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  • 1. Bravo, Andrea G.
    et al.
    Bouchet, Sylvain
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Björn, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Mateos-Rivera, Alejandro
    Bertilsson, Stefan
    Molecular composition of organic matter controls methylmercury formation in boreal lakes2017Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 8, artikel-id 14255Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A detailed understanding of the formation of the potent neurotoxic methylmercury is neededto explain the large observed variability in methylmercury levels in aquatic systems. While it is known that organic matter interacts strongly with mercury, the role of organic matter composition in the formation of methylmercury in aquatic systems remains poorly understood. Here we show that phytoplankton-derived organic compounds enhance mercurymethylation rates in boreal lake sediments through an overall increase of bacterial activity. Accordingly, in situ mercury methylation defines methylmercury levels in lake sediments strongly influenced by planktonic blooms. In contrast, sediments dominated by terrigenous organic matter inputs have far lower methylation rates but higher concentrations of methylmercury, suggesting that methylmercury was formed in the catchment and imported into lakes. Our findings demonstrate that the origin and molecular composition of organic matter are critical parameters to understand and predict methylmercury formation and accumulation in boreal lake sediments.

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  • 2. Bravo, Andrea G.
    et al.
    Peura, Sari
    Buck, Moritz
    Ahmed, Omneya
    Mateos-Rivera, Alejandro
    Ortega, Sonia Herrero
    Schaefer, Jeffra K.
    Bouchet, Sylvain
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Björn, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Bertilsson, Stefan
    Methanogens and iron-reducing bacteria: the overlooked members of mercury-methylating microbial communities in boreal lakes2018Ingår i: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 84, nr 23, artikel-id e01774-18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    ABSTRACT: Methylmercury is a potent human neurotoxin which biomagnifies in aquatic food webs. Although anaerobic microorganisms containing the hgcA gene potentially mediate the formation of methylmercury in natural environments, the diversity of these mercury-methylating microbial communities remains largely unexplored. Previous studies have implicated sulfate-reducing bacteria as the main mercury methylators in aquatic ecosystems. In the present study, we characterized the diversity of mercury-methylating microbial communities of boreal lake sediments using high-throughput sequencing of 16S rRNA and hgcA genes. Our results show that in the lake sediments, Methanomicrobiales and Geobacteraceae also represent abundant members of the mercury-methylating communities. In fact, incubation experiments with a mercury isotopic tracer and molybdate revealed that only between 38% and 45% of mercury methylation was attributed to sulfate reduction. These results suggest that methanogens and iron-reducing bacteria may contribute to more than half of the mercury methylation in boreal lakes.

    IMPORTANCE: Despite the global awareness that mercury, and methylmercury in particular, is a neurotoxin to which millions of people continue to be exposed, there are sizable gaps in the understanding of the processes and organisms involved in methylmercury formation in aquatic ecosystems. In the present study, we shed light on the diversity of the microorganisms responsible for methylmercury formation in boreal lake sediments. All the microorganisms identified are associated with the processing of organic matter in aquatic systems. Moreover, our results show that the well-known mercury-methylating sulfate-reducing bacteria constituted only a minor portion of the potential mercury methylators. In contrast, methanogens and iron-reducing bacteria were important contributors to methylmercury formation, highlighting their role in mercury cycling in the environment.

