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  • 1.
    Bigler, Christian
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Grahn, E.
    Larocque, I.
    Jeziorski, A.
    Hall, Roland
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Holocene environmental change at Lake Njulla (999 m asl), northern Sweden: a comparison with four small nearby lakes along an altitudinal gradient2003In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 29, no 1, p. 13-29Article in journal (Refereed)
    Abstract [en]

    We assess Holocene environmental change at alpine Lake Njulla (68degrees22'N, 18degrees42'E, 999 m a.s.l.) in northernmost Sweden using sedimentary remains of chironomid head capsules and diatoms. We apply regional calibration sets to quantitatively reconstruct mean July air temperature (using chironomids and diatoms) and lake-water pH (using diatoms). Both chironomids and diatoms infer highest temperatures (1.7-2.3degreesC above present-day estimates, including, a correction for glacio-isostatic land up-lift by 0.6degreesC) during the early Holocene (c. 9,500-8,500 cal. yrs BP). Diatoms suggest a decreasing lake-water pH trend (c. 0.6 pH units) since the early Holocene. Using detrended canonical correspondence analysis (DCCA), we compare the Holocene development of diatom communities in Lake Njulla with four other nearby lakes (Lake 850, Lake Tibetanus, Vuoskkujavri, Vuolep Njakajaure) located along an altitudinal gradient. All five lakes show similar initial DCCA scores after deglaciation, suggesting that similar environmental processes such as high erosion rates and low light availability associated with high summer temperature appear to have regulated the diatom community, favouring high abundances of Fragilaria species. Subsequently, the diatom assemblages develop in a directional manner, but timing and scale of development differ substantially between lakes. This is attributed primarily to differences in the local geology, which is controlling the lake-water pH. Imposed on the basic geological setting, site-specific processes such as vegetation development, climate, hydrological setting and in-lake processes appear to control lake development in northern Sweden.

  • 2.
    Bigler, Christian
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Hall, Roland I
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Diatoms as indicators of climatic and limnological change in Swedish Lapland: A 100-lake calibration set and its validation for paleoecological reconstructions2002In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 27, no 1, p. 97-115Article in journal (Refereed)
    Abstract [en]

    This study investigated the distribution of subfossil diatom assemblages in surficial sediments of 100 lakes along steep ecological and climatic gradients in northernmost Sweden (Abisko region, 67.07degrees N to 68.48degrees N latitude, 17.67degrees E to 23.52degrees E longitude) to develop and cross-validate transfer functions for paleoenvironmental reconstruction. Of 19 environmental variables determined for each site, 15 were included in the statistical analysis. Lake-water pH (8.0%), sedimentary loss-on-ignition (LOI, 5.9%) and estimated mean July air temperature (July T, 4.8%) explained the greatest amounts of variation in the distribution of diatom taxa among the 100 lakes. Temperature and pH optima and tolerances were calculated for abundant taxa. Transfer functions, based on WA-PLS (weighted averaging partial least squares), were developed for pH (r(2) = 0.77, root-mean-square-error of prediction (RMSEP) = 0.19 pH units, maximum bias = 0.31, as assessed by leave-one-out cross-validation) based on 99 lakes and for July T (r(2) = 0.75, RMSEP = 0.96 degreesC, max. bias = 1.37 degreesC) based on the full 100 lake set. We subsequently assessed the ability of the diatom transfer functions to estimate lake-water pH and July T using a form of independent cross-validation. To do this, the 100-lake set was divided in two subsets. An 85-lake training-set (based on single limnological measurements) was used to develop transfer functions with similar performance as those based on the full 100 lakes, and a 15-lake test-set (with 2 years of monthly limnological measurements throughout the ice-free seasons) was used to test the transfer functions developed from the 85-lake training-set. Results from the intra-set cross-validation exercise demonstrated that lake-specific prediction errors (RMSEP) for the 15-lake test-set corresponded closely with the median measured values (pH) and the estimations based on spatial interpolations of data from weather stations (July T). The prediction errors associated with diatom inferences were usually within the range of seasonal and interannual variability. Overall, our results confirm that diatoms can provide reliable and robust estimates of lake-water pH and July T, that WA-PLS is a robust calibration method and that long-term environmental data are needed for further improvement of paleolimnological transfer functions.

  • 3.
    Bindler, Richard
    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.
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Establishing natural sediment reference conditions for metals and the legacy of long-range and local pollution on lakes in Europe2011In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 45, no 4, p. 519-531Article in journal (Refereed)
    Abstract [en]

    The intention of the European Water Framework Directive (WFD) and the national guidelines that implement the WFD is that present-day conditions and future management strategies are to be based on an understanding of reference conditions for the particular water body of interest. In the context of non-synthetic pollutants such as lead, mercury and cadmium, the criteria for a high ecological status are that "concentrations [are] within the range normally associated with undisturbed conditions". How this normal range is to be defined is open to interpretation; for example, in Sweden reference conditions based on sediment records are defined as the conditions prior to modern industrialization, i.e. prior to the mid-1800's. These pre-industrial reference conditions would correspond to sediments 15-30 cm depth. However, 'reference conditions' are not always synonymous with 'natural background conditions'. Analyses of long sediment profiles from Swedish lakes and from a few other areas, however, have shown that pre-industrial pollution-at least with regard to lead-was extensive. Atmospheric lead pollution has its origin in antiquity, with a small, well-defined peak already during the Greek-Roman period 2,000 years ago. Sediments deposited 300-500 years in Sweden and Scotland, for example, show a dominance of pollution lead, and in some sediment records also cadmium and copper pollution was extensive. Thus, in order to characterize natural background concentrations of metals, long sediment profiles are needed to reach sediments unaffected by pollution (> 3,000 years BP); this can correspond to sediments below 50 cm in some lakes, but in others sediments below 300 cm or more.

