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  • 1. Algesten, Grete
    et al.
    Brydsten, Lars
    Jonsson, Per
    Kortelainen, Pirkko
    Löfgren, Stefan
    Rahm, Lars
    Räike, Antti
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution.
    Wikner, Johan
    Jansson, Mats
    Organic carbon budget for the Gulf of Bothnia2006In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 63, no 3-4, p. 155-161Article in journal (Refereed)
    Abstract [en]

    We calculated input of organic carbon to the unproductive, brackish water basin of the Gulf of Bothnia from rivers, point sources and the atmosphere. We also calculated the net exchange of organic carbon between the Gulf of Bothnia and the adjacent marine system, the Baltic Proper. We compared the input with sinks for organic carbon; permanent incorporation in sediments and mineralization and subsequent evasion of CO2 to the atmosphere. The major fluxes were riverine input (1500 Gg C year(-1)), exchange with the Baltic Proper (depending on which of several possible DOC concentration differences between the basins that was used in the calculation, the flux varied between an outflow of 466 and an input of 950 Gg C year(-1)), sediment burial (1100 Gg C year) and evasion to the atmosphere (3610 Gg C year(-1)). The largest single net flux was the emission of CO2 to the atmosphere, mainly caused by bacterial mineralization of organic carbon. Input and output did not match in our budget which we ascribe uncertainties in the calculation of the exchange of organic carbon between the Gulf of Bothnia and the Baltic Proper, and the fact that CO2 emission, which in our calculation represented 1 year (2002) may have been overestimated in comparison with long-term means. We conclude that net heterotrophy of the Gulf of Bothnia was due to input of organic carbon from both the catchment and from the Baltic Proper and that the future degree of net heterotrophy will be sensible to both catchment export of organic carbon and to the ongoing eutrophication of the Baltic Proper.

  • 2. Algesten, Grete
    et al.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Bergström, Ann-Kristin
    Jonsson, Anders
    Tranvik, Lars J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Jansson, Mats
    Contribution of sediment respiration to summer CO2 emission from low productive boreal and subarctic lakes2005In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 50, no 4, p. 529-535Article in journal (Refereed)
    Abstract [en]

    We measured sediment production of carbon dioxide (CO2) and methane (CH4) and the net flux of CO2 across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were made in situ under ambient light conditions. The flux of CO2 between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m−2 day−1 from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated to dissolved organic carbon (DOC) concentration in the water (r 2 = 0.61). The net flux of CO2 across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed layer (r 2 = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration. Lakes with DOC concentrations <5.6 mg L−1 had net consumption of CO2 in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic (<2.6 mg L−1) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources.

  • 3. Algesten, Grete
    et al.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Bergström, Ann-Kristin
    Ågren, Anneli
    Tranvik, Lars J.
    Jansson, Mats
    Role of lakes for organic carbon cycling in the boreal zone2004In: Global Change Biology, Vol. 10, p. 141-147Article in journal (Refereed)
  • 4. Algesten, Grete
    et al.
    Wikner, Johan
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology. Limnologi.
    Tranvik, Lars J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology. Limnologi.
    Jansson, Mats
    Seasonal variation of CO2 saturation in the Gulf of Bothnia: indications of marine net heterotrophy2004In: Global Biogeochemical Cycles, ISSN 1944-9224 EISSN, Vol. 18, no 4, p. GB4021-Article in journal (Refereed)
    Abstract [en]

    [1] Seasonal variation of pCO2 and primary and bacterioplankton production were measured in the Gulf of Bothnia during an annual cycle. Surface water was supersaturated with CO2 on an annual basis, indicating net heterotrophy and a source of CO2 to the atmosphere. However, the Gulf of Bothnia oscillated between being a sink and a source of CO2 over the studied period, largely decided by temporal variation in bacterial respiration (BR) and primary production (PP) in the water column above the pycnocline. The calculated annual respiration-production balance (BR-PP) was very similar to the estimated CO2 emission from the Gulf of Bothnia, which indicates that these processes were major determinants of the exchange of CO2 between water and atmosphere. The southern basin (the Bothnian Sea) had a lower net release of CO2 to the atmosphere than the northern Bothnian Bay (7.1 and 9.7 mmol C m−2 d−1, respectively), due to higher primary production, which to a larger extent balanced respiration in this basin.

  • 5.
    Almeida, Rafael M.
    et al.
    Cornell University, USA.
    Paranaíba, José R.
    Federal University of Juiz de Fora, Brazil.
    Barbosa, Ícaro
    Federal University of Juiz de Fora, Brazil.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kosten, Sarian
    University Nijmegen, The Netherlands.
    Linkhorst, Annika
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Mendonça, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Federal University of Juiz de Fora, Brazil.
    Quadra, Gabrielle
    Federal University of Juiz de Fora, Brazil.
    Roland, Fábio
    Federal University of Juiz de Fora, Brazil.
    Barros, Nathan
    Federal University of Juiz de Fora, Brazil.
    Carbon dioxide emission from drawdown areas of a Brazilian reservoir is linked to surrounding land cover2019In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 81, article id 68Article in journal (Refereed)
    Abstract [en]

    Reservoir sediments exposed to air due to water level fluctuations are strong sources of atmospheric carbon dioxide (CO2). The spatial variability of CO2 fluxes from these drawdown areas are still poorly understood. In a reservoir in southeastern Brazil, we investigated whether CO2 emissions from drawdown areas vary as a function of neighboring land cover types and assessed the magnitude of CO2 fluxes from drawdown areas in relation to nearby water surface. Exposed sediments near forestland (average = 2733 mg C m−2 day−1) emitted more CO2 than exposed sediments near grassland (average = 1261 mg C m−2 day−1), congruent with a difference in organic matter content between areas adjacent to forestland (average = 12.2%) and grassland (average = 10.9%). Moisture also had a significant effect on CO2 emission, with dry exposed sediments (average water content: 13.7%) emitting on average 2.5 times more CO2 than wet exposed sediments (average water content: 23.5%). We carried out a systematic comparison with data from the literature, which indicates that CO2 efflux from drawdown areas globally is about an order of magnitude higher than CO2 efflux from adjacent water surfaces, and within the range of CO2 efflux from terrestrial soils. Our findings suggest that emissions from exposed sediments may vary substantially in space, possibly related to organic matter supply from uphill vegetation, and that drawdown areas play a disproportionately important role in total reservoir CO2 emissions with respect to the area they cover.

  • 6. Almeida, Rafael M.
    et al.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Huszar, Vera L. M.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Mendonca, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Barros, Nathan
    Boemer, Gina
    Arantes, Joao Durval, Jr.
    Roland, Fabio
    Phosphorus transport by the largest Amazon tributary (Madeira River, Brazil) and its sensitivity to precipitation and damming2015In: INLAND WATERS, ISSN 2044-2041, E-ISSN 2044-205X, Vol. 5, no 3, p. 275-282Article in journal (Refereed)
    Abstract [en]

    Originating in the Bolivian and Peruvian Andes, the Madeira River is the largest tributary of the Amazon River in terms of discharge. Andean rivers transport large quantities of nutrient-rich suspended sediments and are the main source of phosphorus (P) to the Amazon basin. Here, we show the seasonal variability in concentrations and loads of different P forms (total, particulate, dissolved, and soluble reactive P) in the Madeira River through 8 field campaigns between 2009 and 2011. At our sampling reach in Porto Velho, Brazil, the Madeira River transports similar to 177-247 Gg yr(-1) of P, mostly linked to particles (similar to 85%). Concentrations and loads of all P forms have a maximum at rising waters and a minimum at low waters. Total P concentrations were substantially higher at a given discharge at rising water than at a similar discharge at falling water. The peak of P concentrations matched the peak of rainfall in the upper basin, suggesting an influence of precipitation-driven erosion. Projected precipitation increase in the eastern slopes of the Andes could enhance sediment yield and hence the P transport in the Madeira River. Because most of the P is particulate, however, we hypothesize that the planned proliferation of hydropower dams in the Madeira basin has the potential to reduce P loads substantially, possibly counteracting any precipitation-related increases. In the long term, this could be detrimental to highly productive downstream floodplain forests that are seasonally fertilized with P-rich deposits.

