Veronika Gälman

Umeå University

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Speciation of iron and sulphur in seasonal layers of varved lake sediment: an XPS study

Surface and Interface Analysis (2008)

Andrey Shchukarev Veronika Gälman Johan Rydberg Staffan Sjöberg Ingemar Renberg

Abstract 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 SO 4 2− together with Fe(III) hydroxides were found. Copyright © 2008 John Wiley & Sons, Ltd.

Varve

10.1002/sia.2704

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Citations (30)

Using a decadal diatom sediment trap record to unravel seasonal processes important for the formation of the sedimentary diatom signal

Journal of Paleolimnology (2018)

Dominique Béatrice Maier Veronika Gälman Ingemar Renberg Christian Bigler

Sediment trap studies and high frequency monitoring are of great importance to develop a deeper understanding of how seasonal environmental processes are imprinted in sediment signal formation. We collected whole year diatom assemblages from 2002 to 2014 with a sequential sediment trap from a varved boreal lake (Nylandssjön, Sweden) together with environmental and limnological parameters, and compared them with the corresponding diatom record of the annual laminated sediment. Our data set indicates a large year-to-year variability of diatom succession and abundance patterns, which is well reflected in the varved sediments. Specifically, Cyclotella glomerata dominated the annual sediment trap record (as well as in the corresponding sediment varves) in years with warmer air temperatures in March/April, and Asterionella formosa dominated the annual sediment assemblages as a consequence of years characterized by higher runoff before lake over-turn. Years succeeding forest clearance in the lake catchment showed marked increase in diatom and sediment flux. The DCA scores of the yearly diatom trap assemblages clearly resemble the lake’s thermal structure, which indicates that the relative abundance of major taxa seems primarily controlled by the timing of seasonal environmental events, such as above-average winter air temperature and/or autumn runoff and the current thermal structure of the lake. The high seasonal variability between environmental drivers in combination with the physical limnology leaves us with several possible scenarios leading to either an A. formosa versus C. glomerata dominated annual diatom sediment signal. With this study we highlight that short-term environmental events and seasonal limnological conditions are of major importance for interpreting annual sediment signals.

Varve

Sediment trap

Paleolimnology

Limnology

10.1007/s10933-018-0020-5

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Citations (19)

A Comparison of Sediment Varves (1950–2003 AD) in Two Adjacent Lakes in Northern Sweden

Journal of Paleolimnology (2006)

Veronika Gälman Gunilla Petterson Ingemar Renberg

Varve

Biogenic silica

10.1007/s10933-005-5952-x

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Citations (33)

Varved lake sediments and diagenetic processes

Veronika Gälman

Varved (annually laminated) sediments are of great interest for inference of past environmental conditions, as they provide dated records with high time resolution. After deposition, the sediment v ...

Varve

Source

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Citations (0)

The role of iron and sulfur in the visual appearance of lake sediment varves

Journal of Paleolimnology (2008)

Veronika Gälman Johan Rydberg Andrei Shchukarev Staffan Sjöberg Antonio Martı́nez Cortizas

Varve

Paleolimnology

Biogenic silica

10.1007/s10933-008-9267-6

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Citations (23)

Decadal diagenetic effects on δ¹³C and δ¹⁵N studied in varved lake sediment

Limnology and Oceanography (2009)

Veronika Gälman Johan Rydberg Christian Bigler

To assess the long‐term (27 yr) effects of sediment aging on stable carbon and nitrogen isotope values (δ 13 C and δ 15 N), we used a collection of eight freeze cores of annually laminated (varved) lake sediment collected from 1979 to 2007 in Nylandssjon (northern Sweden). Previous research has shown that 20‐23% of carbon and 35% of nitrogen is lost in 27 yr. Material from specific years was compared in the cores, e.g., δ 13 C and δ 15 N of the surface varve of the 1979 core was followed in cores retrieved in 1980, 1989, 1993, 2002, 2004, and 2006. δ 13 C increased by 0.4‐1.5% during the first 5 yr. After this initial increase, only minor fluctuations were recorded. There is a good correlation between the magnitude in δ 13 C changes and the initial carbon and nitrogen concentrations, indicating that the initial sediment composition is important for the 13 C fractionation. δ 15 N gradually decreased by 0.3‐0.7% over the entire 27‐yr period. The lack of correlation with the initial sediment composition and the gradual decrease in δ 15 N indicates a microbial control on δ 15 N change. The diagenetic changes in the stable isotope values that occur in Nylandssjon are small, but of the same magnitude as the down‐core variation in the varves deposited 1950‐2006. Diagenetic effects should be considered when δ 13 C and δ 15 N are used to study organic matter sources or paleoproductivity, especially when dealing with recent trends or small changes. Based on our findings, diagenetic effects for δ 13 C are observed during the first 5‐10 yr, whereas no delimitation can be recommended for δ 15 N.

Varve

Isotopes of nitrogen

10.4319/lo.2009.54.3.0917

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Citations (77)

Carbon and nitrogen loss rates during aging of lake sediment: Changes over 27 years studied in varved lake sediment

Limnology and Oceanography (2008)

Veronika Gälman Johan Rydberg Sara Sjöstedt de‐Luna Richard Bindler Ingemar Renberg

We used a collection of ten freeze cores of annually laminated (varved) lake sediment from Nylandssjön in northern Sweden collected from 1979 to 2007 to follow the long‐term loss of carbon (C) and nitrogen (N) due to processes that occur in the lake bottom as sediment ages. We compared specific years in the different cores. For example, the loss of C from the surface varve of the 1979 core (sediment deposited during 1978) was followed in the cores from 1980, 1985, 1989, and so on until 2006. The C concentration of the sediment decreased by 20% and N decreased by 30% within the first five years after deposition, and after 27 yr in the sediment, there was a 23% loss of C and 35% loss of N. Because the relative loss of C with time was smaller than loss of N, the C:N ratio increased with increasing age of the sediment; the surface varves start with a ratio of ~10, which then increases to ~12.

Varve

Sediment core

Deposition

10.4319/lo.2008.53.3.1076

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Citations (224)