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Steger, Kristin
Publications (6 of 6) Show all publications
Steger, K., Premke, K., Gudasz, C., Boschker, H. T. & Tranvik, L. J. J. (2015). Comparative study on bacterial carbon sources in lake sediments: the role of methanotrophy. Aquatic Microbial Ecology, 76(1), 39-47
Open this publication in new window or tab >>Comparative study on bacterial carbon sources in lake sediments: the role of methanotrophy
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2015 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 76, no 1, p. 39-47Article in journal (Refereed) Published
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 delta C-13-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 C-13:C-12 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.

Keywords
Benthic microbes, Boreal lakes, Methanotrophic bacteria, Phospholipid-derived fatty acid, PLFA, Stable isotopes
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-265605 (URN)10.3354/ame01766 (DOI)000362667300004 ()
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning
Available from: 2015-11-02 Created: 2015-11-02 Last updated: 2020-01-28Bibliographically approved
Koehler, B., Corre, M. D., Steger, K., Well, R., Zehe, E., Sueta, J. P. & Veldkamp, E. (2012). An in-depth look into tropical lowland forest soil: nitrogen-addition effects on the content of N2O, CO2 and CH4 ad N2O isotopic signatures down to 2-m depth. Biogeochemistry, 111(1-3), 695-713
Open this publication in new window or tab >>An in-depth look into tropical lowland forest soil: nitrogen-addition effects on the content of N2O, CO2 and CH4 ad N2O isotopic signatures down to 2-m depth
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2012 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 111, no 1-3, p. 695-713Article in journal (Refereed) Published
Abstract [en]

Atmospheric nitrogen (N) deposition is rapidly increasing in tropical regions. We investigated how a decade of experimental N addition (125 kg N ha−1 year−1) to a seasonal lowland forest affected depth distribution and contents of soil nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4), as well as natural abundance isotopic signatures of N2O, nitrate (NO3 ) and ammonium (NH4 +). In the control plots during dry season, we deduced limited N2O production by denitrification in the topsoil (0.05–0.40 m) as indicated by: ambient N2O concentrations and ambient 15N-N2O signatures, low water-filled pore space (35–60%), and similar 15N signatures of N2O and NO3 . In the subsoil (0.40–2.00 m), we detected evidence of N2O reduction to N2 during upward diffusion, indicating denitrification activity. During wet season, we found that N2O at 0.05–2.00 m was mainly produced by denitrification with substantial further reduction to N2, as indicated by: lighter 15N-N2O than 15N-NO3 throughout the profile, and increasing N2O concentrations with simultaneously decreasing 15N-N2O enrichment with depth. These interpretations were supported by an isotopomer map and by a positive correlation between 18O-N2O and 15N-N2O site preferences. Long-term N addition did not affect dry-season soil N2O-N contents, doubled wet-season soil N2O-N contents, did not affect 15N signatures of NO3 , and reduced wet-season 15N signatures of N2O compared to the control plots. These suggest that the increased NO3 concentrations have stimulated N2O production and decreased N2O-to-N2 reduction. Soil CO2-C contents did not differ between treatments, implying that N addition essentially did not influence soil C cycling. The pronounced seasonality in soil respiration was largely attributable to enhanced topsoil respiration as indicated by a wet-season increase in the topsoil CO2-C contents. The N-addition plots showed reduced dry-season soil CH4-C contents and threshold CH4 concentrations were reached at a shallower depth compared to the control plots, revealing an N-induced stimulation of methanotrophic activity. However, the net soil CH4 uptake rates remained similar between treatments possibly because diffusive CH4 supply from the atmosphere largely limited CH4 oxidation.

Keywords
Carbon dioxide, Isotopes, Methane, Nitrogen, Nitrous oxide, Panama, PLFA, Tropical forest
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-190973 (URN)10.1007/s10533-012-9711-6 (DOI)000314063200043 ()
Note

Correction in Biogeochemistry, vol. 111, issue 1-3, pages 715-717.

