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  • 1. Bartels, Pia
    et al.
    Cucherousset, Julien
    Gudasz, Cristian
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persson, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Premke, Katrin
    Rubach, Anja
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Steger, Kristin
    Tranvik, Lars J.
    Eklov, Peter
    Terrestrial subsidies to lake food webs: an experimental approach2012Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 168, nr 3, s. 807-818Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cross-ecosystem movements of material and energy are ubiquitous. Aquatic ecosystems typically receive material that also includes organic matter from the surrounding catchment. Terrestrial-derived (allochthonous) organic matter can enter aquatic ecosystems in dissolved or particulate form. Several studies have highlighted the importance of dissolved organic carbon to aquatic consumers, but less is known about allochthonous particulate organic carbon (POC). Similarly, most studies showing the effects of allochthonous organic carbon (OC) on aquatic consumers have investigated pelagic habitats; the effects of allochthonous OC on benthic communities are less well studied. Allochthonous inputs might further decrease primary production through light reduction, thereby potentially affecting autotrophic resource availability to consumers. Here, an enclosure experiment was carried out to test the importance of POC input and light availability on the resource use in a benthic food web of a clear-water lake. Corn starch (a C-4 plant) was used as a POC source due to its insoluble nature and its distinct carbon stable isotope value (delta C-13). The starch carbon was closely dispersed over the bottom of the enclosures to study the fate of a POC source exclusively available to sediment biota. The addition of starch carbon resulted in a clear shift in the isotopic signature of surface-dwelling herbivorous and predatory invertebrates. Although the starch carbon was added solely to the sediment surface, the carbon originating from the starch reached zooplankton. We suggest that allochthonous POC can subsidize benthic food webs directly and can be further transferred to pelagic systems, thereby highlighting the importance of benthic pathways for pelagic habitats.

  • 2. Berggren, Martin
    et al.
    Gudasz, Cristian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Guillemette, Francois
    Hensgens, Geert
    Ye, Linlin
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Systematic microbial production of optically active dissolved organic matter in subarctic lake water2020Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 65, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ecology and biogeochemistry of lakes in the subarctic region are particularly sensitive to changes in the abundance and optical properties of dissolved organic matter (DOM). External input of colored DOM to these lakes is an extensively researched topic, but little is known about potential reciprocal feedbacks between the optical properties of DOM and internal microbial processes in the water. We performed 28-day dark laboratory incubation trials on water from 101 subarctic tundra lakes in northern Sweden, measuring the microbial decay of DOM and the resulting dynamics in colored (CDOM) and fluorescent (FDOM) DOM components. While losses in dissolved oxygen during the incubations corresponded to a 20% decrease in mean DOM, conversely the mean CDOM and total FDOM increased by 22% and 30%, respectively. However, the patterns in microbial transformation of the DOM were not the same in all lakes. Notably, along the gradient of increasing ambient CDOM (water brownness), the lakes showed decreased microbial production of protein-like fluorescence, lowered DOM turnover rates and decreasing bacterial growth per unit of DOM. These trends indicate that browning of subarctic lakes systematically change the way that bacteria interact with the ambient DOM pool. Our study underscores that there is no unidirectional causal link between microbial processes and DOM optical properties, but rather reciprocal dependence between the two.

  • 3. Gudasz, Cristian
    et al.
    Bastviken, David
    Premke, Katrin
    Steger, Kristin
    Tranvik, Lars J.
    Constrained microbial processing of allochthonous organic carbon in boreal lake sediments2012Inngår i: LIMNOLOGY AND OCEANOGRAPHY, ISSN 0024-3590, Vol. 57, nr 1, s. 163-175Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 4.
    Gudasz, Cristian
    et al.
    Limnology, Department of Ecology and Evolution, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden.
    Bastviken, David
    Steger, Kristin
    Premke, Katrin
    Sobek, Sebastian
    Tranvik, Lars J
    Temperature-controlled organic carbon mineralization in lake sediments2010Inngår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 466, nr 7305, s. 478-481Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Peatlands, soils and the ocean floor are well-recognized as sites of organic carbon accumulation and represent important global carbon sinks. Although the annual burial of organic carbon in lakes and reservoirs exceeds that of ocean sediments, these inland waters are components of the global carbon cycle that receive only limited attention. 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 from a compilation of published data from a wide 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 could result in a 4-27 per cent (0.9-6.4 Tg C yr(-1)) decrease in annual organic carbon burial in boreal lakes.

