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  • 1.
    Alling, Vanja
    et al.
    Stockholm University.
    Humborg, Christoph
    Stockholm University.
    Morth, Carl-Magnus
    Stockholm University.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Pollehne , Falk
    Rostock, Germany.
    Tracing terrestrial organic matter by delta S-34 and delta C-13 signatures in a subarctic estuary2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, p. 2594-2602Article in journal (Refereed)
    Abstract [en]

    A key issue to understanding the transformations of terrestrial organic carbon in the ocean is to disentangle the latter from marine-produced organic matter. We applied a multiple stable isotope approach using delta S-34 and delta C-13 isotope signatures from estuarine dissolved organic matter (DOM), enabling us to constrain the contribution of terrestrial-derived DOM in an estuarine gradient of the northern Baltic Sea. The stable isotope signatures for dissolved organic sulfur (delta S-34(DOS)) have twice the range between terrestrial and marine end members compared to the stable isotope signatures for dissolved organic carbon (delta C-13(DOC)); hence, the share of terrestrial DOM in the total estuarine DOM can be calculated more precisely. DOM samples from the water column were collected using ultrafiltration on board the German RV Maria S Merian during a winter cruise, in the Bothnian Bay, Bothnian Sea, and Baltic proper. We calculated the terrestrial fraction of the estuarine DOC (DOCter) from both delta C-13(DOC) and delta S-34(DOS) signatures and applying fixed C: S ratios for riverine and marine end members to convert S isotope signatures into DOC concentrations. The delta S-34(DOS) signature of the riverine end member was +7.02 parts per thousand, and the mean signatures from Bothnian Bay, Bothnian Sea, and Baltic proper were +10.27, +12.51, and +13.67 parts per thousand, respectively, showing an increasing marine signal southwards (d34SDOS marine end member = 18.1 parts per thousand). These signatures indicate that 87%, 75%, and 67%, respectively, of the water column DOC is of terrestrial origin (DOCter) in these basins. Comparing the fractions of DOCter in each basin-that are still based on few winter values only-with the annual river input of DOC, it appears that the turnover time for DOCter in the Gulf of Bothnia is much shorter than the hydraulic turnover time, suggesting that high-latitude estuaries might be efficient sinks for DOCter.

  • 2.
    Bastviken, David
    et al.
    Linköping University, Department of Thematic Studies, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Persson, Linn
    Institute of Applied Environmental Research, Stockholm University, Sweden.
    Odham, Göran
    Institute of Applied Environmental Research, Stockholm University, Sweden.
    Tranvik, Lars
    Department of Limnology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Degradation of dissolved organic matter in oxic and anoxic lake water2004In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 49, no 1, p. 109-116Article in journal (Refereed)
    Abstract [en]

    Decades of conflicting results have fueled a debate about how O-2 affects organic matter (OM) degradation and carbon cycling. In a laboratory study, using both OM taken directly from a humic lake and chemically isolated fulvic acid, we monitored the mineralization of dissolved OM in freshwater under purely oxic and anoxic conditions, under oxic then anoxic conditions, and under anoxic then oxic conditions, for 426 d. Between 5% and 24% of the initial OM was mineralized, with most extensive mineralization occurring under purely oxic and anoxic-oxic conditions. A sequential change in the O-2 regime did not result in greater overall degradation, but initially anoxic conditions favored subsequent oxic mineralization. A substantially greater fraction of the OM was degraded than in previous shorter studies, with as much as 50% of the total OM degradation occurring after 147 d into the experiment. Three fractions of the degradable OM were identified: OM degraded only under oxic conditions (68-78%), OM degraded more rapidly under anoxic conditions than under oxic conditions (16-18%), and OM degraded at equal rates under both oxic and anoxic conditions (6-14%). The degradation patterns of natural dissolved OM from a humic lake and chemically isolated fulvic acid were very similar, which indicates a similar level of bioavailability. The difference between anoxic and oxic degradation was greater in our long-term studies than in previous short-term experiments, which indicates that the oxic and anoxic degradation potentials vary with increasing overall OM recalcitrance and that similar oxic and anoxic degradation rates can be expected in short-term experiments in which <30% of the long-term degradable OM is allowed to decompose.

