| 1. |
- Andersson, Martin G. I., et al.
(författare)
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Effects of sterilization on dissolved organic carbon (DOC) composition and bacterial utilization of DOC from lakes
- 2018
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 82:2, s. 199-208
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Andersson, Martin, et al.
(författare)
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Response and effect interactions between bacterial communities and organic matter
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The interaction between bacteria and dissolved organic matter (DOM) is crucial for the global carbon cycling. Despite decades of research there are, however, few consistent patterns regarding the relationship between bacterial diversity and community composition and DOM. Here we hypothesized that one reason for such inconsistences among studies is that bacterial communities can adapt to a DOM source over time, whereby a change in the functioning of a community can be, at least partly, decoupled from its composition and diversity. To test this idea we performed a reciprocal transplant experiment with medium (i.e. DOM source) and bacterial communities from two boreal lakes. In this experiment the two communities were allowed to adapt to their indigenous and their foreign source of DOM over 42 days. Bacterial community composition (BCC) was measured throughout the experiment. In addition we measured the capacity of the communities to use DOM, in repeated short (5 days) separated bioassays. The results show a response of bacterial community composition to the DOM sources which was influenced by the origin of the community. In contrast, we could not show an effect of BCC on DOM-processing and functional performance. Indeed, communities of different origin processed the two DOM sources equally well even at the beginning of the experiment. This work demonstrates that the DOM pool can be a strong selective force for BCC but not vice versa.
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| 3. |
- Andersson, Martin, et al.
(författare)
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The relative importance of richness and BCC for DOC degradation
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The importance of biodiversity has been of primary interest for ecologist the last 20 years, giving rise to biodiversity ecosystem function (BEF) studies. Within the traditional field of ecology reoccurring patterns have emerged but within microbial ecology the importance of species richness for functioning is still poorly understood with few consistent patterns. In this study we examined the effect of species richness for dissolved organic matter degradation in lakes. This was examined within a smaller span of species richness compared to what is typically in microbial BEF experiments. Bacterial communities of reduced species richness were exposed to a range of DOC environments to test if reduced richness changed the functioning of communities and if the effect was similar among DOC environments. This was conducted in a full factorial design of 3 levels, with 6 dilutions, 5 media and 3 inocula resulting in 90 treatments. Overall, richness and community composition appeared to have effects on DOC degradation, but these effects were minor compared to the variation caused by the different DOC sources. Further, the importance of species richness varied among media and, thus, the chemical complexity of the environment influenced the biodiversity-ecosystem functioning relationship.
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| 4. |
- Attermeyer, Katrin, et al.
(författare)
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Carbon dioxide fluxes increase from day to night across European streams
- 2021
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Ingår i: Communications Earth & Environment. - : Springer Nature. - 2662-4435. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majority originates from streams and rivers. Despite the global significance of fluvial carbon dioxide emissions, little is known about their diel dynamics. Here we present a large-scale assessment of day- and night-time carbon dioxide fluxes at the water-air interface across 34 European streams. We directly measured fluxes four times between October 2016 and July 2017 using drifting chambers. Median fluxes are 1.4 and 2.1mmolm(-2) h(-1) at midday and midnight, respectively, with night fluxes exceeding those during the day by 39%. We attribute diel carbon dioxide flux variability mainly to changes in the water partial pressure of carbon dioxide. However, no consistent drivers could be identified across sites. Our findings highlight widespread day-night changes in fluvial carbon dioxide fluxes and suggest that the time of day greatly influences measured carbon dioxide fluxes across European streams. Diel patterns can greatly impact total stream carbon dioxide emissions, with 39% greater carbon dioxide flux during the night-time relative to the day-time, according to a study of 34 streams across Europe.
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| 5. |
- Attermeyer, Katrin, et al.
(författare)
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Organic Carbon Processing During Transport Through Boreal Inland Waters : Particles as Important Sites
- 2018
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 123:8, s. 2412-2428
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Attermeyer, Katrin, et al.
(författare)
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Potential terrestrial influence on transparent exopolymer particle (TEP) concentrations in boreal freshwaters
- 2019
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Ingår i: Journal of limnology. - : Wiley. - 1129-5767 .- 1723-8633. ; 64:6, s. 2455-2466
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Bengtsson, Mia M., et al.
(författare)
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Interactive effects on organic matter processing from soils to the ocean : are priming effects relevant in aquatic ecosystems?
