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  • 1401. Wong, Fiona
    et al.
    Jantunen, Liisa M
    Papakyriakou, Tim
    Staebler, Ralf M
    Stern, Gary A
    Bidleman, Terry F
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Comparison of micrometeorological and two-film estimates of air-water gas exchange for alpha-hexachlorocyclohexane in the Canadian archipelago2012In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 19, no 6, p. 1908-1914Article in journal (Refereed)
    Abstract [en]

    The air-sea gas exchange of alpha-hexachlorocyclohexane (alpha-HCH) in the Canadian Arctic was estimated using a micrometeorological approach and the commonly used Whitman two-film model. Concurrent shipboard measurements of alpha-HCH in air at two heights (1 and 15 m) and in surface seawater were conducted during the Circumpolar Flaw Lead study in 2008. Sampling was carried out during eight events in the early summer time when open water was encountered. The micrometeorological technique employed the vertical gradient in air concentration and the wind speed to estimate the flux; results were corrected for atmospheric stability using the Monin-Obukhov stability parameter. The Whitman two-film model used the concentrations of alpha-HCH in surface seawater, in bulk air at 1 and 15 m above the surface, and the Henry's law constant adjusted for temperature and salinity to derive the flux. Both approaches showed that the overall net flux of alpha-HCH was from water to air. Mean fluxes calculated using the micrometeorological technique ranged from -3.5 to 18 ng m(-2) day(-1) (mean 7.4), compared to 3.5 to 14 ng m(-2) day(-1) (mean 7.5) using the Whitman two-film model. Flux estimates for individual events agreed in direction and within a factor of two in magnitude for six of eight events. For two events, fluxes estimated by micrometeorology were zero or negative, while fluxes estimated with the two-film model were positive, and the reasons for these discrepancies are unclear. Improvements are needed to shorten air sampling times to ensure that stationarity of meteorological conditions is not compromised over the measurement periods. The micrometeorological technique could be particularly useful to estimate fluxes of organic chemicals over water in situations where no water samples are available.

  • 1402. Wu, Pianpian
    et al.
    Kainz, Martin
    Akerblom, Staffan
    Garcia Bravo, Andrea
    Sonesten, Lars
    Branfireun, Brian
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Natural Sciences, University of Agder, Kristiansand, Norway; Norwegian Institute for Water Research (NIVA), Grimstad, Norway.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bishop, Kevin
    Terrestrial diet influences mercury bioaccumulation in zooplankton and macroinvertebrates in lakes with differing dissolved organic carbon concentrations2019In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 669, p. 821-832Article in journal (Refereed)
    Abstract [en]

    Dietary uptake is a key step in conveying both toxic mercury (Hg; particularly as highly bioavailable methylmercury, MeHg) and essential dietary biochemicals, such as polyunsaturated fatty acids (PUFA), across trophic levels within aquatic food webs. Using stable isotopes and fatty acids we evaluated the role of food sources in size-fractioned plankton and littoral macroinvertebrates for the bioaccumulation of total Hg and MeHg in six oligotrophic and one mesotrophic Swedish lakes with differing concentrations of dissolved organic carbon (DOC). We found that the consumption of both algal and terrestrial diets (assessed by PUFA and long-chain saturated fatty acids, respectively) predicted >66% of the Hg concentration variability in meso- (100-500 mu m) and macrozooplankton (>500 mu m) in oligotrophic lakes. In the mesotrophic lake, total Hg bioaccumulation in higher trophic level biota, carnivorous macroinvertebrates was also significantly related to terrestrial diet sources (R-2 = 0.65, p < 0.01). However, lake pH and DOC correlated to total Hg bioaccumulation and bioconcentration across all lakes, suggesting the consumption of different diet sources is mediated by the influence of lake characteristics. This field study reveals that using dietary biomarkers (stable isotopes and fatty acids) together with the physico-chemical lake parameters pH and nutrients together improve our ability to predict Hg bioaccumulation in aquatic food webs. Fatty acids used as dietary biomarkers provide correlative evidence of specific diet source retention in consumers and their effect on Hg bioaccumulation, while pH and nutrients are the underlying physico-chemical lake parameters controlling differences in Hg bioaccumulation between lakes. 

  • 1403. Xu, Jing
    et al.
    Marsac, Remi
    Wei, Cheng
    Wu, Feng
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hanna, Khalil
    Cobinding of Pharmaceutical Compounds at Mineral Surfaces: Mechanistic Modeling of Binding and Cobinding of Nalidixic Acid and Niflumic Acid at Goethite Surfaces2017In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 51, no 20, p. 11617-11624Article in journal (Refereed)
    Abstract [en]

    Although emerging contaminants rarely exist individually in environmental contaminated systems, only limited information on their adsorption mechanisms in multi-component solutions is currently available. To address this shortcoming, this work examines for the first time the accuracy of a surface complexation model in predicting the cooperative adsorption of nalidixic acid (NA) and niflurnic acid (NFA) at goethite (alpha-FeOOH) surfaces. Our model adequately predicts cobinding of an outer-sphere (OS) complex of NFA onto NA bound to goethite through metal-bonded (MB), hydrogen-bonded (HB), or OS complexes. More positive charge is introduced in the system via sodium interactions in order to describe the NFA adsorption at high NaCl concentrations in both single and binary systems. Our model confidently predict multilayers of NA on goethite as well as NFA binding on goethite-bound NA over a large range of pH and salinity values as well as NA and NFA loadings. These findings have strong implications in the assessment and prediction of contaminant fate in multicomponent contaminated systems by invoking a nontraditional form of ligand-ligand interaction in this field of study.

  • 1404.
    Yeşilbaş, Merve
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Thin water and ice films on minerals: a molecular level study2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Minerals in Earth’s crust and suspended in the atmosphere form water or ice films as thin as a few nanometers to as thick as a few micrometers, and beyond. Mineral-bound water and ice films in terrestrial systems (e.g. vadose zones, permafrosts) can impact the bio(geo)chemistry of nutrients and contaminants, water cycling, as well as possible land-air exchanges in terrestrial environments. In the atmosphere, films are tied to clouds and rain formation, and can influence the absorption and scattering of solar radiation of dust mineral aerosols. Water films are, at the same time, of interest to technology. They are even of interest in the study of asteroids, comets, and planet Mars. Still, their formation on the various types of minerals common to the environment is misunderstood.

    The aim of this thesis is to gain fundamental insight on the roles that minerals play on forming and stabilising thin water and ice films. This work is separated in two parts, with Part A associated with Papers I-II, and Part B with Papers III-V of the appendix of this thesis.

    In Part A of this work (Papers I-II), water loadings and vibrational signatures of thin water films were collected on 21 different minerals (metal oxides, silicates, carbonates) relevant to terrestrial environments, atmosphere and perhaps outer-space. Measurements were made on minerals of varied (i) composition, (ii) structure, (iii) morphology, (iv) particle size and (v) surface roughness. Loadings, measured by a microgravimetric Dynamic Vapour Sorption technique, were of a few monolayers in sub-micrometer-sized particles but of several hundreds to thousands of water layers in micrometer-sized particles (Paper I). This was seen in the Fourier Transform Infrared (FTIR) spectra of sub-micrometer-sized particles with different hydrogen bonding environments than liquid water. Micrometer-sized particles formed liquid-like films regardless of the mineral. Similar observations were made in the spectra of the thinnest water films remaining on these minerals after long periods of sublimation of ice overcoatings at sub-freezing temperatures (Paper II).