  • 5.
    Gudasz, Cristian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bastviken, David
    Department of Thematic Studies - Environmental Change, Linköping University, Linköping, Sweden.
    When does temperature matter for ecosystem respiration?2021Inngår i: Environmental Research Communications (ERC), E-ISSN 2515-7620, Vol. 3, nr 12, artikkel-id 121001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The temperature response of ecosystem processes is key to understand and predict impacts of climate change. This is especially true for respiration, given its high temperature sensitivity and major role in the global carbon cycle. However, similar intrinsic temperature sensitivity for respiration does not mean comparable temperature effects across ecosystems and biomes because non-temperature factors can be more important. Here we analyzed soil and sediment respiration data and found that in temperature ranges corresponding to high latitude mean temperatures, absolute respiration rates aremore sensitive to non-temperature factors than to projected direct temperature effects. However, at higher temperatures (>20 °C) the direct effect of temperature mediated by temperature sensitivity will likely be more important over changes in non-temperature factors in shaping how respiration change over time. This supports past suggestions that the relatively small projected temperature increase at low (tropical) latitudes may have a large direct impact on absolute respiration. In contrast, absolute respiration rates at high (boreal/arctic) latitudes will likely bemore sensitive on the development of the non-temperature factors than on the direct effects of the large projected temperature increase there.

    Social media abstract: Respirationmay be less dependent to changes in temperature at higher than lower latitudes.

    Fulltekst (pdf)
    fulltext
  • 6.
    Gudasz, Cristian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Limnology, Department of Ecology and Genetics, Limnology, Uppsala University, Uppsala, Sweden.
    Ruppenthal, Marc
    Kalbitz, Karsten
    Cerli, Chiara
    Fielder, Sabine
    Oelmann, Yvonne
    Andersson, August
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Contributions of terrestrial organic carbon to northern lake sediments2017Inngår i: Limnology and Oceanography Letters, E-ISSN 2378-2242, Vol. 2, nr 6, s. 218-227Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sediments of northern lakes sequester large amounts of organic carbon (OC), but direct evidence of the relative importance of their sources is lacking. We used stable isotope ratios of nonexchangeable hydrogen (δ2Hn) in topsoil, algae, and surface sediments in order to measure the relative contribution of terrestrial OC in surface sediments of 14 mountainous arctic and lowland boreal lakes in Sweden. The terrestrial contribution to the sediment OC pool was on average 66% (range 46–80) and similar between arctic and boreal lakes. Proxies for the supply of terrestrial and algal OC explained trends in the relative contribution of terrestrial OC across lakes. However, the data suggest divergent predominant sources for terrestrial OC of sediments in Swedish lakes, with dissolved matter dominating in lowland boreal lakes and particulate OC in mountainous arctic lakes.

    Fulltekst (pdf)
    fulltext
  • 7.
    Gudasz, Cristian
    et al.
    ARCUM.
    Sobek, Sebastian
    Bastviken, David
    Koehler, Birgit
    Tranvik, Lars J.
    Temperature sensitivity of organic carbon mineralizationin contrasting lake sediments2015Inngår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, nr 7, s. 1215-1225Artikkel i tidsskrift (Fagfellevurdert)
    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°C for five months. Compared to soil and litter mineralization, sediment OC mineralization rates were low in spite of low apparent activation energy (Ea). 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 32 years. 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.