  • 3.
    Capo, Eric
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Marine Biology, Institut de Ciències del Mar, CSIC, Barcelona, Spain.
    Rydberg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
    Domaizon, Isabelle
    Debroas, Didier
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    How Does Environmental Inter-annual Variability Shape Aquatic Microbial Communities?: A 40-Year Annual Record of Sedimentary DNA From a Boreal Lake (Nylandssjon, Sweden)2019Ingår i: Frontiers in Ecology and Evolution, E-ISSN 2296-701X, Vol. 7, artikel-id 245Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To assess the sensitivity of lakes to anthropogenically-driven environmental changes (e.g., nutrient supply, climate change), it is necessary to first isolate the effects of between-year variability in weather conditions. This variability can strongly impact a lake's biological community especially in boreal and arctic areas where snow phenology play an important role in controlling the input of terrestrial matter to the lake. Identifying the importance of this inherent variability is difficult without time series that span at least several decades. Here, we applied a molecular approach (metabarcoding on eukaryotic 18S rRNA genes and qPCR on cyanobacterial 16S rRNA genes) to sedimentary DNA (sed-DNA) to unravel the annual variability of microbial community in 40 years' sediment record from the boreal lake Nylandssjon which preserve annually-laminated sediments. Our comparison between seasonal meteorological data, sediment inorganic geochemistry (X-ray fluorescence analyses) and organic biomarkers (pyrolysis-gas chromatography/mass spectrometry analyses), demonstrated that inter-annual variability strongly influence the sediment composition in Nylandssjon. Spring temperature, snow and ice phenology (e.g., the percentage of snow loss in spring, the timing of lake ice-off) were identified as important drivers for the inputs of terrestrial material to the lake, and were therefore also important for shaping the aquatic biological community. Main changes were detected in the late-80s/mid-90s and mid-2000s associated with increases in algal productivity, in total richness of the protistan community and in relative abundances of Chlorophyta, Dinophyceae as well as Cyanobacteria abundance. These changes could be linked to a decline in terrestrial inputs to the lake during the snow melt and run-off period, which in turn was driven by warmer winter temperatures. Even if our data shows that meteorological factors do affect the sediment composition and microbial communities, they only explain part of the variability. This is most likely a consequence of the high inter-annual variability in abiotic and biotic parameters highlighting the difficulty to draw firm conclusions concerning drivers of biological changes at an annual or sub-annual resolution even with the 40-year varved sediment record from Nylandssjon. Hence, it is necessary to have an even longer time perspective in order to reveal the full implications of climate change.

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  • 4. Guedron, S.
    et al.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland; ETH Zürich, Zürich, Switzerland.
    Brisset, E.
    Sabatier, P.
    Perrot, V.
    Bouchet, S.
    Develle, A. L.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Cossa, D.
    Fritz, S. C.
    Baker, P. A.
    Late Holocene volcanic and anthropogenic mercury deposition in the western Central Andes (Lake Chungará, Chile)2019Ingår i: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 662, s. 903-914Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Volcanismis one of the major natural processes emitting mercury (Hg) to the atmosphere, representing a significant component of the global Hg budget. The importance of volcanic eruptions for local-scale Hg deposition was investigated using analyses of Hg, inorganic elemental tracers, and organic biomarkers in a sediment sequence from Lake Chungara (4520 m a.s.l.). Environmental change and Hg deposition in the immediate vicinity of the Parinacota volcano were reconstructed over the last 2700 years, encompassing the pre-anthropogenic and anthropogenic periods. Twenty eruptions delivering large amounts of Hg (1 to 457 mu g Hg m(-2) yr(-1) deposited at the timescale of the event) were locally recorded. Peaks of Hg concentration recorded after most of the eruptions were attributed to a decrease in sedimentation rate together with the rapid re-oxidation of gaseous elemental Hg and deposition with fine particles and incorporation into lake primary producers. Over the study period, the contribution of volcanic emissions has been estimated as 32% of the total Hg input to the lake. Sharp depletions in primary production occurred at each eruption, likely resulting from massive volcaniclastic inputs and changes in the lake-water physico-chemistry. Excluding the volcanic deposition periods, Hg accumulation rates rose from natural background values (1.9 +/- 0.5 mu g m(-2) yr(-1)) by a factor of 2.3 during the pre-colonial mining period (1400-900 yr cal. BP), and by a factor of 6 and 7.6, respectively, during the Hispanic colonial epoch (400-150 yr cal. BP) and the industrial era (similar to 140 yr cal. BP to present). Altogether, the dataset indicates that lake primary production has been the main, but not limiting, carrier for Hg to the sediment. Volcanic activity and climate change are only secondary drivers of local Hg deposition relative to the magnitude of regional and global anthropogenic emissions.