    In Part B of this work (Papers III-V), focus on the expandable clay mineral montmorillonite was made to study (i) intercalated water, (ii) ice and cryosalt formation inside microporous gels, and (iii) its interactions with intercalated CO2.  FTIR extracted spectral components reflecting interlayer hydration states of ~0W, 1W and 2W monolayers of water (Paper III). Thermal dehydration/dehydroxylation experiments showed that the driest forms of montmorillonite strongly retained low levels of crystalline water in its structure.  FTIR also showed that frozen wet gels of montmorillonite form ice and the cryosalt mineral hydrohalite. Ice was seen in rigid gels and aggregated compact particles, as well as low particle density with low salt content. In contrast, concentrated (>> 10 g/L) saline gels host hydrohalite, probably between and/or near aggregated clay particle walls. Field-Emission Cryogenic Scanning Electron Microscopy showed that ice microcrystals form in micropores of the gels (Paper IV). Finally, release rates of CO2 trapped in interlayers of montmorillonite, monitored by FTIR spectroscopy, were larger in the presence of 1-2W. The activation energy of CO2 release from~0W montmorillonite (34 kJ/mol) is comparable to other mineral surfaces. This study highlights that the most stabilised CO2 occur in of dry and cold conditions.

    This thesis will hopefully serve as a springboard for further work exploring the chemistry and physics of water and ice films at minerals surfaces. It should contribute to improve our understanding of the geochemistry of Earth’s soils, processes in the atmosphere, and even of space chemistry.

  • 1405.
    Yeşilbaş, Merve
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Holmboe, Michael
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Residence times of nanoconfined CO2 in layered aluminosilicates2019In: Environmental Science: Nano, ISSN 2051-8153, Vol. 6, no 1, p. 146-151Article in journal (Refereed)
    Abstract [en]

    Nanoconfinement of CO2 in layered aluminosilicates contributes to the capture and release of this greenhouse gas in soils. In this work, we show that the residence times of CO2 in montmorillonite are lowered by 15 min for each 1 degrees C increment in temperature during venting. Molecular simulations showed that activation energies of release are no more than half of the experimentally derived value of 34 kJ mol(-1). This raised the possibility of additional processes limiting CO2 mobility in real materials, including (chemi)sorption at reactive sites or frayed edges or defects. The residence times (approximate to 1616 min at -50 degrees C to approximate to 6 min at 60 degrees C) for some of the driest (approximate to 1.4 mmol H2O per g) montmorillonites that can be produced at ambient temperatures are readily lowered by inclusion of additional water. They are, in turn, prolonged again as the water content and interlayer spacing become smaller through venting. These efforts showed that soil-building clay minerals will lose their propensity to dynamically exchange CO2 as temperatures continue to rise, yet they may retain CO2 more efficiently in cold seasons as soils will become depleted in moisture content.

  • 1406.
    Yeşilbaş, Merve
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Holmboe, Michael
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cohesive vibrational and structural depiction of intercalated water in montmorillonite2018In: ACS Earth and Space Chemistry, E-ISSN 2472-3452, Vol. 2, no 1, p. 38-47Article in journal (Refereed)
    Abstract [en]

    The vibrational spectral profiles of Na- and Ca-montmorillonite (MMT) of controlled water layer populations (nW) was extracted by chemometric analysis of new Fourier transform infrared (FTIR) spectroscopy data and validated by mixed-layer modeling of previously published X-ray diffraction data. These efforts resolved FTIR spectral profiles of 0W, 1W, and 2W interlayers, which can now be used to explore the distinct hydration states of MMT. These spectral profiles reflect water populations organized around interlayer cations (Na+, Ca2+), interacting with siloxane groups of the basal face of the interlayer, and with other bound and “free” water molecules. This cohesive description of water-bearing clays provides the link needed to relate vibrational to structural attributes of these geochemically important materials.

  • 1407.
    Yeşilbaş, Merve
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Holmboe, Michael
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Trapping and release of atmospheric carbon dioxide by claysManuscript (preprint) (Other academic)
  • 1408.
    Yeşilbaş, Merve
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lee, Cheng Choo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ice and cryosalt formation in saline microporous clay gels2018In: ACS Earth and Space Chemistry, ISSN 2472-3452, Vol. 2, no 4, p. 314-319Article in journal (Refereed)
    Abstract [en]

    Hydrated clay minerals that are common to Earth’s atmosphere and terrestrial and aquatic environments can form gels that host saline solutions. Using cryogenic electron microscopy and vibration spectroscopy, we show that saline gels of montmorillonite frozen at < −90 °C host elongated hexagonal ice (Ih) microcrystals embedded in a network of honeycomb micropores. Freezing segregates salts into walls of aggregated clay nanoparticles sharing face-to-face contacts. Above ∼ −50 °C, clay gels that are sufficiently dense (≫10 g/L) and flexible (Na-exchanged montmorillonite) also host the cryosalt mineral hydrohalite (NaCl·2H2O), either co-existing or entirely replacing Ih in the gels. Hydrohalite does not form in gels of low-density (<10 g/L) or rigid (Ca-exchange montmorillonite) clay particles. These results suggest that hydrohalite forms in expandable clay gels that are sufficiently dense and flexible to retain saline solutions within their walls, possibly through interparticle capillary and hydration forces. These forces effectively oppose water diffusion to growing ice microcrystals within micropores, thus prolonging the lifetime of hydrohalite within these hydrated clay gels. Our findings tie the fate of ice and cryosalt nucleation and growth to the water-retention capability of expandable clay gels.

  • 1409. Yin, Ge
    et al.
    Zhou, Yihui
    Strid, Anna
    Zheng, Ziye
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Environmental Science and Analytical Chemistry, Stockholm University, 11418 Stockholm, Sweden.
    Bignert, Anders
    Ma, Taowu
    Athanassiadis, Ioannis
    Qiu, Yanling
    Spatial distribution and bioaccumulation of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in snails (Bellamya aeruginosa) and sediments from Taihu Lake area, China2017In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 24, no 8, p. 7740-7751Article in journal (Refereed)
    Abstract [en]

    Taihu Lake area is one of the densest metropolitan areas in the world including diverse industrial activity. In the present study, the snail (Bellamya aeruginosa) and sediment were collected from the Taihu Lake area to investigate the contamination status, congener pattern, spatial distribution, and bioaccumulation effect of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). The samples underwent liquid extraction, lipid removal by sulfuric acid, and acidic silica gel column, and subsequently analyzed by gas chromatography-electron capture detector (GC-ECD) and gas chromatography-mass spectrometry (GC-MS). Concentration of S22PCBs ranged between 90 and 680 ng g(-1) lipid weight in the snails and between 0.018 and 0.82 ng g(-1) dry weight in the sediments. Concentration of S24PBDEs varied from 25 to 200 ng g(-1) lipid weight in the snails and from 0.62 to 67 ng g(-1) dry weight in the sediments. The levels of PCBs and PBDEs observed were in the medium to low range compared with other studies in the world. CB-153 was the predominant PCB congener in both snails and sediments whereas BDE-209 showed a low bioavailability in the snails, even if it contributed up to 70% of S24PBDEs in the sediments. The spatial distribution showed that the highest concentration of PCBs and PBDEs were detected in samples from Zhushan Lake. East Taihu Lake and Dianshan Lake showed lower concentration of PCBs and PBDEs than the other sampling sites. Biota-sediment accumulation was found between snails and sediments of most of PCB and PBDE congeners except for the highly brominated BDEs (i.e., BDE-209). Therefore, sediment is suggested to be an appropriate matrix to monitor BDE-209 while aquatic species such as the snail could be good for monitoring of PCBs and lower brominated BDE congeners. No significant correlation (Spearman correlation test, two-tailed) of CB-153 (r = 0.54, p = 0.27) or BDE-47 (r = 0.60, p = 0.21) was found between snails and sediments.

