86:10, s. 2737-2750
-
Tidskriftsartikel (refereegranskat)abstract
- Whole-lake additions of dissolved inorganic C-13 were used to measure allochthony (the terrestrial contribution of organic carbon to aquatic consumers) in two unproductive lakes (Paul and Peter Lakes in 2001), a nutrient-enriched lake (Peter Lake in 2002), and a dystrophic lake (Tuesday Lake in 2002). Three kinds of dynamic models were used to estimate allochthony: a process-rich, dual-isotope flow model based on mass balances of two carbon isotopes in 12 carbon pools; simple univariate time-series models driven by observed time courses of delta(13)CO(2); and multivariate autoregression models that combined information from time series of delta(13)C in several interacting carbon pools. All three models gave similar estimates of allochthony. In the three experiments without nutrient enrichment, flows of terrestrial carbon to dissolved and particulate organic carbon, zooplankton, Chaoborus, and fishes were substantial. For example, terrestrial sources accounted for more than half the carbon flow to juvenile and adult largemouth bass, pumpkinseed sunfish, golden shiners, brook sticklebacks, and fathead minnows in the unenriched experiments. Allochthony was highest in the dystrophic lake and lowest in the nutrient-enriched lake. Nutrient enrichment of Peter Lake decreased allochthony of zooplankton from 0.34-0.48 to 0-0.12, and of fishes from 0.51-0.80 to 0.25-0.55. These experiments show that lake ecosystem carbon cycles, including carbon flows to consumers, are heavily subsidized by organic carbon from the surrounding landscape.
|
|
| 30. |
- Domènech-Gil, Guillem, Mr. Doctor, et al.
(författare)
-
Efficient Methane Monitoring with Low-Cost Chemical Sensorsand Machine Learning
- 2024
-
Konferensbidrag (refereegranskat)abstract
- We present a method to monitor methane at atmospheric concentrations with errors inthe order of tens of parts per billion. We use machine learning techniques and periodic calibrationswith reference equipment to quantify methane from the readings of an electronic nose. The resultsobtained demonstrate versatile and robust solution that outputs adequate concentrations in a varietyof different cases studied, including indoor and outdoor environments with emissions arising fromnatural or anthropogenic sources. Our strategy opens the path to a wide-spread use of low-costsensor system networks for greenhouse gas monitoring.
|
|
| 31. |
- Domènech-Gil, Guillem, Mr. Doctor, et al.
(författare)
-
Electronic Nose for Improved Environmental Methane Monitoring
- 2024
-
Ingår i: Environmental Science and Technology. - : AMER CHEMICAL SOC. - 0013-936X .- 1520-5851. ; 58, s. 352-361
-
Tidskriftsartikel (refereegranskat)abstract
- Reducing emissions of the key greenhouse gas methane (CH4) is increasingly highlighted as being important to mitigate climate change. Effective emission reductions require cost-effective ways to measure CH4 to detect sources and verify that mitigation efforts work. We present here a novel approach to measure methane at atmospheric concentrations by means of a low-cost electronic nose strategy where the readings of a few sensors are combined, leading to errors down to 33 ppb and coefficients of determination, R-2, up to 0.91 for in situ measurements. Data from methane, temperature, humidity, and atmospheric pressure sensors were used in customized machine learning models to account for environmental cross-effects and quantify methane in the ppm-ppb range both in indoor and outdoor conditions. The electronic nose strategy was confirmed to be versatile with improved accuracy when more reference data were supplied to the quantification model. Our results pave the way toward the use of networks of low-cost sensor systems for the monitoring of greenhouse gases.
|
|
| 32. |
- Ekblad, Alf, 1957-, et al.
