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  • 1.
    Gälman, V
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Pettersson, G
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Renberg, I
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A comparison of sediment varves (1950–2003 AD) in two adjacent lakes in northern Sweden2006In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 35, p. 837-853Article in journal (Refereed)
    Abstract [en]

    Koltjärnen and Nylandssjön are two closely situated lakes (<2 km apart) in northern Sweden. During the past century, distinct varved sediments have formed in these lakes. Nylandssjön has two varved, deep basins. Since lake and catchment characteristics superficially appear very similar for the two lakes and they are exposed to the same climate, one would expect the sediment varves to be similar. This investigation compares the varves in the two deep basins of Nylandssjön, and in the two lakes. The comparison of basins of Nylandssjön shows that varve thickness, water content and annual accumulation rates of organic matter and nitrogen are correlated for the period (1970–2003). The grey-scale curves are only clearly similar in about 50% of the varves. In the between-lake comparison varve thickness, water content and annual accumulation rates of organic matter and nitrogen are correlated for the period (1950–1996). However, the annual accumulation rates of dry mass, minerogenic matter and biogenic silica differ between the lakes, as well as within-varve successions in grey-scale. A general explanation to the differences is that the prerequisites for varve formation are not totally similar because of differences in catchment size, catchment- to-lake material fluxes, lake productivity and land-use influence. This study illustrates the complex relationships that exist between a lake, its catchment, in-lake productivity and formation of sediment varves. As a consequence, we must not apply a too simplistic view of the potential of varves as past climatic indicators, especially if the lakes are affected by land-use.

  • 2.
    Gälman, Veronika
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rydberg, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Martínez-Cortizas, A
    Bindler, Richard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The role of iron and sulfur in the visual appearance of lake sediment varves2009In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 42, no 1, p. 141-153Article in journal (Refereed)
    Abstract [en]

    Easily discernible sediment varves (annual laminations) may be formed in temperate zone lakes, and reflect seasonal changes in the composition of the accumulating material derived from the lake and its catchment (minerogenic and organic material). The appearance of varves may also be influenced by chemical processes. We assessed the role of iron (Fe) and sulfur (S) in the appearance of varves in sediments from Lake Nylandssjön in northern Sweden. We surveyed Fe in the lake water and established whether there is internal transport of Fe within the sediment. We used a unique collection of seven stored freeze cores of varved sediment from the lake, collected from 1979 to 2004. This suite of cores made it possible to follow long-term changes in Fe and S in the sediment caused by processes that occur in the lake bottom when the sediment is ageing. We compared Fe and S concentrations using X-ray fluorescence spectroscopy (XRF) in specific years in the different cores. No diagenetic front was found in the sediment and the data do not suggest that there is substantial vertical transport of Fe and S in the sediment. We also modeled Fe and S based on thermodynamic, limnological, and sediment data from the lake. The model was limited to the five components H+, e-, Fe3+, SO42-, H2CO3 and included the formation of solid phases such as Fe(OH)3 (amorphous), FeOOH (aged, microcrystalline), FeS and FeCO3. Modeling showed that there are pe (redox) ranges within which either FeS or Fe(OH)3/FeOOH is the only solid phase present and there are pe ranges within which the two solid phases co-exist, which supports the hypothesis that blackish and grey-brownish layers that occur in the varves were formed at the time of deposition. This creates new possibilities for deciphering high-temporal-resolution environmental information from varves.

  • 3. Kahlert, Maria
    et al.
    Albert, Raino-Lars
    Anttila, Eeva-Leena
    Bengtsson, Roland
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Eskola, Tiina
    Gälman, Veronika
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gottschalk, Steffi
    Herlitz, Eva
    Jarlman, Amelie
    Kasperoviciene, Jurate
    Kokociński, Mikołaj
    Luup, Helen
    Miettinen, Juha
    Paunksnyte, Ieva
    Piirsoo, Kai
    Quintana, Isabel
    Raunio, Janne
    Sandell, Bernt
    Simola, Heikki
    Sundberg, Irene
    Vilbaste, Sirje
    Weckström, Jan
    Harmonization is more important than experience—results of the first Nordic–Baltic diatom intercalibration exercise 2007 (stream monitoring)2009In: Journal of Applied Phycology, ISSN 0921-8971, E-ISSN 1573-5176, Vol. 21, no 4, p. 471-482Article in journal (Refereed)
    Abstract [en]

