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  • 1.
    Attermeyer, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Andersson, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Catalán, Núria
    Catalan Institute for Water Research (ICRA), Girona, Spain.
    Einarsdóttir, Karólina
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Groeneveld, Marloes M.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Szekely, Anna J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Potential terrestrial influence on transparent exopolymer particle (TEP) concentrations in boreal freshwaters2019In: Journal of limnology, ISSN 1129-5767, E-ISSN 1723-8633, Vol. 64, no 6, p. 2455-2466Article in journal (Refereed)
    Abstract [en]

    Transparent exopolymer particles (TEP) are ubiquitous in aquatic ecosystems and contribute, for example, to sedimentation of organic matter in oceans and freshwaters. Earlier studies indicate that the formation of TEP is related to the in situ activity of phytoplankton or bacteria. However, terrestrial sources of TEP and TEP precursors are usually not considered. We investigated TEP concentration and its driving factors in boreal freshwaters, hypoth- esizing that TEP and TEP precursors can enter freshwaters via terrestrial inputs. In a field survey, we measured TEP concentrations and other environmental factors across 30 aquatic ecosystems in Sweden. In a mesocosm experi- ment, we further investigated TEP dynamics over time after manipulating terrestrial organic matter input and light conditions. The TEP concentrations in boreal freshwaters ranged from 83 to 4940 μg Gum Xanthan equivalent L−1, which is comparable to other studies in freshwaters. The carbon fraction in TEP in the sampled boreal freshwaters is much higher than the phytoplanktonic carbon, in contrast to previous studies in northern temperate and Medi- terranean regions. Boreal TEP concentrations were mostly related to particulate organic carbon, dissolved organic carbon, and optical indices of terrestrial influence but less influenced by bacterial abundance, bacterial production, and chlorophyll a. Hence, our results do not support a major role of the phytoplankton community or aquatic bac- teria on TEP concentrations and dynamics. This suggests a strong external control of TEP concentrations in boreal freshwaters, which can in turn affect particle dynamics and sedimentation in the recipient aquatic ecosystem.

  • 2.
    Attermeyer, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. WasserCluster Lunz, Lunz Am See, Austria.
    Catalan, Nuria
    Catalan Inst Water Res ICRA, Girona, Spain.
    Einarsdóttir, Karólina
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Freixa, Anna
    Catalan Inst Water Res ICRA, Girona, Spain.
    Groeneveld, Marloes M.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Hawkes, Jeffrey A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Bergquist, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Organic Carbon Processing During Transport Through Boreal Inland Waters: Particles as Important Sites2018In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 123, no 8, p. 2412-2428Article in journal (Refereed)
    Abstract [en]

    The degradation and transformation of organic carbon (C) in inland waters result in significant CO2 emissions from inland waters. Even though most of the C in inland waters occurs as dissolved organic carbon (DOC), studies on particulate organic carbon (POC) and how it influences the overall reactivity of organic C in transport are still scarce. We sampled 30 aquatic ecosystems following an aquatic continuum including peat surface waters, streams, rivers, and lakes. We report DOC and POC degradation rates, relate degradation patterns to environmental data across these systems, and present qualitative changes in dissolved organic matter and particulate organic matter during degradation. Microbial degradation rates of POC were approximately 15 times higher compared to degradation of DOC, with POC half-lives of only 17 +/- 3 (mean +/- SE) days across all sampled aquatic ecosystems. Rapid POC decay was accompanied by a shift in particulate C: N ratios, whereas dissolved organic matter composition did not change at the time scale of incubations. The faster degradation of the POC implies a constant replenishment to sustain natural POC concentrations. We suggest that degradation of organic matter transported through the inland water continuum might occur to a large extent via transition of DOC into more rapidly cycling POC in nature, for example, triggered by light. In this way, particles would be a dominant pool of organic C processing across the boreal aquatic continuum, partially sustained by replenishment via flocculation of DOC.

