| 1. |
- Donis, Daphne, et al.
(author)
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Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer
- 2021
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In: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:12, s. 4314-4333
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Journal article (peer-reviewed)abstract
- To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L-1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4 degrees C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature.
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| 2. |
- Mantzouki, Evanthia, et al.
(author)
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Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins
- 2018
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In: Toxins. - : MDPI. - 2072-6651. ; 10:4
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Journal article (peer-reviewed)abstract
- Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.
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| 3. |
- Attermeyer, Katrin, et al.
(author)
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Carbon dioxide fluxes increase from day to night across European streams
- 2021
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In: Communications Earth & Environment. - : Springer Nature. - 2662-4435. ; 2:1
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Journal article (peer-reviewed)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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| 4. |
- Bravo, Andrea G., et al.
(author)
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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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In: Water Research. - : Elsevier. - 0043-1354 .- 1879-2448. ; 144, s. 172-182
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Journal article (peer-reviewed)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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| 5. |
- Bravo, Andrea G., et al.
(author)
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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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In: Water Research. - : Pergamon. - 0043-1354 .- 1879-2448. ; 144, s. 172-182
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Journal article (peer-reviewed)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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| 6. |
- Catalan, Jordi, et al.
(author)
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Global change revealed by palaeolimnological records from remote lakes : a review
- 2013
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In: Journal of Paleolimnology. - : Springer Netherlands. - 0921-2728 .- 1573-0417. ; 49:3, s. 513-535
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Journal article (peer-reviewed)abstract
- Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with respect to past, purely natural variability in lake systems. Fostering conceptual and methodological bridges with other environmental disciplines will upturn contribution of remote lake palaeolimnology in solving existing and emerging questions in global change science and planetary stewardship.
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| 7. |
- Cordero-Edwards, Kumara, et al.
(author)
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Flexoelectric Fracture-Ratchet Effect in Ferroelectrics
- 2019
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In: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 122:13
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Journal article (peer-reviewed)abstract
- The propagation front of a crack generates large strain gradients and it is therefore a strong source of gradient-induced polarization (flexoelectricity). Herein, we demonstrate that, in piezoelectric materials, a consequence of flexoelectricity is that crack propagation is helped or hindered depending on whether it is parallel or antiparallel to the piezoelectric polar axis. The discovery of crack propagation asymmetry proves that fracture physics cannot be assumed to be symmetric in polar materials, and indicates that flexoelectricity should be incorporated in any realistic model.
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| 8. |
- Hampton, Stephanie E., et al.
(author)
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Ecology under lake ice
- 2017
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In: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 20:1, s. 98-111
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Research review (peer-reviewed)abstract
- Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer ‘growing seasons’. We executed the first global quantitative synthesis on under-ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter-summer patterns for dissolved organic carbon (DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake-specific, species-specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass.
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| 9. |
- Nagler, Magdalena, et al.
(author)
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Abundance and biogeography of methanogenic and methanotrophic microorganisms across European streams
- 2021
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In: Journal of Biogeography. - : John Wiley & Sons. - 0305-0270 .- 1365-2699. ; 48:4, s. 947-960
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Journal article (peer-reviewed)abstract
- Aim: Although running waters are getting recognized as important methane sources, large‐scale geographical patterns of microorganisms controlling the net methane balance of streams are still unknown. Here we aim at describing community compositions of methanogenic and methanotrophic microorganisms at large spatial scales and at linking their abundances to potential sediment methane production (PMP) and oxidation rates (PMO).Location: The study spans across 16 European streams from northern Spain to northern Sweden and from western Ireland to western Bulgaria.Taxon: Methanogenic archaea and methane‐oxidizing microorganisms.Methods: To provide a geographical overview of both groups in a single approach, microbial communities and abundances were investigated via 16S rRNA gene sequencing, extracting relevant OTUs based on literature; both groups were quantified via quantitative PCR targeting mcrA and pmoA genes and studied in relation to environmental parameters, sediment PMP and PMO, and land use.Results: Diversity of methanogenic archaea was higher in warmer streams and of methanotrophic communities in southern sampling sites and in larger streams. Anthropogenically altered, warm and oxygen‐poor streams were dominated by the highly efficient methanogenic families Methanospirillaceae, Methanosarcinaceae and Methanobacteriaceae, but did not harbour any specific methanotrophic organisms. Contrastingly, sediment communities in colder, oxygen‐rich waters with little anthropogenic impact were characterized by methanogenic Methanosaetaceae, Methanocellaceae and Methanoflorentaceae and methanotrophic Methylococcaceae and Cd. Methanoperedens. Representatives of the methanotrophic Crenotrichaceae and Methylococcaceae as well as the methanogenic Methanoregulaceae were characteristic for environments with larger catchment area and higher discharge. PMP increased with increasing abundance of methanogenic archaea, while PMO rates did not show correlations with abundances of methane‐oxidizing bacteria.Main conclusions: Methanogenic and methanotrophic communities grouping into three habitat types suggest that future climate‐ and land use changes may influence the prevailing microbes involved in the large‐scale stream‐related methane cycle, favouring the growth of highly efficient hydrogenotrophic methane producers. Based on these results, we expect global change effect on PMP rates to especially impact rivers adjacent to anthropogenically disturbed land uses.
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