  • 4.
    Boes, Xavier
    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.
    Martinez-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.
    Evaluation of conservative lithogenic elements (Ti, Zr, Al, and Rb) to study anthropogenic element enrichments in lake sediments2011In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 46, no 1, p. 75-87Article in journal (Refereed)
    Abstract [en]

    In lake sediment investigations of heavy metal pollution history, it has become a common approach to calculate enrichment factors (EFs) by normalizing elemental distributions to a reference lithogenic element. However, this approach requires that the reference element remains stable once it has been deposited to the sediment (it is not affected by diagenetic processes). This is rarely studied in well-controlled field experiments. Here, we test the commonly used reference elements titanium (Ti), zirconium (Zr), aluminum (Al), and rubidium (Rb). We use a unique series of freeze cores collected in different years since 1979 in Lake Nylandssjon in northern Sweden. This lake has sediment with distinct varves (annually laminated deposit). Element concentrations in individual varves were analyzed using X-ray fluorescence (XRF) spectroscopy. By tracking the newly formed surface varve from different cores across this core series, i.e., following the element concentration in a specific varve as it becomes progressively aged, it was possible to assess the potential impact of diagenetic processes on geochemical signatures. Results confirm the conservative character of the studied elements; there was neither an increasing nor a decreasing concentration trend with time during sediment ageing for any of these elements. Secondly, we addressed the question 'which of them is the most appropriate for EFs estimates with the aim of distinguishing anthropogenic from geogenic inputs, for example in pollution studies'. To assess the reliability of the EFs we used lead (Pb) as an example, because anthropogenic Pb in the sediment could be independently calculated using stable Pb isotopes. When anthropogenic Pb concentrations calculated with Pb-EFs were compared to the anthropogenic Pb concentrations derived from stable Pb isotopes, the differences found were 20% for Ti, 10% for Zr, 11% for Al, and 27% for Rb when upper continental crust concentrations were used for the background ratio. Based on the results from Nylandssjon our suggestions are that (1) when using EFs on a single core, which is the normal case in paleolimnology, multiple reference elements should be used together and (2) the results from those should be critically evaluated.

  • 5. Bonk, Alicja
    et al.
    Kinder, Małgorzata
    Enters, Dirk
    Grosjean, Martin
    Meyer-Jacob, Carsten
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Tylmann, Wojciech
    Sedimentological and geochemical responses of Lake Żabińskie (north-eastern Poland) to erosion changes during the last millennium2016In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 56, no 2-3, p. 239-252Article in journal (Refereed)
    Abstract [en]

    Increased erosion triggered by land-use changes is a major process that influences lake sedimentation. We explored the record of erosion intensity in annually laminated sediments of Lake Żabińskie, northeast Poland. A 1000-year-long, annually resolved suite of sedimentological (varve thickness, sediment accumulation rate) and geochemical data (scanning XRF, loss on ignition, biogenic silica) was analyzed with multivariate statistics. PCA indicated erosion was a major process responsible for changes in the chemical composition of the sediments. Analysis of sedimentary facies enabled identification of major phases of erosion that influenced lake sedimentation. These phases are consistent with the history of land use, inferred from pollen analysis. From AD 1000 to 1610, conditions around and in Lake Żabińskie were relatively stable, with low erosion intensity in the catchment and a dominance of carbonate sedimentation. Between AD 1610 and 1740, higher lake productivity and increased delivery of minerogenic material were caused by development of settlements in the region and widespread deforestation. The most prominent changes were observed between AD 1740 and 1880, when further land clearance and increased agricultural activity caused intensified soil erosion and higher lake productivity. Landscape clearance also created better conditions for water column mixing, which led to changes in redox conditions in the hypolimnion. The most recent period (AD 1880–2010) was characterized by partial reforestation and a gradual decrease in the intensity of erosional processes.

  • 6.
    Capo, Eric
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. CARRTEL, INRA, Universite´ de Savoie Mont Blanc, 74000 Thonon-Les-Bains, France.
    Domaizon, Isabelle
    Maier, Dominique
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Debroas, Didier
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    To what extent is the DNA of microbial eukaryotes modified during burying into lake sediments?: A repeat-coring approach on annually laminated sediments2017In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 58, no 4, p. 479-495Article in journal (Refereed)
    Abstract [en]

    Paleogenetics provides a powerful framework to reconstruct the long-term temporal dynamics of various biological groups from aquatic sediments. However, validations are still required to ensure the authenticity of the molecular signal obtained from sedimentary DNA. Here, we investigated the effects of early diagenesis on the DNA signal from micro-eukaryotes preserved in sediments by comparing metabarcoding inventories obtained for two sediment cores sampled in 2007 and 2013 respectively. High-throughput sequencing (Illumina MiSeq) of sedimentary DNA was utilized to reconstruct the composition of microbial eukaryotic communities by targeting the V7 region of the 18S rDNA gene. No significant difference was detected between the molecular inventories obtained for the two cores both for total richness and diversity indices. Moreover, community structures obtained for the two cores were congruent as revealed by procrustean analysis. Though most of the eukaryotic groups showed no significant difference in terms of richness and relative proportion according to the core, the group of fungi was found to differ both in terms of richness and relative proportion (possibly due to their spatial heterogeneity and potential activity in sediments). Considering the OTUs level (i.e. Operational Taxonomic Units as a proxy of ecological species), our results showed that, for the older analyzed strata (age: 15-40 years), the composition and structure of communities were very similar for the two cores (except for fungi) and the DNA signal was considered stable. However, for the uppermost strata (age < 15 years), changes of moderate magnitude were detected in the relative abundance of few OTUs. Overall, this study points out that, in Nylandssjon sediments, early diagenesis did not induce marked modifications in the micro-eukaryotic DNA signal, thus opening new perspectives based on the analysis of eukaryotic sedimentary DNA to address scientific issues both in the domains of paleolimnology and microbial ecology. Because this study site is ideal for DNA preservation in sediment (quick sedimentation processes, no sediment resuspension, anoxic conditions at sediment-water interface), the generalization of our conclusions, in particular for less favorable sites, must be considered cautiously.

  • 7. Catalan, Jordi
    et al.
    Pla-Rabes, Sergi
    Wolfe, Alexander P.
    Smol, John P.
    Ruehland, Kathleen M.
    Anderson, N. John
    Kopacek, Jiri
    Stuchlik, Evzen
    Schmidt, Roland
    Koinig, Karin A.
    Camarero, Lluis
    Flower, Roger J.
    Heiri, Oliver
    Kamenik, Christian
    Korhola, Atte
    Leavitt, Peter R.
    Psenner, Roland
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Global change revealed by palaeolimnological records from remote lakes: a review2013In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 49, no 3, p. 513-535Article in journal (Refereed)
    Abstract [en]

    Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with respect to past, purely natural variability in lake systems. Fostering conceptual and methodological bridges with other environmental disciplines will upturn contribution of remote lake palaeolimnology in solving existing and emerging questions in global change science and planetary stewardship.