  • 3.
    Attermeyer, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz Inst Freshwater Ecol & Inland Fisheries C, Muggelseedamm 310, D-12587 Berlin, Germany..
    Flury, S.
    Leibniz Inst Freshwater Ecol & Inland Fisheries C, Muggelseedamm 310, D-12587 Berlin, Germany.;Univ Geneva, Fac Sci, Blvd Carl Vogt 66, CH-1211 Geneva, Switzerland..
    Jayakumar, R.
    IITM, IGCS, Madras 600036, Tamil Nadu, India.;IITM, Environm & Water Resources Engn Div, Dept Civil Engn, Madras 600036, Tamil Nadu, India..
    Fiener, P.
    Univ Augsburg, Dept Geog, Alter Postweg 118, D-86159 Augsburg, Germany..
    Steger, K.
    IITM, IGCS, Madras 600036, Tamil Nadu, India..
    Arya, V.
    IITM, Environm & Water Resources Engn Div, Dept Civil Engn, Madras 600036, Tamil Nadu, India..
    Wilken, F.
    Univ Augsburg, Dept Geog, Alter Postweg 118, D-86159 Augsburg, Germany.;BTU, Chair Soil Protect & Recultivat, Konrad Wachsmann Allee 6, D-03013 Cottbus, Germany..
    van Geldern, R.
    Univ Erlangen Nurnberg, GeoZentrum Nordbayern, Schlossgarten 5, D-91054 Erlangen, Germany..
    Premke, K.
    Leibniz Inst Freshwater Ecol & Inland Fisheries C, Muggelseedamm 310, D-12587 Berlin, Germany.;Leibniz Ctr Agr Landscape Res ZALF, Inst Landscape Biogeochem, Eberswalder Str 84, D-15374 Muncheberg, Germany..
    Invasive floating macrophytes reduce greenhouse gas emissions from a small tropical lake2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 20424Article in journal (Refereed)
    Abstract [en]

    Floating macrophytes, including water hyacinth (Eichhornia crassipes), are dominant invasive organisms in tropical aquatic systems, and they may play an important role in modifying the gas exchange between water and the atmosphere. However, these systems are underrepresented in global datasets of greenhouse gas (GHG) emissions. This study investigated the carbon (C) turnover and GHG emissions from a small (0.6 km(2)) water-harvesting lake in South India and analysed the effect of floating macrophytes on these emissions. We measured carbon dioxide (CO2) and methane (CH4) emissions with gas chambers in the field as well as water C mineralization rates and physicochemical variables in both the open water and in water within stands of water hyacinths. The CO2 and CH4 emissions from areas covered by water hyacinths were reduced by 57% compared with that of open water. However, the C mineralization rates were not significantly different in the water between the two areas. We conclude that the increased invasion of water hyacinths and other floating macrophytes has the potential to change GHG emissions, a process that might be relevant in regional C budgets.

  • 4.
    Attermeyer, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Chemical Analytics and Biogeochemistry, Germany.
    Grossart, Hans-Peter
    Leibniz-Institute of Freshwater Ecology and InlandFisheries, Experimental Limnology, Germany; Institute for Biochemistry and Biology, Potsdam University, Germany.
    Flury, Sabine
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Chemical Analytics and Biogeochemistry, Germany; Faculty of Science, University of Geneva, Switzerland.
    Premke, Katrin
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Chemical Analytics and Biogeochemistry, Germany; Leibniz Centre for Agricultural Landscape Research (ZALF), Institute for Landscape Biogeochemistry, Germany.
    Bacterial processes and biogeochemical changes in the water body of kettle holes: mainly driven by autochthonous organic matter?2017In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 79, no 3, p. 675-687Article in journal (Refereed)
    Abstract [en]

    Kettle holes are small inland waters formed from glacially-created depressions often situated in agricultural landscapes. Due to their high perimeter-to-area ratio facilitating a high aquatic-terrestrial coupling, kettle holes can accumulate high concentrations of organic carbon and nutrients, fueling microbial activities and turnover rates. Thus, they represent hotspots of carbon turnover in the landscape, but their bacterial activities and controlling factors have not been well investigated. Therefore, we aimed to assess the relative importance of various environmental factors on bacterial and biogeochemical processes in the water column of kettle holes and to disentangle their variations. In the water body of ten kettle holes in north-eastern Germany, we measured several physico-chemical and biological parameters such as carbon quantity and quality, as well as bacterial protein production (BP) and community respiration (CR) in spring, early summer and autumn 2014. Particulate organic matter served as an indicator of autochthonous production and represented an important parameter to explain variations in BP and CR. This notion is supported by qualitative absorbance indices of dissolved molecules in water samples and C:N ratios of the sediments, which demonstrate high fractions of autochthonous organic matter (OM) in the studied kettle holes. In contrast, dissolved chemical parameters were less important for bacterial activities although they revealed strong differences throughout the growing season. Pelagic bacterial activities and dynamics might thus be regulated by autochthonous OM in kettle holes implying a control of important biogeochemical processes by internal primary production rather than facilitated exchange with the terrestrial surrounding due to a high perimeter-to-area ratio.