  • 5.
    Guédron, Stéphane
    et al.
    Université Grenoble Alpes, Institut des Sciences de la Terre, Institut de Recherche pour le Développement, Grenoble, France.
    Delaere, Christophe
    Centre de Recherches en Archéologie et Patrimoine, Université libre de Bruxelles, Brussels, Belgium.
    Fritz, Sherilyn C.
    Department of Earth and Atmospheric Sciences and School of Biological Sciences, University of Nebraska - Lincoln, Lincoln, NE 68588.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland; ETH Zürich, Zürich, Switzerland.
    Sabatier, Pierre
    Univ. Savoie Mont Blanc, Centre National de la Recherche Scientifiquel, Environnements Dynamiques et Territoires de la Montagne, Chambéry, France.
    Devel, Anne-Lise
    Univ. Savoie Mont Blanc, Centre National de la Recherche Scientifiquel, Environnements Dynamiques et Territoires de la Montagne, Chambéry, France.
    Heredia, Carlos
    Laboratorio de Hidroquímica - Instituto de Investigaciones Químicas - Universidad Mayor de San Andres, Campus Universitario de Cota Cotacasilla 3161, La Paz, Bolivia.
    Vérin, Claire
    Université Grenoble Alpes, Institut des Sciences de la Terre, Institut de Recherche pour le Développement, Grenoble, France.
    Alves, Eduardo Q.
    Royal Belgian Institute of Natural Sciences, Bruxelles, Belgium.
    Baker, Paul A.
    Division of Earth and Climate Sciences, Duke University, Durham, United Kingdom.
    Holocene variations in Lake Titicaca water level and their implications for sociopolitical developments in the central Andes2023Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 120, nr 2, artikel-id 2215882120Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Holocene climate in the high tropical Andes was characterized by both gradual and abrupt changes, which disrupted the hydrological cycle and impacted landscapes and societies. High-resolution paleoenvironmental records are essential to contextualize archaeological data and to evaluate the sociopolitical response of ancient societies to environmental variability. Middle-to-Late Holocene water levels in Lake Titicaca were reevaluated through a transfer function model based on measurements of organic carbon stable isotopes, combined with high-resolution profiles of other geochemical variables and paleoshoreline indicators. Our reconstruction indicates that following a prolonged low stand during the Middle Holocene (4000 to 2400 BCE), lake level rose rapidly ~15 m by 1800 BCE, and then increased another 3 to 6 m in a series of steps, attaining the highest values after ~1600 CE. The largest lake-level increases coincided with major sociopolitical changes reported by archaeologists. In particular, at the end of the Formative Period (500 CE), a major lake-level rise inundated large shoreline areas and forced populations to migrate to higher elevation, likely contributing to the emergence of the Tiwanaku culture.

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  • 6.
    Hansson, Sophia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Downwash of atmospherically deposited trace metals in peat and the influence of rainfall intensity: an experimental test2015Ingår i: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 506-507, s. 95-101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Accumulation records of pollutant metals in peat have been frequently used to reconstruct past atmospheric deposition rates. While there is good support for peat as a record of relative changes in metal deposition over time, questions remain whether peat archives represent a quantitative or a qualitative record. Several processes can potentially influence the quantitative record of which downwashing is particularly pertinent as it would have a direct influence on how and where atmospherically deposited metals are accumulated in peat. The aim of our study was two-fold: first, to compare and contrast the retention of dissolved Pb, Cu, Zn and Ni in peat cores; and second, to test the influence of different precipitation intensities on the potential downwashing of metals. We applied four 'rainfall' treatments to 13 peat cores over a 3-week period, including both daily (2 or 5.3 mm day(-1)) and event-based additions (37 mm day(-1), added over 1 h or over a 10 h rain event). Two main trends were apparent: 1) there was a difference in retention of the added dissolved metals in the surface layer (0-2 cm): 21-85% for Pb, 18-63% for Cu, 10-25% for Zn and 10-20% for Ni. 2) For all metals and both peat types (sphagnum lawn and fen), the addition treatments resulted in different downwashing depths, i.e., as the precipitation-addition increased so did the depth at which added metals could be detected. Although the largest fraction of Pb and Cu was retained in the surface layer and the remainder effectively immobilized in the upper peat (<= 10 cm), there was a smearing effect on the overall retention, where precipitation intensity exerts an influence on the vertical distribution of added trace metals. These results indicate that the relative position of a deposition signal in peat records would be preserved, but it would be quantitatively attenuated. 