- 2018
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Ingår i: Hydrobiologia. - : Springer. - 0018-8158 .- 1573-5117. ; 822:1, s. 1-17
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Forskningsöversikt (refereegranskat)abstract
- Organic matter (OM) is degraded during transport from soils to oceans. However, there are spatial and temporal variabilities along the aquatic continuum, which hamper the development of carbon cycling models. One concept that has been applied in this context is the priming effect (PE), describing non-additive effects on OM degradation after mixing sources of contrasting bioavailability. Studies on the aquatic PE report divergent results from positive (increased OM degradation rates) to neutral, to negative (decreased OM degradation rates) effects upon mixing. Here, we aim to condense the outcomes of these studies on aquatic PE. Based on a literature review, we discuss differences in the reported PEs across freshwater and marine ecosystems, identifying system-specific features that could favour non-additive effects on OM degradation. Using a quantitative meta-analysis approach, we evaluated the occurrence, direction (positive vs. negative) and magnitude of aquatic PE. The meta-analysis revealed a mean PE of 12.6%, which was not significantly different from zero across studies. Hence, mixing of contrasting OM sources in aquatic ecosystems does not necessarily result in a change in OM degradation rates. Therefore, we suggest to focus on molecular and microbial diversity and function, which could provide a better mechanistic understanding of processes driving OM interactions.
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| 8. |
- Bravo, Andrea G., et al.
(författare)
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The interplay between total mercury, methylmercury and dissolved organic matter in fluvial systems : A latitudinal study across Europe
- 2018
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Ingår i: Water Research. - : Elsevier. - 0043-1354 .- 1879-2448. ; 144, s. 172-182
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-mercury (MeHg) concentrations in aquatic ecosystems. Studies attempting to link dissolved organic matter (DOM) to levels of THg or MeHg are few and geographically constrained. Additionally, stream and river systems have been understudied as compared to lakes. Hence, the aim of this study was to examine the influence of DOM concentration and composition, morphological descriptors, land uses and water chemistry on THg and MeHg concentrations and the percentage of THg as MeHg (%MeHg) in 29 streams across Europe spanning from 41°N to 64°N. THg concentrations (0.06–2.78 ng L−1) were highest in streams characterized by DOM with a high terrestrial soil signature and low nutrient content. MeHg concentrations (7.8–159 pg L−1) varied non-systematically across systems. Relationships between DOM bulk characteristics and THg and MeHg suggest that while soil derived DOM inputs control THg concentrations, autochthonous DOM (aquatically produced) and the availability of electron acceptors for Hg methylating microorganisms (e.g. sulfate) drive %MeHg and potentially MeHg concentration. Overall, these results highlight the large spatial variability in THg and MeHg concentrations at the European scale, and underscore the importance of DOM composition on mercury cycling in fluvial systems.
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| 9. |
- Bravo, Andrea G., et al.
(författare)
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The interplay between total mercury, methylmercury and dissolved organic matter in fluvial systems : A latitudinal study across Europe
- 2018
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Ingår i: Water Research. - : Pergamon. - 0043-1354 .- 1879-2448. ; 144, s. 172-182
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-mercury (MeHg) concentrations in aquatic ecosystems. Studies attempting to link dissolved organic matter (DOM) to levels of THg or MeHg are few and geographically constrained. Additionally, stream and river systems have been understudied as compared to lakes. Hence, the aim of this study was to examine the influence of DOM concentration and composition, morphological descriptors, land uses and water chemistry on THg and MeHg concentrations and the percentage of THg as MeHg (%MeHg) in 29 streams across Europe spanning from 41°N to 64 °N. THg concentrations (0.06–2.78 ng L−1) were highest in streams characterized by DOM with a high terrestrial soil signature and low nutrient content. MeHg concentrations (7.8–159 pg L−1) varied non-systematically across systems. Relationships between DOM bulk characteristics and THg and MeHg suggest that while soil derived DOM inputs control THg concentrations, autochthonous DOM (aquatically produced) and the availability of electron acceptors for Hg methylating microorganisms (e.g. sulfate) drive %MeHg and potentially MeHg concentration. Overall, these results highlight the large spatial variability in THg and MeHg concentrations at the European scale, and underscore the importance of DOM composition on mercury cycling in fluvial systems.
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| 10. |
- Casas-Ruiz, Joan P., et al.
(författare)
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A tale of pipes and reactors : Controls on the in-stream dynamics of dissolved organic matter in rivers
- 2017
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 62, s. S85-S94
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Tidskriftsartikel (refereegranskat)abstract
- The potential for rivers to alter the flux of dissolved organic matter (DOM) from land to ocean is widely accepted. Yet anticipating when and where rivers behave as active reactors vs. passive pipes of DOM stands as a major knowledge gap in river biogeochemistry, resulting in uncertainties for global carbon models. Here, we investigate the controls on in-stream DOM dynamics by evaluating changes in DOM concentration and composition along several reaches of a medium-sized river network over one full hydrological year. Roughly half of the observations over time and space showed active reactor conditions and, among these, similar pro-portion of gains and losses was measured. High water residence times promoted the active over passive behavior of the reaches, while DOM properties and nitrate availability determined whether they supplied or removed DOM from the river. Among different DOM fractions, protein-like DOM both of terrestrial and aquatic origin seemed to drive bulk DOM patterns. Our study emphasizes the role of water residence time as a physical constraint for in-stream processes, and provides new insights into the key factors governing the net balance between in-stream gains and losses of DOM in rivers.
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