  • 5.
    Bengtsson, Mia M.
    et al.
    Ernst Moritz Arndt Univ Greifswald, Inst Microbiol, Felix Hausdorff Str 8, D-17489 Greifswald, Germany.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. WasserCluster Lunz, Dr Carl Kupelwieser Promenade 5, A-3293 Lunz Am See, Austria.
    Catalan, Nuria
    Catalan Inst Water Res ICRA, Emili Grahit 101, Girona 17003, Spain.
    Interactive effects on organic matter processing from soils to the ocean: are priming effects relevant in aquatic ecosystems?2018In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 822, no 1, p. 1-17Article, review/survey (Refereed)
    Abstract [en]

    Organic matter (OM) is degraded during transport from soils to oceans. However, there are spatial and temporal variabilities along the aquatic continuum, which hamper the development of carbon cycling models. One concept that has been applied in this context is the priming effect (PE), describing non-additive effects on OM degradation after mixing sources of contrasting bioavailability. Studies on the aquatic PE report divergent results from positive (increased OM degradation rates) to neutral, to negative (decreased OM degradation rates) effects upon mixing. Here, we aim to condense the outcomes of these studies on aquatic PE. Based on a literature review, we discuss differences in the reported PEs across freshwater and marine ecosystems, identifying system-specific features that could favour non-additive effects on OM degradation. Using a quantitative meta-analysis approach, we evaluated the occurrence, direction (positive vs. negative) and magnitude of aquatic PE. The meta-analysis revealed a mean PE of 12.6%, which was not significantly different from zero across studies. Hence, mixing of contrasting OM sources in aquatic ecosystems does not necessarily result in a change in OM degradation rates. Therefore, we suggest to focus on molecular and microbial diversity and function, which could provide a better mechanistic understanding of processes driving OM interactions.

  • 6. Bravo, Andrea G.
    et al.
    Kothawala, Dolly
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Tessier, Emmanuel
    Bodmer, Pascal
    Ledesma, José L.J.
    Audet, Joachim
    Casas-Ruiz, Joan Pere
    Catalán, Núria
    Cauvy-Fraunié, Sophie
    Colls, Miriam
    Deininger, Anne
    Evtimova, Vesela V.
    Fonvielle, Jérémy A.
    Fuß, Thomas
    Gilbert, Peter
    Herrero Ortega, Sonia
    Liu, Liu
    Mendoza-Lera, Clara
    Monteiro, Juliana
    Mor, Jordi-René
    Nagler, Magdalena
    Niedrist, Georg H.
    Nydahl, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Pastor, Ada
    Pegg, Josephine
    Gutmann Roberts, Catherine
    Pilotto, Francesca
    Portela, Ana Paula
    González-Quijano, Clara Romero
    Romero, Ferran
    Rulík, Martin
    Amouroux, David
    The interplay between total mercury, methylmercury and dissolved organic matter in fluvial systems: A latitudinal study across Europe2018In: Water Research, ISSN 0043-1354, Vol. 144, p. 172-182Article in journal (Refereed)
    Abstract [en]

    Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-mercury (MeHg) concentrations in aquatic ecosystems. Studies attempting to link dissolved organic matter (DOM) to levels of THg or MeHg are few and geographically constrained. Additionally, stream and river systems have been understudied as compared to lakes. Hence, the aim of this study was to examine the influence of DOM concentration and composition, morphological descriptors, land uses and water chemistry on THg and MeHg concentrations and the percentage of THg as MeHg (%MeHg) in 29 streams across Europe spanning from 41°N to 64 °N. THg concentrations (0.06–2.78 ng L−1) were highest in streams characterized by DOM with a high terrestrial soil signature and low nutrient content. MeHg concentrations (7.8–159 pg L−1) varied non-systematically across systems. Relationships between DOM bulk characteristics and THg and MeHg suggest that while soil derived DOM inputs control THg concentrations, autochthonous DOM (aquatically produced) and the availability of electron acceptors for Hg methylating microorganisms (e.g. sulfate) drive %MeHg and potentially MeHg concentration. Overall, these results highlight the large spatial variability in THg and MeHg concentrations at the European scale, and underscore the importance of DOM composition on mercury cycling in fluvial systems.