(författare)
-
Deforestation releases old carbon
- 2019
-
Ingår i: Nature Geoscience. - : Nature Publishing Group. - 1752-0894 .- 1752-0908. ; 12:7, s. 499-500
-
Tidskriftsartikel (refereegranskat)abstract
|
|
| 33. |
- Ekstrand, Eva-Maria, 1985-
(författare)
-
Anaerobic digestion in the kraft pulp and paper industry : Challenges and possibilities for implementation
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The pulp and paper industry is a large producer of wastewater and sludge, putting high pressure on waste treatment. In addition, more rigorous environmental legislation for pollution control and demands to increase the use of renewable energy have put further pressure on the pulp and paper industry’s waste treatment, where anaerobic digestion (AD) and the production of methane could pose a solution. Kraft pulping makes up 80% of the world production of virgin wood pulp, thus, the wastewaters from this sector represent a large unused potential for methane production.There are three main types of substrates available for AD at pulp and paper mills, the wastewaters, the primary sludge/fibre sludge, and the waste activated sludge. AD treatment of these streams has been associated with several challenges, such as the presence of inhibiting compounds or low degradability during AD. The aim of this thesis was to experimentally address these challenges and potentials, focusing on wastes from kraft mills.Methane potential batch tests showed that many wastewater streams still posed challenges to AD, but the alkaline elemental chlorine-free bleaching stream and the condensate effluents had good methane potentials. Further, the methane potential of kraft mill fibre sludge was high, and co-digestion of kraft mill fibre sludge and waste activated sludge was feasible in stirred tank reactors with sludge recirculation. By increasing the organic loading in a pilot-scale activated sludge facility and thereby lowering the sludge age, the degradability of the waste activated sludge was improved. The higher wastewater treatment capacity achieved by this method provides an opportunity for the mills to increase their pulp and paper production. Further, by dewatering the digestate after AD and returning the liquid to the activated sludge treatment, costs for nutrient supplementation can be reduced.In conclusion, the thesis shows that AD of wastes from the kraft pulp and paper industry was feasible and carried many benefits regarding the generation of methane as a renewable energy carrier, improved wastewater treatment and reduced costs. Different strategies on how AD may be implemented in the kraft pulp and paper industry were formulated and discussed.
|
|
| 34. |
- Jansen, Joachim, 1989-, et al.
(författare)
-
Global increase in methane production under future warming of lake bottom waters
- 2022
-
Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 28:18, s. 5427-5440
-
Tidskriftsartikel (refereegranskat)abstract
- Lakes are significant emitters of methane to the atmosphere, and thus are important components of the global methane budget. Methane is typically produced in lake sediments, with the rate of methane production being strongly temperature dependent. Local and regional studies highlight the risk of increasing methane production under future climate change, but a global estimate is not currently available. Here, we project changes in global lake bottom temperatures and sediment methane production rates from 1901 to 2099. By the end of the 21st century, lake bottom temperatures are projected to increase globally, by an average of 0.86-2.60 degrees C under Representative Concentration Pathways (RCPs) 2.6-8.5, with greater warming projected at lower latitudes. This future warming of bottom waters will likely result in an increase in methane production rates of 13%-40% by the end of the century, with many low-latitude lakes experiencing an increase of up to 17 times the historical (1970-1999) global average under RCP 8.5. The projected increase in methane production will likely lead to higher emissions from lakes, although the exact magnitude of the emission increase requires more detailed regional studies.
|
|
| 35. |
- Karlson, Martin, 1980-, et al.
(författare)
-
Multi‐Source Mapping of Peatland Types Using Sentinel‐1, Sentinel‐2, and Terrain Derivatives—A Comparison Between Five High‐Latitude Landscapes
- 2023
-
Ingår i: Journal of Geophysical Research - Biogeosciences. - : John Wiley & Sons. - 2169-8953 .- 2169-8961. ; 128:4
-
Tidskriftsartikel (refereegranskat)abstract
- Mapping wetland types in northern-latitude regions with Earth Observation (EO) data is important for several practical and scientific applications, but at the same time challenging due to the variability and dynamic nature in wetland features introduced by differences in geophysical conditions. The objective of this study was to better understand the ability of Sentinel-1 radar data, Sentinel-2 optical data and terrain derivatives derived from Copernicus digital elevation model to distinguish three main peatland types, two upland classes, and surface water, in five contrasting landscapes located in the northern parts of Alaska, Canada and Scandinavia. The study also investigated the potential benefits for classification accuracy of using regional classification models constructed from region-specific training data compared to a global classification model based on pooled reference data from all five sites. Overall, the results show high promise for classifying peatland types and the three other land cover classes using the fusion approach that combined all three EO data sources (Sentinel-1, Sentinel-2 and terrain derivatives). Overall accuracy for the individual sites ranged between 79.7% and 90.3%. Class specific accuracies for the peatland types were also high overall but differed between the five sites as well as between the three classes bog, fen and swamp. A key finding is that regional classification models consistently outperformed the global classification model by producing significantly higher classification accuracies for all five sites. This suggests for progress in identifying effective approaches for continental scale peatland mapping to improve scaling of for example, hydrological- and greenhouse gas-related processes in Earth system models.
