Lake Zurich Research Articles

Sedimentary DNA Reveals Cyanobacterial Community Diversity over 200 Years in Two Perialpine Lakes.

Cyanobacterial blooms can produce toxins that affect water quality, especially under eutrophic conditions, which are a consequence of human-induced climate warming and increased nutrient availability. Lakes worldwide have suffered from regular cyanobacterial blooms over the last century. The lack of long-term data limits our understanding of how these blooms form. We successfully reconstructed the past diversity of whole cyanobacterial communities over two hundred years by sequencing genes preserved in the sediments of two perialpine lakes in Switzerland. We identified changes in diversity over time and validated our results using existing data collected in the same two lakes over the past 40 years. This work shows the potential of our approach for addressing important ecological questions about the effects of a changing environment on lake ecology.

Compound-specific carbon and nitrogen isotopic compositions of chlorophyll a and its derivatives reveal the eutrophication history of Lake Zurich (Switzerland)

Compound-specific carbon and nitrogen isotopic compositions of chlorophyll a and its derivatives reveal the eutrophication history of Lake Zurich (Switzerland)

Lake Dwellings in Baden-Württemberg. Conservation Projects In Situ at Lake Constance and the Federsee Moor

The Baden-Württemberg shoreline of Lake Constance and the lakes and moors of Upper Swabia contain important prehistoric wetland sites. From 1979, new research has brought up not only important finds and scientific results but also increasing information about bank erosion in the lakes and desiccation in the moorlands. At Lake Constance, early attempts were made in the 1980s to protect sites threatened by erosion by covering them with geo-textile and gravel. With further protective projects the know-how improved, but crucial questions still remained: What are the best practical solutions? How about ecological compatibility? Do we have other options? The INTERREG IV 2008–2011 international project ‘Erosion and Archaeological Heritage Protection in Lake Constance and Lake Zurich’ brought deeper insights and opened the field for new experiments with protective measures. At the Federsee Moor a long-term project started in 1980 with close collaboration between nature conservation and archaeological heritage management. With archaeological stocktaking, acquisition of land, establishment of new nature reserves, exchange of landholding and hydrographic engineering, the project was completed with the help of European Union funding by LIFE+in 2013.

Distributions and compound-specific isotopic signatures of sedimentary chlorins reflect the composition of photoautotrophic communities and their carbon and nitrogen sources in Swiss lakes and the Black Sea

We examined the distributions of tetrapyrrole pigments (i.e. intact chlorophylls and bacteriochlorophylls, pheopigments) as well as their compound-specific carbon and nitrogen isotopic compositions in the sediments of three Swiss lakes (Lakes Rotsee, Cadagno and Zurich) and the Black Sea to investigate the biogeochemical cycling of carbon and nitrogen mediated by phototrophic eukaryotes (algae) and bacteria. The factors controlling chlorin isotope variations are discussed and the feasibility to use chlorins as indicators for reconstructions of surface water environments is evaluated. Chlorophyll a and its derivatives including pheophytin a, a pheophytin a epimer, pyropheophytin a, 132,173-cyclopheophorbide-a-enol, chlorophyllone a as well as steryl and carotenol chlorin esters were detected in all sediments. The presence of bacteriochlorophylls e and their derivatives confirmed the presence of brown strains of green phototrophic sulfur bacteria (Chlorobiaceae; GSB) in all three lakes. In the shallower Lakes Rotsee and Cadagno, purple sulfur bacteria (Chromatiaceae; PSB) were also present as confirmed by bacteriochlorophyll a derivatives. Despite the different degrees of water column hypoxia at the studied sites, the chlorins in all sediments were attributed to rapid transformation of intact tetrapyrroles and the formation of related pheopigments. The scatter of compound-specific carbon isotopic compositions of Chl a and its derivatives resulted from different timing of pheopigment formation, likely due to the interaction of blooms of various phytoplankton communities at different times of the year and the variable degrees of carbon limitation and/or different contributions of recycled organic matter (OM). The nitrogen isotopic composition of the chloropigments mainly derived from nitrate assimilation in Lake Zurich and the Black Sea, whereas ammonium and nitrate assimilation were predominant in Lake Rotsee. In the epilimnion of the meromictic Lake Cadagno, dissolved organic nitrogen (DON) supplied to the surface water from ammonium assimilation in the chemocline may be the main nitrogen source. Phototrophic sulfur bacteria in Lakes Rotsee and Cadagno thrived mainly under dissolved organic carbon depleted conditions within the chemocline and in the hypolimnion. GSB may use predominantly ammonium and at least in Lake Cadagno also perform N2 fixation. In contrast, the nitrogen source of PSB could not be reconstructed with δ15N values of bacteriochlorins, because nitrogen isotopic fractionation during BChl a synthesis seems to be almost independent of the assimilated substrate.