  • 7. Bravo, Andrea Garcia
    et al.
    Kothawala, Dolly
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Tessier, Emmanuel
    Bodmer, Pascal
    Amouroux, David
    Cleaning and sampling protocol for analysis of mercury and dissolved organic matter in freshwater systems2018In: MethodsX, ISSN 1258-780X, E-ISSN 2215-0161, Vol. 5, p. 1017-1026Article in journal (Refereed)
    Abstract [en]

    Mercury (Hg), and in particular its methylated form (methylmercury, MeHg), is a hazardous substance with the potential to produce significant adverse neurological and other health effects. Enhanced anthropogenic emissions and long-range transport of atmospheric Hg have increased Hg concentrations above background levels in aquatic systems. In this context, the Minamata Convention, a global legally binding agreement that seeks to prevent human exposure to Hg, was signed and enforced by 128 countries, and today more than 90 Parties have ratified it. All these Parties have committed to develop Hg monitoring programs to report the effectiveness of the convention. For this purpose, we provide a standardized cleaning and water sampling protocol for the determination of total-Hg and MeHg in freshwaters at ambient levels. As Hg and organic matter are tightly bound, the protocol also describes sample collection for dissolved organic carbon (DOC) concentration and characterization of dissolved organic matter (DOM) composition by fluorescence spectroscopy. This protocol is highly useful to non-experts without a prior background in Hg sampling and analysis, and can serve as a useful basis for national monitoring programs. Furthermore, this protocol should help increase quantitative inventories of DOC, inorganic-Hg (IHg) and MeHg concentrations and DOM composition in freshwater, which are severely lacking at a global scale. • Provides a standardized method to collect water samples for IHg, MeHg, DOC and DOM composition from freshwater ecosystems.

  • 8.
    Engel, Fabian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Ayala, Ana I
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Fischer, Helmut
    Kirchesch, Volker
    Pierson, Don
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Phytoplankton gross primary production increases along cascading impoundments in a temperate, low-discharge river: Insights from high frequency water quality monitoring2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 6701Article in journal (Refereed)
    Abstract [en]

    Damming alters carbon processing along river continua. Estimating carbon transport along rivers intersected by multiple dams requires an understanding of the effects of cascading impoundments on the riverine metabolism. We analyzed patterns of riverine metabolism and phytoplankton biomass (chlorophyll a; Chla) along a 74.4-km river reach intersected by six low-head navigation dams. Calculating gross primary production (GPP) from continuous measurements of dissolved oxygen concentration, we found a maximum increase in the mean GPP by a factor of 3.5 (absolute difference of 0.45 g C m−3 d−1) along the first 26.5 km of the study reach, while Chla increased over the entire reach by a factor of 2.9 (8.7 µg l−1). In the intermittently stratified section of the deepest impoundment the mean GPP between the 1 and 4 m water layer differed by a factor of 1.4 (0.31 g C m−3 d−1). Due to the strong increase in GPP, the river featured a wide range of conditions characteristic of low- to medium-production rivers. We suggest that cascading impoundments have the potential to stimulate riverine GPP, and conclude that phytoplankton CO2 uptake is an important carbon flux in the river Saar, where a considerable amount of organic matter is of autochthonous origin.

  • 9. Lischke, Betty
    et al.
    Mehner, Thomas
    Hilt, Sabine
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz Inst Freshwater Ecol & Inland Fisheries, Stechlin, Germany.
    Brauns, Mario
    Brothers, Soren
    Grossart, Hans Peter
    Köhler, Jan
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz Inst Freshwater Ecol & Inland Fisheries, Berlin, Germany.
    Gaedke, Ursula
    Benthic carbon is inefficiently transferred in the food webs of two eutrophic shallow lakes2017In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 62, no 10, p. 1693-1706Article in journal (Refereed)
    Abstract [en]

