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Nydahl, A., Wallin, M., Tranvik, L., Hiller, C., Attermeyer, K., Garrison, J. A., . . . Weyhenmeyer, G. A. (2019). Colored organic matter increases CO2 in meso-eutrophic lake water through altered light climate and acidity. Limnology and Oceanography, 64(2), 744-756
Open this publication in new window or tab >>Colored organic matter increases CO2 in meso-eutrophic lake water through altered light climate and acidity
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2019 (English)In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 64, no 2, p. 744-756Article in journal (Refereed) Published
Abstract [en]

Many surface waters across the boreal region are browning due to increased concentrations of colored allochthonous dissolved organic carbon (DOC). Browning may stimulate heterotrophic metabolism, may have a shading effect constraining primary production, and may acidify the water leading to decreased pH with a subsequent shift in the carbonate system. All these effects are expected to result in increased lake water carbon dioxide (CO2) concentrations. We tested here these expectations by assessing the effects of both altered allochthonous DOC input and light conditions through shading on lake water CO2 concentrations. We used two mesocosm experiments with water from the meso‐eutrophic Lake Erken, Sweden, to determine the relative importance of bacterial activities, primary production, and shifts in the carbonate system on CO2 concentrations. We found that DOC addition and shading resulted in a significant increase in partial pressure of CO2 (pCO2) in all mesocosms. Surprisingly, there was no relationship between bacterial activities and pCO2. Instead the experimental reduction of light by DOC and/or shading decreased the photosynthesis to respiration ratio leading to increased pCO2. Another driving force behind the observed pCO2 increase was a significant decrease in pH, caused by a decline in photosynthesis and the input of acidic DOC. Considering that colored allochthonous DOC may increase in a warmer and wetter climate, our results could also apply for whole lake ecosystems and pCO2 may increase in many lakes through a reduction in the rate of photosynthesis and decreased pH.

National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-366220 (URN)10.1002/lno.11072 (DOI)000461865500022 ()
Available from: 2018-11-18 Created: 2018-11-18 Last updated: 2019-08-15Bibliographically approved
Hawkes, J. A., Sjöberg, P. J. R., Bergquist, J. & Tranvik, L. (2019). Complexity of dissolved organic matter in the molecular size dimension: insights from coupled size exclusion chromatography electrospray ionisation mass spectrometry. Faraday discussions (Online)
Open this publication in new window or tab >>Complexity of dissolved organic matter in the molecular size dimension: insights from coupled size exclusion chromatography electrospray ionisation mass spectrometry
2019 (English)In: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498Article in journal (Refereed) Epub ahead of print
Abstract [en]

This paper investigates the relationship between apparent size distribution and molecular complexity of dissolved organic matter from the natural environment. We used a high pressure size exclusion chromatography (HPSEC) method coupled to UV-Vis diode array detection (UV-DAD) and electrospray ionisation mass spectrometry (ESI-MS) in order to compare the apparent size of natural organic matter, determined by HPSEC-UV and the molecular mass determined online by ESI-MS. We found that there was a clear discrepancy between the two methods, and found evidence for an important pool of organic matter that has a strong UV absorbance and no ESI-MS signal. Contrary to some previous research, we found no evidence that apparently high molecular weight organic matter is constituted by aggregates of low molecular weight (<1000 Da) material. Furthermore, our results suggest that the majority of apparent size variability within the ESI ionisable pool of organic matter is due to secondary interaction and exclusion effects on the HPSEC column, and not true differences in hydrodynamic size or intermolecular aggregation.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-384038 (URN)10.1039/c8fd00222c (DOI)
Available from: 2019-06-04 Created: 2019-06-04 Last updated: 2019-06-10Bibliographically approved
Kayler, Z. E., Premke, K., Gessler, A., Gessner, M., Gribler, C., Hilt, S., . . . Grossart, H.-P. (2019). Integrating aquatic and terrestrial perspectives to improve insights into organic matter cycling at the landscape scale. Frontiers in Earth Science, 7, Article ID 127.
Open this publication in new window or tab >>Integrating aquatic and terrestrial perspectives to improve insights into organic matter cycling at the landscape scale
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2019 (English)In: Frontiers in Earth Science, ISSN 2296-6463, Vol. 7, article id 127Article in journal (Refereed) Published
Abstract [en]