Prolongation, deepening and warming of the metalimnion change habitat conditions of the harmful filamentous cyanobacterium Planktothrix rubescens in a prealpine lake

The most prominent responses of Lake Zurich to climate warming include the increase of surface water temperatures, a reduced depth of spring mixing, and the persistent thriving of the harmful cyanobacterium Planktothrix rubescens, a low-light adapted species concentrating in the metalimnion during summer. To study changes of its habitat, we assessed the spatio-temporal metalimnetic boundaries by applying low-pass filtering and binary thresholding to temperature profiles of long-term data (1978–2013, weekly measurements). Due to increasing temperatures over the last 3.5 decades, the onset and duration of metalimnion formation changed significantly (stratification increased by 33 days). Moreover, the upper metalimnetic boundary has undergone a significant drawdown of 2.3 m, accounting for an overall decrease in metalimnion thickness. Being the most abundant species in this zone, P. rubescens was not negatively affected by altered temporal or spatial stratification patterns during its phase of net growth (July–September), as the zone of its optimal light-dependent buoyancy was still located within the metalimnion. The biomass of P. rubescens in August was even significantly related to increasing temperatures. Nevertheless, a further depression of the metalimnetic top boundary may eventually restrict P. rubescens by forcing it into layers of unfavourable light conditions or into the turbulent epilimnetic zone.

High-throughput determination of dissolved free amino acids in unconcentrated freshwater by ion-pairing liquid chromatography and mass spectrometry

We developed a procedure for the direct determination of dissolved free amino acids (DFAAs) in freshwater samples employing ion-pairing liquid chromatography and mass spectrometry. Our approach allowed accurate quantification of subnanomolar concentrations of DFAAs without prior concentration, derivatization or sample clean-up steps, achieving a throughput of three samples per hour. DFAAs were separated on a C-18 resin using tridecafluoroheptanoic acid as an ion-pairing agent controlling the overall retention. The relative standard deviation of DFAA measurements was <10% in samples from the mesotrophic Lake Zurich (Switzerland), and across concentrations of 0.5–500nM. Recoveries of DFAAs ranged from 94 to 102% within the range of 0.2–10nM. The limits of quantification for individual DFAAs varied between 50pM to 2nM (median, 0.5nM). The new method was employed to compare the spatial variability of DFAA concentrations in samples obtained by two devices. Epilimnetic samples of different size (ml, l) were collected at various spatial scales (cm, m, km) with a traditional 5l Friedinger sampler and with a custom-made multi-syringe sampling apparatus. Concentrations of total DFAAs ranged from 30 to 330nM. Alanine, serine, glutamic acid, arginine and glycine constituted 65% of the total pool, while methionine and tryptophan occurred at sub-nM concentrations only. Concentrations of individual DFAAs varied spatially over 2 orders of magnitude. Their spatial distribution was positively skewed, as characterized by rare peaks, most strongly so for glutamate, glycine and asparagine. The composition of DFAAs significantly differed at all examined spatial scales, and this could be mainly attributed to alanine, aspartic acid, and glycine. Our new method equals or outperforms existing ones in terms of sensitivity and reproducibility, while its procedural simplicity renders it superior for the high-throughput analysis of freshwater samples.

Efficacy of a nAg modified orthodontic primer reducing demineralization around brackets: an in vivo study