    1. The sum of benthic autotrophic and bacterial production often exceeds the sum of pelagic autotrophic and bacterial production, and hence may contribute sub- stantially to whole-lake carbon fluxes, especially in shallow lakes. Furthermore, both benthic and pelagic autotrophic and bacterial production are highly edible and of sufficient nutritional quality for animal consumers. We thus hypothesised that pelagic and benthic transfer efficiencies (ratios of production at adjacent trophic levels) in shallow lakes should be similar. 2. We performed whole ecosystem studies in two shallow lakes (3.5 ha, mean depth 2 m), one with and one without submerged macrophytes, and quantified pelagic and benthic biomass, production and transfer efficiencies for bacteria, phytoplank- ton, epipelon, epiphyton, macrophytes, zooplankton, macrozoobenthos and fish. We expected higher transfer efficiencies in the lake with macrophytes, because these provide shelter and food for macrozoobenthos and may thus enable a more efficient conversion of basal production to consumer production. 3. In both lakes, the majority of the whole-lake autotrophic and bacterial produc- tion was provided by benthic organisms, but whole-lake primary consumer pro- duction mostly relied on pelagic autotrophic and bacterial production. Consequently, transfer efficiency of benthic autotrophic and bacterial production to macrozoobenthos production was an order of magnitude lower than the transfer efficiency of pelagic autotrophic and bacterial production to rotifer and crustacean production. Between-lake differences in transfer efficiencies were minor. 4. We discuss several aspects potentially causing the unexpectedly low benthic transfer efficiencies, such as the food quality of producers, pelagic–benthic links, oxygen concentrations in the deeper lake areas and additional unaccounted con- sumer production by pelagic and benthic protozoa and meiobenthos at interme- diate or top trophic levels. None of these processes convincingly explain the large differences between benthic and pelagic transfer efficiencies. 5. Our data indicate that shallow eutrophic lakes, even with a major share of auto- trophic and bacterial production in the benthic zone, can function as pelagic sys- tems with respect to primary consumer production. We suggest that the benthic autotrophic production was mostly transferred to benthic bacterial production, which remained in the sediments, potentially cycling internally in a similar way to what has previously been described for the microbial loop in pelagic habitats. Understanding the energetics of whole-lake food webs, including the fate of the substantial benthic bacterial production, which is either mineralised at the sedi- ment surface or permanently buried, has important implications for regional and global carbon cycling

  • 10. Lischke, Betty
    et al.
    Weithoff, Guntram
    Wickham, Stephen
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Grossart, Hans-Peter
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Hilt, Sabine
    Gaedke, Ursula
    Large biomass of small feeders: Ciliates may dominate herbivory in eutrophic lakes2016In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 38, no 1, p. 2-15Article in journal (Refereed)
    Abstract [en]

    The importance of ciliates as herbivores and in biogeochemical cycles is increasingly recognized. An opportunity to observe the potential consequences of zooplankton dominated by ciliates arose when winter fish kills resulted in strong suppression of crustaceans by young planktivorous fish in two shallow lakes. On an annual average, ciliates made up 38-76% of the total zooplankton biomass in both lakes during two subsequent years. Consequently, ciliate biomass and their estimated grazing potential were extremely high compared with other lakes of various trophic states and depths. Grazing estimates based on abundance and size suggest that ciliates should have cleared the water column of small (<5 mu m) and intermediate (5-50 mu m) sized phytoplankton more than once a day. Especially, small feeders within the ciliates were important, likely exerting a strong top-down control on small phytoplankton. Particle-attached bacteria were presumably strongly suppressed by intermediate-sized ciliate feeders. In contrast to other lakes, large phytoplankton was proportionately very abundant. The phytoplankton community had a high evenness, which may be attributed to the feeding by numerous fast growing and selective ciliate species. Our study highlights ciliates as an important trophic link and adds to the growing awareness of the role of winter processes for plankton dynamics.

