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  • 1.
    Becher, Marina
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Cryogenic soil processes in a changing climate2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    A considerable part of the global pool of terrestrial carbon is stored in high latitude soils. In these soils, repeated cycles of freezing and thawing creates soil motion (cryoturbation) that in combination with other cryogenic disturbance processes may play a profound role in controlling the carbon balance of the arctic soil. Conditions for cryogenic soil processes are predicted to dramatically change in response to the ongoing climate warming, but little is known how these changes may affect the ability of arctic soils to accumulate carbon. In this thesis, I utilize a patterned ground system, referred to as non-sorted circles, as experimental units and quantify how cryogenic soil processes affect plant communities and carbon fluxes in arctic soils. I show that the cryoturbation has been an important mechanism for transporting carbon downwards in the studied soil over the last millennia. Interestingly, burial of organic material by cryoturbation appears to have mainly occurred during bioclimatic events occurring around A.D. 900-1250 and A.D. 1650-1950 as indicated by inferred 14C ages. Using a novel photogrammetric approach, I estimate that about 0.2-0.8 % of the carbon pool is annually subjected to a net downward transport induced by the physical motion of soil. Even though this flux seems small, it suggests that cryoturbation is an important transporter of carbon over centennial and millennial timescales and contributes to translocate organic matter to deeper soil layers where respiration proceeds at slow rates. Cryogenic processes not only affect the trajectories of the soil carbon, but also generate plant community changes in both species composition and abundance, as indicated by a conducted plant survey on non-sorted circles subjected to variable differential frost heave during the winter. Here, disturbance-tolerant plant species, such as Carex capillaris and Tofieldia pusilla, seem to be favoured by disturbance generated by the differential heave. Comparison with findings from a previous plant survey on the site conducted in the 1980s suggest that the warmer temperatures during the last decades have resulted in decreased differential heave in the studied non-sorted circles. I argue that this change in cryogenic activity has increased abundance of plants present in the 1980s. The fact that the activity and function of the non-sorted circles in Abisko are undergoing changes is further supported by their contemporary carbon dioxide (CO2) fluxes. Here, my measurements of CO2 fluxes suggest that all studied non-sorted circles act as net CO2 sources and thus that the carbon balance of the soils are in a transition state. My results highlight the complex but important relationship between cryogenic soil processes and the carbon balance of arctic soils.

  • 2.
    Campeau, Audrey
    Uppsala universitet, Luft-, vatten och landskapslära.
    Carbon in Boreal Streams: Isotopic Tracing of Terrestrial Sources2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The boreal biome comprises vast areas of coniferous forests, dotted with millions of peatlands. Plants harbouring these ecosystems fix CO2 from the atmosphere, which is later incorporated into the vegetation biomass and subsequently buried in soils. Over the course of millennia, this process has led to the formation of a large repository of organic C, currently stored in boreal soils. Streams draining this landscape are typically enriched with carbon dioxide (CO2), methane (CH4) and dissolved organic carbon (DOC). As a consequence, streams tend to emit CO2 and CH4 to the atmosphere, two potent greenhouse gases, and thus contribute positively to radiative climate forcing. The sources fuelling C to boreal streams are not well understood. This thesis aims to unravel these sources, and promote a better consolidation of terrestrial and aquatic C biogeochemical processes. The work is largely based on stable and radiogenic C isotope characterization of various dissolved C forms in stream and groundwater, within contrasting ecosystem types across Sweden.

    This thesis identifies boreal soils as the main source of CO2 in streams. Soil respiration (i.e. biogenic sources) overwhelmingly supply CO2 to streams, leaving only a few exceptions where geogenic CO2 sources were present. An array of biological processes also transform CO2 during its transport from soils to streams. These include; methanogenesis, aquatic DOC mineralization and primary production. The majority of C in boreal streams is sustained by the decomposition of recent photosynthates, with ancient C substrates holding a negligible share of the total C export. While these results suggest that the repository of ancient soil organic C is currently stable, within boreal forests and peatlands, the close connection with recently occurring photosynthesis suggest that forecasted alterations in plant C allocation patterns, driven by climate and land-use changes, will produce a rapid response in stream CO2 emissions. Isotopic characterization of C in stream and groundwater can help reveal these sources and transformation processes, but its interpretation must be made with care.