  • 1410. Ylänne, Henni
    et al.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Oksanen, Lauri
    Stark, Sari
    Consequences of grazer-induced vegetation transitions on ecosystem carbon storage in the tundra2018In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 32, no 4, p. 1091-1102Article in journal (Refereed)
    Abstract [en]

    1. Large herbivores can control plant community composition and, under certain conditions, even induce vegetation shifts to alternative ecosystem states. As different plant assemblages maintain contrasting carbon (C) cycling patterns, herbivores have the potential to alter C sequestration at regional scales. Their influence is of particular interest in the Arctic tundra, where a large share of the world's soil C reservoir is stored.

    2. We assessed the influence of grazing mammals on tundra vegetation and C stocks by resampling two sites located along pasture rotation fences in northern Norway. These fences have separated lightly grazed areas from heavily grazed areas (in close proximity to the fences) and moderately grazed areas (further away from the fences) for the past 50years. Fourteen years earlier, the lightly and moderately grazed areas were dominated by dwarf shrubs, whereas heavy grazing had promoted the establishment of graminoid-dominated vegetation. Since then, both reindeer densities and temperatures have increased, and more time has passed for transient dynamics to be expressed. We expected that the vegetation and C stocks would have changed under all grazing intensities, but not necessarily in the same way.

    3. At the site where relative reindeer numbers and trampling intensity had increased the most, graminoid-dominated vegetation was now also found in the moderately grazed area. At the other site, the dominant vegetation types under all grazing intensities were the same as 14 years earlier.

    4. We show that the heavily grazed, graminoid-dominated areas stored less C above-ground than the lightly grazed, shrub-dominated areas. Yet, the below-ground consequences of grazing-induced grassification varied between the sites: Grazing did not alter organic soil C stocks at the site where both evergreen and deciduous shrubs were abundant in the lightly grazed area, whereas heavy grazing increased organic soil C stocks at the site where the deciduous shrub Betula nana was dominant.

    5. Our results indicate that, despite the negative impacts of grazers on above-ground C storage, their impact on below-ground C may even be positive. We suggest that the site-specific responses of organic soil C stocks to grazing could be explained by the differences in vegetation under light grazing. This would imply that the replacement of deciduous shrubs by graminoids, as a consequence of grazing could be beneficial for C sequestration in tundra soils.

  • 1411. Yoo, Kyungsoo
    et al.
    Fisher, Beth
    Ji, Junling
    Aufdenkampe, Anthony
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The geochemical transformation of soils by agriculture and its dependence on soil erosion: An application of the geochemical mass balance approach2015In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 521, p. 326-335Article in journal (Refereed)
    Abstract [en]

    Agricultural activities alter elemental budgets of soils and thus their long-term geochemical development and suitability for food production. This study examined the utility of a geochemical mass balance approach that has been frequently used for understanding geochemical aspect of soil formation, but has not previously been applied to agricultural settings. Protected forest served as a reference to quantify the cumulative fluxes of Ca, P, K, and Pb at a nearby tilled crop land. This comparison was made at two sites with contrasting erosional environments: relatively flat Coastal Plain in Delaware vs. hilly Piedmont in Pennsylvania. Mass balance calculations suggested that liming not only replenished the Ca lost prior to agricultural practice but also added substantial surplus at both sites. At the relatively slowly eroding Coastal Plain site, the agricultural soil exhibited enrichment of P and less depletion of K, while both elements were depleted in the forest soil. At the rapidly eroding Piedmont site, erosion inhibited P enrichment. In similar, agricultural Pb contamination appeared to have resulted in Pb enrichment in the relatively slowly eroding Coastal Plain agricultural soil, while not in the rapidly eroding Piedmont soils. We conclude that agricultural practices transform soils into a new geochemical state where current levels of Ca, P, and Pb exceed those provided by the local soil minerals, but such impacts are significantly offset by soil erosion.

  • 1412.
    Yoo, Kyungsoo
    et al.
    Department of Soil, Water, and Climate, University of Minnesota–Twin Cities, St. Paul, Minnesota, USA.
    Ji, Junling
    Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware, USA.
    Aufdenkampe, Anthony
    Stroud Water Research Center, Avondale, Pennsylvania, USA.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rates of soil mixing and associated carbon fluxes in a forest vs. tilled agricultural field:  Implications for modeling the soil carbon cycle2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no G01014Article in journal (Refereed)
    Abstract [en]

    In natural ecosystems, bioturbation is an essential component of soil formation, whereas tillage drives soil mixing in agricultural soils. Yet soil mixing is commonly neglected in modeling soil organic carbon (SOC) as it responds to land use changes. Here, in order to determine mixing-driven carbon fluxes, we combine a mass balance model with measurements of 210Pb activities and SOC contents. Soil mixing rates by tillage decrease from 3.4 ± 2.3 cm yr−1 at the surface to 0.8 ± 0.2 cm yr−1 at a depth of ∼20 cm, causing the SOC stored in the upper 25 cm of the soil to be physically turned over via mixing annually. In contrast, the bioturbation-driven soil mixing velocity at the forest increases from 0.6 ± 0.1 cm yr−1 at the surface to 2.7 ± 0.5 cm yr−1 at a depth of ∼10 cm, which results in physically turning over SOC in the A horizon via mixing on years to decadal time scales. Therefore, SOC fractions with different susceptibilities to decomposition may have significantly different physical trajectories within the soils over their lifespans, and thus the assumption of C-cycling models that all SOC fractions experience identical environmental conditions is unlikely to be realistic. Carbon sinks, excesses of plant carbon inputs over decomposition carbon losses, are found within the top portion of the A horizons. These carbon excesses are transferred, via mixing, to the lower portion of the A horizon, where they are decomposed. By quantifying mixing-derived SOC fluxes, this study shows a previously unrecognized complexity in understanding SOC dynamics associated with land use changes.

  • 1413. Young, Amanda B.
    et al.
    Cairns, David M.
    Lafon, Charles W.
    Moen, Jon
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Geometrid moth outbreaks and their climatic relations in northern Sweden2014In: Arctic, Antarctic and Alpine research, ISSN 1523-0430, E-ISSN 1938-4246, Vol. 46, no 3, p. 659-668Article in journal (Refereed)
    Abstract [en]

    The alpine treeline in northern Fennoscandia is composed primarily of mountain birch (Betula pubescens ssp. czerepanovii), a deciduous tree that experiences episodic defoliation due to outbreaks of the autumnal moth (Epirrita autumnata) and winter moth (Operophtera brumata). Here, we use an extensive dendroecological data set to reconstruct historic defoliating outbreaks and relate them to climatic conditions. Our data are from 25 sites in eight valleys in northern Sweden. We used the computer program OUTBREAK to reconstruct moth outbreaks. The reconstructed outbreak record matches the historical record well. There is a significant, but weak relationship between the outbreak severity and temperatures in February, April, July, and August of the outbreak year. Temperatures in the previous May and November were also positively correlated with outbreak severity. For seasonally aggregated temperatures, only autumn temperatures are correlated with outbreak severity. There was no significant correlation between NAO index and outbreak severity. A spatiotemporal semivariogram analysis showed that sites within approximately 100 km of each other show similar patterns in outbreak severity. Our analyses suggest that moths are affected by climatic variations. The influence of climate on outbreaks is weak because background climatic conditions alone cannot induce an outbreak. Outbreaks also depend on nonclimatic factors, such as tree age, and the outbreak status of neighboring areas.