|
|
| 36. |
- Klaus, Marcus, et al.
(författare)
-
Greenhouse gas emissions from boreal inland waters unchanged after forest harvesting
- 2018
-
Ingår i: Biogeosciences. - Goettingen, Germany : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 15:18, s. 5575-5594
-
Tidskriftsartikel (refereegranskat)abstract
- Forestry practices often result in an increased export of carbon and nitrogen to downstream aquatic systems. Although these losses affect the greenhouse gas (GHG) budget of managed forests, it is unknown if they modify GHG emissions of recipient aquatic systems. To assess this question, air-water fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were quantified for humic lakes and their inlet streams in four boreal catchments using a before-after control-impact experiment. Two catchments were treated with forest clear-cuts followed by site preparation (18 % and 44 % of the catchment area). GHG fluxes and hydrological and physicochemical water characteristics were measured at multiple locations in lakes and streams at high temporal resolution throughout the summer season over a 4-year period. Both lakes and streams evaded all GHGs. The treatment did not significantly change GHG fluxes in streams or lakes within 3 years after the treatment, despite significant increases of CO2 and CH4 concentrations in hillslope groundwater. Our results highlight that GHGs leaching from forest clear-cuts may be buffered in the riparian zone-stream continuum, likely acting as effective biogeochemical processors and wind shelters to prevent additional GHG evasion via downstream inland waters. These findings are representative of low productive forests located in relatively flat landscapes where forestry practices cause only a limited initial impact on catchment hydrology and biogeochemistry.
|
|
| 37. |
- Lauerwald, R., et al.
(författare)
-
Natural lakes are a minor global source of N2O to the atmosphere
- 2019
-
Ingår i: Global Biogeochemical Cycles. - : Wiley-Blackwell. - 0886-6236 .- 1944-9224. ; 33:12, s. 1564-1581
-
Tidskriftsartikel (refereegranskat)abstract
- Natural lakes and reservoirs are important, yet not well constrained sources of greenhouse gasses to the atmosphere. In particular for N2O emissions, a huge variability is observed in the few, observation‐driven flux estimates that have been published so far. Recently, a process‐based, spatially explicit model has been used to estimate global N2O emissions from more than 6,000 reservoirs based on nitrogen (N) and phosphorous inflows and water residence time. Here, we extend the model to a dataset of 1.4 million standing water bodies comprising natural lakes and reservoirs. For validation, we normalized the simulated N2O emissions by the surface area of each water body and compared them against regional averages of N2O emission rates taken from the literature or estimated based on observed N2O concentrations. We estimate that natural lakes and reservoirs together emit 4.5±2.9 Gmol N2O‐N yr‐1 globally. Our global scale estimate falls in the far lower end of existing, observation‐driven estimates. Natural lakes contribute only about half of this flux, although they contribute 91% of the total surface area of standing water bodies. Hence, the mean N2O emission rates per surface area are substantially lower for natural lakes than for reservoirs with 0.8±0.5 mmol N m‐2yr‐1 vs. 9.6±6.0 mmol N m‐2yr‐1, respectively. This finding can be explained by on average lower external N inputs to natural lakes. We conclude that upscaling based estimates, which do not distinguish natural lakes from reservoirs, are prone to important biases.
|
|
| 38. |
- Lundqvist, Johan, et al.