  • 8.
    Karlsson, Jan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Gudasz, Cristian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rodriguez, Patricia
    Hein, Catherine
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Terrestrial organic matter input suppresses biomass production in lake ecosystems2015Inngår i: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, nr 11, s. 2870-2876Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Terrestrial ecosystems export large amounts of organic carbon (t-OC) but the net effect of this OC on the productivity of recipient aquatic ecosystems is largely unknown. In this study of boreal lakes, we show that the relative contribution of t-OC to individual top consumer (fish) biomass production, and to most of their potential prey organisms, increased with the concentration of dissolved organic carbon (DOC; dominated by t-OC sources) in water. However, the biomass and production of top consumers decreased with increasing concentration of DOC, despite their substantial use (up to 60%) of t-OC. Thus, the results suggest that although t-OC supports individual consumer growth in lakes to a large extent, t-OC input suppresses rather than subsidizes population biomass production.

  • 9. Marotta, H
    et al.
    Pinho, L
    Gudasz, Cristian
    ARCUM; Department of Ecology and Genetics, Limnology, Uppsala University, 752 36 Uppsala, Sweden; Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544-2016, USA.
    Bastviken, D
    Tranvik, L J
    Enrich-Prast, A
    Greenhouse gas production in low-latitude lake sediments responds strongly to warming2014Inngår i: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 4, nr 6, s. 467-470Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Inland water sediments receive large quantities of terrestrial organic matter and are globally important sites for organic carbon preservation. Sediment organic matter mineralization is positively related to temperature across a wide range of high-latitude ecosystems, but the situation in the tropics remains unclear. Here we assessed temperature effects on the biological production of CO2 and CH4 in anaerobic sediments of tropical lakes in the Amazon and boreal lakes in Sweden. On the basis of conservative regional warming projections until 2100 (ref. ), we estimate that sediment CO2 and CH4 production will increase 9-61% above present rates. Combining the CO2 and CH4 as CO2 equivalents (CO2eq; ref. ), the predicted increase is 2.4-4.5 times higher in tropical than boreal sediments. Although the estimated lake area in low latitudes is 3.2 times smaller than that of the boreal zone, we estimate that the increase in gas production from tropical lake sediments would be on average 2.4 times higher for CO2 and 2.8 times higher for CH4. The exponential temperature response of organic matter mineralization, coupled with higher increases in the proportion of CH4 relative to CO2 on warming, suggests that the production of greenhouse gases in tropical sediments will increase substantially. This represents a potential large-scale positive feedback to climate change.

  • 10. Osman, Omneya A
    et al.
    Gudasz, Cristian
    Bertilsson, Stefan
    Diversity and abundance of aromatic catabolic genes in lake sediments in response to temperature change2014Inngår i: FEMS Microbiology Ecology, ISSN 0168-6496, E-ISSN 1574-6941, Vol. 88, nr 3, s. 468-481Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The abundance and composition of genes involved in the catabolism of aromatic compounds provide important information on the biodegradation potential of organic pollutants and naturally occurring compounds in the environment. We studied catechol 2, 3 dioxygenase (C23O) and benzylsuccinate synthase (bssA) genes coding for key enzymes of aerobic and anaerobic degradation of aromatic compounds in experimental incubations with sediments from two contrasting lakes; humic lake Svarttjärn and eutrophic Vallentunasjön, respectively. Sediment cores from both lakes were incubated continuously for 5 months at constant temperatures ranging from 1.0 to 21.0 °C. The difference in C23O gene composition of the sediment analyzed at the end of the experiment was larger between lakes, than among temperature treatments within each lake. The abundance of C23O gene copies and measured respiration was positively correlated with temperature in Vallentunasjön, whereas putative C23O genes were present in lower concentrations in Svarttjärn sediments. Putative bssA genes were only detected in Svarttjärn. For both lakes, the two catabolic genes were most abundant in the surface sediment. The results emphasize the important role of temperature and nutrient availability in controlling the functional potential of sediment microorganisms and reveal differences between systems with contrasting trophic status. A better understanding of catabolic pathways and enzymes will enable more accurate forecasting of the functional properties of ecosystems under various scenarios of environmental change. 