  • 1414. Yu, Changxun
    et al.
    Joonas J. Virtasalo, Virtasalo
    Torbjörn, Karlsson
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Pasi Peltola, Pasi
    Peter Österholm, Peter
    Burton, Edward D.
    Arppe, Laura
    Hogmalm, Johan K.
    Ojala, Antti E.K.
    Åström, Mats E.
    Iron behavior in a northern estuary: Large pools of non-sulfidized Fe(II)associated with organic matter2015In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 413, p. 73-85Article in journal (Refereed)
    Abstract [en]

    The estuaries of the Northern Baltic Sea (Gulf of Bothnia) receive an abundance of diagenetically reactivecatchment-derived Fe, which is to a large degree complexed with organic matter or present as Fe (hydr-)oxides.However, our understanding of sedimentary Fe diagenesis in these estuaries is limited. To address this limitation,the present study examines Fe geochemistry in a 3.5-m-thick estuarine benthic mud layer and three samples ofsuspended particulate matter of a catchment on the eastern Gulf of Bothnia. The age–depth model of the mud,constructed on the basis of sedimentary features as well as 137Cs and aquatic plant 14C determinations, revealeda high average rate of sedimentation (5 cm · yr−1) for the upper mud unit (0–182.5 cm, corresponding to1973–2011), in response to intensive land-use (ditching) in the catchment since the 1960s and 1970s. The intensiveland-use has resulted in a strong increase in the Fe accumulation rates, but has not caused a recognizableimpact on the diagenetic processes of Fe including features such as degree of sulfidization and solid-phasepartitioning. Iron X-ray absorption spectroscopy (XAS) indicated that in the suspended particulate matter,large proportions (47–58%) of Fe occur as Fe(III)-organic complexes and 2-line ferrihydrite. In the mud, the formeris completely reduced, and reactive Fe (defined via extraction with 1MHCl) was high throughout (52–68%,median=61%) and strongly dominated by Fe(II). This reactive Fe(II) pool was sulfidized to only a limited extent(degree of reactive sulfidization = 11–26%, median = 17%). This phenomenon is attributed to the brackishwaterconditions (i.e. low in sulfate) and the abundant input of reactive Fe(III) from the catchment, leading toa surplus of dissolved Fe2+ over dissolved sulfide in the sediment. The low availability of dissolved sulfide, incombinationwith the high average sedimentation rate, limits the formation of intermediate reduced sulfur compoundsat the water–sediment interface, thereby retarding the conversion of FeS into pyrite (ratios of pyrite-S toAVS=0.17–1.73, median=0.37; degree of pyritization=1–17%, median=3%). Iron XAS, in combinationwithwavelet transform analysis, of representative sediment segments from the upper and lower mud units suggeststhat the non-sulfidized Fe(II) pool is dominantly complexed by organic matter, with the remaining Fe(II) occurringas mackinawite. This has implications for the understanding of early Fe diagenesis in settings with a highinput of organic matter and relatively low supply of sulfate.

  • 1415.
    Yu, Jun
    et al.
    SLU, Centre of Biostochastics.
    Ranneby, Bo
    SLU, Centre of Biostochastics.
    Nonparametric and probabilistic classification of agricultural crops using multitemporal images2007In: Journal of Remote Sensing, ISSN 1007-4619, Vol. 11, no 5, p. 748-755Article in journal (Refereed)
    Abstract [en]

    In this paper, a new approach for classification of multitemporal satellite data sets, combining multispectral and change detection techniques is proposed. The algorithm is based on the nearest neighbor method and derived in order to optimize the average probability for correct classification, i.e. each class is equally important. The new algorithm was applied to a study area where satellite images (SPOT and Landsat TM) from different seasons were used. It showed that using five seasonal images can substantially improve the classification accuracy compared to using a single image. As a large scale application, the approach was applied to the River Dalälven drainage basin.

    As the distributions for different classes are highly overlapping it is not possible to get satisfactory accuracy at pixel level. Instead it is necessary to introduce a new concept, pixel-wise probabilistic classifiers. The pixel-wise vectors of probabilities can be used to judge how reliable a traditional classification is and to derive measures of the uncertainty (entropy) for the individual pixels. The probabilistic classifier gives also unbiased area estimates overarbitrary areas. It has been tested on two test sites of arable land with different characteristics.

  • 1416.
    Yurova, Alla
    et al.
    Lund Univ, Dept Phys Geog & Ecosyst Anal, Solvegatan 12, SE-22362 Lund, Sweden..
    Wolf, Annett
    Umeå University. Lund Univ, Dept Phys Geog & Ecosyst Anal, Solvegatan 12, SE-22362 Lund, Sweden..
    Sagerfors, Jorgen
    Nilsson, Mats
    Variations in net ecosystem exchange of carbon dioxide in a boreal mire: Modeling mechanisms linked to water table position2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no G2Article in journal (Refereed)
    Abstract [en]

    [1] In mires, which occupy large areas of the boreal region, net ecosystem CO2 exchange ( NEE) rates vary significantly over various timescales. In order to examine the effect of one of the most influencing variables, the water table depth, on NEE the general ecosystem model GUESS-ROMUL was modified to predict mire daily CO2 exchange rates. A simulation was conducted for a lawn, the most common microtopographical feature of boreal oligotrophic minerotrophic mires. The results were validated against eddy covariance CO2 flux measurements from Degero Stormyr, northern Sweden, obtained during the period 2001 - 2003. Both measurements and model simulations revealed that CO2 uptake was clearly controlled by interactions between water table depth and temperature. Maximum uptake occurred when the water table level was between 10 and 20 cm and the air temperature was above 15 degrees C. When the water table was higher, the CO2 uptake rate was lower, owing to reduced rates of photosynthetic carbon fixation. When the water table was lower, NEE decreased owing to the increased rate of decomposition of organic matter. When the water table level was between 10 and 20 cm, the NEE was quite stable and relatively insensitive to both changes within this range and any air temperature changes above + 15 degrees C. The optimal water table level range for NEE corresponds to that characteristic of mire lawn plant communities, indicating that the annual NEE will not change dramatically if climatic conditions remain within the optimal range for the current plant community.

  • 1417.
    Zabel, Astrid
    et al.
    Berner Fachhochshule.
    Bostedt, Göran
    CERE, Center of Environmental and Resource Economics and Department of Forest Economics, Swedish University of Agricultural Sciences, SLU, Umeå, Sweden.
    Engel, Stefanie
    ETH Zurich.
    Performance payments for groups: the case of carnivore conservation in Northern Sweden2014In: Environmental and Resource Economics, ISSN 0924-6460, E-ISSN 1573-1502, Vol. 59, no 4, p. 613-631Article in journal (Refereed)
    Abstract [en]

    This paper presents a first empirical assessment of carnivore conservation under a performance payment scheme. In Sweden, reindeer herder villages are paid based on the number of lynx (lynx lynx) and wolverine (gulo gulo) offspring certified on their pastures. The villages decide on the internal payment distribution. It is generally assumed that benefit distribution rules are exogenous. We investigate them as an endogenous decision. The data reveals that villages’ group size has a direct negative effect on conservation outcomes and an indirect positive effect which impacts conservation outcomes through the benefit distribution rule. This result revises the collective action hypothesis on purely negative effects of group size.