(författare)
-
Innovative drinking water treatment techniques reduce the disinfection-induced oxidative stress and genotoxic activity
- 2019
-
Ingår i: Water Research. - : Elsevier. - 0043-1354 .- 1879-2448. ; 5, s. 182-192
-
Tidskriftsartikel (refereegranskat)abstract
- Disinfection of drinking water using chlorine can lead to the formation of genotoxic by-products whenchlorine reacts with natural organic matter (NOM). A vast number of such disinfection by-products(DBPs) have been identified, making it almost impossible to routinely monitor all DBPs with chemicalanalysis. In this study, a bioanalytical approach was used, measuring oxidative stress (Nrf2 activity),genotoxicity (micronucleus test), and aryl hydrocarbon receptor (AhR) activation to evaluate an innovativewater treatment process, including suspended ion exchange, ozonation, in-line coagulation,ceramic microfiltration, and granular activated carbon. Chlorination was performed in laboratory scaleafter each step in the treatment process in order to investigate the effect of each treatment process to theformation of DBPs. Suspended ion exchange had a high capacity to remove dissolved organic carbon(DOC) and to decrease UV absorbance and Nrf2 activity in non-chlorinated water. High-dose chlorination(10 mg Cl2 L-1) of raw water caused a drastic induction of Nrf2 activity, which was decreased by 70% inwater chlorinated after suspended ion exchange. Further reduction of Nrf2 activity following chlorinationwas achieved by ozonation and the concomitant treatment steps. The ozonation treatment resulted indecreased Nrf2 activity in spite of unchanged DOC levels. However, a strong correlation was found betweenUV absorbing compounds and Nrf2 activity, demonstrating that Nrf2 inducing DBPs were formedfrom pre-cursors of a specific NOM fraction, constituted of mainly aromatic compounds. Moreover, highdosechlorination of raw water induced genotoxicity. In similarity to the DOC levels, UV absorbance andNrf2 activity, the disinfection-induced genotoxicity was also reduced by each treatment step of theinnovative water treatment technique. AhR activity was observed in the water produced by the conventionalprocess and in the raw water, but the activity was clearly decreased by the ozonation step inthe innovative water treatment process.
|
|
| 39. |
- MacIntyre, Sally, et al.
(författare)
-
Turbulence in a small boreal lake: Consequences for air-water gas exchange
- 2021
-
Ingår i: Limnology and Oceanography. - : WILEY. - 0024-3590 .- 1939-5590. ; 66:3, s. 827-854
-
Tidskriftsartikel (refereegranskat)abstract
- The hydrodynamics within small boreal lakes have rarely been studied, yet knowing whether turbulence at the air-water interface and in the water column scales with metrics developed elsewhere is essential for computing metabolism and fluxes of climate-forcing trace gases. We instrumented a humic, 4.7 ha, boreal lake with two meteorological stations, three thermistor arrays, an infrared (IR) camera to quantify surface divergence, obtained turbulence as dissipation rate of turbulent kinetic energy (epsilon) using an acoustic Doppler velocimeter and a temperature-gradient microstructure profiler, and conducted chamber measurements for short periods to obtain fluxes and gas transfer velocities (k). Near-surface epsilon varied from 10(-8) to 10(-6) m(2) s(-3) for the 0-4 m s(-1) winds and followed predictions from Monin-Obukhov similarity theory. The coefficient of eddy diffusivity in the mixed layer was up to 10(-3) m(2) s(-1) on the windiest afternoons, an order of magnitude less other afternoons, and near molecular at deeper depths. The upper thermocline upwelled when Lake numbers (L-N) dropped below four facilitating vertical and horizontal exchange. k computed from a surface renewal model using epsilon agreed with values from chambers and surface divergence and increased linearly with wind speed. Diurnal thermoclines formed on sunny days when winds were < 3 m s(-1), a condition that can lead to elevated near-surface epsilon and k. Results extend scaling approaches developed in the laboratory and for larger water bodies, illustrate turbulence and k are greater than expected in small wind-sheltered lakes, and provide new equations to quantify fluxes.
|
|
| 40. |
- Montelius, Malin, 1984-, et al.