    The goal of this study was a harmonization of diatom identification and counting among diatomists from the Scandinavian and Baltic countries to improve the comparison of diatom studies in this geographical area. An analysis of the results of 25 diatomists following the European standard EN 14407 during an intercalibration exercise showed that a high similarity was achieved by harmonization and not because of a long experience with diatoms. Sources of error were wrong calibration scales, overlooking of small taxa, especially small Navicula s.l., misidentifications (Eunotia rhomboidea was mistaken for Eunotia incisa) and unclear separation between certain taxa in the identification literature. The latter was discussed during a workshop with focus on the Achnanthes minutissima group, the separation of Fragilaria capucina var. gracilis from F. capucina var. rumpens, and Nitzschia palea var. palea from N. palea var. debilis. The exercise showed also that the Swedish standard diatom method tested here worked fine with acceptable error for the indices IPS (Indice de Polluo-sensibilité Spécifique) and ACID (ACidity Index for Diatoms) when diatomists with a low similarity (Bray–Curtis <60%) with the auditor in at least one of the samples are excluded.

  • 4.
    Rydberg, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gälman, Veronika
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bindler, Richard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lambertsson, Lars
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Martínez-Cortizas, Antonio
    Departmento de Edafologia y Quimica Agricola, Faculty of Biology, University of Santiago de Compostela, E-15706 Santiago de Compostela, Spain.
    Assessing the stability of mercury and methylmercury in a varved lake sediment deposit2008In: Environmental Science & Technology, ISSN 0013-936X, Vol. 42, no 12, p. 4391-4396Article in journal (Refereed)
    Abstract [en]

    Using lake sediments to infer past total mercury and methylmercury loading to the environment requires that diagenetic processes within the sediment do not significantly affect the concentrations or net accumulation rates of the mercury species. Because carbon is lost during early sediment diagenesis, the close link between carbon and mercury raises the question of how reliable lake sediments are as archives of total mercury and methylmercury loading. In this study we used a series of freeze cores taken in a lake with varved (annually laminated) sediment to assess the stability of total mercury and methylmercury over time. By tracking material deposited in specific years in cores collected in different years, we found that despite a 20–25% loss of carbon in the first 10–15 years, there was no apparent loss of total mercury over time; hence, lake sediments can be considered as reliable archives. However, over the first 5–8 years after sedimentation, about 30–40% of the methylmercury was lost (a decrease of 0.025–0.030 μg MeHg m−2 yr−1), suggesting that sediment profiles showing increasing methylmercury concentrations toward the sediment surface are in large part an artifact of diagenetic processes (net demethylation), rather than a record of changes in methylmercury loading.

  • 5.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gälman, Veronika
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rydberg, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Speciation of iron and sulphur in seasonal layers of varved lake sediment: an XPS study2008In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 40, no 3-4, p. 354-357Article in journal (Refereed)
    Abstract [en]

    Under specific conditions, annually-laminated (varved) sediments are formed in lakes. Such lake sediments are rare, but of great interest to studies of past environmental conditions since they provide annual or even seasonal time resolution, and can be used to follow environmental changes over hundreds or thousands of years. The chemical composition of the varves and speciation of chemical elements reveal information on past conditions. The colour of sediment varves can vary between light brown to almost black, and it was hypothesised that black layers were deposited in seasons with oxygen deficit in the hypolimnion (summer and winter) and light layers were formed at spring and autumn over-turn periods when oxygen-rich water flow occurred near the lake bottom. We have tested this hypothesis by analyses of seasonal layers of varves formed in 1968 and 2005 using X-ray photoelectron spectroscopy with fast-frozen samples. We found that the organic (C, N, O, S) and inorganic (Al, Si, Ca, Fe, S) elemental composition was similar for all samples studied, but the chemical states of iron and sulphur differed remarkably depending on the season. The black colour of the summer layer was caused by the precipitation of inorganic FeS, while in the light layers only organic thiol (SH) and sulphate SO42- together with Fe(III) hydroxides were found.

1 - 5 of 5
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