  • 1418.
    Zakrzewski-Sharma, Karan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    PLANT MIGRATION AT THE END OF THE WEICHSELIAN GLACIATION: Macrofossil evidence of early coniferous trees at two northern Swedish sites2019Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    Studies of vegetation history bring a new incentive to our understanding of plant survival and migration in arctic environments. For decades, environmental research was based on palynological data and these studies created a notion that tree species such as larch (Larix sibirica) and Scots pine (Pinus sylvestris) did not grow in northern Scandinavia at the end of Weichselian glaciation. However, findings of macro- and megafossils of these trees dating back to glacial times has been reported in the Swedish mountain range, questioning this view of a late arrival of these trees in Scandinavia. The apparent contrasting views on the composition of the first plants arriving to Scandinavia create uncertainties about the bioclimatic conditions prevailing at the end of the Weichselian glaciation. To improve our understanding about the first vegetation arriving to Scandinavia I probed the macrofossil composition of two novel sedimentary records from northern Sweden. Twelve sediment cores from material underlying Holocene peat deposits were used as archives of early Holocene plants. In these records, I found: I) larch needles dating back to 4.6 and 4.1 calibrated thousand years (cal. kyr) BP; II) pine macrofossils dating back to 9.5 and 8.7 cal. kyr BP; III) fossils from dwarf shrubs (willow and heather) dating back to 9.9 cal. kyr BP; and IV) a birch fossil dating back to 9.5 cal. kyr BP. Also found in the same depth was fragment of a spruce cone. Based on my findings, I concluded that the landscape behind the retreating Weichselian ice-sheet was surpassingly colonised by pine and larch trees, a forest that has no contemporary analogue in Scandinavia. It seems as if this early forest also contained spruce, which is enigmatic as the main spruce invasion is expected to occur across the region during the next millennia. Finally, there is an instigation for future discussion on how our present knowledge of plant behaviour in changing conditions can help minimise the impacts of ever-expanding climate change.

  • 1419.
    Zale, Rolf
    Umeå University.
    Lake sediments around the Antarctic Peninsula: archives of climatic and environmental changes1993Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Lakes and lake sediments from four areas around the Antarctic Peninsula are described.

    The concentrations of trace metals in sediment are found to be a useful tool in distinguishing between the different sedimentary phases during a transition from marine to limnic environment.

    A tephrochronology based on Deception Island tephra is developed, and used to cross date sediments from different lakes in order to overcome the radiocarbon dating problem of the area.

    The fluctuating concentrations of copper and phosphorus from penguin guano in the sediment of Lake Boeckella are used as a proxy for the penguin inpact on the sediment, and the size of the penguin rookery on the shores of the lake. Anthropogenic activities in the area, as well as climatic changes are discussed in relation to the rookery size.

    A radiocarbon dating model developed for the sediment of Lake Boeckella showed that the radiocarbon correction factor in the sediment depends on the amount and apparent age of the penguin guano washed down into the lake, and the amount of particulate carbon from the watershed present in the sediment. Neither the "old" meltwater from the glaciers nor dissolved carbonates contributes significantly to the correction factor. The model is used to achieve more accurate radiocarbon dates of the Lake Boeckella sediment. This model, or a modified version, may contribute to a higher dating accuracy and a better understanding of the dating problems in Antarctica.

    Deglaciation dates, as well as data on the climatic and environmental history of Byers Peninsula on Livingston Island, South Shetland Islands, of Hope Bay, Antarctic Peninsula and of Hidden Lake area, James Ross Island are given.

  • 1420.
    Zale, Rolf
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Huang, Y. -T
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wood, J. R.
    Dalén, L.
    Wang, Xiao-Ru
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Segerström, U.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Growth of plants on the Late Weichselian ice-sheet during Greenland interstadial-1?2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 185, p. 222-229Article in journal (Refereed)
    Abstract [en]

    Unglaciated forelands and summits protruding from ice-sheets are commonly portrayed as areas where plants first establish at the end of glacial cycles. But is this prevailing view of ice-free refugia too simplistic? Here, we present findings suggesting that surface debris supported plant communities far beyond the rim of the Late Weichselian Ice-sheet during Greenland interstadial 1 (GI-1 or Bolling-Altered interstadial). We base our interpretations upon findings from terrigenous sediments largely resembling 'plant-trash' deposits in North America (known to form as vegetation established on stagnant ice became buried along with glacial debris during the deglaciation). In our studied deposit, we found macrofossils (N = 10) overlapping with the deglaciation period of the area (9.5-10 cal kyr BP) as well as samples (N = 2) with ages ranging between 12.9 and 13.3 cal kyr BP. The latter ages indicate growth of at least graminoids during the GI-1 interstadial when the site was near the geographic center of the degrading ice-sheet. We suggest that exposure of englacial material during GI-1 created patches of supraglacial debris capable of supporting vascular plants three millennia before deglaciation. The composition and resilience of this early plant community remain uncertain. Yet, the younger group of macrofossils, in combination with pollen and ancient DNA analyses of inclusions, imply that shrubs (Salix sp., Betula sp. and Ericaceae sp) and even tree species (Larix) were present in the debris during the final deglaciation stage. 

  • 1421. Zhang, Feng
    et al.
    Zhou, Guangsheng
    Wang, Yu
    Yang, Fulin
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Evapotranspiration and crop coefficient for a temperate desert steppe ecosystem using eddy covariance in Inner Mongolia, China2012In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 26, no 3, p. 379-386Article in journal (Refereed)
    Abstract [en]

    Evapotranspiration (ET), which links water, energy and the carbon cycle in terrestrial ecosystems, is an important eco-hydrological process, especially in arid and semi-arid regions. To determine the crop coefficient (K-c) over a 2-year period for a temperate desert steppe in Inner Mongolia, China, ET was measured using the eddy covariance method and the reference evapotranspiration (ET0) was estimated from site meteorological data. The results showed that the seasonal variation of ET differed on an annual timescale between the 2 consecutive years, exhibiting a multi-peak curve in 2008 and a single peak in 2009. The mean daily K-c values were 0.15 and 0.17 in 2 years, varying from 0.009 to 0.75 in 2008 and from 0.005 to 0.58 in 2009. The 5-day moving average for K-c values was mainly affected by SWC10cm and R-n, and the regression coefficients (R-2) were 58.9 and 69.5%, respectively. These results will aid in making accurate and quantitative assessments of the vulnerability of the sparse vegetation to climate change.

    Copyright (C) 2011 John Wiley & Sons, Ltd.