  • 8. Cunningham, Laura
    et al.
    Bishop, Kevin
    Mettavainio, Eva
    Rosén, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Paleoecological evidence of major declines in total organic carbon concentrations since the nineteenth century in four nemoboreal lakes2011In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 45, no 4, p. 507-518Article in journal (Refereed)
    Abstract [en]

    A decade of widespread increases in surface water concentrations of total organic carbon (TOC) in some regions has raised questions about longer term patterns in this important constituent of water chemistry. This study uses near-infrared spectroscopy (NIRS) to infer lake water TOC far beyond the decade or two of observational data generally available. An expanded calibration dataset of 140 lakes across Sweden covering a TOC gradient from 0.7 to 24.7 mg L-1 was used to establish a relationship between the NIRS signal from surface sediments (0-0.5 cm) and the TOC concentration of the water mass. Internal cross-validation of the model resulted in an R (2) of 0.72 with a root mean squared error of calibration (RMSECV) of 2.6 mg L-1. The TOC concentrations reconstructed from surface sediments in four Swedish lakes were typically within the range of concentrations observed in the monitoring data during the period represented by each sediment layer. TOC reconstructions from the full sediment cores of four lakes indicated that TOC concentrations were approximately twice as high a century ago.

  • 9. de Jong, Rixt
    et al.
    Kamenik, Christian
    Westover, Karlyn
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Grosjean, Martin
    A chrysophyte stomatocyst-based reconstruction of cold-season air temperature from Alpine Lake Silvaplana (AD 1500-2003); methods and concepts for quantitative inferences2013In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 50, no 4, p. 519-533Article in journal (Refereed)
    Abstract [en]

    Relatively little is known about past cold-season temperature variability in high-Alpine regions because of a lack of natural cold-season temperature proxies as well as under-representation of high-altitude sites in meteorological, early-instrumental and documentary data sources. Recent studies have shown that chrysophyte stomatocysts, or simply cysts (sub-fossil algal remains of Chrysophyceae and Synurophyceae), are among the very few natural proxies that can be used to reconstruct cold-season temperatures. This study presents a quantitative, high-resolution (5-year), cold-season (Oct-May) temperature reconstruction based on sub-fossil chrysophyte stomatocysts in the annually laminated (varved) sediments of high-Alpine Lake Silvaplana, SE Switzerland (1,789 m a.s.l.), since AD 1500. We first explore the method used to translate an ecologically meaningful variable based on a biological proxy into a simple climate variable. A transfer function was applied to reconstruct the 'date of spring mixing' from cyst assemblages. Next, statistical regression models were tested to convert the reconstructed 'dates of spring mixing' into cold-season surface air temperatures with associated errors. The strengths and weaknesses of this approach are thoroughly tested. One much-debated, basic assumption for reconstructions ('stationarity'), which states that only the environmental variable of interest has influenced cyst assemblages and the influence of confounding variables is negligible over time, is addressed in detail. Our inferences show that past cold-season air-temperature fluctuations were substantial and larger than those of other temperature reconstructions for Europe and the Alpine region. Interestingly, in this study, recent cold-season temperatures only just exceed those of previous, multi-decadal warm phases since AD 1500. These findings highlight the importance of local studies to assess natural climate variability at high altitudes.

  • 10. Finsinger, Walter
    et al.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science. NCCR Climate, Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013, Bern, Switzerland.
    Kraehenbuehl, Urs
    Lotter, Andre F
    Ammann, Brigitta
    Human impacts and eutrophication patterns during the past similar to 200 years at Lago Grande di Avigliana (N. Italy)2006In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 36, no 1, p. 55-67Article in journal (Refereed)
    Abstract [en]

    A short sediment core from Lago Grande di Avigliana (Piedmont, Italy), the second most eutrophied lake in Italy, was analysed for pollen and diatoms to reconstruct land-use changes and to estimate baseline conditions for total phosphorus (TP) in the water column. Varve counts on sediment thin-sections and (210)Pb, (226)Ra, and (137)Cs dating provided a reliable chronology for the past similar to 200 years. The main pollen-inferred land-use changes showed a sharp decrease of hemp retting around AD 1900, as well as a gradual change to less intensive agriculture and increasing abundance of exotic plants since AD similar to 1970. Diatom-inferred TP reconstructions indicated stable TP concentrations until AD similar to 1950, revealing baseline mesotrophic conditions (TP < 25 mu g l(-1)). After AD similar to 1950, TP values increased distinctly and continuously, culminating in the late 1960s with concentrations of 150 mu g l(-1). Subsequently, diatoms implied a linear decrease of TP, with an inferred value of 40 mu g l(-1) in the surface sediment sample. Comparison with instrumental TP measurements from the water column since AD 1980 showed a rapid recovery and allowed a direct validation of the diatom TP inference. However, although the TP concentration has decreased considerably, baseline conditions have not yet been reached. When compared to the limnological effects of sewage discharges on inferred-TP concentration, our results indicated that agricultural land use played a minor role in the lake's eutrophication.

  • 11.
    Guhrén, Matilda
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Bigler, Christian
    Renberg, Ingemar
    Liming placed in a long-term perspective: a paleolimnological study of 12 lakes in the Swedish liming program2007In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 37, no 2, p. 247-258Article in journal (Refereed)
    Abstract [en]

    Since the 1970s liming has been practised on a large scale in Sweden to mitigate acidification and several thousand lakes and streams are limed repeatedly. The Swedish monitoring program ISELAW (Integrated Studies of the Effects of Liming Acidified Waters) studies the long-term effects of liming. This paper summarizes the paleolimnological part of the program. Sediment cores from 12 lakes were analysed to study the development of the lakes from pre-industrial time until the present, and address questions about natural conditions and the effects of early human impact, acidification, and liming. Diatoms were used to reconstruct the pH history and to study shifts in species composition due to acidification and liming. Analyses of lead and spheroidal carbonaceous particles were applied for indirect dating and as indicators of the atmospheric deposition of pollutants associated with acid rain. Pollen analysis was performed in eight of the lakes to study the vegetation and agricultural history. The natural pH (prior to human disturbance) was between 5.3 and 6.5 in the eight lakes where the complete post-glacial sediment sequence was recovered. Pollen from anthropochores and apophytes indicated early agricultural land use in the vicinity of the lakes from 1000 to 2000 years ago, and pH increased with land use in six of these lakes. Five of the lakes have been acidified during recent decades, and in all 12 lakes some effects of liming were recorded in the diatom assemblage. The lakes show different responses to liming, including a return to a pre-acidification diatom composition or a shift to a state previously not recorded in the lake’s histories. This study accentuates the complexity of biological response to acidification and liming, and highlights the importance of historical perspectives to assess the current state of a lake’s ecosystem and to establish adequate restoration goals.