  • 3.
    Bertilsson, S
    et al.
    Uppsala Univ, Evolutionary Biol Ctr, Dept Limnol, S-75236 Uppsala, Sweden Linkoping Univ, Dept Water & Environm Studies, S-58183 Linkoping, Sweden.
    Tranvik, LJ
    Uppsala Univ, Evolutionary Biol Ctr, Dept Limnol, S-75236 Uppsala, Sweden Linkoping Univ, Dept Water & Environm Studies, S-58183 Linkoping, Sweden.
    Photochemical transformation of dissolved organic matter in lakes2000In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 45, no 4, p. 753-762Article in journal (Refereed)
    Abstract [en]

    In a survey of photochemical transformation of dissolved organic matter (DOM) in lake water, we found photochemical production of dissolved inorganic carbon (DIC) and low molecular weight carboxylic acids (oxalic, malonic, formic, and acetic acid), upon simulated solar ultraviolet (UV) radiation exposure of filter-sterilized surface water from 38 investigated lakes. Given the large variability in water chemistry of the studied systems, we suggest that these photoproducts are universally produced in sunlight exposed lake water. The measured production of carboxylic acid carbon corresponded to 34.4% (median) of the produced DIC. The production of DIC and carboxylic acids during 8 h of mild UV irradiation corresponded to an average of 4.7% (SD 2.9) of the total dissolved organic carbon pool. Hence, photochemical degradation could be a major sink for DOM in the surface layer of lakes. All photoreaction rates were strongly correlated to the total radiation absorbed during UV exposure (r(2) > 0.8), which depends mainly on amount of colored DOM in the water. The variability in DIC production after normalizing for absorbed radiation energy could partly be attributed to general water chemistry parameters (e.g., pH, iron concentration, conductivity).

  • 4.
    Bertilsson, Stefan
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Tranvik, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Photochemically Produced Carboxylic Acids as Substrates for Freshwater Bacterioplankton1998In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 43, no 5, p. 885-895Article in journal (Refereed)
  • 5.
    Chmiel, Hannah E.
    et al.
    Uppsala University, Sweden.
    Kokic, Jovana
    Uppsala University, Sweden.
    Denfeld, Blaize A.
    Uppsala University, Sweden.
    Einarsdottir, Karolina
    Uppsala University, Sweden.
    Wallin, Marcus B.
    Uppsala University, Sweden.
    Koehler, Birgit
    Uppsala University, Sweden.
    Isidorova, Anastasija
    Uppsala University, Sweden.
    Bastviken, David
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Ferland, Marie-Eve
    University of Quebec, Canada.
    Sobek, Sebastian
    Uppsala University, Sweden.
    The role of sediments in the carbon budget of a small boreal lake2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, no 5, p. 1814-1825Article in journal (Refereed)
    Abstract [en]

    We investigated the role of lake sediments as carbon (C) source and sink in the annual C budget of a small (0.07 km(2)) and shallow (mean depth, 3.4 m), humic lake in boreal Sweden. Organic carbon (OC) burial and mineralization in the sediments were quantified from Pb-210-dated sediment and laboratory sediment incubation experiments, respectively. Burial and mineralization rates were then upscaled to the entire basin and to one whole year using sediment thickness derived from sub-bottom profiling, basin morphometry, and water column monitoring data of temperature and oxygen concentration. Furthermore, catchment C import, open water metabolism, photochemical mineralization as well as carbon dioxide (CO2) and methane (CH4) emissions to the atmosphere were quantified to relate sediment processes to other lake C fluxes. We found that on a whole-basin and annual scale, sediment OC mineralization was three times larger than OC burial, and contributed about 16% to the annual CO2 emission. Other contributions to CO2 emission were water column metabolism (31%), photochemical mineralization (6%), and catchment imports via inlet streams and inflow of shallow groundwater (22%). The remainder (25%) could not be explained by our flux calculations, but was most likely attributed to an underestimation in groundwater inflow. We conclude that on an annual and whole-basin scale (1) sediment OC mineralization dominated over OC burial, (2) water column OC mineralization contributed more to lake CO2 emission than sediment OC mineralization, and (3) catchment import of C to the lake was greater than lake-internal C cycling.

