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  • 1.
    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. 

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  • 2.
    Grasset, Charlotte
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Moras, Simone
    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.
    Couture, Raoul-Marie
    Linkhorst, Annika
    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.
    An empirical model to predict methane production in inland water sediment from particular organic matter supply and reactivity2021In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 66, no 10, p. 3643-3655Article in journal (Refereed)
    Abstract [en]

    The highest CH4 production rates can be found in anoxic inland water surface sediments however no model quantifies CH4 production following fresh particular organic matter (POM) deposition on anoxic sediments. This limits our capability of modeling CH4 emissions from inland waters to the atmosphere. To generate such a model, we quantified how the POM supply rate and POM reactivity control CH4 production in anoxic surface sediment, by amending sediment at different frequencies with different quantities of aquatic and terrestrial POM. From the modeled CH4 production, we derived parameters related to the kinetics and the extent of CH4 production. We show that the extent of CH4 production can be well predicted by the quality (i.e., C/N ratio) and the quantity of POM supplied to an anoxic sediment. In particular, within the range of sedimentation rates that can be found in aquatic systems, we show that CH4 production increases linearly with the quantity of phytoplankton-derived and terrestrially derived POM. A high frequency of POM addition, which is a common situation in natural systems, resulted in higher peaks in CH4 production rates. This suggests that relationships derived from earlier incubation experiments that added POM only once, may result in underestimation of sediment CH4 production. Our results quantitatively couple CH4 production in anoxic surface sediment to POM sedimentation flux, and are therefore useful for the further development of mechanistic models of inland water CH4 emission.

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  • 3.
    Isidorova, Anastasija
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    The origin and fate of sediment organic carbon in tropical reservoirs2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Recently, the construction of reservoirs has boomed, particularly in the tropics, but the impact of reservoirs on the global carbon cycle is not evident. Reservoirs accumulate sediments that simultaneously bury organic carbon (OC) and thus act as a C sink, and also produce methane (CH4) and thus emit a strong greenhouse gas. High temperature, internal production and sedimentation rates in tropical reservoirs may enhance both OC burial and CH4 production, however to a currently unknown extent. This thesis investigates the efficiency of the OC sink as well as the OC sources that feed into OC burial and CH4 production in four contrasting tropical reservoirs in Brazil. 

    The results demonstrate that reservoir sediments receive both terrestrial and aquatic OC, and that terrestrial OC is more prevalent in reservoirs with low internal production, and in river inflow bays. Aquatic OC is present in the sediments of all studied reservoirs, particularly in the reservoirs with high internal production and at sites that are closer to the dam. Reservoirs that experience anoxic conditions or high sediment deposition rates are likely to bury terrestrial OC at higher efficiency than oxic environments, such as oxygenated reservoirs, rivers, floodplains and sea, while aquatic OC degrades as similar rates in both oxic and anoxic environments. Deposition of OC in anoxic sediment, however, results in high CH4formation rates that strongly depend on sediment age and nitrogen content. The CH4 formation decreases exponentially with sediment age, but never ceases completely in the studied reservoir sediment. CH4 formation is highest but decreases more rapidly over time in sediment with a high share of nitrogen-rich aquatic OC, indicating that management of nutrient input into the reservoir may decrease sediment CH4 formation.

    The thesis illustrates that reservoir sediments bury aquatic OC and also bury terrestrial OC with high efficiency, which represents an anthropogenic carbon sink that decreases the carbon footprint of hydropower. Simultaneously, the reservoir sediment produces CH4 that may be emitted into the atmosphere and consequently elevates the carbon footprint of hydropower. However, reservoir CH4 emission may be mitigated by reducing nutrient input into rivers and reservoirs.

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  • 4.
    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.

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  • 5.
    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, 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.

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  • 6.
    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.

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  • 7.
    Lehoux, Alizée
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Natural Resources and Sustainable Development.
    Isidorova, Anastasija
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Collin, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Natural Resources and Sustainable Development.
    Koestel, John
    Swedish Univ Agr Sci, Dept Soil & Environm, Box 7014, SE-75007 Uppsala, Sweden.;Forschungsanstalt Agroscope Reckenholz Tanikon, Reckenholzstr 191, CH-8046 Zurich, Switzerland..
    Snowball, Ian
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Natural Resources and Sustainable Development.
    Dahlberg, Anna-Karin
    Swedish Univ Agr Sci, Dept Aquat Sci & Assessment, Box 7050, SE-75007 Uppsala, Sweden..
    Extreme gas production in anthropogenic fibrous sediments: An overlooked biogenic source of greenhouse gas emissions2021In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 781, article id 146772Article in journal (Refereed)
    Abstract [en]

    Fibrous sediments that originated from old pulp and paper industry emissions are recognized as a potential threat to the aquatic environment because they are highly contaminated. In addition, biogenic degradation of the organic material from so-called "fiberbanks" has a high potential to produce greenhouse gases (GHG). In this study, X-ray tomography, optical sensors and gas analyzers were used to identify and quantify the gas produced and released from samples of two different fiberbanks. We show that a finer fibrous structure allows the formation of larger gas bubbles and higher gas production rates compared to coarser material composed of wood pieces. High contents of methane (average 56% to 65%) and carbon dioxide (average 18% to 20%) were measured in the gas emitted from both types of fiberbank. Measured methane production rates from the fiberbanks samples are one to three orders of magnitude higher than previously reported rates from sediments within the studied temperature range (between 0.03 and 0.51 mu m CH4/h/g dw over 4.7 to 20 degrees C). The potential for methane and carbon dioxide production in the fiberbank volume likely present in Sweden is estimated to correspond to 7% of Sweden's total known GHG emissions for 2019. These findings show that fiberbanks have the potential to be a significant emitter of GHG.