  • 7. Andersson, Eva
    et al.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Comparison of a mass balance and an ecosystem model approach when evaluating the carbon cycling in a lake ecosystem2006In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 35, no 8, p. 476-483Article in journal (Refereed)
  • 8. Bergström, Ann-Kristin
    et al.
    Algesten, Grete
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution. Limnologi. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution. Limnologi. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Jansson, Mats
    Emission of CO2 from hydroelectric reservoirs in northern Sweden2004In: Archiv für Hydrobiologie, Vol. 159, p. 25-42Article in journal (Refereed)
    Abstract [en]

    Carbon dioxide in Swedish hydroelectric reservoirs and natural lakes was studied to assess whether the emission of CO2 from inland waters has increased due to construction of reservoirs, and to gauge how the CO2-emission from reservoirs relates to CO2-emission from combustion plants used for electricity production. We found that emission of CO2 from Swedish reservoirs was low and, at corresponding dissolved organic carbon concentration, similar to the CO2-emission from natural oligotrophic lakes. The total annual CO2-emission due to regulation for the seven rivers included in this study (which collectively represents 87% of the total hydroelectricity production in Sweden) was 50,000 tonnes of CO2. This emission represents 1.5 % of the yearly CO2-emission from Swedish electricity combustion plants. Thus, the CO2-emission from Swedish hydropower is much lower per unit of electricity produced than the emission from Swedish combustion plants. Emission of CO2 from Swedish reservoirs was lower than from most reservoirs in other boreal regions of the world. This difference is probably due to that a majority of the Swedish reservoirs are constructed by damming of natural lakes in alpine and upland boreal forest areas, which results in flooding of comparatively small areas with thin layers of soil organic carbon.

  • 9.
    Cardoso, Simone J.
    et al.
    Laboratory of Aquatic Ecology, Federal University of Juiz de Fora, Juiz de Fora, Brazil.
    Vidal, Luciana O.
    Laboratory of Aquatic Ecology, Federal University of Juiz de Fora, Juiz de Fora, Brazil.
    Mendonça, Raquel F.
    Laboratory of Aquatic Ecology, Federal University of Juiz de Fora, Juiz de Fora, Brazil.
    Tranvik, Lars J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Fábio, Roland
    Laboratory of Aquatic Ecology, Federal University of Juiz de Fora, Juiz de Fora, Brazil.
    Spatial variation of sediment mineralization supports differential CO2 emissions from a tropical hydroelectric reservoir2013In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 4, p. 101-Article in journal (Refereed)
    Abstract [en]

    Substantial amounts of organic matter (OM) from terrestrial ecosystems are buried as sediments in inland waters. It is still unclear to what extent this OM constitutes a sink of carbon, and how much of it is returned to the atmosphere upon mineralization to carbon dioxide (CO2). The construction of reservoirs affects the carbon cycle by increasing OM sedimentation at the regional scale. In this study we determine the OM mineralization in the sediment of three zones (river, transition, and dam) of a tropical hydroelectric reservoir in Brazil as well as identify the composition of the carbon pool available for mineralization. We measured sediment organic carbon mineralization rates and related them to the composition of the OM, bacterial abundance and pCO2 of the surface water of the reservoir. Terrestrial OM was an important substrate for the mineralization. In the river and transition zones most of the OM was allochthonous (56 and 48%, respectively) while the dam zone had the lowest allochthonous contribution (7%). The highest mineralization rates were found in the transition zone (154.80 ± 33.50 mg C m-2 d-1) and the lowest in the dam (51.60 ± 26.80 mg C m-2 d-1). Moreover, mineralization rates were significantly related to bacterial abundance (r2= 0.50, p < 0.001) and pCO2 in the surface water of the reservoir (r2 = 0.73, p < 0.001). The results indicate that allochthonous OM has different contributions to sediment mineralization in the three zones of the reservoir. Further, the sediment mineralization, mediated by heterotrophic bacteria metabolism, significantly contributes to CO2supersaturation in the water column, resulting in higher pCO2 in the river and transition zones in comparison with the dam zone, affecting greenhouse gas emission estimations from hydroelectric reservoirs.

  • 10.
    Chmiel, Hannah Elisa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kokic, Jovana
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Denfeld, Blaize Amber
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Einarsdóttir, Karólina
    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, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Köhler, Birgit
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Isidorova, Anastasija
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Bastviken, David
    Linköping University.
    Ferland, Marie-Ève
    Université du Québec à Montréal, Québec, Canada.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    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 km2), shallow (mean depth 3.4 m), and humic lake (mean DOC concentration 17 mg L-1) in boreal Sweden. Organic carbon (OC) burial and mineralization in sediments were quantified from 210Pb-dated sediment and laboratory sediment incubation experiments, respectively, and upscaled to the entire basin and to one whole year, by using sediment thickness derived 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 from the lake to the atmosphere. Remaining contributions to the CO2 emission were attributed to water column metabolism (31%), photochemical mineralization (6%), and catchment imports via inlet streams and inflow of shallow groundwater (47%). 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 than sediments to lake CO2 emission, and 3) catchment import of C to the lake was greater than lake-internal C cycling. 

  • 11.
    Chmiel, Hannah Elisa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Niggemann, Jutta
    University of Oldenburg, Germany.
    Kokic, Jovana
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Ferland, Marie-Ève
    Université du Québec à Montréal, Québec, Canada.
    Dittmar, Thorsten
    University of Oldenburg, Germany.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Uncoupled organic matter burial and quality in boreal lake sediments over the Holocene2015In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 9, p. 1751-1763Article in journal (Refereed)
    Abstract [en]

    Boreal lake sediments are important sites of organic carbon (OC) storage, which have accumulated substantial amounts of OC over the Holocene epoch; the temporal evolution and the strength of this Holocene carbon (C) sink is, however, not well constrained. In this study we investigated the temporal record of carbon mass accumulation rates (CMARs), and assessed qualitative changes of terrestrially derived OC in the sediment profiles of seven Swedish boreal lakes, in order to evaluate the variability of boreal lake sediments as a C sink over time.

    CMARs were resolved on a short-term (centennial) and long-term (i.e. over millennia of the Holocene) time scale, using radioactive lead (210 Pb) and carbon (14C) isotope dating. Sources and degradation state of terrestrially derived OC were identified and characterized by molecular analyses of lignin phenols.

    We found that CMARs varied substantially on both short-term and long-term scales, and that the variability was mostly attributed to sedimentation rates and uncoupled from the OC content in the sediment profiles. The lignin phenol analyses revealed that woody material from gymnosperms was a dominant and constant OC source to the sediments over the Holocene. Furthermore, lignin-based degradation indices, such as acid-to-aldehyde ratios, indicated that post-depositional degradation in the sediments was very limited on longer time scales, implying that terrestrial OC is stabilized in the sediments on a permanent basis.

  • 12.
    Chmiel, Hannah
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Hofmann, Hilmar
    Environmental Physics Group, Limnological Institute, University of Konstanz, Konstanz, Germany.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Efremova, Tatyana
    Northern Water Problems Institute, Karelian Research Centre, Russian Academy of Sciences, Petrozavodsk, Russia.
    Pasche, Natacha
    Physics of Aquatic Systems Laboratory, Margaretha Kamprad Chair, ENAC, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; Limnology Center, ENAC, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
    Where does the river end ?: Drivers of spatiotemporal variability in CO2 concentration and flux in the inflow area of a large boreal lake2019In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590Article in journal (Refereed)
    Abstract [en]

    River inflow affects the spatiotemporal variability of carbon dioxide (CO2) in the water column of lakes and may locally influence CO2 gas exchange with the atmosphere. However, spatiotemporal CO2 variability at river inflow sites is often unknown leaving estimates of lake‐wide CO2 emission uncertain. Here, we investigated the CO2 concentration and flux variability along a river‐impacted bay and remote sampling locations of Lake Onego. During 3 years, we resolved spatial CO2 gradients between river inflow and central lake and recorded the temporal course of CO2 in the bay from the ice‐covered period to early summer. We found that the river had a major influence on the spatial CO2 variability during ice‐covered periods and contributed ~ 35% to the total amount of CO2 in the bay. The bay was a source of CO2 to the atmosphere at ice‐melt each year emitting 2–15 times the amount as an equally sized area in the central lake. However, there was large interannual variability in the spring CO2 emission from the bay related to differences in discharge and climate that affected the hydrodynamic development of the lake during spring. In early summer, the spatial CO2 variability was unrelated to the river signal but correlated negatively with dissolved oxygen concentrations instead indicating a stronger biological control on CO2. Our study reveals a large variability of CO2 and its drivers at river inflow sites at the seasonal and at the interannual time scale. Understanding these dynamics is essential for predicting lake‐wide CO2 fluxes more accurately under a warming climate.