  • 6.
    Grasset, Charlotte
    et al.
    Univ Fed Juiz de Fora, Brazil; Uppsala Univ, Sweden.
    Mendonca, Raquel
    Univ Fed Juiz de Fora, Brazil; Uppsala Univ, Sweden.
    Saucedo, Gabriella Villamor
    Univ Fed Juiz de Fora, Brazil; Uppsala Univ, Sweden.
    Bastviken, David
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Roland, Fabio
    Univ Fed Juiz de Fora, Brazil.
    Sobek, Sebastian
    Uppsala Univ, Sweden.
    Large but variable methane production in anoxic freshwater sediment upon addition of allochthonous and autochthonous organic matter2018In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, no 4, p. 1488-1501Article in journal (Refereed)
    Abstract [en]

    An important question in the context of climate change is to understand how CH4 production is regulated in anoxic sediments of lakes and reservoirs. The type of organic carbon (OC) present in lakes is a key factor controlling CH4 production at anoxic conditions, but the studies investigating the methanogenic potential of the main OC types are fragmented. We incubated different types of allochthonous OC (alloOC; terrestrial plant leaves) and autochthonous OC (autoOC; phytoplankton and two aquatic plants species) in an anoxic sediment during 130 d. We tested if (1) the supply of fresh alloOC and autoOC to an anoxic refractory sediment would fuel CH4 production and if (2) autoOC would decompose faster than alloOC. The addition of fresh OC greatly increased CH4 production and the delta C-13-CH4 partitioning indicated that CH4 originated exclusively from the fresh OC. The large CH4 production in an anoxic sediment fueled by alloOC is a new finding which indicates that all systems with anoxic conditions and high sedimentation rates have the potential to be CH4 emitters. The autoOC decomposed faster than alloOC, but the total CH4 production was not higher for all autoOC types, one aquatic plant species having values as low as the terrestrial leaves, and the other one having values as high as phytoplankton. Our study is the first to report such variability, suggesting that the extent to which C fixed by aquatic plants is emitted as greenhouse gases or buried as OC in sediment could more generally differ between aquatic vegetation types.

  • 7.
    Gudasz, Cristian
    et al.
    Uppsala University.
    Bastviken, David
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Premke, Katrin
    Uppsala University.
    Steger, Kristin
    Uppsala University.
    Tranvik, Lars J.
    Uppsala University.
    Constrained microbial processing of allochthonous organic carbon in boreal lake sediments2012In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 57, no 1, p. 163-175Article in journal (Refereed)
    Abstract [en]

    We investigated sediment bacterial metabolism in eight lakes with different inputs of allochthonous and autochthonous organic carbon in south-central Sweden. Sediment bacterial production, mineralization, and biomass were measured seasonally and along a lake depth gradient in lakes with different water and sediment characteristics. Sediment bacterial metabolism was primarily controlled by temperature but also by the quality and origin of organic carbon. Metabolism was positively correlated to measures of autochthonous influence on the sediment organic carbon, but did not show a similar increase with increasing input of allochthonous organic carbon. Hence, in contrast to what is currently known for the water column, increasing terrestrial organic carbon influence does not result in enhanced sediment bacterial metabolism. The role of allochthonous organic carbon as the main driver of sediment bacterial metabolism suggested so far is contrary to our findings. Meio- and macrobenthic invertebrate biomass were, at most, weakly correlated to bacterial metabolism and biomass, suggesting limited control of sediment bacteria by grazing. Bacterial metabolism in boreal lake sediments is constrained by low temperatures and by the recalcitrant nature of the dominant organic carbon, resulting in sediments being an effective sink of organic carbon.

  • 8.
    Humborg, Christoph
    et al.
    Department of Systems Ecology, Stockholm University.
    Smedberg, Erik
    Department of Systems Ecology, Stockholm University.
    Blomqvist, Sven
    Department of Systems Ecology, Stockholm University.
    Mörth, Carl-Magnus
    Department of Geology and Geochemistry, Stockholm University.
    Brink, Jenni
    Department of Geology and Geochemistry, Stockholm University.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Danielsson, Åsa
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Sahlberg, Jörgen
    Swedish Meteorological and Hydrological Institute,.
    Nutrient variations in boreal and subarctic Swedish rivers: Landscape control of land–sea fluxes2004In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 49, no 5, p. 1871-1883Article in journal (Refereed)
    Abstract [en]

    We examined the hypothesis that the extent of vegetation cover governs the fluxes of nutrients from boreal and subarctic river catchments to the sea. Fluxes of total organic carbon (TOC) and dissolved inorganic nitrogen, phosphorus, and dissolved silicate (DIN, DIP, and DSi, respectively) are described from 19 river catchments and subcatchments (ranging in size from 34 to 40,000 km2) in northern Sweden with a detailed analysis of the rivers Lulea¨lven and Kalixa¨lven. Fluxes of TOC, DIP, and DSi increase by an order of magnitude with increasing proportion of forest and wetland area, whereas DIN did not follow this pattern but remained constantly low. Principal component analysis on landscape variables showed the importance of almost all land cover and soil type variables associated with vegetation, periglacial environment, soil and bedrock with slow weathering rates, boundary of upper tree line, and percentage of lake area. A cluster analysis of the principal components showed that the river systems could be separated into mountainous headwaters and forest and wetland catchments. This clustering was also valid in relation to river chemistry (TOC, DIP, and DSi) and was confirmed with a redundancy analysis, including river chemistry and principal components as environmental variables. The first axis explains 89% of the variance in river chemistry and almost 100% of the variance in the relation between river chemistry and landscape variables. These results suggest that vegetation change during interglacial periods is likely to have had a major effect on inputs of TOC, DIP, and DSi into the past ocean.