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  • 8.
    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.

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  • 9.
    Peter, Simone
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz Inst Balt Sea Res, Rostock, Germany.
    Isidorova, Anastasija
    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.
    Enhanced carbon loss from anoxic lake sediment through diffusion of dissolved organic carbon2016In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 7, p. 1959-1977Article in journal (Refereed)
    Abstract [en]

    Lakes are highly relevant players in the global carbon cycle as they can store large amounts of organic carbon (OC) in sediments, thereby removing OC from the actively cycling pool. However, sediment OC can be released to pore water under anoxic conditions and diffuse into the water column. In carbon budgets of lake ecosystems, this potential OC loss pathway from sediments is generally disregarded. Combining field observations and incubation experiments, we quantitatively investigated dissolved OC (DOC) diffusion from sediments into anoxic water of a boreal lake. We observed substantial increases of bottom water DOC (26% in situ, 16% incubation), translating into a DOC flux from the sediment that was comparable to anoxic sediment respiration (3.3 versus 5.1mmolm(-2)d(-1)). Optical characterization indicated that colored and aromatic DOC was preferentially released. Reactivity assays showed that DOC released from anoxic sediment enhanced water column respiration and flocculation in reoxygenated water. Upon water oxygenation, flocculation was the most important loss pathway removing similar to 77% of released DOC, but the remaining similar to 23% was mineralized, constituting a pathway of permanent loss of sediment OC. DOC diffusion from lake sediment during anoxia and subsequent mineralization in oxic water during mixing increases overall OC loss from anoxic sediments by similar to 15%. This study enlarges our understanding of lake ecosystems by showing that under anoxic conditions significant amounts of DOC can be released from OC stored in sediments and enter the active aquatic carbon cycle again.

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  • 10.
    Quadra, Gabrielle R.
    et al.
    Laboratório de Ecologia Aquática, Programa de Pós-Graduação em Ecologia, Universidade Federal de Juiz de Fora, 36036 900, Juiz de Fora, Brazil.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Paranaíba, José R.
    Laboratório de Ecologia Aquática, Programa de Pós-Graduação em Ecologia, Universidade Federal de Juiz de Fora, 36036 900, Juiz de Fora, Brazil.
    Isidorova, Anastasija
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Roland, Fábio
    Laboratório de Ecologia Aquática, Programa de Pós-Graduação em Ecologia, Universidade Federal de Juiz de Fora, 36036 900, Juiz de Fora, Brazil.
    do Vale, Roseilson
    Instituto de Engenharia e Geociências, Universidade Federal do Oeste do Pará, 68040 255, Santarém, Brazil.
    Mendonça, Raquel
    Laboratório de Ecologia Aquática, Programa de Pós-Graduação em Ecologia, Universidade Federal de Juiz de Fora, 36036 900, Juiz de Fora, Brazil.
    High organic carbon burial but high potential for methane ebullition in the sediments of an Amazonian hydroelectric reservoir2020In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 17, no 6, p. 1495-1505Article in journal (Refereed)
    Abstract [en]

    Reservoir sediments sequester significant amounts of organic carbon (OC), but at the same time, high amounts of methane (CH4) can be produced and emitted during the degradation of sediment OC. While the greenhouse gas emission of reservoirs has received a lot of attention, there is a lack of studies focusing on OC burial. In particular, there are no studies on reservoir OC burial in the Amazon, even though hydropower is expanding in the basin. Here we present results from the first investigation of OC burial and CH4 concentrations in the sediments of an Amazonian hydroelectric reservoir. We performed sub-bottom profiling, sediment coring and sediment pore water analysis in the Curuá Una (CUN) reservoir (Amazon, Brazil) during rising- and falling-water periods. The spatially resolved average sediment accumulation rate was 0.6 cm yr−1, and the average OC burial rate was 91 g C m−2 yr−1. This is the highest OC burial rate on record for low-latitude hydroelectric reservoirs. Such a high rate probably results from a high OC deposition onto the sediment, which compensates the high OC mineralization at a 28–30 ∘C water temperature. Elevated OC burial was found near the dam and close to major river inflow areas. C:N ratios between 10.3 and 17 (average ± SD: 12.9±2.1) suggest that both land-derived and aquatic OC accumulate in CUN sediments. About 23 % of the sediment pore water samples had dissolved CH4 above the saturation concentration. This represents a higher share than in other hydroelectric reservoirs, indicating a high potential for CH4 ebullition, particularly in river inflow areas.

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