(författare)
-
Radiotracer evidence that the rhizosphere is a hot-spot for chlorination of soil organic matter
- 2019
-
Ingår i: Plant and Soil. - : Springer. - 0032-079X .- 1573-5036. ; 443:1-2, s. 245-257
-
Tidskriftsartikel (refereegranskat)abstract
- AimsThe ubiquitous and extensive natural chlorination of organic matter in soils, leading to levels of chlorinated soil organic matter that often exceed the levels of chloride, remains mysterious in terms of its causes and regulation. While the composition of plant species and the availability of labile organic matter was recently shown to be important, the physical localization of chlorination in soils remains unclear but is a key for understanding regulation and patterns observed. Here we assess the relative importance of organic matter chlorination in (a) bulk soil, (b) the plant roots plus the rhizosphere zone surrounding the roots, and (c) above-ground plant biomass, in an experimental plant-soil system.MethodsA radiotracer, 36Cl, was added to study translocation and transformations of Cl− and Clorg in agricultural soil with and without wheat (Triticum vulgare) over 50 days.ResultsThe specific chlorination rates (the fraction of the added 36Cl− converted to 36Clorg per day) in soil with plants was much higher (0.02 d−1) than without plants (0.0007 d−1) at peak growth (day 25). The plant root and rhizosphere showed much higher formation of 36Clorg than the bulk soil, suggesting that the rhizosphere is a hotspot for chlorination in the soil. In addition, the treatment with plants displayed a rapid and high plant uptake of Cl−.ConclusionsOur results indicate that the rhizosphere harbour the most extensive in-situ chlorination process in soil and that root-soil interaction may be key for terrestrial chlorine cycling.
|
|
| 41. |
- Safaric, Luka, 1988-, et al.
(författare)
-
Effect of Cobalt, Nickel, and Selenium/Tungsten Deficiency on Mesophilic Anaerobic Digestion of Chemically Defined Soluble Organic Compounds
- 2020
-
Ingår i: Microorganisms. - : MDPI. - 2076-2607. ; 8:4
-
Tidskriftsartikel (refereegranskat)abstract
- Trace elements (TEs) are vital for anaerobic digestion (AD), due to their role as cofactors in many key enzymes. The aim of this study was to evaluate the effects of specific TE deficiencies on mixed microbial communities during AD of soluble polymer-free substrates, thus focusing on AD after hydrolysis. Three mesophilic (37 degrees C) continuous stirred-tank biogas reactors were depleted either of Co, Ni, or a combination of Se and W, respectively, by discontinuing their supplementation. Ni and Se/W depletion led to changes in methane kinetics, linked to progressive volatile fatty acid (VFA) accumulation, eventually resulting in process failure. No significant changes occurred in the Co-depleted reactor, indicating that the amount of Co present in the substrate in absence of supplementation was sufficient to maintain process stability. Archaeal communities remained fairly stable independent of TE concentrations, while bacterial communities gradually changed with VFA accumulation in Ni- and Se-/W-depleted reactors. Despite this, the communities remained relatively similar between these two reactors, suggesting that the major shifts in composition likely occurred due to the accumulating VFAs. Overall, the results indicate that Ni and Se/W depletion primarily lead to slower metabolic activities of methanogenic archaea and their syntrophic partners, which then has a ripple effect throughout the microbial community due to a gradual accumulation of intermediate fermentation products.
|
|
| 42. |
|
|
| 43. |
- Safaric, Luka, 1988-, et al.