    The full text will be freely available from 2020-11-20 09:28
  • 13. Del Sontro, Tonya
    et al.
    McGinnis, Daniel F.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Ostrovsky, Ilia
    Wehrli, Bernhard
    Extreme methane emissions from a Swiss hydropower reservoir: contribution from bubbling sediments2010In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 44, no 7, p. 2419-2425Article in journal (Refereed)
    Abstract [en]

    Methane emission pathways and their importance were quantified during a yearlong survey of a temperate hydropower reservoir. Measurements using gas traps indicated very high ebullition rates, but due to the stochastic nature of ebullition a mass balance approach was crucial to deduce system-wide methane sources and losses. Methane diffusion from the sediment was generally low and seasonally stable and did not account for the high concentration of dissolved methane measured in the reservoir discharge. A strong positive correlation between water temperature and the observed dissolved methane concentration enabled us to quantify the dissolved methane addition from bubble dissolution using a system-wide mass balance. Finally, knowing the contribution due to bubble dissolution, we used a bubble model to estimate bubble emission directly to the atmosphere. Our results indicated that the total methane emission from Lake Wohlen was on average >150 mg CH4 m−2 d−1, which is the highest ever documented for a midlatitude reservoir. The substantial temperature-dependent methane emissions discovered in this 90-year-old reservoir indicate that temperate water bodies can be an important but overlooked methane source.

  • 14.
    Denfeld, Blaize A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus B.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sahlée, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kokic, Jovana
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Chmiel, Hannah E.
    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.
    Temporal and spatial carbon dioxide concentration patterns in a small boreal lake in relation to ice cover dynamics2015In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 20, no 6, p. 679-692Article in journal (Refereed)
    Abstract [en]

    Global carbon dioxide (CO2) emission estimates from inland waters commonly neglect the ice-cover season. To account for CO2 accumulation below ice and consequent emissions into the atmosphere at ice-melt we combined automatically-monitored and manually- sampled spatially-distributed CO2 concentration measurements from a small boreal ice-covered lake in Sweden. In early winter, CO2 accumulated continuously below ice, whereas, in late winter, CO2 concentrations remained rather constant. At ice-melt, two CO2 concentration peaks were recorded, the first one reflecting lateral CO2 transport within the upper water column, and the second one reflecting vertical CO2 transport from bottom waters. We estimated that 66%–85% of the total CO2 accumulated in the water below ice left the lake at ice-melt, while the remainder was stored in bottom waters. Our results imply that CO2 accumulation under ice and emissions at ice-melt are more dynamic than previously reported, and thus need to be more accurately integrated into annual CO2 emission estimates from inland waters.

  • 15.
    Denfeld, Blaize
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kortelainen, Pirkko
    Finnish Environment Institute.
    Rantakari, Miitta
    Department of Environmental Sciences, University of Helsinki.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Weyhenmeyer, Gesa
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Regional Variability and Drivers of Below Ice CO2 in Boreal and Subarctic Lakes2016In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 19, no 3, p. 461-476Article in journal (Refereed)
    Abstract [en]

    Northern lakes are ice-covered for considerable portions of the year, where carbon dioxide (CO2) can accumulate below ice, subsequently leading to high CO2 emissions at ice-melt. Current knowledge on the regional control and variability of below ice partial pressure of carbon dioxide (pCO(2)) is lacking, creating a gap in our understanding of how ice cover dynamics affect the CO2 accumulation below ice and therefore CO2 emissions from inland waters during the ice-melt period. To narrow this gap, we identified the drivers of below ice pCO(2) variation across 506 Swedish and Finnish lakes using water chemistry, lake morphometry, catchment characteristics, lake position, and climate variables. We found that lake depth and trophic status were the most important variables explaining variations in below ice pCO(2) across the 506 lakes(.) Together, lake morphometry and water chemistry explained 53% of the site-to-site variation in below ice pCO(2). Regional climate (including ice cover duration) and latitude only explained 7% of the variation in below ice pCO(2). Thus, our results suggest that on a regional scale a shortening of the ice cover period on lakes may not directly affect the accumulation of CO2 below ice but rather indirectly through increased mobility of nutrients and carbon loading to lakes. Thus, given that climate-induced changes are most evident in northern ecosystems, adequately predicting the consequences of a changing climate on future CO2 emission estimates from northern lakes involves monitoring changes not only to ice cover but also to changes in the trophic status of lakes.

  • 16.
    Einarsdóttir, Karólina
    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.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    High terrestrial carbon load via groundwater to a boreal lake dominated by surface water inflow2017In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122, no 1, p. 15-29Article in journal (Refereed)
    Abstract [en]

    The input of dissolved organic and inorganic carbon (DOC and DIC) via direct groundwater seepage to boreal lakes is often assumed to be small in noncarbonaceous areas. However, measurements are rare. We estimated the terrestrial load of DOC, DIC, and methane (CH4) to a small boreal lake for the open water period, on the basis of measured concentrations of carbon species in near-shore groundwater wells and inlet streams, and measured area-specific discharge. The subcatchment directly draining into the lake via groundwater seepage contributed 18% to the total water input during the open water season. Compared to stream and lake water, near-shore groundwater concentrations of DOC were slightly elevated, and groundwater DIC and CH4concentrations were highly elevated. Consequently, direct groundwater seepage contributed 27% to the total DOC load, 64% to the total DIC load, and 96% to the total CH4 load from the catchment to the lake. Groundwater DIC import corresponded only to 5–8% of lake carbon dioxide (CO2) emission. In incubation experiments, we observed higher photochemical DOC loss rates in stream and groundwater samples (18–55% DOC loss upon 72 h UV-A exposure) than in lake water (15% DOC loss) and detected significant DOC flocculation in groundwater samples in both light and dark incubations (2–24% DOC loss). We conclude that even in regions where lake hydrology is dominated by surface water inflow via inlet streams, direct groundwater seepage can represent an important carbon source to boreal lakes, and groundwater DOC may be susceptible to in-lake removal via degradation and flocculation.

  • 17.
    Eugster, W.
    et al.
    ETH Zurich, Institute of Agricultural Sciences.
    DelSontro, T.
    Eawag, Swiss Federal Institute of Aquatic Science and Technology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Eddy covariance flux measurements confirm extreme CH(4) emissions from a Swiss hydropower reservoir and resolve their short-term variability2011In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, no 9, p. 2815-2831Article in journal (Refereed)
    Abstract [en]

    Greenhouse gas budgets quantified via land-surface eddy covariance (EC) flux sites differ significantly from those obtained via inverse modeling. A possible reason for the discrepancy between methods may be our gap in quantitative knowledge of methane (CH(4)) fluxes. In this study we carried out EC flux measurements during two intensive campaigns in summer 2008 to quantify methane flux from a hydropower reservoir and link its temporal variability to environmental driving forces: water temperature and pressure changes (atmospheric and due to changes in lake level). Methane fluxes were extremely high and highly variable, but consistently showed gas efflux from the lake when the wind was approaching the EC sensors across the open water, as confirmed by floating chamber flux measurements. The average flux was 3.8 +/- 0.4 mu g C m(-2) s(-1) (mean +/- SE) with a median of 1.4 mu g C m(-2) s(-1), which is quite high even compared to tropical reservoirs. Floating chamber fluxes from four selected days confirmed such high fluxes with 7.4 +/- 1.3 mu g C m(-2) s(-1). Fluxes increased exponentially with increasing temperatures, but were decreasing exponentially with increasing atmospheric and/or lake level pressure. A multiple regression using lake surface temperatures (0.1 m depth), temperature at depth (10 m deep in front of the dam), atmospheric pressure, and lake level was able to explain 35.4% of the overall variance. This best fit included each variable averaged over a 9-h moving window, plus the respective short-term residuals thereof. We estimate that an annual average of 3% of the particulate organic matter (POM) input via the river is sufficient to sustain these large CH(4) fluxes. To compensate the global warming potential associated with the CH(4) effluxes from this hydropower reservoir a 1.3 to 3.7 times larger terrestrial area with net carbon dioxide uptake is needed if a European-scale compilation of grass-lands, croplands and forests is taken as reference. This indicates the potential relevance of temperate reservoirs and lakes in local and regional greenhouse gas budgets.

  • 18.
    Grasset, Charlotte
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Laboratory of Aquatic Ecology, Department of Biology, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil.
    Abril, Gwenaël
    Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), Muséum National d'Histoire Naturelle, Paris cedex 05, France; Programa de Geoquímica, Universidade Federal Fluminense, Niterói, Rio de Janeiro, Brazil.
    Mendonca, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Laboratory of Aquatic Ecology, Department of Biology, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil.
    Roland, Fabio
    Laboratory of Aquatic Ecology, Department of Biology, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    The transformation of macrophyte-derived organic matter to methane relates to plant water and nutrient contents2019In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 64, no 4, p. 1737-1749Article in journal (Refereed)
    Abstract [en]

    Macrophyte detritus is one of the main sources of organic carbon (OC) in inland waters, and it is potentially available for methane (CH4) production in anoxic bottom waters and sediments. However, the transformation of macrophyte‐derived OC into CH4 has not been studied systematically, thus its extent and relationship with macrophyte characteristics remains uncertain. We performed decomposition experiments of macrophyte detritus from 10 different species at anoxic conditions, in presence and absence of a freshwater sediment, in order to relate the extent and rate of CH4 production to the detritus water content, C/N and C/P ratios. A significant fraction of the macrophyte OC was transformed to CH4 (mean = 7.9%; range = 0–15.0%) during the 59‐d incubation, and the mean total C loss to CO2 and CH4 was 17.3% (range = 1.3–32.7%). The transformation efficiency of macrophyte OC to CH4 was significantly and positively related to the macrophyte water content, and negatively to its C/N and C/P ratios. The presence of sediment increased the transformation efficiency to CH4 from an average of 4.0% (without sediment) to 11.8%, possibly due to physicochemical conditions favorable for CH4 production (low redox potential, buffered pH) or because sediment particles facilitate biofilm formation. The relationship between macrophyte characteristics and CH4 production can be used by future studies to model CH4 emission in systems colonized by macrophytes. Furthermore, this study highlights that the extent to which macrophyte detritus is mixed with sediment also affects CH4 production.