Across a landscape, aquatic-terrestrial interfaces within and between ecosystems are hotspots of organic matter (OM) mineralization. These interfaces are characterized by sharp spatio-temporal changes in environmental conditions, which affect OM properties and thus control OM mineralization and other transformation processes. Consequently, the extent of OM movement at and across aquatic-terrestrial interfaces is crucial in determining OM turnover and carbon (C) cycling at the landscape scale. Here, we propose expanding current concepts in aquatic and terrestrial ecosystem sciences to comprehensively evaluate OM turnover at the landscape scale. We focus on three main concepts toward explaining OM turnover at the landscape scale: the landscape spatio-temporal context, OM turnover described by priming and ecological stoichiometry, and anthropogenic effects as a disruptor of natural OM transfer magnitudes and pathways. A conceptual framework is introduced that allows for discussing the disparities in spatial and temporal scales of OM transfer, changes in environmental conditions, ecosystem connectivity, and microbial–substrate interactions. The potential relevance of priming effects in both terrestrial and aquatic systems is addressed. For terrestrial systems, we hypothesize that the interplay between the influx of OM and its corresponding elemental composition and the elemental demand of the microbial communities – stoichiometric question – may alleviate spatial and metabolic thresholds. In comparison, substrate level OM dynamics may be substantially different in aquatic systems due to matrix effects that accentuate the role of abiotic conditions, substrate quality, and microbial community dynamics. We highlight the disproportionate impact anthropogenic activities can have on OM cycling across the landscape including reversing natural OM flows through the landscape, disrupting ecosystem connectivity, and nutrient additions that cascade across the landscape. This knowledge is crucial for a better understanding of OM cycling in a landscape context, in particular since terrestrial and aquatic compartments may respond differently to the ongoing changes in climate, land use, and other anthropogenic interferences.

Keywords
Landscape connectivity, Organic matter mineralization, Priming effects (PEs), Ecological stoichiometry, Aquatic-terrestrial interfaces
National Category
Other Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-384357 (URN)10.3389/feart.2019.00127 (DOI)000470916700001 ()
Available from: 2019-06-04 Created: 2019-06-04 Last updated: 2019-07-05Bibliographically approved
Attermeyer, K., Andersson, S., Catalán, N., Einarsdóttir, K., Groeneveld, M. M., Szekely, A. J. & Tranvik, L. (2019). Potential terrestrial influence on transparent exopolymer particle (TEP) concentrations in boreal freshwaters. Journal of limnology
Open this publication in new window or tab >>Potential terrestrial influence on transparent exopolymer particle (TEP) concentrations in boreal freshwaters
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2019 (English)In: Journal of limnology, ISSN 1129-5767, E-ISSN 1723-8633Article in journal (Refereed) Epub ahead of print
Abstract [en]