  • 11. Peter, Hannes
    et al.
    Ylla, Irene
    Gudasz, Cristian
    Limnology, Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden.
    Romani, Anna M.
    Sabater, Sergi
    Tranvik, Lars J.
    Multifunctionality and diversity in bacterial biofilms2011Inngår i: PLOS ONE, E-ISSN 1932-6203, Vol. 6, nr 8, artikkel-id e23225Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bacteria are highly diverse and drive a bulk of ecosystem processes. Analysis of relationships between diversity and single specific ecosystem processes neglects the possibility that different species perform multiple functions at the same time. The degradation of dissolved organic carbon (DOC) followed by respiration is a key bacterial function that is modulated by the availability of DOC and the capability to produce extracellular enzymes. In freshwater ecosystems, biofilms are metabolic hotspots and major sites of DOC degradation. We manipulated the diversity of biofilm forming communities which were fed with DOC differing in availability. We characterized community composition using molecular fingerprinting (T-RFLP) and measured functioning as oxygen consumption rates, the conversion of DOC in the medium, bacterial abundance and the activities of five specific enzymes. Based on assays of the extracellular enzyme activity, we calculated how the likelihood of sustaining multiple functions was affected by reduced diversity. Carbon source and biofilm age were strong drivers of community functioning, and we demonstrate how the likelihood of sustaining multifunctionality decreases with decreasing diversity.

  • 12. Premke, Karin
    et al.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Steger, Kristin
    Gudasz, Cristian
    Limnology, Department of Ecology and Evolution, EBC, Uppsala University, Norbyva¨gen 18 D, 75 236 Uppsala, Sweden.
    von Wachenfeldt, Eddie
    Tranvik, Lars J.
    Stable isotope analysis of benthic fauna and their food sources in boreal lakes2010Inngår i: Journal of The North American Benthological Society, ISSN 0887-3593, E-ISSN 1937-237X, Vol. 29, s. 1339-1348Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The origin of organic C supporting zoobenthic communities in 8 boreal lakes with different concentrations of dissolved organic C (DOC) was assessed by stable-isotope analysis. Profundal zoobenthos was depleted in 13C compared to littoral zoobenthos, and this difference increased with decreasing DOC concentration. The δ13C of littoral zoobenthos suggested reliance on benthic algae, whereas depleted 13C of profundal zoobenthos could be explained by contributions from allochthonous and autochthonous C sources. In deeper lakes, profundal zoobenthos diets also included C processed by methanotrophic bacteria. Littoral zoobenthos δ13C decreased with increasing DOC concentration in the lake water. Our results suggest that littoral benthic fauna are mainly supported by benthic algae in low-DOC lakes and by phytoplankton and allochthonous organic C in high-DOC lakes and that this difference is a result of light absorbance and energy supply by allochthonous organic C. Increasing allochthonous DOC inputs, as expected in a warmer and wetter climate, might reduce benthic algal production and alter the organic C base for benthic food webs in lake ecosystems.

  • 13. Santoro, Ana Lúcia
    et al.
    Bastviken, David
    Gudasz, Cristian
    Department of Ecology and Evolution - Limnology, Uppsala University, Uppsala, Sweden.
    Tranvik, Lars
    Enrich-Prast, Alex
    Dark Carbon Fixation: An Important Process in Lake Sediments2013Inngår i: PLOS ONE, E-ISSN 1932-6203, Vol. 8, nr 6, artikkel-id e65813Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Close to redox boundaries, dark carbon fixation by chemoautotrophic bacteria may be a large contributor to overall carbon fixation. Still, little is known about the relative importance of this process in lake systems, in spite the potentially high chemoautotrophic potential of lake sediments. We compared rates of dark carbon fixation, bacterial production and oxygen consumption in sediments from four Swedish boreal and seven tropical Brazilian lakes. Rates were highly variable and dark carbon fixation amounted up to 80% of the total heterotrophic bacterial production. The results indicate that non-photosynthetic carbon fixation can represent a substantial contribution to bacterial biomass production, especially in sediments with low organic matter content.