  • 9.
    Natchimuthu, Sivakiruthika
    et al.
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Sundgren, Ingrid
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Gålfalk, Magnus
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Klemedtsson, Leif
    Department of Earth Sciences, University of Gothenburg, Göteborg, Sweden.
    Crill, Patrick
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden.
    Danielsson, Åsa
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Bastviken, David
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Spatio-temporal variability of lake CH4 fluxes and its influence on annual whole lake emission estimates2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, p. S13-S26Article in journal (Refereed)
    Abstract [en]

    Lakes are major sources of methane (CH4) to the atmosphere that contribute significantly to the global budget. Recent studies have shown that diffusive fluxes, ebullition and surface water CH4 concentrations can differ significantly within lakes—spatially and temporally. CH4 fluxes may be affected at longer scales in response to seasons, temperature, lake mixing events, short term weather events like pressure variations, shifting winds and diel cycles. Frequent measurements of fluxes in the same system and integrated assessments of the impacts of the spatio-temporal variability are rare. Thereby, large scale assessments frequently lack information on this variability which can potentially lead to biased estimates. In this study, we analysed the variability of CH4 fluxes and surface water CH4 concentrations across open water areas of lakes in a small catchment in southwest Sweden over two annual cycles. Significant patterns in CH4 concentrations, diffusive fluxes, ebullition and total fluxes were observed in space (between and within lakes) and in time (over diel cycles to years). Differences observed among the lakes can be associated with lake characteristics. The spatial variability within lakes was linked to depth or distance to stream inlets. Temporal variability was observed at diel to seasonal scales and was influenced by weather events. The fluxes increased exponentially with temperature in all three lakes, with stronger temperature dependence with decreasing depth. By comparing subsets of our data with estimates using all data we show that considering the spatio-temporal variability in CH4 fluxes is critical when making whole lake or annual budgets.

  • 10.
    Podgrajsek, E.
    et al.
    Uppsala University, Sweden.
    Sahlee, E.
    Uppsala University, Sweden.
    Bastviken, David
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Natchimuthu, Sivakiruthika
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Kljun, N.
    Swansea University, Wales.
    Chmiel, H. E.
    Uppsala University, Sweden.
    Klemedtsson, L.
    University of Gothenburg, Sweden.
    Rutgersson, A.
    Uppsala University, Sweden.
    Methane fluxes from a small boreal lake measured with the eddy covariance method2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, p. S41-S50Article in journal (Refereed)
    Abstract [en]

    Fluxes of methane, CH4, were measured with the eddy covariance (EC) method at a small boreal lake in Sweden. The mean CH4 flux during the growing season of 2013 was 20.1 nmol m(-2) s(-1) and the median flux was 16 nmol m(-2) s(-1) (corresponding to 1.7 mmol m(-2) d(-1) and 1.4 mmol m(-2) d(-1)). Monthly mean values of CH4 flux measured with the EC method were compared with fluxes measured with floating chambers (FC) and were in average 62% higher over the whole study period. The difference was greatest in April partly because EC, but not FC, accounted for fluxes due to ice melt and a subsequent lake mixing event. A footprint analysis revealed that the EC footprint included primarily the shallow side of the lake with a major inlet. This inlet harbors emergent macrophytes that can mediate high CH4 fluxes. The difference between measured EC and FC fluxes can hence be explained by different footprint areas, where the EC system sees the part of the lake presumably releasing higher amounts of CH4. EC also provides more frequent measurements than FC and hence more likely captures ebullition events. This study shows that small lakes have CH4 fluxes that are highly variable in time and space. Based on our findings we suggest to measure CH4 fluxes from lakes as continuously as possible and to aim for covering as much of the lakes surface as possible, independently of the selected measuring technique.