  • 7.
    Meyer-Jacob, Carsten
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Yang, Handong
    Environmental Change Research Centre, University College London, London WC1E 6BT, United Kingdom.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Early land use and centennial scale changes in lake-water organic carbon prior to contemporary monitoring2015Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 112, nr 21, s. 6579-6584Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Organic carbon concentrations have increased in surface waters across parts of Europe and North America during the past decades, but the main drivers causing this phenomenon are still debated. A lack of observations beyond the last few decades inhibits a better mechanistic understanding of this process and thus a reliable prediction of future changes. Here we present past lake-water organic carbon trends inferred from sediment records across central Sweden that allow us to assess the observed increase on a centennial to millennial time scale. Our data show the recent increase in lake-water carbon but also that this increase was preceded by a landscape-wide, long-term decrease beginning already A. D. 1450-1600. Geochemical and biological proxies reveal that these dynamics coincided with an intensification of human catchment disturbance that decreased over the past century. Catchment disturbance was driven by the expansion and later cessation of widespread summer forest grazing and farming across central Scandinavia. Our findings demonstrate that early land use strongly affected past organic carbon dynamics and suggest that the influence of historical landscape utilization on contemporary changes in lake-water carbon levels has thus far been underestimated. We propose that past changes in land use are also a strong contributing factor in ongoing organic carbon trends in other regions that underwent similar comprehensive changes due to early cultivation and grazing over centuries to millennia.

  • 8.
    Ninnes, Sofia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Meyer-Jacob, Carsten
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Forest Research Institute, Université du Québec en Abitibi-Témiscamingue, Canada.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Environmental Systems Science, ETH Zurich, Switzerland; Department of Water Resources and Drinking Water, Eawag, Switzerland.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Martínez Cortizas, Antonio
    CRETUS, EcoPast (GI-1553), Faculty of Biology, University of Santiago de Compostela, Campus Sur, Spain.
    Application of mid-infrared spectroscopy for the quantitative and qualitative analysis of organic matter in Holocene sediment records2024Ingår i: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 34, nr 3, s. 259-273Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The organic matter composition of lake sediments influences important in-lake biogeochemical processes and stores information on environmental changes. Extracting this information is notoriously difficult because of the complexity of the organic matter matrix, which routinely imposes trade-offs between high temporal and analytical detail in the selection of methods of analysis. Here, we demonstrate the potential of diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) for achieving both of these objectives using untreated bulk samples from two Holocene lake-sediment cores from central Sweden. We develop quantitative models for sediment total organic carbon (TOC) with the same predictive abilities as models based on samples diluted with KBr and qualitatively characterize the organic matter using a spectra processing-pipeline combined with principal component analysis. In the qualitative analysis we identified four organic matter sub-fractions and the interpretation of these is supported and further advanced with molecular data from pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Within these organic fractions, compound groups such as aromatics, lignin, aliphatics, proteins and polysaccharides were identified by means of DRIFTS and the analyses and processes outlined here enables rapid and detailed quantitative and qualitative analysis of sediment organic matter. The DRIFTS approach can be used as stand-alone method for OM characterization with high temporal resolution in Holocene sediment records. It may also function as a screening process for more specific analyses of sample subsets, such as when coupled with pyrolysis-GC/MS to further tease apart the OM composition, identify sources and determine degradation status.