Transparent exopolymer particles (TEP) are ubiquitous in aquatic ecosystems and contribute, for example, to sedimentation of organic matter in oceans and freshwaters. Earlier studies indicate that the formation of TEP is related to the in situ activity of phytoplankton or bacteria. However, terrestrial sources of TEP and TEP precursors are usually not considered. We investigated TEP concentration and its driving factors in boreal freshwaters, hypoth- esizing that TEP and TEP precursors can enter freshwaters via terrestrial inputs. In a field survey, we measured TEP concentrations and other environmental factors across 30 aquatic ecosystems in Sweden. In a mesocosm experi- ment, we further investigated TEP dynamics over time after manipulating terrestrial organic matter input and light conditions. The TEP concentrations in boreal freshwaters ranged from 83 to 4940 μg Gum Xanthan equivalent L−1, which is comparable to other studies in freshwaters. The carbon fraction in TEP in the sampled boreal freshwaters is much higher than the phytoplanktonic carbon, in contrast to previous studies in northern temperate and Medi- terranean regions. Boreal TEP concentrations were mostly related to particulate organic carbon, dissolved organic carbon, and optical indices of terrestrial influence but less influenced by bacterial abundance, bacterial production, and chlorophyll a. Hence, our results do not support a major role of the phytoplankton community or aquatic bac- teria on TEP concentrations and dynamics. This suggests a strong external control of TEP concentrations in boreal freshwaters, which can in turn affect particle dynamics and sedimentation in the recipient aquatic ecosystem.

National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-384035 (URN)10.1002/lno.11197 (DOI)
Funder
Swedish Research Council, 2014-04264Knut and Alice Wallenberg Foundation, KAW 2013.0091German Research Foundation (DFG), AT 185/1-1
Available from: 2019-06-04 Created: 2019-06-04 Last updated: 2019-06-10Bibliographically approved
Andersson, M. G. I., Catalán, N., Rahman, Z., Tranvik, L. J. & Lindström, E. S. (2018). Effects of sterilization on dissolved organic carbon (DOC) composition and bacterial utilization of DOC from lakes. Aquatic Microbial Ecology, 82(2), 199-208
Open this publication in new window or tab >>Effects of sterilization on dissolved organic carbon (DOC) composition and bacterial utilization of DOC from lakes
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2018 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 82, no 2, p. 199-208Article in journal (Refereed) Published
Abstract [en]

Sterilization of dissolved organic carbon (DOC) is an essential step in research on interactions between DOC and organisms, for example where the effect of different microbial communities on DOC is studied or vice versa. However, few studies have gone beyond acknowledging that sterilization of DOC influences its characteristics. Here, we aimed to provide further knowledge that enables scientists to better tailor their sterilization methods to their research question. To meet this aim, we conducted a sterilization experiment with DOC from 4 boreal lakes treated with 4 sterilization methods, i.e. 2 filtrations (0.2 µm, 0.1 µm) and 2 autoclaving approaches (single and double autoclaving with a single pH adjustment). Quantity and spectroscopic properties of DOC, before and after sterilization, were studied, and DOC was further tested as a substrate for bacterial growth. We found that the filtration methods better preserved the different DOC measures. In contrast, autoclaving caused major inconsistent shifts in both qualitative and quantitative measures of DOC, as well as an increase of the maximum abundance of bacteria in growth experiments. Nonetheless, there remains a trade-off between retaining the quality of DOC and achieving sterile conditions. Therefore, the sterilization method of choice should be guided by the scientific question at hand.

Keywords
sterilization, autoclave, filtration, dissolved organic carbon, excitation emission matrices, parallel factor analysis
National Category
Biological Sciences
Research subject
Microbiology
Identifiers
urn:nbn:se:uu:diva-331676 (URN)10.3354/ame01890 (DOI)000454321300006 ()
Note

Title in Thesis list of papers: Effects of sterilization on composition and bacterial utilization of dissolved organic carbon

Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2019-01-15Bibliographically approved
Hawkes, J. A., Patriarca, C., Sjöberg, P. J. R., Tranvik, L. & Bergquist, J. (2018). Extreme isomeric complexity of dissolved organic matter found across aquatic environments. Limnology and Oceanography Letters, 3(2), 21-30
Open this publication in new window or tab >>Extreme isomeric complexity of dissolved organic matter found across aquatic environments
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2018 (English)In: Limnology and Oceanography Letters, E-ISSN 2378-2242, Vol. 3, no 2, p. 21-30Article in journal (Refereed) Published
Abstract [en]