  • 14.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA.
    Carr, Joel A.
    Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA.
    Gudasz, Cristian
    Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Upscaling carbon dioxide emissions from lakes2014Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, nr 21, s. 7555-7559Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Quantifying CO2 fluxes from lakes to the atmosphere is important for balancing regional and global-scale carbon budgets. CO2 emissions are estimated through statistical upscaling procedures that aggregate data from a large number of lakes. However, aggregation can bias flux estimates if the physical and chemical factors determining CO2 exchange between water and the atmosphere are not independent. We evaluated the magnitude of aggregation biases with moment expansions and pCO(2) data from 5140 Swedish lakes. The direction of the aggregation bias depends on lake size; mean flux was overestimated by 4% for small lakes (0.01-0.1 km(2)) but underestimated by 13% for large lakes (100-1000 km(2)). Simple covariance-based correction factors were generated to adjust for upscaling biases. These correction factors represent an easily interpretable and implemented approach to improving the accuracy of regional and global estimates of lake CO2 emissions.

    Fulltekst (pdf)
    fulltext
  • 15.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Gudasz, Cristian
    Department of Ecology and Genetics/Limnology, Uppsala University, Uppsala, Sweden.
    Long-term pCO(2) trends in Adirondack Lakes2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 10, s. 5109-5115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lakes are globally significant sources of CO2 to the atmosphere. However, there are few temporally resolved records of lake CO2 concentrations and long-term patterns are poorly characterized. We evaluated annual trends in the partial pressure of CO2 (pCO2) based on chemical measurements from 31 Adirondack Lakes taken monthly over an 18 year period. All lakes were supersaturated with CO2 and were sources of CO2 to the atmosphere. There were significant pCO2 trends in 29% of lakes. The median magnitude of significant positive trends was 32.1 µatm yr−1. Overall, 52% of lakes had pCO2 trends greater than those reported for the atmosphere and ocean. Significant trends in lake pCO2 were attributable to regional recovery from acid deposition and changing patterns of ice cover. These results illustrate that lake pCO2 can respond rapidly to environmental change, but the lack of significant trend in 71% of lakes indicates substantial lake-to-lake variation in magnitude of response.

  • 16.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia.
    Lapierre, Jean-Francois
    Pace, Michael L.
    Gudasz, Cristian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey.
    Sobek, Sebastian
    Tranvik, Lars J.
    Regional-scale variation of dissolved organic carbon concentrations in Swedish lakes2014Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, nr 5, s. 1612-1620Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We assessed spatial variability in dissolved organic carbon (DOC) concentrations measured in nearly 2000 Swedish lakes. Inter-lake variance peaked at two different scales, representing within-region and between-region variability. The variation between regions was greater than the variation among lakes within regions. We tested relationships between DOC and runoff, drainage ratio, and altitude for spatial heterogeneity using geographically weighted regression. Relationships varied geographically, but cluster analysis delineated two contiguous regions of similar relationships. Altitude had a significant inverse relationship with DOC in the highlands, and drainage ratio had a significant positive relationship with DOC in the lowlands. These heterogeneous relationships explained regional patterns in DOC concentrations. We conclude that regions, rather than individual lakes, are a key, emergent scale of spatial variability for DOC concentrations. This scale of variability reflects the intersection of environmental gradients (e.g., altitude) with spatially heterogeneous relationships (e.g., DOC-drainage ratio relationship). Regional-scale structure in limnological patterns indicates that individual lakes are not independent from one another, but are emergent groups where DOC concentrations are a function of similar environmental patterns and processes.