  • 12.
    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.

  • 13.
    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.

  • 14. Holmgren, Sofia U.
    et al.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ingólfsson, Ólafur
    Wolfe, Alexander P.
    The Holocene–Anthropocene transition in lakes of western Spitsbergen, Svalbard (Norwegian High Arctic): climate change and nitrogen deposition2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 43, no 2, p. 393-412Article in journal (Refereed)
    Abstract [en]

    Lake sediments from four small lakes on western Spitsbergen (Svalbard Archipelago, Norwegian High Arctic) preserve biostratigraphic and isotopic evidence for a complex suite of twentieth century environmental changes. At Lake Skardtjørna and Lake Tjørnskardet on Nordenskiöldkysten, there is a marked diatom floristic change coupled to increased diatom concentrations beginning around 1920. At Lake Istjørna and Lake Istjørnelva, 25 km southwest of Longyearbyen, both diatom total valve and chrysophyte stomatocyst concentrations have increased dramatically since the beginning of the 1900s. The early twentieth century changes are probably related to climate warming after the Little Ice Age. However, the most pronounced changes in diatom assemblages seem to have occurred in the last few decades. At the same time, nitrogen stable isotopes in sediment organic matter in two of the lakes became progressively depleted by ~2‰, which is consistent with diffuse atmospheric inputs from anthropogenic sources and attendant fertilization. These data suggest that climate change and nitrogen deposition may be acting together in driving these lakes towards new ecological states that are unique in the context of the Holocene.

  • 15. Jones, V. J.
    et al.
    Solovieva, N.
    Self, A. E.
    McGowan, S.
    Rosén, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Salonen, J. S.
    Seppa, H.
    Valiranta, M.
    Parrott, E.
    Brooks, S. J.
    The influence of Holocene tree-line advance and retreat on an arctic lake ecosystem: a multi-proxy study from Kharinei Lake, North Eastern European Russia2011In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 46, no 1, p. 123-137Article in journal (Refereed)
    Abstract [en]

    A consequence of predicted climate warming will be tree-line advance over large areas of the Russian tundra. Palaeolimnological techniques can be used to provide analogues of how such changes in tree-line advance and subsequent retreat affected lake ecosystems in the past. A Holocene sediment core taken from Kharinei Lake (Russia) was dated radiometrically and used for multi-proxy analyses with the aim of determining how climate and tree-line dynamics affected the productivity, community structure, carbon cycling and light regime in the lake. Pollen and macrofossil analyses were used to determine the dates of the arrival and retreat of birch and spruce forest. C:N ratios and percent loss-on-ignition were used to infer past changes in sediment organic matter. Visible-near-infrared spectroscopy and diatom analysis were used to infer past changes in lake-water carbon. Algal pigments and aquatic macrophytes were used to determine changes in lake productivity and light. Chironomids together with remains of the aquatic flora and fauna were used to provide information on past July temperature and continentality. Lake sedimentation was initiated shortly before 11,000 cal. years BP, when both chironomid- and pollen-inferred temperature reconstructions suggest higher summer temperatures than present, between 1 and 2 degrees C warmer, and lake productivity was relatively high. A few trees were already present at this time. The spruce forest expanded at 8,000 cal. year BP remaining in the vicinity of the lake until 3,500 cal. year BP. This period coincided with a high concentration of organic material in the water column, and relatively high benthic productivity, as indicated by a high benthic: planktonic diatom ratio. After tree-line retreat, the optical transparency of the lake increased, and it became more open and exposed, and was thus subject to greater water-column mixing resulting in a higher abundance of diatom phytoplankton, especially heavily silicified Aulocoseira species. The colder climate resulted in a shorter ice-free period, the lake was less productive and there was a loss of aquatic macrophytes. Increased wind-induced mixing following forest retreat had a greater influence on the lake ecosystem than the effects of decreasing organic matter concentration and increased light penetration.

  • 16. Kokfelt, Ulla
    et al.
    Reuss, Nina
    Struyf, Eric
    Sonesson, Mats
    Rundgren, Mats
    Skog, Göran
    Rosén, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hammarlund, Dan
    Wetland development, permafrost history and nutrient cycling inferred from later Holocene peat and lake sediment records in subarctic Sweden2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 44, no 1, p. 327-342Article in journal (Refereed)
    Abstract [en]

    Permafrost in peatlands of subarctic Sweden is presently thawing at accelerated rates, which raises questions about the destiny of stored carbon and nutrients and impacts on adjacent freshwater ecosystems. In this study we use peat and lake sediment records from the Stordalen palsa mire in northern Sweden to address the late Holocene (5,000 cal BP-present) development of the mire as well as related changes in carbon and nutrient cycling. Formation, sediment accumulation and biogeochemistry of two studied lakes are suggested to be largely controlled by the development of the mire and its permafrost dynamics. Peat inception took place at ca. 4,700 cal BP as a result of terrestrialisation. Onset of organic sedimentation in the adjacent lakes occurred at ca. 3,400 and 2,650 cal BP in response to mire expansion and permafrost aggradation, respectively. Mire erosion, possibly due to permafrost decay, led to re-deposition of peat into one of the lakes after ca. 2,100 cal BP, and stimulated primary productivity in the other lake at ca. 1,900–1,800 cal BP. Carbonate precipitation appears to have been suppressed when acidic poor fen and bog (palsa) communities dominated the catchment mire, and permafrost-induced changes in hydrology may further have affected the inflow of alkaline water from the catchment. Elevated contents of biogenic silica and diatom pigments in lake sediments during periods of poor fen and bog expansion further indicate that terrestrial vegetation influenced the amount of nutrients entering the lake. Increased productivity in the lake likely caused bottom-water anoxia in the downstream lake and led to recycling of sediment phosphorous, bringing the lake into a state of self-sustained eutrophication during two centuries preceding the onset of twentieth century permafrost thaw. Our results give insight into nutrient and permafrost dynamics in a subarctic wetland and imply that continued permafrost decay and related vegetation changes towards minerotrophy may increase carbon and nutrient storage of mire deposits and reduce nutrient fluxes in runoff. Rapid permafrost degradation may on the other hand lead to widespread mire erosion and to relatively short periods of significantly increased nutrient loading in adjacent lakes.