  • 1422.
    Zhang, Lai
    et al.
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics. School of Mathematical Science, Yangzhou University, Si Wang Ting Road, Yangzhou 225002, People’s Republic of China.
    Takahashi, Daisuke
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Hartvig, Martin
    Andersen, Ken H.
    Food-web dynamics under climate change2017In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 284, no 1867, article id 20171772Article in journal (Refereed)
    Abstract [en]

    Climate change affects ecological communities through its impact on the physiological performance of individuals. However, the population dynamic of species well inside their thermal niche is also determined by competitors, prey and predators, in addition to being influenced by temperature changes. We use a trait-based food-web model to examine how the interplay between the direct physiological effects from temperature and the indirect effects due to changing interactions between populations shapes the ecological consequences of climate change for populations and for entire communities. Our simulations illustrate how isolated communities deteriorate as populations go extinct when the environment moves outside the species' thermal niches. High-trophic-level species are most vulnerable, while the ecosystem function of lower trophic levels is less impacted. Open communities can compensate for the loss of ecosystem function by invasions of new species. Individual populations show complex responses largely uncorrelated with the direct impact of temperature change on physiology. Such complex responses are particularly evident during extinction and invasion events of other species, where climaticallywell-adapted species may be brought to extinction by the changed food-web topology. Our results highlight that the impact of climate change on specific populations is largely unpredictable, and apparently well-adapted species may be severely impacted.

  • 1423. Zhang, W.
    et al.
    Blum, Kristin M.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gros, M.
    Ahrens, L.
    Jernstedt, H.
    Wiberg, K.
    Andersson, P. L.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björlenius, B.
    Renman, G.
    Removal of micropollutants and nutrients in household wastewater using organic and inorganic sorbents2018In: Desalination and Water Treatment, ISSN 1944-3994, E-ISSN 1944-3986, Vol. 120, p. 88-108Article in journal (Refereed)
    Abstract [en]

    The efficiency of five organic and five inorganic sorbents in removing 19 organic micropollutants (MPs), phosphorus, nitrogen, and dissolved organic carbon (DOC) was tested in a two-week column experiment using household wastewater spiked with pharmaceuticals (n = 6), biocides/pesticides (n = 4), organophosphates (n = 3), a fragrance, a UV-stablizer, a food additive, a rubber additive, a plasticizer and a surfactant. Two types of granular activated carbon (GAC), two types of lignite, a pine bark product, and five mineral-based sorbents were tested. All the organic sorbents except pine bark achieved better removal efficiencies of DOC (on average, 70 +/- 27%) and MPs (93 +/- 11%) than the inorganic materials (DOC: 44 +/- 7% and MPs: 66 +/- 38%). However, the organic sorbents (i.e. GAC and xyloid lignite) removed less phosphorus (46 +/- 18%), while sorbents with a high calcium or iron content (i.e. Polonite (R) and lignite) generally removed phosphorus more efficiently (93 +/- 3%). Ammonium- nitrogen was well removed by sorbents with a pH between 7 and 9, with an average removal of 87%, whereas lignite (pH 4) showed the lowest removal efficiency (50%). Some MPs were well removed by all sorbents (>= 97%) including biocides (hexachlorobenzene, triclosan and terbutryn), organophosphates (tributylphosphate, tris-(1,3-dichloro-2-propyl) phosphate and triphenylphosphate) and one fragrance (galaxolide). The pesticide 2,6-dichlorobenzamide and the pharmaceutical diclofenac were poorly removed by the pine bark and inorganic sorbents (on average, 4%), while organic sorbents achieved high removal of these chemicals (87%).

  • 1424.
    Zheng, Ziye
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Peters, Gregory M.
    Arp, Hans Peter H.
    Andersson, Patrik L.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Combining in Silico Tools with Multicriteria Analysis for Alternatives Assessment of Hazardous Chemicals: A Case Study of Decabromodiphenyl Ether Alternatives2019In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 53, no 11, p. 6341-6351Article in journal (Refereed)
    Abstract [en]

    Alternatives assessment is applied for minimizing the risk of unintentionally replacing a hazardous chemical with another hazardous chemical. Central challenges are the diversity of properties to consider and the lack of high-quality experimental data. To address this, a novel alternatives assessment procedure was developed based on in silico data and multicriteria decision analysis (MCDA) methods. As a case study, 16 alternatives to the flame retardant decabromodiphenyl ether were considered. The hazard properties included persistence (P), bioaccumulation potential (B), toxicities (T), and mobility in water (M). Databases were consulted and 2866 experimental data points were collected for the target chemicals; however, these were mostly replicate data points for some hazard criteria for a subset of alternatives. Therefore, in silico data and three MCDA strategies were tested including heat mapping, multiattribute utility theory (MAUT), and Elimination Et Choix Traduisant la REalite (ELECTRE III). The heat map clearly showed that none of the target chemicals are hazard-free, whereas MAUT and ELECTRE III agreed on ranking the "least worst" choices. This study identified several challenges and the complexity in the alternatives assessment processes motivating more case studies combining in silico and MCDA approaches.

  • 1425.
    Zhu, Wei
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China.
    Lin, Che-Jen
    Wang, Xun
    Sommar, Jonas
    Fu, Xuewu
    Feng, Xinbin
    Global observations and modeling of atmosphere-surface exchange of elemental mercury: a critical review2016In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 16, no 7, p. 4451-4480Article, review/survey (Refereed)
    Abstract [en]

    Reliable quantification of air-surface fluxes of elemental Hg vapor (Hg-0) is crucial for understanding mercury (Hg) global biogeochemical cycles. There have been extensive measurements and modeling efforts devoted to estimating the exchange fluxes between the atmosphere and various surfaces (e.g., soil, canopies, water, snow, etc.) in the past three decades. However, large uncertainties remain due to the complexity of Hg-0 bidirectional exchange, limitations of flux quantification techniques and challenges in model parameterization. In this study, we provide a critical review on the state of science in the atmosphere-surface exchange of Hg-0. Specifically, the advancement of flux quantification techniques, mechanisms in driving the air-surface Hg exchange and modeling efforts are presented. Due to the semi-volatile nature of Hg-0 and redox transformation of Hg in environmental media, Hg deposition and evasion are influenced by multiple environmental variables including seasonality, vegetative coverage and its life cycle, temperature, light, moisture, atmospheric turbulence and the presence of reactants (e.g., O-3, radicals, etc.). However, the effects of these processes on flux have not been fundamentally and quantitatively determined, which limits the accuracy of flux modeling. We compile an up-to-date global observational flux database and discuss the implication of flux data on the global Hg budget. Mean Hg-0 fluxes obtained by micrometeorological measurements do not appear to be significantly greater than the fluxes measured by dynamic flux chamber methods over unpolluted surfaces (p = 0.16, one-tailed, Mann-Whitney U test). The spatiotemporal coverage of existing Hg-0 flux measurements is highly heterogeneous with large data gaps existing in multiple continents (Africa, South Asia, Middle East, South America and Australia). The magnitude of the evasion flux is strongly enhanced by human activities, particularly at contaminated sites. Hg-0 flux observations in East Asia are comparatively larger in magnitude than the rest of the world, suggesting substantial re-emission of previously deposited mercury from anthropogenic sources. The Hg-0 exchange over pristine surfaces (e.g., background soil and water) and vegetation needs better constraints for global analyses of the atmospheric Hg budget. The existing knowledge gap and the associated research needs for future measurements and modeling efforts for the air-surface exchange of Hg-0 are discussed.