The natural aquatic environment contains an enormous pool of dissolved reduced carbon, present as ultra‐complex mixtures that are constituted by an unknown number of compounds at vanishingly small concentrations. We attempted to separate individual structural isomers from several samples using online reversed‐phase chromatography with selected ion monitoring/tandem mass spectrometry, but found that isomeric complexity still presented a boundary to investigation even after chromatographic simplification of the samples. However, it was possible to determine that the structural complexity differed among samples. Our results also suggest that extreme structural complexity was a ubiquitous feature of dissolved organic matter (DOM) in all aquatic systems, meaning that this diversity may play similar roles for recalcitrance and degradation of DOM in all tested environments.

National Category
Chemical Sciences Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-369282 (URN)10.1002/lol2.10064 (DOI)000456695800001 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Energy Agency
Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2019-02-12Bibliographically approved
Tranvik, L. (2018). New light on black carbon. Nature Geoscience, 11(8), 547-548
Open this publication in new window or tab >>New light on black carbon
2018 (English)In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 11, no 8, p. 547-548Article in journal (Other academic) Published
Abstract [en]

Much of the carbon in rivers originates from wildfires and is ultimately buried in the oceanic carbon sink, suggest measurements from 18 rivers globally. Rivers transport almost a gigaton of carbon to the oceans every year.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
National Category
Geochemistry
Identifiers
urn:nbn:se:uu:diva-365678 (URN)10.1038/s41561-018-0181-x (DOI)000440301400003 ()
Available from: 2018-11-16 Created: 2018-11-16 Last updated: 2018-11-16Bibliographically approved
Patriarca, C., Bergquist, J., Sjöberg, P. J., Tranvik, L. & Hawkes, J. A. (2018). Online HPLC-ESI-HRMS Method for the Analysis and Comparison of Different Dissolved Organic Matter Samples. Environmental Science and Technology, 52(4), 2091-2099
Open this publication in new window or tab >>Online HPLC-ESI-HRMS Method for the Analysis and Comparison of Different Dissolved Organic Matter Samples
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2018 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 52, no 4, p. 2091-2099Article in journal (Refereed) Published
Abstract [en]

Natural dissolved organic matter (DOM) is an ultracomplex mixture that is essential to global carbon cycling but is poorly understood because of its complexity. The most powerful tool for the DOM characterization is high-resolution mass spectrometry (HRMS) generally combined to direct infusion (DI) as sample introduction. Liquid chromatography (LC) represents a compelling alternative to DI; however, state-of-the-art techniques involve only offline LC-HRMS approaches, which have important logistical drawbacks that make DOM analysis more challenging. This study introduces a new method based on online coupling of liquid chromatography to high resolution mass spectrometry, able to overcome the disadvantages of usual approaches. It is characterized by high reproducibility (% Bray–Curtis dissimilarity among replicates ≈ 2.5%), and it reduces transient complexity and contaminant interferences, thus increasing the signal-to-noise ratio (S/N), leading to the identification of an overall larger number of formulas in the mixture. Moreover, the application of an in silico fractionation prior to the statistical analysis allows an easy, flexible, fast, and detailed comparison of DOM samples from a variety of sources with a single chromatographic run.

National Category
Analytical Chemistry
Research subject
Chemistry with specialization in Analytical Chemistry
Identifiers
urn:nbn:se:uu:diva-341015 (URN)10.1021/acs.est.7b04508 (DOI)000426143300045 ()
Funder
Knut and Alice Wallenberg Foundation, 2013.0091Swedish Research Council, SRC 2015-4870Swedish Research Council, SRC 2014-04264
Available from: 2018-02-06 Created: 2018-02-06 Last updated: 2018-12-12Bibliographically approved
Attermeyer, K., Catalan, N., Einarsdóttir, K., Freixa, A., Groeneveld, M. M., Hawkes, J. A., . . . Tranvik, L. (2018). Organic Carbon Processing During Transport Through Boreal Inland Waters: Particles as Important Sites. Journal of Geophysical Research - Biogeosciences, 123(8), 2412-2428
Open this publication in new window or tab >>Organic Carbon Processing During Transport Through Boreal Inland Waters: Particles as Important Sites
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2018 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 123, no 8, p. 2412-2428Article in journal (Refereed) Published
Abstract [en]