  • 17. Sobek, Sebastian
    et al.
    Gudasz, Cristian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Arktiskt centrum vid Umeå universitet (Arcum). Department of Ecology and Genetics/Limnology, Uppsala University, Uppsala, Sweden.
    Koehler, Birgit
    Tranvik, Lars J.
    Bastviken, David
    Morales-Pineda, Maria
    Temperature dependence of apparent respiratory quotients and oxygen penetration depth in contrasting lake sediments2017Inngår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122, nr 11, s. 3076-3087Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lake sediments constitute an important compartment in the carbon cycle of lakes, by burying carbon over geological timescales and by production and emission of greenhouse gases. The degradation of organic carbon (OC) in lake sediments is linked to both temperature and oxygen (O-2), but the interactive nature of this regulation has not been studied in lake sediments in a quantitative way. We present the first systematic investigation of the effects of temperature on the apparent respiratory quotient (RQ, i.e., the molar ratio between carbon dioxide (CO2) production and O-2 consumption) in two contrasting lake sediments. Laboratory incubations of sediment cores of a humic lake and an eutrophic lake across a 1-21 degrees C temperature gradient over 157days revealed that both CO2 production and O-2 consumption were positively, exponentially, and similarly dependent on temperature. The apparent RQ differed significantly between the lake sediments (0.630.26 and 0.990.28 in the humic and the eutrophic lake, respectively; meanSD) and was significantly and positively related to temperature. The O-2 penetration depth into the sediment varied by a factor of 2 over the 1-21 degrees C temperature range and was significantly, negatively, and similarly related to temperature in both lake sediments. Accordingly, increasing temperature may influence the overall extent of OC degradation in lake sediments by limiting O-2 supply to aerobic microbial respiration to the topmost sediment layer, resulting in a concomitant shift to less effective anaerobic degradation pathways. This suggests that temperature may represent a key controlling factor of the OC burial efficiency in lake sediments.

  • 18. Steger, K.
    et al.
    Premke, K.
    Gudasz, Cristian
    Boschker, H.T.S.
    Tranvik, L. J.
    Comparative study on bacterial carbon sources in lake sediments: the role of methanotrophy2015Inngår i: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 76, nr 1, s. 39-47Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Methane-derived carbon can be important in both benthic and pelagic food webs. Either generated in the anaerobic layers of the sediment or in the anaerobic hypolimnion of stratified eutrophic lakes, methane is an excellent carbon source for aerobic methanotrophic bacteria. The very negative methane δ13C-signal in the methanotrophic biomass provides an excellent opportunity to trace the use of methane-derived carbon in food webs. We studied carbon sources of benthic bacteria in a range of Swedish lakes with different inputs of terrestrial organic carbon and indigenous primary production. We analyzed the 13C:12C ratios in phospholipid-derived fatty acids, which serve as biomarkers for specific groups of Bacteria. We demonstrate that methane is an important carbon source for sediment bacteria, not only for the methanotrophic community but also for the non-methanotrophic heterotrophic bacteria. This most likely indirect utilization of isotopically highly depleted methane masks the stable isotope signatures for terrestrial input and local primary production in the heterotrophic bacterial community.

  • 19. Steger, Kristin
    et al.
    Premke, Katrin
    Gudasz, Cristian
    Department of Ecology and Genetics/Limnology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Sundh, Ingvar
    Tranvik, Lars J.
    Microbial biomass and community composition in boreal lake sediments2011Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 56, nr 2, s. 725-733Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We used phospholipid fatty acids (PLFA) to determine microbial biomass and community structure in the sediments of eight boreal lakes with different loadings of allochthonous organic carbon and total phosphorus (TP) in the water during the course of a year. The total concentration of PLFA, an estimate of the microbial biomass, depended more on TP, a proxy for pelagic primary production, but not on dissolved organic carbon, a proxy for terrestrial organic carbon input. The composition of PLFAs varied considerably over time, demonstrating seasonal dynamics in microbial community composition. When PLFA profiles in all lakes and seasons are compared, community composition is more similar within season than within lakes.