  • 1426.
    Zhu, Wei
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Song, Yu
    Adediran, Gbotemi A.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jiang, Tao
    Reis, Ana T.
    Pereira, Eduarda
    Skyllberg, Ulf
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mercury transformations in resuspended contaminated sediment controlled by redox conditions, chemical speciation and sources of organic matter2018In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 220, p. 158-179Article in journal (Refereed)
    Abstract [en]

    Mercury (Hg) contaminated sediments can be significant sources of Hg in aquatic ecosystems and, through re-emission processes, to the atmosphere. Transformation and release of Hg may be enhanced by various sediment perturbation processes, and controlling biogeochemical factors largely remain unclear. We investigated how rates of Hg transformations in pulp-fiber enriched sediment contaminated by Hg from chlor-alkali industry were controlled by (i) transient redox-changes in sulfur and iron chemistry, (ii) the chemical speciation and solubility of Hg, and (iii) the sources and characteristics of organic matter (OM). Sediment-bottom water microcosm systems were exposed to four combinations of air and nitrogen gas for a total time of 24 h. The treatments were: 24 h N-2, 0.5 h air + 23.5 h N-2, 4 h air + 20 h N-2 and 24 h of air exposure. As a result of these treatments, microcosms spanned a wide range of redox potential, as reflected by the dissolved sulfide concentration range of <= 0.3-97 mu M. Four different chemical species of inorganic divalent Hg (Hg-II) and methyl mercury (MeHg), enriched in different Hg isotope tracers, were added to the microcosms: 201 Hg(NO3)(2)(aq), Hg-202(II) adsorbed to OM (Hg-202(II)-OM(ads)), Hg-198(II) as microcrystalline metacinnabar (beta-(HgS)-Hg-198(s)) and (MeHgCl)-Hg-204(aq). Microcosm systems were composed of bottom water mixed with sediment taken at 0-2, 0-5 and 0-10 cm depth intervals. The composition of OM varied with sediment depth such that compared to deeper sediment, the 0-2 cm depth-interval had a 2-fold higher contribution of labile OM originating from algal and terrestrial inputs, serving as metabolic electron-donors for microorganisms. The potential methylation rate constant (k(meth)) of Hg tracers and net formation of ambient MeHg (MeHg/THg molar ratio) increased up to 50% and 400%, respectively at intermediate oxidative conditions, likely because of an observed 2-fold increase in sulfate concentration stimulating the activity of sulfate reducing bacteria with a capability of methylating Hg-II. Due to differences in Hg-II water-sediment partitioning, k(meth) varied by a factor of 11-70 for the different isotope-enriched Hg tracers. The chemical form of Hg-II was a major controlling factor for k(meth) and its response to the resuspension-oxidation of the system. The beta-(HgS)-Hg-198(s) tracer had the lowest k(meth) and it was mainly constrained by redox-driven Hg-II solubility. The Hg-202(II)-OM(ads) tracer showed an intermediate value on k(meth). It was controlled by both Hg-II solubility and availability of electron donors and acceptors, regulating bacterial activity. The Hg-201(NO3)(2)(aq) tracer had the highest value on k(meth) which was limited mainly by bacterial activity. The k(meth) was up to a factor of 3 higher in the 0-2 cm sediment depth-interval than in 0-5 and 0-10 cm intervals due to a larger contribution of labile OM in the 0-2 cm sediment. Reduction of Hg-II to Hg-0 followed by volatilization exclusively occurred at high sulfidic conditions in the top 0-2 cm sediment. Aromatic moieties of terrestrial OM, present mainly in the top sediment, is suggested to control the reduction of Hg-II. The Hg-0 volatilization rate constant for the Hg-202(II)-OM (ads) tracer exceeded that for beta-(HgS)-Hg-198(s) by one order of magnitude. Our results suggest that contaminated sediments posing a high risk for reactivation of legacy Hg following transient redox resuspension events are characterized by depletion of sulfate in the sediment porewater prior to resuspension, predominance of Hg-II species with solubility exceeding that of crystalline beta-HgS(s), and conditions promoting in situ formation and/ or import of labile OM from algal and terrestrial sources.

  • 1427. Zockler, Christoph
    et al.
    Miles, Lera
    Fish, Lucy
    Wolf, Annett
    Umeå University. ETH Zentrum, CH-8092 Zurich, Switzerland.
    Rees, Gareth
    Danks, Fiona
    Potential impact of climate change and reindeer density on tundra indicator species in the Barents Sea region2008In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 87, no 1-2, p. 119-130Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to alter the distribution of habitats and thus the distribution of species connected with these habitats in the terrestrial Barents Sea region. It was hypothesised that wild species connected with the tundra and open-land biome may be particularly at risk as forest area expands. Fourteen species of birds were identified as useful indicators for the biodiversity dependent upon this biome. By bringing together species distribution information with the LPJ-GUESS vegetation model, and with estimates of future wild and domestic reindeer density, potential impacts on these species between the present time and 2080 were assessed. Over this period there was a net loss of open land within the current breeding range of most bird species. Grazing reindeer were modelled as increasing the amount of open land retained for nine of the tundra bird species.

  • 1428.
    Åberg, Annika
    Umeå University, Faculty of Science and Technology, Chemistry.
    Fate and exposure assessment of PCDD/Fs at contaminated sites2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzo-furans (PCDFs) belong to the most toxic compounds known to science and they are defined as Persistent Organic Pollutants (POPs) under the Stock-holm Convention. The general human exposure to PCDD/Fs is primarily through dietary intake. The importance of contaminated sites as secondary PCDD/F sources (i.e. sources that once received its contamination from a primary source) are getting increased attention. To be able to assess the risks for human exposure at PCDD/F contaminated sites, the environmen-tal distribution of PCDD/Fs and the potential mobilization between dif-ferent environmental media (e.g. food chain transfer) must be known. The primary aim of the work presented in this thesis was to investigate human exposure pathways associated with PCDD/F contaminated sites by combining field measurements and modeling. Site specific field measurements were made at a PCDD/F contaminated site in Sweden and multimedia modeling scenarios were evaluated against site specific data and national reference data.

    The results show that the congener distributions in exposure media affected by contaminated soil may differ significantly from the distribu-tions found in media from reference locations. Higher chlorinated PCDD/Fs may be transferred into food chains where they contribute to a large fraction of the toxic equivalent concentration (TEQ). Ingestion of locally produced animal food may be an important exposure pathway al-ready at low or moderate PCDD/F soil concentrations. However, the con-gener composition of the source is critical for the exposure. The signifi-cance of the individual exposure routes varies depending on e.g. the spatial distribution and magnitude of the soil contamination, the pro-perties of the exposure media and the human behavior. Multimedia mo-deling can be used in risk assessments as long as model algorithms and model parameters are representative for the superhydrophobic properties of PCDD/Fs. However, selection of physical-chemical PCDD/F properties is a challenge due to large variation in reported values. For some proper-ties, data is scattered or completely lacking

  • 1429.
    Åberg, Jan
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Production and emission of CO2 in two unproductive lakes in northern Sweden2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Unproductive lakes are one of few natural landscape compartments with net release of carbon to the atmosphere. Lakes also generally decrease the net terrestrial carbon uptake, since most of the CO2 production in unproductive lakes are derived from organic carbon produced on land (e.g. in forests). High latitude lakes are predicted to be particularly affected by the global climate change. The carbon cycling in these lakes and their role in the landscape are therefore important to study.

    In this thesis, carbon turnover processes were studied in two lakes above the arctic circle (Lake Diktar-Erik and Lake Merasjärvi) in year 2004 and 2005. Both lakes were net heterotrophic, with large variations in CO2 concentrations both on shorter (30min) and longer (24h) time-scales. The pelagic habitat supported a major part of the net production of CO2, with larger dynamics in the CO2 production than the sediments. The CO2 variations of the surface water were related to respiration of allochthonous organic carbon, and were affected by the concentration and quality of the DOC, as well as the whole lake water temperatures, and vertical water movements.