  • 17. Kylander, Malin E.
    et al.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wohlfarth, Barbara
    Loewemark, Ludvig
    Geochemical responses to paleoclimatic changes in southern Sweden since the late glacial: the Hasseldala Port lake sediment record2013In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 50, no 1, p. 57-70Article in journal (Refereed)
    Abstract [en]

    There is a relatively good understanding of the paleoenvironmental changes that have occurred in southern Sweden since the Late Glacial. A main exception, however, is the sedimentary response of lacustrine systems during this period of rapid climate shifts. To address this, high-resolution X-ray fluorescence core scanning, Total Organic Carbon (TOC), C/N and delta C-13 analyses were made on a core from Hasseldala Port, a paleolake in the region. Site-specific geochemical analyses documented variations in silicate inputs (Zr/Ti, Si/Ti, K/Ti and K/Rb), productivity (TOC, Ca/Ti and Sr/Ti), as well as redox conditions in the sediment (delta C-13, Mn/Ti and Fe/Ti), which were then linked to the regional climatic framework. During the Bolling/Older Dryas sediment accumulation was at its highest, particularly prior to colonization by terrestrial vegetation, and hydrological transport dominated. No clear signal of the Older Dryas was detected in the elemental chemistry. The Allerod was a period of relatively constant sediment accumulation, with the exception of during the Gerzensee oscillation when rates increased. There is evidence for increased within-lake and -catchment productivity and a change in silicate source during parts of the Allerod. As opposed to other records from the region, constant sediment accumulation rates were found during the Younger Dryas. Other proxies also suggest that this was a rather static period at Hasseldala Port. A gradual change in productivity and hydrological activity was observed from 12,000 cal year BP. The Preboreal section is rather short but the geochemical response was similar to that seen during other periods with milder climate conditions. The geochemical record archived in the sediments at Hasseldala Port was found to be the integrated result of physical erosion, landscape and soil development, vegetation changes, basin hydrology and moisture and temperature variations and it fills an important information gap in our understanding of the geochemical response of lake sediments to past climate change.

  • 18. Larocque , I
    et al.
    Grosjean , M
    Heiri , O
    Bigler , Christian
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Blass , C
    Comparison between chironomid-inferred July temperatures and meteorological data AD 1850-2001 from varved Lake Silvaplana, Switzerland2009In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 41, no 2, p. 329-342Article in journal (Refereed)
    Abstract [en]

    Inferred temperatures from chironomids preserved in the varved sediment of Lake Silvaplana in the Eastern Swiss Alps were compared with instrumental data obtained from a meteorological station in Sils-Maria, on the shore of Lake Silvaplana, for the time interval 1850-2001. At near-annual resolution, the general patterns of chironomid-inferred temperature changes followed the meteorological record over the last 150 years (r (Pearson) = 0.65, P = 0.01) and 87% of the inferences had deviations from the instrumental data below the root-mean-square error of prediction (RMSEP). When the inferences were compared with a 2-year running mean in the meteorological data, 94% of the inferences had differences with the instrumental data below the RMSEP, indicating that more than half of the inaccurate inferences may have been due to errors in varve counting. Larger deviations from the instrumental data were also obtained from samples with low percentages of fossil taxa represented in the training set used for temperature reconstruction and/or assemblages with poor fit to temperature. Changes in total phosphorus (TP, as inferred by diatoms) and/or greater precipitation were possible factors affecting the accuracy of the temperature reconstruction. Although these factors might affect the quantitative estimates, obtaining > 80% accurate temperature inferences suggests that chironomid analysis is a reliable tool for reconstructing mean July air temperature quantitatively over the last 150 years in Lake Silvaplana.

  • 19. Martinez Cortizas, Antonio
    et al.
    Lopez-Merino, Lourdes
    Bindler, Richard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Mighall, Timothy
    Kylander, Malin
    Atmospheric Pb pollution in N Iberia during the late Iron Age/Roman times reconstructed using the high-resolution record of La Molina mire (Asturias, Spain)2013In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 50, no 1, p. 71-86Article in journal (Refereed)
    Abstract [en]

    Extensive mining took place in Spain during the Iron Age and Roman times, although a detailed chronology is still lacking due to the inherent difficulties in dating mining structures. In this study we sampled and analyzed a core from La Molina mire in the Asturias region, northern Spain. Because more than 100 Roman mines have thus far been found within 20 km of the mire, our aim was to shed light on local mining history, which we can then compare to the wider narrative of early mining pollution in Spain. We focus on the section from similar to 500 BC to AD similar to 600, which has a high temporal resolution of 6-15 year per sample. Geochemical analyses included the determination of major, minor and trace lithogenic elements (Si, Al, Fe, Ti, Ga, Rb, Y, Zr, Th) as markers of mineral content of the peat, and trace metals/metalloids (Mn, Cu, Ni, As, Pb) as well stable Pb isotopes, as potential markers of atmospheric metal pollution. The use of principal components analysis enabled the identification of a dominant geogenic component and a secondary pollution component. The earliest pollution signal of the covered period was recorded by similar to 300 BC, coinciding with the late local Iron Age. Average Pb-206/Pb-207 ratios of samples with ages older than this date was 1.204 +/- A 0.002, while all samples with a younger age had a less radiogenic ratio. Based on the metal pollution component four phases were identified: I, similar to 500 to 300 BC; II, similar to 300 to 20 BC; III, similar to 20 BC-AD 480; IV, AD similar to 480 to 600. The lowest isotopic ratio and highest proportion of pollution Pb (Pb-206/Pb-207 ratio of 1.157 and 89 % of total accumulated Pb) was reached at peak Pb production during Roman times (AD similar to 180 to 340), indicating that this was the period of most intense metal contamination in the area over the studied period. It is remarkable that the La Molina record shows a more extended period (two centuries) of active mining in comparison with other areas in Iberia, and a pattern of repeated shifts in Pb pollution of short duration, which is likely related to the local history of exploitation and exhaustion of mines within the area.