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  • 9.
    Ninnes, Sofia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Meyer-Jacob, Carsten
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Mighall, Tim M.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Investigating molecular changes in organic matter composition in two Holocene lake-sediment records from central Sweden using pyrolysis-GC/MS2017Ingår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122, nr 6, s. 1423-1438Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Organic matter (OM) is a key component of lake sediments, affecting carbon, nutrient, and trace metal cycling at local and global scales. Yet little is known about long-term (millennial) changes in OM composition due to the inherent chemical complexity arising from multiple OM sources and from secondary transformations. In this study we explore how the molecular composition of OM changes throughout the Holocene in two adjacent boreal lakes in central Sweden and compare molecular-level information with conventional OM variables, including total carbon, total nitrogen, C:N ratios, delta C-13, and delta N-15. To characterize the molecular OM composition, we employed a new method based on pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), which yields semiquantitative data on > 100 organic compounds of different origin and degradation status. We identify large changes in OM composition after deglaciation (circa 8500 +/- 500 B.C.), associated with early landscape development, and during the most recent 4050 years, driven by degradation processes. With molecular(-)level information we can also distinguish between natural landscape development and human catchment disturbance during the last 1700 years. Our study demonstrates that characterization of the molecular OM composition by the high-throughput PyGC/MS method is an efficient complement to conventional OM variables for identification and understanding of past OM dynamics in lake-sediment records. Holocene changes observed for pyrolytic compounds and compound classes known for having different reactivity indicate the need for further paleo-reconstruction of the molecular OM composition to better understand both past and future OM dynamics and associated environmental changes.

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  • 10.
    Rydberg, Johan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Cooke, Colin A.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Water Resources and Drinking Water, Eawag, Dübendorf, Switzerland; Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland.
    Wolfe, Alexander P.
    Vinebrooke, Rolf D.
    An assessment of chlorophyll preservation in lake sediments using multiple analytical techniques applied to the annually laminated lake sediments of Nylandssjön2020Ingår i: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 64, nr 4, s. 379-388Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chlorophyll is frequently used as a proxy for autochthonous production in lakes. This use of chlorophyll concentrations in sediments to infer historical changes in lake primary production relies heavily on the assumption that preservation is sufficient to reflect the productivity in a meaningful way. In this study, we use a series of freeze cores from a lake with annually laminated sediments to assess how reliable down-core trends in chlorophyll are, and to what extent chlorophyll is degraded in the sediment. A striking consistency in the down-core chlorophyll trends in four sediment cores collected in different years (1983, 1992, 2002 and 2010) shows that the sediment preserves a consistent chlorophyll signal over longer timescales. However, there are also clear signs that diagenetic processes within the sediment affect the chlorophyll concentration in sediment layers younger than 10-15 years. This implies that care is needed when interpreting chlorophyll trends in recent sediments. Further, our data show that high-performance liquid chromatography (HPLC) and visible reflectance spectroscopy (VRS) detect similar chlorophyll concentrations for recently dried samples. A third analytical technique, pyrolysis-gas chromatography/mass spectrometry, which provides semi-quantitative values for chlorophyll, also produce a temporal trend that is highly correlated with data from the two quantitative techniques. For samples that have been stored dried at room temperature for several years there is, however, a large discrepancy between the two quantitative techniques. The VRS method is more robust with regards to degradation during storage, while HPLC results demonstrate clear storage effects.

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  • 11. Segura, Javier H.
    et al.
    Nilsson, Mats B.
    Sparrman, Tobias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Serk, Henrik
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Schleucher, Juergen
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Tolu, Julie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Öquist, Mats G.
    Boreal tree species affect soil organic matter composition and saprotrophic mineralization rates2019Ingår i: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 441, nr 1-2, s. 173-190Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims: To investigate how different tree species affect the composition of SOM and its mineralization in boreal forest ecosystems.

    Methods: We used pyrolysis GC-MS for molecular-level characterization of the SOM formed under five common boreal tree species at a replicated field experiment similar to 50years after plantation. We incubated soil samples at 4, 9, 14 and 19 degrees C and measured inherent CO2 production and substrate-induced respiration. We then evaluated if the saprotrophic microbial activity and its temperature sensitivity was controlled by the SOM composition.

    Results: The molecular composition of the SOM emerged as key factor influencing SOM properties in plots with different tree species. Most of the variance in the SOM content was explained by the organo-chemical composition of the SOM. More importantly, the fraction of the microbial community able to utilize the native SOM was largely controlled by the SOM organo-chemical composition. Temperature sensitivity of CO2 production (Q(10)) was not explained by SOM composition. However, the microbial access to different SOM pools varied with temperature.