    The emission of CO2 from Lake Merasjärvi was measured with the eddy covariance tech­nique. The results showed that the gas transfer rate during moderate winds were higher than expected, causing the two most commonly used models to underestimate the long term fluxes of CO2 from the lake.

    Taken together, the results of the thesis show that the studied lakes contributed to bring terrestrial organic carbon back into the atmosphere, driven by a substantial internal CO2 production based on mineralization of allochthonous organic carbon. Major results are that the eddy covariance technique indicated that commonly used models tend to underestimate the net release rate of CO2 from lakes to the atmosphere, and that the lake CO2 dynamics can be the results of interactions between biogeochemical and physical processes in the lake water.

  • 1430.
    Åberg, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Importance of water temperature and thermal stratification dynamics for temporal variation of surface water CO2 in a boreal lake2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, no G02024, p. 10PP-Article in journal (Refereed)
    Abstract [en]

    Variation of the surface water CO2 concentration is likely to be the result of biological activity and physical processes as water mixing and gas exchange with the atmosphere. Here we have studied the variations in surface water CO2 during the ice-free period in the humic Lake Merasjärvi in northern Sweden. Meteorological, hydrological and limnological data were collected using data logging equipment permitting high time-resolution. The surface water of the lake was supersaturated with respect to CO2 throughout the study period. There were, however, considerable diurnal and longer-term temporal variations of the surface water CO2 concentrations. Partial least squares (PLS) models were used to link the logged CO2 data to the multivariate dataset. On the longer-term time scale (analyzed with 24h means of the logged data) high concentrations of surface water CO2 were best related to the depth and temperature of the upper warmer layer (epilimnion), and to erosion of the underlying colder layer (hypolimnion). The diurnal variation (analyzed with 30 minute means of the logged data) was best related to the thermal dynamics within the epilimnion, which regulated the surface water access to CO2 stores within this layer. Variables related to CO2 emission and photosynthesis (wind and PAR), showed only weak correlations to variations of the surface water CO2 concentration. Accordingly, the CO2 flux, measured with the eddy-covariance technique, was not correlated to the surface water CO2 concentration.

  • 1431.
    Ågren, Anneli
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Seasonal variation and landscape regulation of dissolved organic carbon concentrations and character in Swedish boreal streams2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The seasonal variation and landscape regulation of dissolved organic carbon (DOC) concentrations in streams have been studied in two watersheds in the boreal zone. The seasonal variation was found to be highly correlated to variations in runoff. An increase in runoff was always accompanied with an increase in DOC concentration. However, there were indications that the TOC concentration was restricted by the soil TOC pool during snowmelt.

    The main factors affecting DOC exports varied between seasons. During winter baseflow the spatial variation in DOC exports was strongly influenced by wetland coverage, during snowmelt the exports were correlated to factors describing the size and location of the catchment, and during the snow-free season they were heavily affected by the proportions of wetlands and forests in the catchments. Small headwaters had the highest terrestrial DOC export, per unit area.

    The properties of the DOC changed during spring flood, towards lower molecular weight and more aliphatic compounds. These changes affected the bioavailability of the DOC, which increased during spring flood. There were also differences in the DOC properties between wetlands and forest soils; the forested soils yielded DOC with lower molecular weight (measured as 254 nm/365 nm light absorbance ratios), largely from superficial layers that were activated during high flow events, while wetland soils generally provided a more constant carbon source with higher molecular weight. The majority of the DOC was exported by wetlands, but most of the short-term bioavailable DOC (BP7) was derived from the forests, during the spring flood period, indicating that bacterial production in streams and lakes is likely to be almost entirely based on DOC exported from forested areas during, and some time after, the spring flood event.

  • 1432.
    Österholm, Emil
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jordbrukets betydelse i stadsnära miljö: En undersökning av Umeå kommuns översiktsplanering för Röbäcksområdet2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This study aimed to examine what role and how the agriculture will be affected in a periurban environment as by the comprehensive plan that the municipal has established for the Röbäck area. The study tried to value the importance and role for the agriculture today and in the future. The methods of this study were interviews with farmers, inhabitants and workers of Röbäck, businesses and a sports club based on two types of interviews one survey-based with fixed questions and one in-depth interview with farmers. The municipal comprehensive plan and accompanying environmental impact assessment along relevant literature and the statistical database from Jordbruksverket were used to extract and compile data. The results show that the fields in and surrounding Röbäck contained good agricultural values and the ability to maintain of self-sufficiency in Västerbottens county is low. In the interviews with farmers the fear of not being able to use the farmland as before as a result of complaints on dust, noises, smells and rules on spreading fertilizers and pesticides raised a concern. The interviews showed that people living in Röbäck liked the combination of being close to Umeå city centrum as well as living close to the nature and the open landscapes, but few saw the link between the agriculture in Röbäck and these. The report concludes that the issue is complex and depends on whose interest should go first. There were both positive and negative outcomes of the plan in all the three pillars of sustainability

  • 1433.
    Östman, Marcus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Fick, Jerker
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tysklind, Mats
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Detailed mass flows and removal efficiencies for biocides and antibiotics in Swedish sewage treatment plants2018In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 640, p. 327-336Article in journal (Refereed)
    Abstract [en]

    Antimicrobial compounds, such as biocides and antibiotics, are widely used in society with significant quantities of these chemicals ending up in sewage treatment plants (STPs). In this study, mass flows and removal efficiency in different treatment steps at three Swedish STPs were evaluated for eleven different biocides and antibiotics. Mass flows were calculated at eight different locations (incoming wastewater, water after the first sedimentation step, treated effluent, primary sludge, surplus sludge, digested sludge, dewatered digested sludge and reject water). Samples were collected for a total of nine days over three weeks. The STPs were able to remove 53-> 99% of the antimicrobial compounds and 0-64% were biodegraded on average in the three STPs. Quaternary ammonium compounds were removed from the wastewater N99%, partly through biodegradation, but 38-96% remained in the digested sludge. Chlorhexidine was not biodegraded but was efficiently removed from the wastewater to the sludge. The biological treatment step was the most important step for the degradation of the studied compounds, but also removed several compounds through the surplus sludge. Compounds that were inefficiently removed included benzotriazoles, trimethoprim and fluconazole. The study provides mass flows and removal efficiencies for several compounds that have been seldom studied. 

  • 1434.
    Östman, Sofi
    et al.
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies, Environmental Archaeology Lab.
    Samuel, Eriksson
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies, Environmental Archaeology Lab.
    Buckland, Philip I.
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies, Environmental Archaeology Lab.
    Preliminär rapport om miljöarkeologisk analys av prover från RAÄ 113:1 och Obj.nr 10. Själevad socken, Örnsköldsvik kommun, Västernorrlands län, Ångermanland2017Report (Other academic)
    Abstract [sv]

    Analysen omfattar makrofossilanalys, markkemisk-fysikalisk (geoarkeologisk) analys, samt vedartsanalys för utplock av daterbart material för 14C. Proverna är tagna från ett område med "koncentrationer av skärvsten med fynd av brända ben samt kvartsavslag" (RAÄ 113:1; Smeds 2016) samt en boplats utan RAÄ-nr vid rapportskrivning (Obj.nr 10; RAÄ Dnr 3.4.2-2662-2015). Syftet med analysen är dels att få fram daterbart material, dels att studera om anläggningarna har varit utsatt för direkt eldpåverkan eller andra aktiviteter.

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