DOI: 10.1007/s10533-012-9780-6

Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2017-12-06Bibliographically approved
Gudasz, C., Bastviken, D., Premke, K., Steger, K. & Tranvik, L. J. (2012). Constrained microbial processing of allochthonous organic carbon in boreal lake sediments. Limnology and Oceanography, 57(1), 163-175
Open this publication in new window or tab >>Constrained microbial processing of allochthonous organic carbon in boreal lake sediments
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2012 (English)In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 57, no 1, p. 163-175Article in journal (Refereed) Published
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 on a seasonal basis and along a lake depth gradient together with different water and sediment characteristics. Sediment bacterial metabolism was primarily controlled by temperature but also regulated by organic carbon quality/origin. 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 amounts of terrestrial organic carbon do not result in enhanced sediment bacterial metabolism.  Meio- and macrobenthic invertebrate biomass were at most weakly correlated to bacterial metabolism and biomass, suggesting limited control of sediment bacteria by grazing. We suggest that the 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.

Keywords
allochthonous organic carbon, microbial metabolism, lake sediments
National Category
Ecology
Research subject
Limnology
Identifiers
urn:nbn:se:uu:diva-150712 (URN)10.4319/lo.2012.57.1.0163 (DOI)000298321300014 ()
Available from: 2011-04-04 Created: 2011-04-04 Last updated: 2020-01-28Bibliographically approved
Bartels, P., Cucherousset, J., Steger, K., Eklöv, P., Tranvik, L. J. & Hillebrand, H. (2012). Reciprocal subsidies between freshwater and terrestrial ecosystems structure consumer-resource dynamics. Ecology, 93(5), 1173-1182
Open this publication in new window or tab >>Reciprocal subsidies between freshwater and terrestrial ecosystems structure consumer-resource dynamics
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2012 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 93, no 5, p. 1173-1182Article in journal (Refereed) Published
Abstract [en]

Cross-ecosystem movements of material and energy, particularly reciprocal resource fluxes across the freshwater-land interface, have received major attention. Freshwater ecosystems may receive higher amounts of subsidies (i.e., resources produced outside the focal ecosystem) than terrestrial ecosystems, potentially leading to increased secondary production in freshwaters. Here we used a meta-analytic approach to quantify the magnitude and direction of subsidy inputs across the freshwater-land interface and to determine subsequent responses in recipient animals. Terrestrial and freshwater ecosystems differed in the magnitude of subsidies they received, with aquatic ecosystems generally receiving higher subsidies than terrestrial ecosystems. Surprisingly, and despite the large discrepancy in magnitude, the contribution of these subsidies to animal carbon inferred from stable isotope composition did not differ between freshwater and terrestrial ecosystems, likely due to the differences in subsidy quality. The contribution of allochthonous subsidies was highest to primary consumers and predators, suggesting that bottom-up and top-down effects may be affected considerably by the input of allochthonous resources. Future work on subsidies will profit from a food web dynamic approach including indirect trophic interactions and propagating effects.

National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-160772 (URN)10.1890/11-1210.1 (DOI)000304368100022 ()
Available from: 2011-10-31 Created: 2011-10-31 Last updated: 2017-12-08Bibliographically approved
Bartels, P., Cucherousset, J., Gudasz, C., Jansson, M., Karlsson, J., Persson, L., . . . Eklöv, P. (2012). Terrestrial subsidies to lake food webs: An experimental approach. Oecologia, 168(3), 807-818
Open this publication in new window or tab >>Terrestrial subsidies to lake food webs: An experimental approach
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2012 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 168, no 3, p. 807-818Article in journal (Refereed) Published
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.

Keywords
Allochthonous, Cross-ecosystem, Autochthonous, Aquatic-terrestrial linkage, Benthic
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-160774 (URN)10.1007/s00442-011-2141-7 (DOI)000301706800020 ()
Available from: 2011-10-31 Created: 2011-10-31 Last updated: 2020-01-28Bibliographically approved
Gudasz, C., Bastviken, D., Steger, K., Premke, K., Sobek, S. & Tranvik, L. J. (2010). Temperature-controlled organic carbon mineralization in lake sediments. Nature, 466(7305), 478-481
Open this publication in new window or tab >>Temperature-controlled organic carbon mineralization in lake sediments
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2010 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 466, no 7305, p. 478-481Article in journal (Refereed) Published
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.

National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-135652 (URN)10.1038/nature09186 (DOI)000280141200033 ()
Note

Correction in Nature, vol. 466, issue 7310, doi 10.1038/nature09383

Available from: 2010-12-08 Created: 2010-12-07 Last updated: 2020-01-28Bibliographically approved
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