  • 20.
    Meyer-Jacob, Carsten
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vogel, Hendrik
    Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern.
    Boxberg, Florian
    Institute of Geology and Mineralogy, University of Cologne; MARUM – Center for Marine Environmental Sciences and Faculty of Geosciences, University of Bremen.
    Rosén, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Weber, Michael E.
    Institute of Geology and Mineralogy, University of Cologne.
    Bindler, Richard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Independent measurement of biogenic silica in sediments by FTIR spectroscopy and PLS regression2014In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 52, no 3, p. 245-255Article in journal (Refereed)
    Abstract [en]

    We present an independent calibration model for the determination of biogenic silica (BSi) in sediments, developed from analysis of synthetic sediment mixtures and application of Fourier transform infrared spectroscopy (FTIRS) and partial least squares regression (PLSR) modeling. In contrast to current FTIRS applications for quantifying BSi, this new calibration is independent from conventional wet-chemical techniques and their associated measurement uncertainties. This approach also removes the need for developing internal calibrations between the two methods for individual sediments records. For the independent calibration, we produced six series of different synthetic sediment mixtures using two purified diatom extracts, with one extract mixed with quartz sand, calcite, 60/40 quartz/calcite and two different natural sediments, and a second extract mixed with one of the natural sediments. A total of 306 samples-51 samples per series-yielded BSi contents ranging from 0 to 100 %. The resulting PLSR calibration model between the FTIR spectral information and the defined BSi concentration of the synthetic sediment mixtures exhibits a strong cross-validated correlation ( = 0.97) and a low root-mean square error of cross-validation (RMSECV = 4.7 %). Application of the independent calibration to natural lacustrine and marine sediments yields robust BSi reconstructions. At present, the synthetic mixtures do not include the variation in organic matter that occurs in natural samples, which may explain the somewhat lower prediction accuracy of the calibration model for organic-rich samples.

  • 21.
    Milan, Manuela
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. IASMA Research and Innovation Centre, E. Mach Foundation-Istituto Agrario di San Michele all’Adige, S. Michele All’Adige, Trento, Italy.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Tolotti, Monica
    Szeroczynska, Krystyna
    Effects of long term nutrient and climate variability on subfossil Cladocera in a deep, subalpine lake (Lake Garda, northern Italy)2017In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 58, no 3, p. 335-351Article in journal (Refereed)
    Abstract [en]

    Albeit subfossil Cladocera remains are considered as a reliable proxy for tracking historical lake development, they have been scarcely studied in large subalpine lakes south of the Alps. In this study, subfossil Cladocera remains from Lake Garda in northern Italy were analyzed to track the lake's environmental changes since the Middle Ages. One core was retrieved from the largest sub-basin of Lake Garda (Brenzone, 350 m deep) and two cores were retrieved from the profundal and littoral zone of the smaller lake sub-basin (Bardolino, 80 and 40 m deep, respectively). The species distribution of Cladocera remains in recent sediment layers was similar to that observed in contemporary water samples. The deepest sections of the three cores were characterized by species sensitive to water temperature, which suggest a key role of major climatic events in driving the lake response during the late Holocene. The most evident change in Cladocera assemblages in the studied cores was observed during the 1960s, when planktonic taxa such as Daphnia spp. and Bosmina spp. became dominant at the expense of littoral taxa. Despite the highly coherent general pattern of subfossil Cladocera, the cores showed a set of minor differences, which were attributed to different morphological and hydrological features of the two basins forming Lake Garda. Multivariate analysis revealed a clear relation of Cladocera to climate variability during periods of low lake nutrient levels (i.e. before the 1960s). This provides additional information on past ecological responses of Lake Garda, as contrast previous data from subfossil diatom and pigment analyses did not fully capture effects of climate change during the same period. Since the 1960s shifts in assemblage composition of Cladocera and diatoms were highly coherent, in response to nutrient increase and the following, less pronounced, decrease in nutrient concentrations. During the last five decades, the response of the Cladocera to climate variability appeared to be masked by nutrient change. This work points up the potential of the multi-proxy approach for disentangling the multifaceted biological responses to multiple environmental stressors in large and deep lakes.

  • 22.
    Norberg, Matilda
    et al.
    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.
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Comparing pre-industrial and post-limed diatom communities in Swedish lakes, with implications for defining realistic management targets2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 44, no 1, p. 233-242Article in journal (Refereed)
    Abstract [en]

    In the 1960s and 1970s, acidification was identified as a major environmental problem in Scandinavia, Great Britain and North America. In Sweden, a liming program was launched in order to counteract the effects of acidification on surface waters. More than 30 years after large-scale liming began, there is still debate about whether liming actually achieves its goals, i.e., to prevent acidification in acid-sensitive surface waters and to restore natural conditions in acidified waters. We used Detrended Correspondence Analysis (DCA) and analogue matching of diatom assemblages in surface sediment samples (recent conditions) from 31 limed lakes and pre-industrial samples from 291 reference lakes to help answer the question as to whether the Swedish liming program achieves its goals. Diatoms are important primary producers in lakes and established indicator organisms for lake-water quality. First we compared pre-industrial with post-limed diatom communities to address the question whether liming causes unnatural conditions, i.e., diatom communities that have not previously occurred in Swedish lakes. Second, we addressed the issue of what is a realistic condition to use as a reference (natural condition) or a target in management programs. We found that the diatom communities in limed lakes were not different from the communities in the reference lakes. Most of the limed lakes had one or more analogues within the reference data set and many of them had at least one within-lake analogue. Hence, liming does not create unique diatom communities in lakes. Based on this and previous paleolimnological studies in Swedish lakes we suggest a conceptual model integrating the natural lake condition, the historical human impact, and the recent and contemporary human impact, when defining realistic targets in management programs.

  • 23.
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A short summary of my forty years in paleolimnology2014In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 51, no 1, p. 145-153Article in journal (Refereed)
  • 24.
    Renberg, Ingemar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hansson, Hans
    HTH-Teknik, Luleå, Sweden.
    Freeze corer No. 3 for lake sediments2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 44, no 2, p. 731-736Article in journal (Refereed)
    Abstract [en]

    Freezing of sediment in situ at the lake bottom using a freeze corer has become an important method for taking samples of soft sediments aimed for detailed stratigraphic analyses. Over the past decades a variety of freeze corers have been designed, from very simple metal tubes filled with dry ice that are dropped into the sediment to high-tech samplers using electric pumps, hydraulics and liquid nitrogen. The freeze corer described here is a compromise of getting good samples without a too complicated technique. It is designed for coring from lake ice, using a steel wire with a stopper on the ice to keep the corer in fixed position during freezing. It consists of a thermos connected to a thin freeze wedge (width 15 cm, length 100 cm, max thickness 6 cm). The dry ice is kept in the thermos until the freeze wedge has been lowered into the sediment to avoid water freezing on the wedge during descent through the water column; a wet steel-wedge surface disturbs the sediment stratigraphy less than a wedge on which rapid freezing occurs. The dry ice is kept in the thermos by a trapdoor that is opened by a messenger. When the trapdoor is opened the dry ice begins to drop into the wedge, which is filled with ethanol. This process continues concurrently with the consumption of ice in the wedge until the thermos is empty. Using 6–8 kg of dry ice and 4 l of ethanol (95%), a 3-cm-thick and up to 80-cm-long crust of frozen sediment is obtained in 20–25 min on each side of the wedge. The crust is easily detached intact from the wedge using a small volume of hot water, poured inside the wedge.