  • 19.
    Grasset, Charlotte
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Laboratory of Aquatic Ecology, Department of Biology, Federal University of Juiz de Fora, Juiz de Fora, Brazil.
    Mendonça, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Federal University of Juiz de Fora, Juiz de Fora, Brazil.
    Villamor Saucedo, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Federal University of Juiz de Fora, Juiz de Fora, Brazil.
    Bastviken, David
    Department of Thematic Studies – Environmental Change, Linköping University, Linköping, Sweden.
    Roland, Fabio
    Federal University of Juiz de Fora, Juiz de Fora, Brazil.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    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 δ13C-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.

  • 20.
    Gudasz, Cristian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Bastviken, David
    Steger, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Premke, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Tranvik, Lars J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Temperature-controlled organic carbon mineralization in lake sediments2010In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 466, no 7305, p. 478-481Article in journal (Refereed)
    Abstract [en]

    Peatlands, soils and the ocean floor are well-recognized as sites of organic carbonaccumulation andrepresentimportant global carbon sinks(1,2). Although the annual burial of organic carbon in lakes and reservoirs exceeds that of ocean sediments(3), these inland waters are components of the global carbon cycle that receive only limited attention(4-6). Of the organic carbon that is being deposited onto the sediments, a certain proportion will be mineralized and the remainder will be buried over geological timescales. Here we assess the relationship between sediment organic carbon mineralization and temperature in a cross-system survey of boreal lakes in Sweden, and with input froma compilation of published data from awide range of lakes that differ with respect to climate, productivity and organic carbon source. We find that the mineralization of organic carbon in lake sediments exhibits a strongly positive relationship with temperature, which suggests that warmer water temperatures lead to more mineralization and less organic carbon burial. Assuming that future organic carbon delivery to the lake sediments will be similar to that under present-day conditions, we estimate that temperature increases following the latest scenarios presented by the Intergovernmental Panel on Climate Change(7) could result in a 4-27 per cent (0.9-6.4 Tg Cyr(-1)) decrease in annual organic carbon burial in boreal lakes.

  • 21.
    Gudasz, Cristian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Bastviken, David
    The Department of Thematic Studies - Water and Environmental Studies Linköping university.
    Koehler, Birgit
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Tranvik, Lars J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Mineralization of organic carbon in lake sediments: temperature sensitivity and a comparison to soilsManuscript (preprint) (Other academic)
    Abstract [en]

    Temperature alone can explain a great amount of variation in sediment organic carbon (OC) mineralization. Studies on decomposition of soil OC suggest that the temperature sensitivity is different for the decomposition of labile and recalcitrant OC, but lake sediments with different contributions of labile and recalcitrant components have been reported to show similar temperature sensitivities. Sediment mineralization is typically measured in short-term incubations. However, whether the mineralization of OC in sediments dominated by recalcitrant and labile OC have different temperature sensitivities at the longer term is not clear. Here we show that during 5 months of continuous incubation of contrasting boreal lake sediments, sediment mineralization was strongly dependent on temperature and OC quality/origin but temperature sensitivity was similar across lakes and over time. Sediment mineralization showed low overall rates in spite of low apparent activation energy (Ea) compared to published rates of soil and litter mineralization. The fraction of the total OC pool that was lost during 5 months varied between 0.4 and 14%. The non-buried sediment OC pool was lost slowly, with apparent turnover times between 2.5 and 32 years. At a large scale, lake sediments, by showing lower mineralization rates than soils are more effective as carbon sinks.

     

  • 22.
    Gudasz, Cristian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Bastviken, David
    Köhler, Birgit
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Tranvik, Lars J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Temperature sensitivity of organic carbon mineralization in contrasting lake sediments2015In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 7, p. 1215-1225Article in journal (Refereed)
    Abstract [en]

    Temperature alone explains a great amount of variation in sediment organic carbon (OC) mineralization. Studies on decomposition of soil OC suggest that (1) temperature sensitivity differs between the fast and slowly decomposition OC and (2) over time, decreasing soil respiration is coupled with increase in temperature sensitivity. In lakes, autochthonous and allochthonous OC sources are generally regarded as fast and slowly decomposing OC, respectively. Lake sediments with different contributions of allochthonous and autochthonous components, however, showed similar temperature sensitivity in short-term incubation experiments. Whether the mineralization of OC in lake sediments dominated by allochthonous or autochthonous OC has different temperature sensitivity in the longer term has not been addressed. We incubated sediments from two boreal lakes that had contrasting OC origin (allochthonous versus autochthonous), and OC characteristics (C/N ratios of 21 and 10) at 1, 3, 5, 8, 13, and 21 degrees C for five months. Compared to soil and litter mineralization, sediment OC mineralization rates were low in spite of low apparent activation energy (E-a). The fraction of the total OC pool that was lost during five months varied between 0.4 and 14.8%. We estimate that the sediment OC pool not becoming long-term preserved was degraded with average apparent turnover times between 3 and 32years. While OC mineralization was strongly dependent on temperature as well as on OC composition and origin, temperature sensitivity was similar across lakes and over time. We suggest that the temperature sensitivity of OC mineralization in lake sediments is similar across systems within the relevant seasonal scales of OC supply and degradation.

  • 23. Harrison, John A.
    et al.
    Barros, Nathan
    Bastviken, David
    Deemer, Bridget
    Evans, Christopher
    Grinham, Alistair
    Harby, Atle
    Lovelock, Catherine
    Peacock, Michael
    Prairie, Yves
    Sherman, Bradford
    Sobek, Sebastian
    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.
    Dams: weigh pros and cons case by case2019In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 568, no 7751, p. 171-171Article in journal (Other (popular science, discussion, etc.))
  • 24. Hastie, Adam
    et al.
    Lauerwald, Ronny
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Verpoorter, Charles
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Univ Lille, Univ Littoral Cole Opale, CNRS, LOG,UMR 8187, Wimereux, France.
    Regnier, Pierre
    CO2 evasion from boreal lakes: Revised estimate, drivers of spatial variability, and future projections2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 2, p. 711-728Article in journal (Refereed)
    Abstract [en]

    Lakes (including reservoirs) are an important component of the global carbon (C) cycle, as acknowledged by the 5th assessment report of the IPCC. In the context of lakes, the boreal region is disproportionately important contributing to 27% of the worldwide lake area, despite representing just 14% of global land surface area. In this study, we used a statistical approach to derive a prediction equation for the partial pressure of CO2 (pCO2) in lakes as a function of lake area, terrestrial net primary productivity (NPP) and precipitation (r2 = 0.56), and to create the first high resolution, circumboreal map (0.5) of lake pCO2. The map of pCO2 was combined with lake area from the recently published GLOWABO database and three different estimates of the gas transfer velocity k to produce a resulting map of CO2 evasion (FCO2). For the boreal region we estimate an average, lake area weighted,pCO2 of 966 (678- 1325) μatm and a total FCO2 of 189 (74-347) Tg C yr−1, and evaluate the corresponding uncertainties based on Monte Carlo simulation. Our estimate of FCO2 is approximately twofold greater than previous estimates, as a result of methodological and data source differences. We use our results along with published estimates of the other C fluxes through inland waters to derive a C budget for the boreal region, and find that FCO2 from lakes is the most significant flux of the land-ocean aquatic continuum, and of a similar magnitude as emissions from forest fires. Using the model and applying it to spatially resolved projections of terrestrial NPP and precipitation while keeping everything else constant, we predict a 107% increase in boreal lake FCO2 under emission scenario RCP8.5 by 2100. Our projections are largely driven by increases in terrestrial NPP over the same period, showing the very close connection between the terrestrial and aquatic C cycle.