The degradation and transformation of organic carbon (C) in inland waters result in significant CO2 emissions from inland waters. Even though most of the C in inland waters occurs as dissolved organic carbon (DOC), studies on particulate organic carbon (POC) and how it influences the overall reactivity of organic C in transport are still scarce. We sampled 30 aquatic ecosystems following an aquatic continuum including peat surface waters, streams, rivers, and lakes. We report DOC and POC degradation rates, relate degradation patterns to environmental data across these systems, and present qualitative changes in dissolved organic matter and particulate organic matter during degradation. Microbial degradation rates of POC were approximately 15 times higher compared to degradation of DOC, with POC half-lives of only 17 +/- 3 (mean +/- SE) days across all sampled aquatic ecosystems. Rapid POC decay was accompanied by a shift in particulate C: N ratios, whereas dissolved organic matter composition did not change at the time scale of incubations. The faster degradation of the POC implies a constant replenishment to sustain natural POC concentrations. We suggest that degradation of organic matter transported through the inland water continuum might occur to a large extent via transition of DOC into more rapidly cycling POC in nature, for example, triggered by light. In this way, particles would be a dominant pool of organic C processing across the boreal aquatic continuum, partially sustained by replenishment via flocculation of DOC.

National Category
Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-363637 (URN)10.1029/2018JG004500 (DOI)000445731100009 ()
Funder
Knut and Alice Wallenberg Foundation, KAW 2013.0091Swedish Research Council, 2014-04264Swedish Research Council, 2015-4870German Research Foundation (DFG), AT 185/1-1
Available from: 2018-10-18 Created: 2018-10-18 Last updated: 2019-06-10Bibliographically approved
Hawkes, J. A., Radoman, N., Bergquist, J., Wallin, M., Tranvik, L. & Löfgren, S. (2018). Regional diversity of complex dissolved organic matter across forested hemiboreal headwater streams. Scientific Reports, 8(1), Article ID 16060.
Open this publication in new window or tab >>Regional diversity of complex dissolved organic matter across forested hemiboreal headwater streams
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2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, no 1, article id 16060Article in journal (Refereed) Published
Abstract [en]

Dissolved organic matter (DOM) from soils enters the aquatic environment via headwater streams. Thereafter, it is gradually transformed, removed by sedimentation, and mineralised. Due to the proximity to the terrestrial source and short water residence time, the extent of transformation is minimal in headwaters. DOM has variable composition across inland waters, but the amount of variability in the terrestrial end member is unknown. This gap in knowledge is crucial considering the potential impact large variability would have on modelling DOM degradation. Here, we used a novel liquid chromatography –mass spectrometry method to characterise DOM in 74 randomly selected, forested headwater streams in an 87,000 km2 region of southeast Sweden. We found a large degree of sample similarity across this region, with Bray-Curtis dissimilarity values averaging 8.4 ± 3.0% (mean ± SD). The identified variability could be reduced to two principle coordinates, correlating to varying groundwater flow-paths and regional mean temperature. Our results indicate that despite reproducible effects of groundwater geochemistry and climate, the composition of DOM is remarkably similar across catchments already as it leaves the terrestrial environment, rather than becoming homogeneous as different headwaters and sub-catchments mix.

National Category
Environmental Sciences Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-366056 (URN)10.1038/s41598-018-34272-3 (DOI)000448745700002 ()30375497 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, 2013.0091Swedish Research Council, 2015-4870Swedish Energy Agency, 81708-3
Available from: 2018-11-15 Created: 2018-11-15 Last updated: 2019-01-08Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-3509-8266

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