  • 11.
    Rahm, Lars
    Swedish Meteorological and Hydrological Institute, Norrköping, Sweden.
    Oxygen consumption in the Baltic proper1987In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 32, no 4, p. 973-978Article in journal (Refereed)
    Abstract [en]

    Total oxygen consumption rate, averaged over 1957-1982, and its variations with salinity in the deep water of the Baltic proper are calculated by a system of diagnostic advection-diffusion equations in a "natural" coordinate frame of reference. Although the data set used is not ideal for a more thorough investigation of the sensitivity of the model, an oxygen budget is formulated. A gross consumption rate of 3 x 10-9 mol m-3 s-1 is obtained. Further, a total consumption of about 0.14 x 10-6 mol m-2 s-1 is found, which is equivalent to an annual carbon input of 10 g C m-2 yr-1.

  • 12.
    Rahm, Lars
    Oceanografiska Institutet, Göteborgs Universitet.
    The thermally forced circulation in a small, ice-covered lake1985In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 30, no 5, p. 1122-1128Article in journal (Refereed)
    Abstract [en]

    A simple, one-dimensional model of the stratification in a small, ice-covered lake is developed. It is shown that the heat flux from the sediments gives rise to a stable stratification and an organized circulation pattern. Data from a field study are compared with the predictions of the model. The good agreement found suggests that the buoyancy layer at the nonhorizontal boundaries is essential in modeling the thermal circulation in this type of lake.

  • 13.
    Ricao Canelhas, Monica
    et al.
    Uppsala University, Sweden.
    Denfeld, Blaize A.
    Uppsala University, Sweden.
    Weyhenmeyer, Gesa A.
    Uppsala University, Sweden.
    Bastviken, David
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Bertilsson, Stefan
    Uppsala University, Sweden.
    Methane oxidation at the water-ice interface of an ice-covered lake2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, p. S78-S90Article in journal (Refereed)
    Abstract [en]

    Lakes are important components of the global methane (CH4) cycle. In seasonally ice-covered lakes, CH4 transported by ebullition (bubbling) from anoxic sediments gets trapped at the water-ice interface. If not oxidized by methane-oxidizing bacteria (MOB), this can potentially lead to high episodic CH4 emissions at ice-melt. To understand the fate of CH4 trapped below ice, we measured depth-distributions of CH4 concentrations in the water column near bubbles trapped below ice in Lake Erken. We also performed a 21 d incubation experiment at low temperature (2.3 +/- 0.2 degrees C) to investigate the potential for CH4 oxidation. During most sampling occasions, we found steep CH4 concentration gradients just below the ice with a 13-fold decrease from the surface to a depth of 20 cm. In vitro incubations revealed that CH4 oxidation can occur at low temperatures typical for the water-ice interface. CH4 oxidation was observed as a significant decrease in CH4 concentration, a significant increase in stable isotope C-13 signature, and an increase in MOB during the incubation. Thus, CH4 accumulating in the top 20 cm of the water column, fed by diffusion from CH4 in trapped bubbles, may fuel significant CH4 oxidation. Since northern latitude lakes can be ice-covered for many months of the year and significant amounts of CH4 accumulate below the ice, the extent of CH4 oxidation under these low temperature-conditions is important for understanding the potential CH4 emissions to the atmosphere during ice-melt.

  • 14.
    Routh, Joyanto
    et al.
    Department of Geology and Geochemistry, Stockholm University, S 10691 Stockholm, Sweden.
    Meyers, Philip A.
    Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109-1063, USA.
    Gustafsson, Örjan
    Department of Geology and Geochemistry, Stockholm University, S 10691 Stockholm, Sweden.
    Baskaran, Mark
    Department of Geology, Wayne State University, Detroit, Michigan 48202, USA.
    Hallberg, Rolf
    Department of Geology and Geochemistry, Stockholm University, S 10691 Stockholm, Sweden.
    Schï¿œldstrï¿œm, Anna
    Department of Geology and Geochemistry, Stockholm University, S 10691 Stockholm, Sweden.
    Sedimentary geochemical record of humanï¿œinduced environmental changes in the Lake Brunnsviken watershed, Sweden2004In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Limnology and Oceanography, Vol. 49, no 5, p. 1560-1569Article in journal (Refereed)
    Abstract [en]

    Environmental changes in Lake Brunnsviken, its watershed, and the greater Stockholm region since the middle of the nineteenth century have left interpretable geochemical imprints in the bottom sediments. These human-induced perturbations within the lakeï¿œs watershed included agriculture, urbanization, sewage and industrial disposal, and water column aeration. Smaller d15Ntotal values, high organic carbon mass accumulation rates, low C:N ratios, and larger d13Corg values identify periods of increased nutrient delivery and elevated primary productivity in the lake. C: S ratios that change from high to low trace the transition from an oxic hypolimnion to an anoxic one during the periods of high productivity. Accumulations of redox-sensitive trace elements increase during the anoxic period and are further magnified during a time of industrial waste discharge into the lake. A recent decrease in black carbon concentrations in sediments reflects the conversion from wood and coal to cleaner forms of energy.