  • 25.
    Isidorova, Anastasija
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Bravo, Andrea G.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Riise, Gunnhild
    Norwegian Univ Life Sci, Dept Environm Sci, Akershus, Norway..
    Bouchet, Sylvain
    Umea Univ, Dept Chem, Umea, Sweden..
    Björn, Erik
    Umea Univ, Dept Chem, Umea, Sweden..
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    The effect of lake browning and respiration mode on the burial and fate of carbon and mercury in the sediment of two boreal lakes2016In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 1, p. 233-245Article in journal (Refereed)
    Abstract [en]

    In many northern temperate regions, the water color of lakes has increased over the past decades (lake browning), probably caused by an increased export of dissolved organic matter from soils. We investigated if the increase in water color in two lakes in Norway has resulted in increased burial of organic carbon (OC) and mercury (Hg) in the sediments and if the Hg was prone to methylation. Lake Solbergvann experienced a threefold water color increase, and OC burial increased approximately twofold concomitant to the water color increase. This lake had prolonged periods of anoxic bottom water, and anoxic OC mineralization rates were only about half of the oxic OC mineralization rates (7.7 and 17.5g C m(-2)yr(-1), respectively), contributing to an efficient OC burial. In Lake Elvaga, where water color increase was only approximately twofold and bottom water was oxygenated, no recent increase in OC burial could be observed. Hg burial increased strongly in both lakes (threefold and 1.6-fold in Lake Solbergvann and Lake Elvaga, respectively), again concomitant to the recent water color increase. The proportion of methylated Hg (MeHg) in surficial sediment was 1 order of magnitude higher in Lake Elvaga (up to 6% MeHg) than in Lake Solbergvann (0.2-0.6% MeHg), probably related to the different oxygenation regimes. We conclude that lake browning can result in increased OC and Hg burial in lake sediments, but the extent of browning and the dominating mode of sediment respiration (aerobic or anaerobic) strongly affect burial and fate of OC and Hg in sediments.

  • 26.
    Isidorova, Anastasija
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Grasset, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Mendonca, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Methane formation in tropical reservoirs predicted from sediment age and nitrogen2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 11017Article in journal (Refereed)
    Abstract [en]

    Freshwater reservoirs, in particular tropical ones, are an important source of methane (CH4) to the atmosphere, but current estimates are uncertain. The CH4 emitted from reservoirs is microbially produced in their sediments, but at present, the rate of CH4 formation in reservoir sediments cannot be predicted from sediment characteristics, limiting our understanding of reservoir CH4 emission. Here we show through a long-term incubation experiment that the CH4 formation rate in sediments of widely different tropical reservoirs can be predicted from sediment age and total nitrogen concentration. CH4 formation occurs predominantly in sediment layers younger than 6-12 years and beyond these layers sediment organic carbon may be considered effectively buried. Hence mitigating reservoir CH4 emission via improving nutrient management and thus reducing organic matter supply to sediments is within reach. Our model of sediment CH4 formation represents a first step towards constraining reservoir CH4 emission from sediment characteristics.

  • 27.
    Isidorova, Anastasija
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Mendonca, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Univ Fed Juiz de Fora, Dept Biol, Lab Aquat Ecol, Juiz De Fora, Brazil.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Reduced Mineralization of Terrestrial OC in Anoxic Sediment Suggests Enhanced Burial Efficiency in Reservoirs Compared to Other Depositional Environments2019In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 124, no 3, p. 678-688Article in journal (Refereed)
    Abstract [en]

    Freshwater reservoirs are important sites of organic carbon (OC) burial, but the extent to which reservoir OC burial is a new anthropogenic carbon sink is currently unclear. While burial of aquatic OC (by, e.g., phytoplankton) in reservoirs may count as a new C sink, the burial of terrestrial OC in reservoirs constitutes a new C sink only if the burial is more efficient in reservoirs than in other depositional environments. We carried out incubation experiments that mimicked the environmental conditions of different depositional environments along the land‐sea continuum (oxic and anoxic freshwater, oxic and anoxic seawater, oxic river bedload, and atmosphere‐exposed floodplain) to investigate whether reservoirs bury OC more efficiently compared to other depositional environments. For sediment OC predominantly of terrestrial origin, OC degradation rates were significantly lower, by a factor of 2, at anoxic freshwater and saltwater conditions compared to oxic freshwater and saltwater, river, and floodplain conditions. However, the transformation of predominantly terrestrial OC to methane was one order of magnitude higher in anoxic freshwater than at other conditions. For sediment OC predominantly of aquatic origin, OC degradation rates were uniformly high at all conditions, implying equally low burial efficiency of aquatic OC (76% C loss in 57 days). Since anoxia is more common in reservoirs than in the coastal ocean, these results suggest that reservoirs are a depositional environment in which terrestrial OC is prone to become buried at higher efficiency than in the ocean but where also the terrestrial OC most efficiently is transformed to methane.

  • 28. Jonsson, Anders
    et al.
    Algesten, Grete
    Bertgström, Ann-Kristin
    Bishop, Kevin
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Jansson, Mats
    Integrating aquatic carbon fluxes in a boreal catchment carbon budget2007In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 334, no 1-2, p. 141-150Article in journal (Refereed)
    Abstract [en]

    In this paper, we assess the extent to which the export of terrestrially fixed carbon to aquatic systems and the aquatic metabolism of this carbon affect the overall accumulation of organic carbon in a boreal catchment. We estimated the contribution of stocks and processes in aquatic environments to the carbon balance of a boreal catchment in northern Sweden. We used published data concerning the net ecosystem exchange (NEE) of CO2 in terrestrial environments, and calculations of loss of terrestrial carbon to surface water and the turnover of terrestrial carbon in aquatic systems. The NEE of terrestrial environments was estimated to be 139 g C/m2 of catchment area per year. The export of terrestrially fixed carbon to aquatic systems was 8.6 g C/m2/yr, resulting in a net accumulation of organic carbon in terrestrial systems of 131 g C/m2/yr. Almost 45% of the terrestrial export was mineralized in streams and lakes and evaded as CO2, while most of the remaining (approximately 55%) terrestrial export was transported to the sea as organic carbon or as dissolved inorganic carbon emanating from soil respiration. The sedimentation of organic carbon and input of organic carbon via aquatic primary production were insignificant when compared to the mineralization and river transport of terrestrial organic carbon. Aquatic fluxes were small compared to the terrestrial NEE, which we consider to be largely a consequence of the studied catchment being subject to intensive forestry resulting in a large annual accumulation of carbon in growing tree biomass.

  • 29.
    Kokic, Jovana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sahlée, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Brand, Andreas
    Swiss Fed Inst Aquat Sci & Technol, Surface Waters Res & Management, Eawag, Kastanienbaum, Switzerland.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Low sediment-water gas exchange in a small boreal lake2016In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 9, p. 2493-2505Article in journal (Refereed)
    Abstract [en]

    Boreal lake sediments are carbon sources by producing CO2. CO2 flux from sediments is partly controlled by turbulence in the water column, which is not given the same attention as CO2production rates in current estimates of CO2 fluxes from sediments. We quantified the in situ CO2flux across the sediment-water interface in a small (0.07 km2) lake in Sweden by measuring the in situ O2 flux with the Eddy Correlation (EC) method and using the apparent respiratory quotient (CO2 production:O2 consumption) derived from sediment incubations. We demonstrate that median CO2 flux estimated by EC was ~70% smaller than estimated by sediment incubations with artificial water mixing (1.0 × 10−2 and 3.6 × 10−2 µmol C m−2 s−1, respectively). Additionally, we show that inducing artificial mixing of supernatant water in the incubation experiment has a positive effect on observed fluxes, enhancing CO2 flux by ~30% compared to not mixing supernatant water. We suggest that the difference between the methods is due to the strong artificial water mixing in sediment incubations compared to the turbulent mixing in this small lake. Additionally, low O2 supply to sediment aerobic heterotrophic microbes during extended periods of low water currents can inhibit respiration and thus CO2 production. These findings suggest that the sediment contribution to total lake CO2 emission might currently be overestimated for small boreal lakes. Care should be taken when upscaling sediment CO2 flux derived from incubation experiments to entire basins of small lakes, as incubation experiments are unlikely to accurately mimic in situ bottom water currents and gas exchange.