  • 25. Reuss, Nina
    et al.
    Leavitt, Peter R.
    Hall, Roland I.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hammarlund, Dan
    Development and application of sedimentary pigments for assessing effects of climatic and environmental changes on subarctic lakes in northern Sweden2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 43, no 1, p. 149-169Article in journal (Refereed)
    Abstract [en]

    A surface-sediment survey of pigments in 100 lakes in the Scandes Mountains, northern Sweden, was combined with a reconstruction of Holocene sedimentary pigments from Lake Seukokjaure to assess the major factors regulating phototrophic communities, and how these controls may have changed during the period from the deglaciation (~9700 cal. years BP) to the present. The study area covers a pronounced gradient of temperature and precipitation, and encompasses the subarctic tree line, an important ecotonal boundary in this region. Lake Seukokjaure is located in a presently treeless basin close to the modern tree line. The spatial survey of sedimentary pigments was analyzed using principle components analysis (PCA) and redundancy analysis (RDA). PCA explained 73–83% of variance in pigment abundance and composition, whereas RDA explained 22–32% of variation in fossil assemblages. Dissolved organic carbon (DOC) content of lake water, sediment δ13C, maximum lake depth, elevation and lake-water conductivity were all identified as environmental variables with significant association with pigment abundances in the spatial survey, although phototrophic communities of lakes situated in different vegetation zones (alpine, birch, conifer/birch) were incompletely distinguished by the ordinations. In the RDAs, the primary pigment variability occurred along a production gradient that was correlated negatively to water-column DOC content and δ13C signature of sediments. This pattern suggested that the important controls of primary production were light regime and terrestrial supplies of 13C-depleted carbon. In contrast, depth, elevation and conductivity were found to be more important for the differentiation of the phototrophic community composition. Application of these spatial survey results to the Holocene sediment record of Lake Seukokjaure demonstrated the importance of DOC for the temporal development of the lake, from an early state of high production to a period of slight oligotrophication. In general, the algal changes were regulated by the interaction of DOC and conductivity, although transitions in the phototrophic community during the late Holocene were less easily interpreted. Terrestrial vegetation development thus appears to be of utmost importance for the regulation of primary production in oligotrophic alpine and subarctic lakes and climate impacts on lakes, whereas other basin-specific factors may control the ontogeny of algal community composition.

  • 26.
    Rosén, P
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hall, R
    Korsman, T
    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.
    Diatom transfer-functions for quantifying past air temperature, pH and total organic carbon concentration from lakes in northern Sweden2000In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 24, no 2, p. 109-123Article in journal (Refereed)
    Abstract [en]

    The relationships between diatoms (Bacillariophyceae) in surface sediments of lakes and summer air temperature, pH and total organic carbon concentration (TOC) were explored along a steep climatic gradient in northern Sweden to provide a tool to infer past climate conditions from sediment cores. The study sites are in an area with low human impact and range from boreal forest to alpine tundra. Canonical correspondence analysis (CCA) constrained to mean July air temperature and pH clearly showed that diatom community composition was different between lakes situated in conifer-, mountain birch- and alpine-vegetation zones. As a consequence, diatoms and multivariate ordination methods can be used to infer past changes in treeline position and dominant forest type. Quantitative inference models were developed to estimate mean July air temperature, pH and TOC from sedimentary diatom assemblages using weighted averaging (WA) and weighted averaging partial least squares (WA-PLS) regression. Relationships between diatoms and mean July air temperature were independent of lake-water pH, TOC, alkalinity and maximum depth. The results demonstrated that diatoms in lake sediments can provide useful and independent quantitative information for estimating past changes in mean July air temperature (R-jack(2) = 0.62, RMSEP = 0.86 degrees C; R-2 and root mean squared error of prediction (RMSEP) based on jack-knifing), pH (R(j)(2)ack = 0.61, RMSEP = 0.30) and TOC (R-jack(2) = 0.49, RMSEP = 1.33 mg l(-1)). The paper focuses mainly on the relationship between diatom community composition and mean July air temperature, but the relationships to pH and TOC are also discussed.

  • 27.
    Rosén, Peter
    et al.
    Climate Impacts Research Centre (CIRC), Umeå University, 98107 Abisko, Sweden.
    Vogel, Hendrik
    Institute for Geology and Mineralogy, University of Cologne, Zuelpicher Str. 49a, 50674 Cologne, Germany.
    Cunningham, Laura
    Climate Impacts Research Centre (CIRC), Umeå University, 98107 Abisko, Sweden.
    Reuss, Nina
    GeoBiosphere Science Centre, Quaternary Sciences, Lund University, Sölvegatan. 12, 223 62 Lund, Sweden.
    Conley, Daniel J
    GeoBiosphere Science Centre, Quaternary Sciences, Lund University, Sölvegatan. 12, 223 62 Lund, Sweden.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Fourier transform infrared spectroscopy, a new method for rapid determination of total organic and inorganic carbon and opal concentration in lake sediments2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 43, no 2, p. 247-259Article in journal (Refereed)
    Abstract [en]

    We demonstrate the use of Fourier transform infrared spectroscopy (FTIRS) to make quantitative measures of total organic carbon (TOC), total inorganic carbon (TIC) and biogenic silica (BSi) concentrations in sediment. FTIRS is a fast and cost-effective technique and only small sediment samples are needed (0.01 g).  Statistically significant models were developed using sediment samples from northern Sweden and were applied to sediment records from Sweden, northeast Siberia and Macedonia. The correlation between FTIRS-inferred values and amounts of biogeochemical constituents assessed conventionally varied between r = 0.84 - 0.99 for TOC, r = 0.85 - 0.99 for TIC, and r = 0.68 - 0.94 for BSi. Because FTIR spectra contain information on a large number of both inorganic and organic components, there is great potential for FTIRS to become an important tool in paleolimnology.