  • 15.
    Schilder, Jos
    et al.
    University of Bern, Switzerland; University of Bern, Switzerland.
    Bastviken, David
    Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    van Hardenbroek, Maarten
    University of Bern, Switzerland; University of Bern, Switzerland; University of Southampton, England.
    Leuenberger, Markus
    University of Bern, Switzerland.
    Rinta, Paeivi
    University of Bern, Switzerland; University of Bern, Switzerland.
    Stoetter, Tabea
    University of Bern, Switzerland; University of Bern, Switzerland.
    Heiri, Oliver
    University of Bern, Switzerland; University of Bern, Switzerland.
    The stable carbon isotopic composition of Daphnia ephippia in small, temperate lakes reflects in-lake methane availability2015In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, no 3, p. 1064-1075Article in journal (Refereed)
    Abstract [en]

    Daphnia can ingest methane-oxidizing bacteria and incorporate methanogenic carbon into their biomass, leading to low stable carbon isotope ratios (expressed as delta C-13 values) of their tissue. Therefore, delta C-13 analysis of Daphnia resting eggs (ephippia) in lake sediment records can potentially be used to reconstruct past in-lake availability of methane (CH4). However, detailed multilake studies demonstrating that delta C-13 values of recently deposited Daphnia ephippia (delta C-13(ephippia)) are systematically related to in-lake CH4 concentrations ([CH4](aq)) are still missing. We measured delta C-13(ephippia) from surface sediments of 15 small lakes in Europe, and compared these values with late-summer [CH4](aq). delta C-13(ephippia) ranged from -51.6 parts per thousand to -25.9 parts per thousand, and was strongly correlated with [CH4](aq) in the surface water and above the sediment (r -0.73 and -0.77, respectively), whereas a negative rather than the expected positive correlation was found with delta C-13 values of carbon dioxide (CO2) (r -0.54), and no correlation was observed with [CO2](aq). At eight sites, offsets between delta(13) C-CO2 and delta C-13(ephippia) exceeded offsets between delta C-13(CO2) and delta C-13(algae) reported in literature. delta C-13(ephippia) was positively correlated with delta C-13 values of sedimentary organic matter (r 0.54), but up to 20.7 parts per thousand lower in all except one of the lakes (average -6.1 parts per thousand). We conclude that incorporation of methanogenic carbon prior to ephippia formation must have been widespread by Daphnia in our study lakes, especially those with high [CH4](aq). Our results suggest a systematic relationship between delta C-13(ephippia) values and [CH4](aq) in small temperate lakes, and that delta C-13(ephippia) analysis on sediment records may provide insights into past changes in in-lake [CH4](aq).

  • 16.
    von Wachenfeldt, E.
    et al.
    Uppsala University.
    Sobek, S.
    Swiss Federal Institute of Technology Zurich .
    Bastviken, D.
    Stockholm University.
    Tranvik, L. J.
    Uppsala University.
    Linking allochthonous dissolved organic matter and boreal lake sediment carbon sequestration: The role of light-mediated flocculation2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Limnology and Oceanography, Vol. 53, no 6, p. 2416-2426Article in journal (Refereed)
    Abstract [en]

    We measured flocculation of dissolved organic carbon (DOC) in the water from a humic lake (DOC = 14.9 mg C L-1) and from an adjacent mire (DOC = 25.7 mg C L-1), in in situ enclosure experiments with different light regimes. Light stimulated the formation of organic particles in both waters, and organic particle formation was observed at all incubation depths, even in the dark controls. Production of phytoplankton biomass was negligible, and allochthonous DOC was the most important precursor of the sinking particles. 8-22% and 25-60% of the loss of DOC in lake and mire water, respectively, could be accounted for by flocculation. Depth-integrated flocculation based on the enclosure experiments was 14.7 mg C m(-2) d(-1). Lake-water DOC concentration and water color has been increasing during the last decade, and sediment trap studies show that gross sedimentation of organic carbon also increased. Thus flocculation of allochthonous DOC, stimulated by light, constitutes a pathway for the sequestration of carbon in lake sediments.

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