  • 30.
    Kokic, Jovana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sahlée, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Vachon, Dominic
    Umeå Univ, Dept Ecol & Environm Sci, Umeå, Sweden.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    High spatial variability of gas transfer velocity in streams revealed by turbulence measurements2018In: INLAND WATERS, ISSN 2044-2041, E-ISSN 2044-205X, Vol. 8, no 4, p. 461-473Article in journal (Refereed)
    Abstract [en]

    Streams are major sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere, but current large-scale estimates are associated with high uncertainties because knowledge concerning the spatiotemporal control on stream emissions is limited. One of the largest uncertainties derives from the choice of gas transfer velocity (k600), which describes the physical efficiency of gas exchange across the water–atmosphere interface. This study therefore explored the variability in k600 and subsequent CO2 and CH4 emission rates within and across streams of different stream order (SO). We conducted, for the first time in streams, direct turbulence measurements using an acoustic Doppler velocimeter (ADV) to determine the spatial variability in k600 across a variety of scales with a consistent methodology. The results show high spatial variability in k600 and corresponding CO2 and CH4 emissions at small spatial scales, both within stream reaches and across SO, especially during high discharge. The k600 was positively related to current velocity and Reynolds number. By contrast, no clear relationship was found between k600 and specific stream characteristics such as width and depth, which are parameters often used in empirical models of k600. Improved understanding of the small-scale variability in the physical properties along streams, especially during high discharge, is therefore an important step to reduce the uncertainty in existing gas transfer models and emissions for stream systems. The ADV method was a useful tool for revealing spatial variability in this work, but it needs further development. We recommend that future studies conduct measurements over shorter time periods (e.g., 10–15 min instead of 40 min) and at more sites across the reach of interest, and thereby derive more reliable mean-reach k600 as well as more information about controls on the spatial variability in k600

  • 31.
    Kokic, Jovana
    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, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Chmiel, Hannah
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Denfeld, Blaize
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Carbon dioxide evasion from headwater systems strongly contributes to the total export of carbon from a small boreal lake catchment2015In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 1, p. 13-28Article in journal (Refereed)
    Abstract [en]

    Inland waters are hotspots for carbon (C) cycling and therefore important for landscape C budgets. Small streams and lakes are particularly important; however, quantifying C fluxes is difficult and has rarely been done for the entire aquatic continuum, composed of connected streams and lakes within the same catchment. We investigated carbon dioxide (CO2) evasion and fluvial fluxes of dissolved inorganic carbon and dissolved organic carbon (DIC and DOC) in stream and lake systems within the 2.3km(2) catchment of a small boreal lake. Our results show pronounced spatial and temporal variability in C fluxes even at a small spatial scale. C loss from the catchment through CO2 evasion from headwaters for the total open water-sampling period was 9.7g C m(-2) catchment, dominating the total catchment C loss (including CO2 evasion, DIC, and DOC export from the lake, which were 2.7, 0.2, and 5.2g C m(-2) catchment, respectively). Aquatic CO2 evasion was dominated by headwater streams that occupy similar to 0.1% of the catchment but contributed 65% to the total aquatic CO2 evasion from the catchment. The importance of streams was mainly an effect of the higher gas transfer velocities than compared to lakes (median, 67 and 2.2cmh(-1), respectively). Accurately estimating the contribution of C fluxes from headwater streams, particularly the temporal and spatial dynamics in their gas transfer velocity, is key to landscape-scale C budgets. This study demonstrates that CO2 evasion from headwaters can be the major pathway of C loss from boreal catchments, even at a small spatial scale.

  • 32.
    Kosten, Sarian
    et al.
    Radboud Univ Nijmegen, Inst Water & Wetland Res, Dept Aquat Ecol & Environm Biol, Nijmegen, Netherlands.
    van den Berg, Sanne
    Radboud Univ Nijmegen, Inst Water & Wetland Res, Dept Aquat Ecol & Environm Biol, Nijmegen, Netherlands; Wageningen Univ, Dept Aquat Ecol & Water Qual Management, Wageningen, Netherlands.
    Mendonça, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Univ Fed Juiz de Fora, Biol Dept, Juiz De Fora, Brazil.
    Paranaíba, José R.
    Univ Fed Juiz de Fora, Biol Dept, Juiz De Fora, Brazil.
    Roland, Fabio
    Univ Fed Juiz de Fora, Biol Dept, Juiz De Fora, Brazil.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Van Den Hoek, Jamon
    Oregon State Univ, Coll Earth Ocean & Atmospher Sci, Geog & Geospatial Sci, Corvallis, OR 97331 USA.
    Barros, Nathan
    Univ Fed Juiz de Fora, Biol Dept, Juiz De Fora, Brazil.
    Extreme drought boosts CO2 and CH4 emissions from reservoir drawdown areas2018In: INLAND WATERS, ISSN 2044-2041, E-ISSN 2044-205X, Vol. 8, no 3, p. 329-340Article in journal (Refereed)
    Abstract [en]

    Although previous studies suggest that greenhouse gas (GHG) emissions from reservoir sediment exposed to the atmosphere during drought may be substantial, this process has not been rigorously quantified. Here we determined carbon dioxide (CO 2) and methane (CH 4) emissions from sediment cores exposed to a drying and rewetting cycle. We found a strong temporal variation in GHG emissions with peaks when the sediment was drained (C emissions from permanently wet sediment and drained sediments were, respectively, 251 and 1646 mg m −2 d −1 for CO 2 and 0.8 and 547.4 mg m −2 d −1 for CH 4) and then again during rewetting (C emissions from permanently wet sediment and rewetted sediments were, respectively, 456 and 1725mg m −2 d −1 for CO 2 and 1.3 and 3.1 mg m −2 d −1 for CH 4). To gain insight into the importance of these emissions at a regional scale, we used Landsat satellite imagery to upscale our results to all Brazilian reservoirs. We found that during the extreme drought of 2014-2015, an additional 1299 km 2 of sediment was exposed, resulting in an estimated emission of 8.5 × 10 11 g of CO 2-eq during the first 15 d after the overlying water disappeared and in the first 33 d after rewetting, the same order of magnitude as the year-round GHG emissions of large (∼mean surface water area 454 km 2) Brazilian reservoirs, excluding the emissions from the draw-down zone. Our estimate, however, has high uncertainty, with actual emissions likely higher. We therefore argue that the effects of drought on reservoir GHG emissions merits further study, especially because climate models indicate an increase in the frequency of severe droughts in the future. We recommend incorporation of emissions during drying and rewetting into GHG budgets of reservoirs to improve regional GHG emission estimates and to enable comparison between GHG emissions from hydroelectric and other electricity sources. We also emphasize that peak emissions at the onset of drought and the later rewetting should be quantified to obtain reliable emission estimates. ARTICLE HISTORY

  • 33. Kutser, T.,
    et al.
    Pierson,, D.,
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution. Limnologi. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Kallio,, K.,
    Reinart, A.,
    Sobek, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution. Limnologi. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Mapping lake CDOM by satellite remote sensing.2005In: Remote Sensing of Environment ., no 94:, p. 535-540Article in journal (Refereed)
  • 34. Kutser, Tiit
    et al.
    Pierson, Donald C.
    Tranvik, L.J.
    Reinart, Anu
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kallio, Kari Y.
    Using satellite remote sensing to estimate the colored dissolved organic matter absorption coefficient in lakes2005In: Ecosystems, Vol. 8, p. 709-720Article in journal (Refereed)
  • 35.
    Langenheder, Silke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Changes in bacterial community composition along a solar radiation gradient in humic waters2006In: AQUATIC SCIENCES, Vol. 68, no 4, p. 415-424Article in journal (Refereed)
  • 36.
    Linkhorst, Annika
    et al.
    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.
    DelSontro, Tonya
    Aquatic Physics Group, Department F.-A. Forel for Environmental and Aquatic Sciences, Faculty of Science, University of Geneva, Geneva, Switzerland.
    Millen Azevedo, Guilherme
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Juiz de Fora, Brazil .
    Barros, Nathan
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Juiz de Fora, Brazil .
    Mendonça, Raquel
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Juiz de Fora, Brazil .
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Comparing methane ebullition variability across space and time in a Brazilian reservoirIn: Article in journal (Other academic)
  • 37.
    Linkhorst, Annika
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Paranaíba, José
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Brazil.
    Barros, Nathan
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Brazil.
    DelSontro, Tonya
    Aquatic Physics Group, Department F.-A. Forel for Environmental and Aquatic Sciences, Faculty of Science, University of Geneva, Switzerland.
    Mendonça, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Brazil.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Deconstructing carbon emission pathways of a diel cycle from four tropical reservoirsIn: Article in journal (Refereed)
  • 38.
    Linkhorst, Annika
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Paranaíba, José
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Brazil .
    Mendonça, Raquel
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Brazil .
    Rudberg, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    DelSontro, Tonya
    Aquatic Physics Group, Department F.-A. Forel for Environmental and Aquatic Sciences, Faculty of Science, University of Geneva, Switzerland.
    Barros, Nathan
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Brazil .
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Upscaling spatially-resolved methane ebullition measurements in two contrasting tropical reservoirsManuscript (preprint) (Other academic)
  • 39. Marotta, H.
    et al.
    Duarte, C. M.
    Sobek, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Enrich-Prast, A.
    Large CO2 disequilibria in tropical lakes2009In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 23Article in journal (Refereed)
    Abstract [en]

    On the basis of a broad compilation of data on pCO(2) in surface waters, we show tropical lakes to be, on average, far more supersaturated and variable in CO2 (geometric mean +/- SE pCO(2) = 1804 +/- 35 mu atm) than temperate lakes (1070 +/- 6 mu atm). There was a significant negative relationship between pCO(2) and latitude, resulting in an average decrease of pCO(2) by 2.8 +/- 0.5% per degree latitude. In addition, we found a general positive relationship between pCO(2) and water temperature across lakes involving an average increase (+/-SE) in 6.7 +/- 0.8% per degrees C. A conservative annual efflux from global lakes to the atmosphere was reestimated to 0.44 Gt C. Our results show tropical lakes maintain large CO2 disequilibria with the atmosphere, playing a disproportionate and variable role in the flux of CO between lakes and the atmosphere, thereby being a significant component of the global C cycle.