(författare)
-
Rheology, Micronutrients, and Process Disturbance in Continuous Stirred-Tank Biogas Reactors
- 2023
-
Ingår i: Industrial & Engineering Chemistry Research. - : AMER CHEMICAL SOC. - 0888-5885 .- 1520-5045. ; 62:43, s. 17372-17384
-
Forskningsöversikt (refereegranskat)abstract
- Anaerobic digestion (AD) is an important technology for achieving sustainability, but it faces challenges in meeting rising production demands while remaining economically profitable. One difficulty is the lack of a comprehensive understanding of the many interactions within anaerobic digesters, which makes it challenging to fully optimize them. This is particularly notable when considering the interlinked dynamics between micronutrient availability and fluid behavior. This study addresses this gap by focusing on key operational parameters affecting the efficiency of the process in continuous stirred-tank biogas reactors, which are the most used AD technology today. It does so by proposing and evaluating a novel conceptual model of the mechanisms behind how different parts of AD processes interact upon disturbance, highlighting strategies for preventing process failure. This article aims to improve our understanding of the complexity of AD biotechnology and to provide a starting point for developing advanced strategies for operational optimization.
|
|
| 44. |
- Schenk, Jonathan, 1992-
(författare)
-
Methane dynamics in northern lakes : Insights from multi-scale observations
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Methane (CH4) is a potent greenhouse gas which is emitted to the atmosphere from both natural and anthropogenic sources. Current evidence indicates that lakes account for a large part of the global emissions of CH4, but their contribution is difficult to quantify because of large temporal and spatial variability in processes leading to CH4 fluxes from lakes to the atmosphere. Making sense of the complexity and variability of CH4 emissions from lakes requires observations covering the range of temporal and spatial scales at which these processes occur, both within and between lakes. Northern regions are of particular interest for such studies because they contain a larger number of lakes than any other region in the world and they are disproportionately affected by climate change, with possible consequences for future CH4 emissions.The aim of this thesis was to investigate patterns of CH4 dynamics and emissions in several lakes distributed in different climatic regions of Sweden, paying particular attention to spatial and temporal variability of CH4 fluxes and concentrations. Fluxes, concentrations, carbon stable isotope signature of CH4, and a range of commonly monitored lake characteristics were measured several times during one year at multiple locations in each lake. The measurements provided an extensive set of observations of CH4 concentrations and fluxes in lakes, together with possible environmental drivers. These observations were then used to investigate patterns of CH4 dynamics in northern lakes and to assess the ability of empirical and process-based models to predict CH4 concentrations and fluxes in lakes.The results indicate that simple empirical models, consisting of linear regressions between explanatory variables and CH4 fluxes and concentrations averaged over the lake surface and ice-free period of the year, can be useful in some specific cases (for example describing ebullitive fluxes from total phosphorus or chlorophyll a concentrations). However, it was also noted that using such models for extrapolation can lead to large errors, especially if the observations do not account for temporal and spatial variability of CH4 fluxes and concentrations. An example of high variability was seen in day-night measurements of CH4 fluxes in four lakes over several months. To try to compensate for some of the shortcomings of empirical models, an established process-based and one-dimensional lake model was used to simulate CH4 concentration in the water column of the studied lakes. Predictions were in good agreement with observations in several of the investigated lakes, considering that the model was not pre-calibrated for any of the lake specifically. However, it was also clear that there can be key processes that require specific consideration in process-based models, and some degree of simplification is needed, especially when detailed information on the modelled systems is not available. The simplifications and assumptions that need to be made can be informed by the study and observation of relevant processes in situ. For example, groundwater was found to potentially contribute a major part of CH4 stored in one small boreal lake using measurements of stable isotope signature of CH4 in littoral sediment and deep water of that lake, as well as in the groundwater in the mire next to it. Stable isotope measurements in five other lakes also revealed consistent differences in CH4 sources to the surface and deep zones of lakes when they are separated by thermal stratification of the water column. Such knowledge could be used in the design of numerical models of lakes with the objective to improve predictions of current and future emissions of CH4 from these environments.Overall, this thesis contributes to the current knowledge on assessment of CH4 emissions from lakes at several temporal and spatial scales. It also emphasizes critical aspects which must be considered to reduce bias in future empirical and process-based models of CH4 in lakes.
|
|
| 45. |
- Svensson, Teresia, 1975-, et al.