  • 11.
    Mehner, Thomas
    et al.
    Leibniz‐Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.
    Lischke, Betty
    Leibniz‐Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz‐Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz‐Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.
    Brothers, Soren
    Leibniz‐Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany;Department of Watershed Sciences and Ecology Center, Utah State University, Logan, Utah, USA.
    Gaedke, Ursula
    Institute for Biochemistry and Biology, University of Potsdam, Potsdam, Germany.
    Hilt, Sabine
    Leibniz‐Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.
    Brucet, Sandra
    Aquatic Ecology Group, University of Vic – Central University of Catalonia, Vic, Barcelona, Catalonia, Spain;Catalan Institution for Research and Advanced Studies ICREA, Barcelona, Catalonia, Spain.
    Empirical correspondence between trophic transfer efficiency in freshwater food webs and the slope of their size spectra2018In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 99, no 6, p. 1463-1472Article in journal (Refereed)
    Abstract [en]

    The density of organisms declines with size, because larger organisms need more energy than smaller ones and energetic losses occur when larger organisms feed on smaller ones. A potential expression of density-size distributions are Normalized Biomass Size Spectra (NBSS), which plot the logarithm of biomass independent of taxonomy within bins of logarithmic organismal size, divided by the bin width. Theoretically, the NBSS slope of multi-trophic communities is exactly - 1.0 if the trophic transfer efficiency (TTE, ratio of production rates between adjacent trophic levels) is 10% and the predator-prey mass ratio (PPMR) is fixed at 10(4). Here we provide evidence from four multi-trophic lake food webs that empirically estimated TTEs correspond to empirically estimated slopes of the respective community NBSS. Each of the NBSS considered pelagic and benthic organisms spanning size ranges from bacteria to fish, all sampled over three seasons in 1 yr. The four NBSS slopes were significantly steeper than -1.0 (range -1.14 to -1.19, with 95% CIs excluding -1). The corresponding average TTEs were substantially lower than 10% in each of the four food webs (range 1.0% to 3.6%, mean 1.85%). The overall slope merging all biomass-size data pairs from the four systems (-1.17) was almost identical to the slope predicted from the arithmetic mean TTE of the four food webs (-1.18) assuming a constant PPMR of 10(4). Accordingly, our empirical data confirm the theoretically predicted quantitative relationship between TTE and the slope of the biomass-size distribution. Furthermore, we show that benthic and pelagic organisms can be merged into a community NBSS, but future studies have yet to explore potential differences in habitat-specific TTEs and PPMRs. We suggest that community NBSS may provide valuable information on the structure of food webs and their energetic pathways, and can result in improved accuracy of TTE-estimates.

  • 12.
    Nydahl, Anna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Hiller, Carolin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Garrison, Julie A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Chaguaceda, Fernando
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Colored organic matter increases CO2 in meso-eutrophic lake water through altered light climate and acidity2019In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 64, no 2, p. 744-756Article in journal (Refereed)
    Abstract [en]

    Many surface waters across the boreal region are browning due to increased concentrations of colored allochthonous dissolved organic carbon (DOC). Browning may stimulate heterotrophic metabolism, may have a shading effect constraining primary production, and may acidify the water leading to decreased pH with a subsequent shift in the carbonate system. All these effects are expected to result in increased lake water carbon dioxide (CO2) concentrations. We tested here these expectations by assessing the effects of both altered allochthonous DOC input and light conditions through shading on lake water CO2 concentrations. We used two mesocosm experiments with water from the meso‐eutrophic Lake Erken, Sweden, to determine the relative importance of bacterial activities, primary production, and shifts in the carbonate system on CO2 concentrations. We found that DOC addition and shading resulted in a significant increase in partial pressure of CO2 (pCO2) in all mesocosms. Surprisingly, there was no relationship between bacterial activities and pCO2. Instead the experimental reduction of light by DOC and/or shading decreased the photosynthesis to respiration ratio leading to increased pCO2. Another driving force behind the observed pCO2 increase was a significant decrease in pH, caused by a decline in photosynthesis and the input of acidic DOC. Considering that colored allochthonous DOC may increase in a warmer and wetter climate, our results could also apply for whole lake ecosystems and pCO2 may increase in many lakes through a reduction in the rate of photosynthesis and decreased pH.