  • 40. Mendonca, Raquel
    et al.
    Kosten, Sarian
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Barros, Nathan
    Cole, Jonathan J.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Roland, Fabio
    Hydroelectric carbon sequestration2012In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 5, no 12, p. 838-840Article in journal (Refereed)
  • 41.
    Mendonca, Raquel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kosten, Sarian
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Barros, Nathan
    J Cole, Jonathan
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Roland, Fábio
    Hydroelectric carbon sequestration2012In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 5, p. 838-840Article in journal (Refereed)
  • 42.
    Mendonca, Raquel
    et al.
    Univ Fed Juiz de Fora, Aquat Ecol Lab, BR-36036900 Juiz De Fora, MG, Brazil; Wageningen Univ, Dept Aquat Ecol & Water Qual Management, NL-6700 AP Wageningen, Netherlands.
    Kosten, Sarian
    Wageningen Univ, Dept Aquat Ecol & Water Qual Management, NL-6700 AP Wageningen, Netherlands; Leibniz Inst Freshwater Ecol & Inland Fisheries I, Berlin, Germany; Radboud Univ Nijmegen, Inst Water & Wetland Res, Dept Aquat Ecol & Environm Biol, NL-6525 ED Nijmegen, Netherlands.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Cole, Jonathan J.
    Cary Inst Ecosyst Studies, Millbrook, NY USA.
    Bastos, Alex
    Univ Fed Espirito Santo, Dept Oceanog & Ecol, Vitoria, ES, Brazil.
    Albuquerque, Ana Luiza
    Univ Fed Fluminense, Dept Geoquim, Niteroi, RJ, Brazil.
    Cardoso, Simone J.
    Univ Fed Juiz de Fora, Aquat Ecol Lab, BR-36036900 Juiz De Fora, MG, Brazil.
    Roland, Fábio
    Univ Fed Juiz de Fora, Aquat Ecol Lab, BR-36036900 Juiz De Fora, MG, Brazil.
    Carbon Sequestration in a Large Hydroelectric Reservoir: An Integrative Seismic Approach2014In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 17, no 3, p. 430-441Article in journal (Refereed)
    Abstract [en]

    Artificial reservoirs likely accumulate more carbon than natural lakes due to their unusually high sedimentation rates. Nevertheless, the actual magnitude of carbon accumulating in reservoirs is poorly known due to a lack of whole-system studies of carbon burial. We determined the organic carbon (OC) burial rate and the total OC stock in the sediments of a tropical hydroelectric reservoir by combining a seismic survey with sediment core sampling. Our data suggest that no sediment accumulation occurs along the margins of the reservoir and that irregular bottom morphology leads to irregular sediment deposition. Such heterogeneous sedimentation resulted in high spatial variation in OC burial-from 0 to 209 g C m(-2) y(-1). Based on a regression between sediment accumulation and OC burial rates (R (2) = 0.94), and on the mean reservoir sediment accumulation rate (0.51 cm y(-1), from the seismic survey), the whole-reservoir OC burial rate was estimated at 42.2 g C m(-2) y(-1). This rate was equivalent to 70% of the reported carbon emissions from the reservoir surface to the atmosphere and corresponded to a total sediment OC accumulation of 0.62 Tg C since the reservoir was created. The approach we propose here allows an inexpensive and integrative assessment of OC burial in reservoirs by taking into account the high degree of spatial variability and based on a single assessment. Because burial can be assessed shortly after the survey, the approach combining a seismic survey and coring could, if applied on a larger scale, contribute to a more complete estimate of carbon stocks in freshwater systems in a relatively short period of time.

  • 43.
    Mendonca, Raquel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Univ Fed Juiz de Fora, Juiz De Fora, Brazil.
    Müller, Roger A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Clow, David
    US Geol Survey, Denver, USA.
    Verpoorter, Charles
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Univ Littoral Cote d´Opale, Univ Lille, Wimereux, France.
    Raymond, Peter
    Yale Sch Forestry & Environm Studies, New Haven, USA.
    Tranvik, Lars J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Organic carbon burial in global lakes and reservoirs2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 1694Article in journal (Refereed)
    Abstract [en]

    Burial in sediments removes organic carbon (OC) from the short-term biosphere-atmosphere carbon (C) cycle, and therefore prevents greenhouse gas production in natural systems. Although OC burial in lakes and reservoirs is faster than in the ocean, the magnitude of inland water OC burial is not well constrained. Here we generate the first global-scale and regionally resolved estimate of modern OC burial in lakes and reservoirs, deriving from a compre- hensive compilation of literature data. We coupled statistical models to inland water area inventories to estimate a yearly OC burial of 0.15 (range, 0.06–0.25) Pg C, of which ~40% is stored in reservoirs. Relatively higher OC burial rates are predicted for warm and dry regions. While we report lower burial than previously estimated, lake and reservoir OC burial cor- responded to ~20% of their C emissions, making them an important C sink that is likely to increase with eutrophication and river damming.

  • 44.
    Mendonça, Raquel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kosten, Sarian
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Cardoso, Simone Jaqueline
    Figueiredo-Barros, Marcos Paulo
    Estrada, Carlos Henrique Duque
    Roland, Fábio
    Organic carbon burial efficiency in a large tropical hydroelectric reservoir2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 11, p. 3331-3342Article in journal (Refereed)
    Abstract [en]

    Hydroelectric reservoirs bury significant amounts of organic carbon (OC) in their sediments. Many reservoirs are characterized by high sedimentation rates, low oxygen concentrations in bottom water and a high share of terrestrially derived OC, and all of these factors have been linked to a high efficiency of OC burial. However, investigations of OC burial efficiency (OCBE, i.e., the ratio between buried and deposited OC) in reservoirs are limited to a few studies, none of which include spatially resolved analyses. In this study we determined the spatial variation in OCBE in a large subtropical reservoir and related it to sediment characteristics. Our results show that the sediment accumulation rate explains up to 92 % of the spatial variability in OCBE, outweighing the effect of other variables, such as OC source and oxygen exposure time. OCBE at the pelagic sites varied from 48 to 86 % (mean 67 %) and decreased towards the dam. At the margins, OCBE was lower (9–17 %) due to the low sediment accumulation in shallow areas. Our data show that the variability in OCBE both along the rivers–dam and the margin–pelagic axes must be considered in whole-reservoir assessments. Combining these results with a spatially resolved assessment of sediment accumulation and OC burial in the studied reservoir, we estimated a spatially resolved mean OC burial efficiency of 57 %. Being the first assessment of OCBE with such a high spatial resolution in a reservoir, these results suggest that reservoirs may bury OC more efficiently than natural lakes.

  • 45.
    Müller, Roger A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Futter, Martyn N.
    Swedish University of Agricultural Sciences (SLU).
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Nisell, J.
    Swedish University of Agricultural Sciences (SLU).
    Bishop, Kevin
    Swedish University of Agricultural Sciences (SLU).
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Water renewal along the aquatic continuum offsets cumulative retention by lakes: implications for the character of organic carbon in boreal lakes2013In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 75, no 4, p. 535-545Article in journal (Refereed)
    Abstract [en]

    The character of organic carbon (OC) in lake waters is strongly dependent on the time water has spent in the landscape as well as in the lake itself due to continuous biogeochemical OC transformation processes. A common view is that upstream lakes might prolong the water retention in the landscape, resulting in an altered OC character downstream. We calculated the number of lakes upstream for 24,742 Swedish lakes in seven river basins spanning from 56º to 68º N. For each of these lakes, we used a lake volume to discharge comparison on a landscape scale to account for upstream water retention by lakes (Tn tot). We found a surprisingly weak relationship between the number of lakes upstream and Tn tot. Accordingly, we found that the coloured fraction of organic carbon was not related to lake landscape position but significantly related to Tn tot when we analysed lake water chemical data from 1,559 lakes in the studied river basins. Thus, we conclude that water renewal along the aquatic continuum by lateral water inputs offsets cumulative retention by lakes. Based on our findings, we suggest integrating Tn tot in studies that address lake landscape position in the boreal zone to better understand variations in the character of organic carbon across lake districts.