(författare)
-
Chlorination of soil organic matter : The role of humus type and land use
- 2022
-
Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 806p2
-
Tidskriftsartikel (refereegranskat)abstract
- The levels of natural organic chlorine (Clorg) typically exceed levels of chloride in most soils and is therefore clearly of high importance for continental chlorine cycling. The high spatial variability raises questions on soil organic matter (SOM) chlorination rates among topsoils with different types of organic matter. We measured Clorg formation rates along depth profiles in six French temperate soils with similar Cl deposition using 36Cl tracer experiments. Three forest sites with different humus types and soils from grassland and arable land were studied. The highest specific chlorination rates (fraction of chlorine pool transformed to Clorg per time unit) among the forest soils were found in the humus layers. Comparing the forest sites, specific chlorination was highest in mull-type humus, characterized by high microbial activity and fast degradation of the organic matter. Considering non-humus soil layers, grassland and forest soils had similar specific chlorination rates in the uppermost layer (0–10 cm below humus layer). Below this depth the specific chlorination rate decreased slightly in forests, and drastically in the grassland soil. The agricultural soil exhibited the lowest specific chlorination rates, similar along the depth profile. Across all sites, specific chlorination rates were correlated with soil moisture and in combination with the patterns on organic matter types, the results suggest an extensive Cl cycling where humus types and soil moisture provided best conditions for microbial activity. Clorg accumulation and theoretical residence times were not clearly linked to chlorination rates. This indicates intensive Cl cycling between organic and inorganic forms in forest humus layers, regulated by humic matter reactivity and soil moisture, while long-term Clorg accumulation seems more linked with overall deep soil organic carbon stabilization. Thus, humus types and factors affecting soil carbon storage, including vegetation land use, could be used as indicators of potential Clorg formation and accumulation in soils.
|
|
| 46. |
- Svensson, Teresia, 1975-, et al.
(författare)
-
Chlorine cycling and the fate of Cl in terrestrial environments
- 2021
-
Ingår i: Environmental Science and Pollution Research. - : Springer. - 0944-1344 .- 1614-7499. ; 28:7, s. 7691-7709
-
Tidskriftsartikel (refereegranskat)abstract
- Chlorine (Cl) in the terrestrial environment is of interest from multiple perspectives, including the use of chloride as a tracer forwater flow and contaminant transport, organochlorine pollutants, Cl cycling, radioactive waste (radioecology; 36Cl is of largeconcern) and plant science (Cl as essential element for living plants).During the past decades, there has been a rapid developmenttowards improved understanding of the terrestrial Cl cycle. There is a ubiquitous and extensive natural chlorination of organicmatter in terrestrial ecosystems where naturally formed chlorinated organic compounds (Clorg) in soil frequently exceed theabundance of chloride. Chloride dominates import and export from terrestrial ecosystems while soil Clorg and biomass Cl candominate the standing stock Cl. This has important implications for Cl transport, as chloride will enter the Cl pools resulting inprolonged residence times. Clearly, these pools must be considered separately in future monitoring programs addressing Clcycling. Moreover, there are indications that (1) large amounts of Cl can accumulate in biomass, in some cases representing themain Cl pool; (2) emissions of volatile organic chlorines could be a significant export pathway of Cl and (3) that there is aproduction of Clorg in tissues of, e.g. plants and animals and that Cl can accumulate as, e.g. chlorinated fatty acids in organisms.Yet, data focusing on ecosystem perspectives and combined spatiotemporal variability regarding various Cl pools are still scarce,and the processes and ecological roles of the extensive biological Cl cycling are still poorly understood.
|
|
| 47. |
- Svensson, Teresia, 1975-, et al.