    Conclusions: These results bridge the gap between the paradigms of short-term litter and long-term SOM decomposition showing that, on an intermediate timescale (similar to 50 years), boreal tree species affect SOM molecular composition and saprotrophic mineralization rates.

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  • 12.
    Tolu, Julie
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Gerber, Lorenz
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    High-throughput characterization of sediment organic matter by pyrolysis-gas chromatography/mass spectrometry and multivariate curve resolution: A promising analytical tool in (paleo) limnology2015Ingår i: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 880, s. 93-102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Molecular-level chemical information about organic matter (OM) in sediments helps to establish the sources of OM and the prevalent degradation/diagenetic processes, both essential for understanding the cycling of carbon (C) and of the elements associated with OM (toxic trace metals and nutrients) in lake ecosystems. Ideally, analytical methods for characterizing OM should allow high sample throughput, consume small amounts of sample and yield relevant chemical information, which are essential for multidisciplinary, high-temporal resolution and/or large spatial scale investigations. We have developed a high-throughput analytical method based on pyrolysis-gas chromatography/mass spectrometry and automated data processing to characterize sedimentary OM in sediments. Our method consumes 200 mg of freeze-dried and ground sediment sample. Pyrolysis was performed at 450 degrees C, which was found to avoid degradation of specific biomarkers (e. g., lignin compounds, fresh carbohydrates/cellulose) compared to 650 degrees C, which is in the range of temperatures commonly applied for environmental samples. The optimization was conducted using the top ten sediment samples of an annually resolved sediment record (containing 16-18% and 1.3-1.9% of total carbon and nitrogen, respectively). Several hundred pyrolytic compound peaks were detected of which over 200 were identified, which represent different classes of organic compounds (i. e., n-alkanes, n-alkenes, 2-ketones, carboxylic acids, carbohydrates, proteins, other N compounds, (methoxy) phenols, (poly) aromatics, chlorophyll and steroids/hopanoids). Technical reproducibility measured as relative standard deviation of the identified peaks in triplicate analyses was 5.5 +/- 4.3%, with 90% of the RSD values within 10% and 98% within 15%. Finally, a multivariate calibration model was calculated between the pyrolytic degradation compounds and the sediment depth (i. e., sediment age), which is a function of degradation processes and changes in OM source type. This allowed validation of the Py-GC/MS dataset against fundamental processes involved in OM cycling in aquatic ecosystems.

  • 13.
    Tolu, Julie
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rydberg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Meyer-Jacob, Carsten
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Gerber, Lorenz
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Spatial variability of organic matter molecular composition and elemental geochemistry in surface sediments of a small boreal Swedish lake2017Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, nr 7, s. 1773-1792Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The composition of sediment organic matter (OM) exerts a strong control on biogeochemical processes in lakes, such as those involved in the fate of carbon, nutrients and trace metals. While between-lake spatial variability of OM quality is increasingly investigated, we explored in this study how the molecular composition of sediment OM varies spatially within a single lake and related this variability to physical parameters and elemental geochemistry. Surface sediment samples (0-10 cm) from 42 locations in Harsvatten - a small boreal forest lake with a complex basin morphometry - were analyzed for OM molecular composition using pyrolysis gas chromatography mass spectrometry for the contents of 23 major and trace elements and biogenic silica. We identified 162 organic compounds belonging to different biochemical classes of OM (e.g., carbohydrates, lignin and lipids). Close relationships were found between the spatial patterns of sediment OM molecular composition and elemental geochemistry. Differences in the source types of OM (i.e., terrestrial, aquatic plant and algal) were linked to the individual basin morphometries and chemical status of the lake. The variability in OM molecular composition was further driven by the degradation status of these different source pools, which appeared to be related to sedimentary physicochemical parameters (e.g., redox conditions) and to the molecular structure of the organic compounds. Given the high spatial variation in OM molecular composition within Harsvatten and its close relationship with elemental geochemistry, the potential for large spatial variability across lakes should be considered when studying biogeochemical processes in-volved in the cycling of carbon, nutrients and trace elements or when assessing lake budgets.

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