  • 13. Wurzbacher, Christian
    et al.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Stechlin, Germany.
    Kettner, Maria Therese
    Flintrop, Clara
    Warthmann, Norman
    Hilt, Sabine
    Grossart, Hans-Peter
    Monaghan, Michael T.
    DNA metabarcoding of unfractionated water samples relates phyto-, zoo- and bacterioplankton dynamics and reveals a single-taxon bacterial bloom2017In: Environmental Microbiology Reports, ISSN 1758-2229, E-ISSN 1758-2229, Vol. 9, no 4, p. 383-388Article in journal (Refereed)
    Abstract [en]

    Most studies of aquatic plankton focus on either macroscopic or microbial communities, and on either eukaryotes or prokaryotes. This separation is primarily for methodological reasons, but can overlook potential interactions among groups. We tested whether DNA metabarcoding of unfractionated water samples with universal primers could be used to qualitatively and quantitatively study the temporal dynamics of the total plankton community in a shallow temperate lake. We found significant changes in the relative proportions of normalized sequence reads of eukaryotic and prokaryotic plankton communities over a three-month period in spring. Patterns followed the same trend as plankton estimates measured using traditional microscopic methods. We characterized the bloom of a conditionally rare bacterial taxon belonging to Arcicella, which rapidly came to dominate the whole lake ecosystem and would have remained unnoticed without metabarcoding. Our data demonstrate the potential of universal DNA metabarcoding applied to unfractionated samples for providing a more holistic view of plankton communities.

  • 14.
    Wurzbacher, Christian
    et al.
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany; Berlin Center for Genomics in Biodiversity Research, Germany; Department of Biological and Environmental Sciences, University of Gothenburg, Sweden.
    Fuchs, Andrea
    Carl-von-Ossietzky University Oldenburg, Germany; Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz-InsLeibniz-Institute of Freshwater Ecology and Inland Fisheries, Germanytitute of Freshwater Ecology and Inland Fisheries, Alte Fischerhütte 2, 16775 Stechlin, Germany.
    Frindte, Katharina
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, 16775 Stechlin, Germany; Institute of Crop Science and Resource Conservation – Molecular Biology of the Rhizosphere, Bonn University, Germany.
    Grossart, Hans-Peter
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany; Institute for Biochemistry and Biology, Potsdam University, Germany.
    Hupfer, Michael
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany.
    Casper, Peter
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany.
    Monaghan, Michael T.
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany; Berlin Center for Genomics in Biodiversity Research, Germany.
    Shifts among Eukaryota, Bacteria, and Archaea define the vertical organization of a lake sediment2017In: Microbiome, ISSN 0026-2633, E-ISSN 2049-2618, Vol. 5, article id 41Article in journal (Refereed)
    Abstract [en]

    Background: Lake sediments harbor diverse microbial communities that cycle carbon and nutrients while being constantly colonized and potentially buried by organic matter sinking from the water column. The interaction of activity and burial remained largely unexplored in aquatic sediments. We aimed to relate taxonomic composition to sediment biogeochemical parameters, test whether community turnover with depth resulted from taxonomic replacement or from richness effects, and to provide a basic model for the vertical community structure in sediments.

    Methods: We analyzed four replicate sediment cores taken from 30-m depth in oligo-mesotrophic Lake Stechlin in northern Germany. Each 30-cm core spanned ca. 170 years of sediment accumulation according to 137Cs dating and was sectioned into layers 1–4 cm thick. We examined a full suite of biogeochemical parameters and used DNA metabarcoding to examine community composition of microbial Archaea, Bacteria, and Eukaryota.

    Results: Community β-diversity indicated nearly complete turnover within the uppermost 30 cm. We observed a pronounced shift from Eukaryota- and Bacteria-dominated upper layers (<5 cm) to Bacteria-dominated intermediate layers (5–14 cm) and to deep layers (>14 cm) dominated by enigmatic Archaea that typically occur in deep-sea sediments. Taxonomic replacement was the prevalent mechanism in structuring the community composition and was linked to parameters indicative of microbial activity (e.g., CO2 and CH4 concentration, bacterial protein production). Richness loss played a lesser role but was linked to conservative parameters (e.g., C, N, P) indicative of past conditions.

    Conclusions: By including all three domains, we were able to directly link the exponential decay of eukaryotes with the active sediment microbial community. The dominance of Archaea in deeper layers confirms earlier findings from marine systems and establishes freshwater sediments as a potential low-energy environment, similar to deep sea sediments. We propose a general model of sediment structure and function based on microbial characteristics and burial processes. An upper “replacement horizon” is dominated by rapid taxonomic turnover with depth, high microbial activity, and biotic interactions. A lower “depauperate horizon” is characterized by low taxonomic richness, more stable “low-energy” conditions, and a dominance of enigmatic Archaea.

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