  • 20.
    Verheijen, Hendricus
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Gudasz, Cristian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Koizumi, Shuntaro
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Vachon, Dominic
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Contrasting impacts of terrestrial organic carbon inputs and warming on lake ecosystemsManuskript (preprint) (Annet vitenskapelig)
  • 21. Vrede, T
    et al.
    Ballantyne, A
    Mille-Lindblom, C
    Algesten, G
    Gudasz, Cristian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. ARCUM.
    Lindahl, S
    Brunberg, A K
    Effects of N: P loading ratios on phytoplankton community composition, primary production and N fixation in a eutrophic lake2009Inngår i: Freshwater Biology, Vol. 54, nr 2, s. 331-344Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    1. The aim of this study was to assess the effects of different nitrogen (N) to phosphorus (P) loading ratios on phytoplankton community composition and primary production in a naturally eutrophic lake. Furthermore, the sources of N fuelling primary production were estimated using (15)N stable isotope tracers.2. A mesocosm experiment was performed with the same amount of P added to all mesocosms (similar to internal loading rates) but with a range of N additions (0-86 mu m N), resulting in a gradient of N : P supply ratios.3. Low N : P supply ratios resulted in a significant shift in the phytoplankton assemblage to a community dominated by N-fixing cyanobacteria and a supply of atmospheric N(2) estimated to be up to 60% of total supply.4. The N : P loading ratio had no significant effect on primary production, total nitrogen (TN) concentration or particulate N concentration.5. Our results imply that a reduced N : P ratio of the nutrient load does not necessarily result in a lower TN concentration and downstream N export due to compensation by N-fixing cyanobacteria.

  • 22. Yvon-Durocher, Gabriel
    et al.
    Allen, Andrew P.
    Bastviken, David
    Conrad, Ralf
    Gudasz, Cristian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. ARCUM; Department of Ecology and Genetics, Limnology, Uppsala University, Norbyvägen 18D, SE-752 36, Uppsala Sweden; Department of Ecology and Evolutionary Biology, Princeton University, Princeton, 106A Guyot Hall, New Jersey 08544, USA.
    St-Pierre, Annick
    Thanh-Duc, Nguyen
    del Giorgio, Paul A.
    Methane fluxes show consistent temperature dependence across microbial to ecosystem scales2014Inngår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 507, nr 7493, s. 488-491Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Methane (CH4) is an important greenhouse gas because it has 25 times the global warming potential of carbon dioxide (CO2) by mass over a century(1). Recent calculations suggest that atmospheric CH4 emissions have been responsible for approximately 20% of Earth's warming since pre-industrial times(2). Understanding how CH4 emissions from ecosystems will respond to expected increases in global temperature is therefore fundamental to predicting whether the carbon cycle will mitigate or accelerate climate change. Methanogenesis is the terminal step in the remineralization of organic matter and is carried out by strictly anaerobic Archaea(3). Like most other forms of metabolism, methanogenesis is temperature-dependent(4,5). However, it is not yet known how this physiological response combines with other biotic processes (for example, methanotrophy(6), substrate supply(3,7), microbial community composition(8)) and abiotic processes (for example, water-table depth(9,10)) to determine the temperature dependence of ecosystem-level CH4 emissions. It is also not known whether CH4 emissions at the ecosystem level have a fundamentally different temperature dependence than other key fluxes in the carbon cycle, such as photosynthesis and respiration. Here we use meta-analyses to show that seasonal variations in CH4 emissions from a wide range of ecosystems exhibit an average temperature dependence similar to that of CH4 production derived from pure cultures of methanogens and anaerobic microbial communities. This average temperature dependence (0.96 electron volts (eV)), which corresponds to a 57-fold increase between 0 and 30 degrees C, is considerably higher than previously observed for respiration (approximately 0.65 eV)(11) and photosynthesis (approximately 0.3 eV)(12). As a result, we show that both the emission of CH4 and the ratio of CH4 to CO2 emissions increase markedly with seasonal increases in temperature. Our findings suggest that global warming may have a large impact on the relative contributions of CO2 and CH4 to total greenhouse gas emissions from aquatic ecosystems, terrestrial wetlands and rice paddies.

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