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Gälman, Veronika
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Publications (5 of 5) Show all publications
Kahlert, M., Albert, R.-L., Anttila, E.-L., Bengtsson, R., Bigler, C., Eskola, T., . . . Weckström, J. (2009). Harmonization is more important than experience—results of the first Nordic–Baltic diatom intercalibration exercise 2007 (stream monitoring). Journal of Applied Phycology, 21(4), 471-482
Open this publication in new window or tab >>Harmonization is more important than experience—results of the first Nordic–Baltic diatom intercalibration exercise 2007 (stream monitoring)
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2009 (English)In: Journal of Applied Phycology, ISSN 0921-8971, E-ISSN 1573-5176, Vol. 21, no 4, p. 471-482Article in journal (Refereed) Published
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.

Identifiers
urn:nbn:se:umu:diva-22772 (URN)10.1007/s10811-008-9394-5 (DOI)
Available from: 2009-05-19 Created: 2009-05-19 Last updated: 2018-06-08Bibliographically approved
Gälman, V., Rydberg, J., Shchukarev, A., Sjöberg, S., Martínez-Cortizas, A., Bindler, R. & Renberg, I. (2009). The role of iron and sulfur in the visual appearance of lake sediment varves. Journal of Paleolimnology, 42(1), 141-153
Open this publication in new window or tab >>The role of iron and sulfur in the visual appearance of lake sediment varves
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2009 (English)In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 42, no 1, p. 141-153Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer Netherlands, 2009
Identifiers
urn:nbn:se:umu:diva-23348 (URN)10.1007/s10933-008-9267-6 (DOI)
Available from: 2009-06-12 Created: 2009-06-12 Last updated: 2018-06-08Bibliographically approved
Rydberg, J., Gälman, V., Renberg, I., Bindler, R., Lambertsson, L. & Martínez-Cortizas, A. (2008). Assessing the stability of mercury and methylmercury in a varved lake sediment deposit. Environmental Science & Technology, 42(12), 4391-4396
Open this publication in new window or tab >>Assessing the stability of mercury and methylmercury in a varved lake sediment deposit
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2008 (English)In: Environmental Science & Technology, ISSN 0013-936X, Vol. 42, no 12, p. 4391-4396Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Chemical Society, 2008
Identifiers
urn:nbn:se:umu:diva-10271 (URN)10.1021/es7031955 (DOI)18605560 (PubMedID)
Available from: 2008-08-06 Created: 2008-08-06 Last updated: 2018-06-09Bibliographically approved
Shchukarev, A., Gälman, V., Rydberg, J., Sjöberg, S. & Renberg, I. (2008). Speciation of iron and sulphur in seasonal layers of varved lake sediment: an XPS study. Surface and Interface Analysis, 40(3-4), 354-357
Open this publication in new window or tab >>Speciation of iron and sulphur in seasonal layers of varved lake sediment: an XPS study
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2008 (English)In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 40, no 3-4, p. 354-357Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
John Wiley & Sons, 2008
Keywords
XPS, lake sediment, iron speciation, sulphur speciation
National Category
Geology
Identifiers
urn:nbn:se:umu:diva-9435 (URN)10.1002/sia.2704 (DOI)000255486200052 ()
Note

Special Issue: Papers Presented at ECASIA'07: The 12th European Conference on Applications of Surface and Interface Analysis, Brussels, Belgium, 9-14 September 2007

Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2019-08-07Bibliographically approved
Gälman, V., Pettersson, G. & Renberg, I. (2006). A comparison of sediment varves (1950–2003 AD) in two adjacent lakes in northern Sweden. Journal of Paleolimnology, 35, 837-853
Open this publication in new window or tab >>A comparison of sediment varves (1950–2003 AD) in two adjacent lakes in northern Sweden
2006 (English)In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 35, p. 837-853Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Dordrecht: Kluwer, 2006
Keywords
Climate change, Grey-scale, Image analysis, Land-use, Sediment accumulation rate, Varve thickness
Identifiers
urn:nbn:se:umu:diva-7420 (URN)10.1007/s10933-005-5952-x (DOI)
Available from: 2008-01-09 Created: 2008-01-09 Last updated: 2018-06-09Bibliographically approved
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