  • 3.
    Jantunen, Liisa
    et al.
    Environment Canada, Canada.
    Wong, Fiona
    Stockholm University.
    Gawor, Anya
    Environment Canada.
    Kylin, Henrik
    Linköpings universitet, Tema Miljöförändring.
    Helm, Paul
    Ontario Ministry of the Environment, Canada.
    Stern, Gary
    University of Manitoba, Canada.
    Strachan, William
    Environment Canada, Canada.
    Burniston, Deborah
    Environment Canada, Canada.
    Bidleman, Terry
    Umeå University.
    20 Years of Air-Water Gas Exchange Observations for Pesticides in the Western Arctic Ocean2015Ingår i: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, nr 23, s. 13844-13852Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Arctic has been contaminated by legacy organochlorine pesticides (OCPs) and currently used pesticides (CUPs) through atmospheric transport and oceanic currents. Here we report the time trends and air−water exchange of OCPs and CUPs from research expeditions conducted between 1993 and 2013. Compounds determined in both air and water were trans- and cis-chlordanes (TC, CC), trans- and cis-nonachlors (TN, CN), heptachlor exo-epoxide (HEPX), dieldrin (DIEL), chlorobornanes (ΣCHBs and toxaphene), dacthal (DAC), endosulfans and metabolite endosulfan sulfate (ENDO-I, ENDO-II, and ENDO SUL), chlorothalonil (CHT), chlorpyrifos (CPF), and trifluralin (TFN). Pentachloronitrobenzene (PCNB and quintozene) and its soil metabolite pentachlorothianisole (PCTA) were also found in air. Concentrations of most OCPs declined in surface water, whereas some CUPs increased (ENDO-I, CHT, and TFN) or showed no significant change (CPF and DAC), and most compounds declined in air. Chlordane compound fractions TC/(TC + CC) and TC/(TC + CC + TN) decreased in water and air, while CC/(TC + CC + TN) increased. TN/(TC + CC + TN) also increased in air and slightly, but not significantly, in water. These changes suggest selective removal of more labile TC and/or a shift in chlordane sources. Water−air fugacity ratios indicated net volatilization (FR > 1.0) or near equilibrium (FR not significantly different from 1.0) for most OCPs but net deposition (FR < 1.0) for ΣCHBs. Net deposition was shown for ENDO-I on all expeditions, while the net exchange direction of other CUPs varied. Understanding the processes and current state of air−surface exchange helps to interpret environmental exposure and evaluate the effectiveness of international protocols and provides insights for the environmental fate of new and emerging chemicals.

  • 4.
    Lundkvist, Markus
    Uppsala universitet, Institutionen för geovetenskaper.
    Accident Risk and Environmental Assessment: Development of an Assessment Guideline with Examination in Northern Scandinavia2005Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    In environmental impact assessment (EIA), accident risk should be considered as one impact. However, few studies have compared assessed risk levels with documented accidents. There is thus a need for assessing accuracy of risk assessment methodologies. The aim of this study was to develop and examine a risk assessment guideline based on environmental assessment. The guideline examination was carried out along the railway and the road between Kiruna and Narvik, Northern Scandinavia. The examined hazards were avalanches, debris flows, rock falls, slush flows, torrents, moose and reindeer. Documented accidents were quantified into an accident level. For each hazard type, six sections/sites were assessed. The propensities of these hazards were analysed through environmental assessments, especially by utilising geomorphology. Then, the accident densities along the sections/sites were compared with assessed accident phase indices describing risk and hazard in both spatial and temporal dimensions. The average uncertainty factors for both the risk and the hazard indices were about 5. This implies a fairly good precision. Risk and hazard indices were also rated and compared to the accident density rates. Thereafter, railway and road information was split up as different proposal alternatives in an EIA context. The total risk for each proposal was compared with the total accident density. The risk assessment guideline proved to be cost-efficient, rapid and relatively reliable in comparing accident risk.

  • 5.
    McLoughlin, Stephen
    et al.
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Bomfleur, Benjamin
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Thomas, Mörs
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    The wierd world of fossil worm cocoons2016Ingår i: Deposits Magazine, ISSN 1744-9588, Vol. 46, s. 399-406Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    Curious fossils in continental sedimentary strata that range from about a millimetre in diameter up to the size of a fingernail and appear to have a net-like coating on the surface have reported for over 150 years and have been variously interpreted as the eggs of insects, parts of lichens, the food-catching devices of ancient invertebrates, the membranous coatings of seeds, or the linings of clubmoss sporangia. Many early palaeobiologists simply labelled them as ‘red eggs’ and avoided assigning them to any particular biological group. However, these fossils match the characteristics of the egg-bearing cocoons of modern leeches and their relatives. During cocoon secretion, micro-organisms from the surrounding environment can become entrapped and entombed in the sticky threads of the cocoon wall, thus escaping decay, and ultimately becoming part of the fossil record.

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