  • 46.
    Paranaíba, José Reinaldo
    et al.
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Juiz de Fora, Brazil .
    Barros, Nathan
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Juiz de Fora, Brazil .
    Almeida, Rafael M.
    Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, USA.
    Mendonça, Raquel
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Juiz de Fora, Brazil .
    Linkhorst, Annika
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    do Vale, Roseilson
    Department of Atmospheric Science, Federal University of West of Pará, Santarém, Brazil.
    Roland, Fábio
    Department of Biology, Institute of Biological Sciences, Federal University of Juiz de Fora, Juiz de Fora, Brazil .
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Spatial heterogeneity of diffusive CO2 and CH4 emission varies seasonally in four tropical reservoirsIn: Article in journal (Refereed)
  • 47.
    Paranaíba, José Reinaldo
    et al.
    Institute of Biological Sciences, Federal University of Juiz de Fora, Minas Gerais.
    Barros, Nathan
    Institute of Biological Sciences, Federal University of Juiz de Fora, Minas Gerais.
    Mendonça, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Institute of Biological Sciences, Federal University of Juiz de Fora, Minas Gerais.
    Linkhorst, Annika
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Isidorova, Anastasija
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Roland, Fábio
    Institute of Biological Sciences, Federal University of Juiz de Fora, Minas Gerais.
    Almeida, Rafael M.
    Institute of Biological Sciences, Federal University of Juiz de Fora, Minas Gerais.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Spatially Resolved Measurements of CO2 and CH4 Concentration and Gas-Exchange Velocity Highly Influence Carbon-Emission Estimates of Reservoirs2018In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 52, no 2, p. 607-615Article in journal (Refereed)
    Abstract [en]

    The magnitude of diffusive carbon dioxide (CO2) and methane (CH4) emission from man-made reservoirs is uncertain because the spatial variability generally is not well-represented. Here, we examine the spatial variability and its drivers for partial pressure, gas-exchange velocity (k), and diffusive flux of CO2 and CH4 in three tropical reservoirs using spatially resolved measurements of both gas concentrations and k. We observed high spatial variability in CO2 and CH4 concentrations and flux within all three reservoirs, with river inflow areas generally displaying elevated CH4 concentrations. Conversely, areas close to the dam are generally characterized by low concentrations and are therefore not likely to be representative for the whole system. A large share (44–83%) of the within-reservoir variability of gas concentration was explained by dissolved oxygen, pH, chlorophyll, water depth, and within-reservoir location. High spatial variability in k was observed, and kCH4 was persistently higher (on average, 2.5 times more) than kCO2. Not accounting for the within-reservoir variability in concentrations and k may lead to up to 80% underestimation of whole-system diffusive emission of CO2 and CH4. Our findings provide valuable information on how to develop field-sampling strategies to reliably capture the spatial heterogeneity of diffusive carbon fluxes from reservoirs.

  • 48.
    Pasche, Natacha
    et al.
    Limnology Center, EPFL-ENT-LIMNC, Lausanne, Switzerland; Physics of Aquatic Systems Laboratory, Margaretha Kamprad Chair, EPFL-ENAC-IEE-APHYS, Lausanne, Switzerland.
    Hofmann, Hilmar
    Environmental Physics Group, University of Konstanz - Limnological Institute, Konstanz, Germany.
    Bouffard, Damien
    Physics of Aquatic Systems Laboratory, Margaretha Kamprad Chair, EPFL-ENAC-IEE-APHYS, Lausanne, Switzerland; Eawag,Swiss Federal Institute of Aquatic Science and Technology, Department of Surface Waters-Research and Management, Kastanienbaum,Switzerland.
    Schubert, Carsten J.
    Eawag,Swiss Federal Institute of Aquatic Science and Technology, Department of Surface Waters-Research and Management, Kastanienbaum, Switzerland.
    Lozovik, Petr A.
    Northern Water Problems Institute, Karelian Research Center, Russian Academy of Sciences, Petrozavodsk, Russia.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Implications of river intrusion and convective mixing on the spatial and temporal variability of under-ice CO22019In: INLAND WATERS, ISSN 2044-2041, E-ISSN 2044-205X, Vol. 9, no 2, p. 162-176Article in journal (Refereed)
    Abstract [en]

    Ice-covered periods might significantly contribute to lake emissions at ice-melt, yet a comprehensive understanding of under-ice carbon dioxide (CO2) dynamics is still lacking. This study investigated the processes driving spatiotemporal patterns of under-ice CO2 in large Lake Onego. In March 2015 and 2016, under-ice CO2, dissolved inorganic carbon (DIC), and dissolved organic carbon (DOC) distributions were measured along a river to an open-lake transect. CO2 decreased from 120/129 μmol L−1 in the river to 51/98 μmol L−1 in the bay, and 34/36 μmol L−1 in the open lake, while DOC decreased from 1.18/1.55 mmol L−1 in the river to 0.67/1.04 mmol L−1 in the bay in 2015 and 2016, respectively. These decreases in concentrations with increasing distance from the river mouth indicate that river discharge modulates spatial patterns of under-ice CO2. The variability between the 2 years was mainly driven by river discharge and ice transparency affecting the extent of under-ice convection. Higher discharge during winter 2016 resulted in higher CO2 concentrations in the bay. By contrast, intensive under-ice convection led to lower, more homogeneously distributed CO2 in 2015. In conclusion, the river-to-bay transition zone is characterized by strong CO2 variability and is therefore an important zone to consider when assessing the CO2 budget of large lakes.

  • 49. Pavel, A.
    et al.
    Durisch-Kaiser, E.
    Balan, S.
    Radan, S.
    Sobek, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wehrli, B.
    Sources and emission of greenhouse gases in Danube Delta lakes2009In: Environmental Science and Pollution Research, Vol. 16, no Suppl 1, p. 86-91Article in journal (Refereed)
    Abstract [en]

    Production of methane and carbon dioxide as well as methane concentrations in surface waters and emissions to the atmosphere were investigated in two flow-through lake complexes (Uzlina–Isac and Puiu–Rosu–Rosulet) in the Danube Delta during post-flood conditions in May and low water level in September 2006. Retained nutrients fuelled primary production and remineralisation of bioavailable organic matter. This led to an observable net release of methane, particularly in the lakes Uzlina, Puiu and Rosu in May. Input from the Danube River, from redbuds and benthic release contributed to CH4 concentrations in surface waters. In addition to significant river input of CO2, this trace gas was released via aerobic remineralisation within the water column and in top sediments. Emission patterns of CO2 widely overlapped with those of CH4. Generally, greenhouse gas emissions peaked in the lake complex adjacent to the Danube River in May due to strong winds and decreased with increasing hydrological distance from the Danube River. Intense remineralisation of organic matter in the Danube Delta lakes results in a net source of atmospheric greenhouse gases.

  • 50.
    Peter, Simone
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Agstam, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Widespread release of dissolved organic carbon from anoxic boreal lake sediments2017In: INLAND WATERS, ISSN 2044-2041, E-ISSN 2044-205X, Vol. 7, no 2, p. 151-163Article in journal (Refereed)
    Abstract [en]

    Sediments in boreal lakes are important components of the carbon cycle because they receive and store large amounts of organic carbon (OC) and at the same time are a source of greenhouse gases. Under anoxic conditions, sediment OC can be lost through dissolution from the solid phase and subsequent diffusion to the water column. Although this process may have implications for sediment OC budgets, it has yet to be studied systematically. We combined laboratory sediment incubation experiments from 4 boreal lakes in central Sweden that differed widely in their biogeochemical conditions with data from the Swedish monitoring program covering >100 lakes to analyze the frequency of occurrence of sediment DOC loss in boreal lakes and identify lake characteristics and the conditions related to high DOC fluxes from anoxic sediments. We found DOC diffusion from anoxic sediments in all the anoxic sediment incubations but at different mean rates (0.7-3.7 mmol m(-2) d(-1)). Similarly, 16 of 17 of the monitoring lakes that developed anoxic bottom water exhibited an increase in bottom-water DOC concentration, corresponding to a mean (and standard deviation) DOC diffusion flux from anoxic sediment of 11.1 (35.4) mmol m(-2) d(-1). The observed variability between lakes was related to particularly large DOC fluxes in humic-rich lakes, which we attribute to their low pH and high share of terrestrial OC favoring the formation of OC-iron aggregates. Accordingly, increasing pH might facilitate the dissolution of sediment OC because high dissolved OC fluxes from anoxic sediments were accompanied by high microbial iron and sulfate reduction, resulting in concomitant pH increase.

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