(författare)
-
Chlorine Distribution in Soil and Vegetation in Boreal Habitats along a Moisture Gradient from Upland Forest to Lake Margin Wetlands
- 2023
-
Ingår i: Environmental Science and Technology. - : AMER CHEMICAL SOC. - 0013-936X .- 1520-5851. ; 57:30, s. 11067-11074
-
Tidskriftsartikel (refereegranskat)abstract
- The assumed dominance of chloride (Cl–) in terrestrial ecosystems is challenged by observations of extensive formation of organically bound Cl (Clorg), resulting in large soil Cl storage and internal cycling. Yet, little is known about the spatial distribution of Cl in ecosystems. We quantified patterns of Cl distribution in different habitats along a boreal hillslope moisture gradient ranging from relatively dry upland coniferous forests to wet discharge areas dominated by alder. We confirmed that dry habitats are important for Cl storage but found that Cl pools tended to be larger in moist and wet habitats. The storage of Clorg was less important in wet habitats, suggesting a shift in the balance between soil chlorination and dechlorination rates. Cl concentrations in the herb layer vegetation were high in wet and moist sites attributed to a shift in plant species composition, indicating plant community-dependent ecosystem Cl cycling. Mass-balance calculations showed that internal Cl cycling increased overall ecosystem Cl residence times at all sites and that plant uptake rates of Cl– were particularly high at wet sites. Our results indicate that habitat characteristics including plant communities and hydrology are key for understanding Cl cycling in the environment.
|
|
| 48. |
- Svensson, Teresia, 1975-, et al.
(författare)
-
Cl distribution in different terrestrial habitats along hill slope gradients in Forsmark
- 2021
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The view of chlorine in nature is undergoing a major change as a result of the recent decades of research. It is now clear that chloride (Cl−), that was previously considered non-reactive and the totally dominating Cl species, instead is reactive and does not always constitute the predominant form of chlorine (Cl) (e.g. Bastviken et al. 2013, Svensson et al. 2007). Extensive natural chlorination of organic matter occurs in many terrestrial ecosystems (Gustavsson et al. 2012, Redon et al. 2011). Experiments with radioactive Cl (36Cl) as tracer have confirmed natural chlorination rates corresponding to as much as 50–300 % of the annual wet deposition of Cl in several types of soils (Bastviken et al. 2007, 2009). Substantial chlorination of organic matter occurs in a wide range of agricultural and forest soils (Gustavsson et al. 2012, Redon et al. 2013). The estimates are based on bulk soil excluding roots, which is likely an underestimation of the chlorination potential as it was later shown that the majority of chlorination occurs in the rhizosphere (Montelius et al. 2019). Available evidence indicates that 29–100 % of Cl in soil is organically bound (Clorg) (Bastviken et al. 2013, Redon et al. 2011). Therefore, it is not surprising that Clorg in soils frequently exceeds the level of Cl−. This dominance of Clorg in soils has been observed in several different types of soils. A study in France reported that > 80 % of the total chlorine was Clorg across grassland, arable and forest soils (Redon et al. 2013).
|
|
| 49. |
- Valle, Juliana, et al.
(författare)
-
Molecular differences between water column and sediment porewater SPE-DOM in ten Swedish boreal lakes
- 2020
-
Ingår i: Water Research. - : Elsevier. - 0043-1354 .- 1879-2448. ; 170
-
Tidskriftsartikel (refereegranskat)abstract
- Boreal lakes are considered hot spots of dissolved organic matter (DOM) processing within the globalcarbon cycle. This study has used FT-ICR mass spectrometry and comprehensive data evaluation to assessthe molecular differences of SPE-DOM between lake column water SPE-DOM and sedimentary porewater SPE-DOM in 10 Swedish boreal lakes of the Malingsbo area, which were selected for their largediversity of physicochemical and morphological characteristics. While lake column water is well mixedand fairly oxygenated, sedimentary pore water is subject to depletion of oxygen and to confinement ofmolecules. Robust trends were deduced from molecular compositions present in all compartments andin all 10 lakes (“common compositions”) with recognition of relative abundance. Sedimentary pore waterSPE-DOM featured higher proportions of heteroatoms N and S, higher average H/C ratios in presence ofhigher DBE/C ratios, and higher average oxygenation than lake column water SPE-DOM. These trendswere observed in all lakes except Ljustj€arn, which is a ground water fed kettle lake with an unique lakebiogeochemistry. Analogous trends were also observed in case of single or a few lakes and operated alsofor compounds present solely in either lake column water or sedimentary pore water. Unique compoundsdetected in either compartments and/or in a few lakes showed higher molecular diversity thanthe “common compositions”. Processing of DOM molecules in sediments included selective preservationfor polyphenolic compounds and microbial resynthesis of selected molecules of considerable diversity.
|
|