     

  • 28. Rouillard, Alexandra
    et al.
    Rosén, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Douglas, Marianne S V
    Pienitz, Reinhard
    Smol, John P
    A model for inferring dissolved organic carbon (DOC) in lakewater from visible-near-infrared spectroscopy (VNIRS) measures in lake sediment: 2011In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 46, no 2, p. 187-202Article in journal (Refereed)
    Abstract [en]

    We developed an inference model to infer dissolved organic carbon (DOC) in lakewater from lake sediments using visible-near-infrared spectroscopy (VNIRS). The inference model used surface sediment samples collected from 160 Arctic Canada lakes, covering broad latitudinal (60–83°N), longitudinal (71–138°W) and environmental gradients, with a DOC range of 0.6–39.6 mg L−1. The model was applied to Holocene lake sediment cores from Sweden and Canada and our inferences are compared to results from previous multiproxy paleolimnological investigations at these two sites. The inferred Swedish and Canadian DOC profiles are compared, respectively, to inferences from a Swedish-based VNIRS-total organic carbon (TOC) model and a Canadian-based diatom-inferred (Di-DOC) model from the same sediment records. The 5-component Partial Least Squares (PLS) model yields a cross-validated (CV) R2CV = 0.61 and a root mean squared error of prediction (RMSEP CV ) = 4.4 mg L−1 (11% of DOC gradient). The trends inferred for the two lakes were remarkably similar to the VNIRS-TOC and the Di-DOC inferred profiles and consistent with the other paleolimnological proxies, although absolute values differed. Differences in the calibration set gradients and lack of analogous VNIRS signatures in the modern datasets may explain this discrepancy. Our results corroborate previous geographically independent studies on the potential of using VNIRS to reconstruct past trends in lakewater DOC concentrations rapidly.

  • 29.
    Rydberg, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Institute für Geoökologie, Technische Universität Braunschweig, Brunswick, Germany.
    Wavelength dispersive X-ray fluorescence spectroscopy as a fast, non-destructive and cost-effective analytical method for determining the geochemical composition of small loose-powder sediment samples2014In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 52, no 3, p. 265-276Article in journal (Refereed)
    Abstract [en]

    X-ray fluorescence spectroscopy (XRF) has been used extensively to analyze many types of environmental samples, including lake sediments. In most cases, however, analyses have required either a relatively large sample mass or sample pretreatment, e.g. lithium borate fusion, and have not taken advantage of the potential of XRF analysis as a non-destructive technique. This paper describes the development of two completely non-destructive calibration methods that use small, i.e. 200- and 500-mg loose-powder sediment samples. Analytical performance of these methods was assessed using ten different certified reference materials and a previously analyzed sediment profile, and for both methods, accuracy and precision were less than +/- 10 % (or a few ppm) for 26 elements (Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Mn, Fe, Ni, Cu, Zn, Ga, As, Br, Rb, Sr, Y, Zr, Sn, Sb, Ba, W and Pb). This shows that quantitative wavelength dispersive X-ray fluorescence analysis, using small loose-powder samples, can be a useful geochemical tool for many paleolimnological applications, especially because lack of pretreatment ensures that samples can be used for further analysis.

  • 30.
    Rydberg, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Martinez-Cortizas, A.
    Geochemical assessment of an annually laminated lake sediment record from northern Sweden: a multi-core, multi-element approach2014In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 51, no 4, p. 499-514Article in journal (Refereed)
    Abstract [en]

    We used seven annually laminated (varved) sediment cores from Nylandssjon, a lake in northern Sweden, to assess between-core variation and diagenetic changes at annual resolution. By using several cores, multiple elements and employing principal components analysis (PCA), we also studied how the geochemical composition changed over time, and assessed to what extent these changes were related to variations in the weather. There are between-core differences for aluminum, silica, lead, titanium, zirconium and dry-mass accumulation rate. Diagenesis causes a decrease in bromine, as well as carbon, nitrogen and varve thickness, as reported in previous publications. In spite of anoxic bottom waters phosphorus is not lost from the sediment. In fact, there is an increase in phosphorus concentrations with time. The PCA identified four principal components (PCs). PC-1 accounts for the relative content of mineral and organic material; PC-2 represents mineral-particle grain size; PC-3 reflects phosphorus loading and PC-4 reflects atmospheric pollution. Variations in the weather partly explain the temporal patterns in PC-1 and PC-2: cold winters, i.e. more accumulation of snow, resulted in more mineral than organic matter (i.e. higher PC-1 scores), and increased the relative amount of coarse-grained mineral particles in the sediment (i.e. lower PC-2 scores). Increased spring precipitation had a weak positive effect on the PC-2 scores by promoting the transport of fine-grained material. However, the influence of weather is weak, explaining at most 30 % of the variance, and hence, other factors, e.g. land use and its effect on soil erosion, seem to be more important for the sediment geochemical composition. The importance of land use is also exemplified by an increase in PC-3 scores in the late 1970s, which can be attributed to a shift in agricultural practices that resulted in increased phosphorus loading to the lake. In summary, our findings show that down-core trends are reproducible between cores, but between-core variability and diagenesis need to be considered when interpreting some elements. We also conclude that there is a need to constrain temporal changes in land use before using lake sediments to study changes in weather or climate.

  • 31. Vogel, Hendrik
    et al.
    Wagner, Bernd
    Zanchetta, Giovanni
    Sulpizio, Roberto
    Rosén, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A paleoclimate record with tephrochronological age control for the last glacial-interglacial cycle from Lake Ohrid, Albania and Macedonia2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 44, no 1, p. 295-310Article in journal (Refereed)
    Abstract [en]

    Lake Ohrid is probably of Pliocene age, and the oldest extant lake in Europe. In this study climatic and environmental changes during the last glacial-interglacial cycle are reconstructed using lithological, sedimentological, geochemical and physical proxy analysis of a 15-m-long sediment succession from Lake Ohrid. A chronological framework is derived from tephrochronology and radiocarbon dating, which yields a basal age of ca. 136 ka. The succession is not continuous, however, with a hiatus between ca. 97.6 and 81.7 ka. Sediment accumulation in course of the last climatic cycle is controlled by the complex interaction of a variety of climate-controlled parameters and their impact on catchment dynamics, limnology, and hydrology of the lake. Warm interglacial and cold glacial climate conditions can be clearly distinguished from organic matter, calcite, clastic detritus and lithostratigraphic data. During interglacial periods, short-term fluctuations are recorded by abrupt variations in organic matter and calcite content, indicating climatically-induced changes in lake productivity and hydrology. During glacial periods, high variability in the contents of coarse silt to fine sand sized clastic matter is probably a function of climatically-induced changes in catchment dynamics and wind activity. In some instances tephra layers provide potential stratigraphic markers for short-lived climate perturbations. Given their widespread distribution in sites across the region, tephra analysis has the potential to provide insight into variation in the impact of climate and environmental change across the Mediterranean.

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