Event Abstract Back to Event Efficacy of a nAg modified orthodontic primer reducing demineralization around brackets: an in vivo study Gabriela Moreno-Meraz1, Facundo Ruiz2, Mauricio Pierdant-Pérez3, Antonio A. Gordillo-Moscoso3, Gylmar Mariel-Cárdenas4, Jairo Mariel-Cárdenas5 and Wulfrano Sánchez-Meraz5 1 UASLP, Faculty of Medicine / Faculty of Sciences, Mexico 2 UASLP, Faculty of Sciences, Mexico 3 UASLP, Faculty of Medicine, Mexico 4 UASLP, Faculty of Engineering, Mexico 5 UASLP, Faculty of Stomatology, Mexico Introduction: Tooth enamel, also called enamel tissue or enamel substance way cap covers the dentin in its coronal portion providing protection to the underlying connective tissue. Since enamel composition is based on 95% inorganic matrix it presents a high hardness. Hydroxyapatite crystals are constituted by calcium phosphate, this represents the inorganic component of enamel. Hydroxyapatite crystals are densely packed and are larger than other mineralized tissues. These crystals are susceptible acid substrate, this component is which increases dental demineralization.[1] Dental demineralization is considered to be the most prevalent iatrogenic effect associated with orthodontic treatment and might be jeopardize the longevity and aesthetics of the dental organ associated. It has been documented that the onset and progression of weakness in the enamel surface or dental caries is directly associated with Streptococcus mutans and its prevalence is related to the complexity of itself. It has been clinically proven, that the formation of white opaque spots around braces can occur within the 4 weeks of starting the treatment.[2][3] Silver nanoparticles have demonstrated efficacy as antimicrobials, and some studies have shown that these antimicrobial properties are particularly effective reducing the population of Streptococcus mutans.[4][5][6][7][8] The aim of this study was to compare changes in enamel adjacent to orthodontic brackets using bonding agents enriched with silver nanoparticles (nAg) compared to a conventional primer adhesive with laser fluorescence. Materials and Methods: According with previous studies, Transbond™ XT Primer was doped with silver nanoparticles, A split-mouth design was applied to 20 healthy patients, (40 teeth)[9] who were to begin orthodontic treatment. The brackets were cemented with the nAg doped primer (TX0) randomly allocated to either the right or the left side of the maxilla and it was applied to the incisors following the manufacturer's protocol. The contralateral teeth had the same type of bracket and a conventional primer (TX1) (with no nAg). DIAGNOdent (KaVo Dental Corporation, Lake Zurich, Ill) [10]measurements were used to assess white spot lesions after 8 weeks. This study is registred in the clinical trials page. Results: All analyses were performed with R software version 3.1.0 and R Commander version 2.0-4 package 95% confidence level. [11]There were no missing observations. To determine the effectiveness of treatment, an analysis of the final measurements an ANOVA was performed. The final model (Demineralizatión~Basal + Tx) was significant F (39) = 31.4, p <0.001. It can be explained 63% of the variation in the set of explanatory variables. The mean in FINAL score when TX0 = 3.25 + 1.99 is lower than the mean of FINAL score when TX1 = 9.85 + 6.39. The difference in scores between the two groups is 6.13 (CI 95%, 3.82 - 8.43). Conclusion: Baseline measurements for both treatments showed demineralization degree as the initial score taken with diagnodent. However, the difference in baseline mean was not significant. The teeth, which were primed with nAg doped Transbond XT, had lower final mean score than those primed with conventional Transbond XT, at 8 weeks from baseline measure. This may be attributed to the antimicrobial effect of silver nanoparticles and this effect is not modified after curing the primer. Other studies to evaluate the type of bracket, and to evaluate whether increasing the amount of nanoparticles, the antimicrobial power of the primer is increased without changing its physical properties, and if it persists over time. are needed. UASLP

Network of Interactions Between Ciliates and Phytoplankton During Spring.

The annually recurrent spring phytoplankton blooms in freshwater lakes initiate pronounced successions of planktonic ciliate species. Although there is considerable knowledge on the taxonomic diversity of these ciliates, their species-specific interactions with other microorganisms are still not well understood. Here we present the succession patterns of 20 morphotypes of ciliates during spring in Lake Zurich, Switzerland, and we relate their abundances to phytoplankton genera, flagellates, heterotrophic bacteria, and abiotic parameters. Interspecific relationships were analyzed by contemporaneous correlations and time-lagged co-occurrence and visualized as association networks. The contemporaneous network pointed to the pivotal role of distinct ciliate species (e.g., Balanion planctonicum, Rimostrombidium humile) as primary consumers of cryptomonads, revealed a clear overclustering of mixotrophic/omnivorous species, and highlighted the role of Halteria/Pelagohalteria as important bacterivores. By contrast, time-lagged statistical approaches (like local similarity analyses, LSA) proved to be inadequate for the evaluation of high-frequency sampling data. LSA led to a conspicuous inflation of significant associations, making it difficult to establish ecologically plausible interactions between ciliates and other microorganisms. Nevertheless, if adequate statistical procedures are selected, association networks can be powerful tools to formulate testable hypotheses about the autecology of only recently described ciliate species.

The use of flint-stone fragments as “fire-strikers” during the Neolithic period: Complementary micro-analytical evidences

The construction of an underground parking garage in the centre of Zurich (Zurich Opéra Parking, Switzerland) unearthed remains of seven Neolithic settlements from the 4th and 3rd millennium BC. The greatest number of prehistoric founds were retrieved from the 3175 BC layer (Horgen culture). Among the findings, several thousand flint-stone fragments were excavated. According to archaeologists’ interpretation, based on wear patterns, some of them were certainly used to produce fire. Remarkably, a limited number of the flint-stones revealed additional characteristic metallic traces of potential anthropogenic origin. The contingent relation of these fragments to fire production was to be elucidated. An advanced, non-destructive micro-analytical approach was needed to characterise these unusual features. Seven flints were thus analysed by laboratory-based μ-XRF and RAMAN spectroscopy complemented by two-dimensional microscopic chemical imaging based on combined μ-XRD–μ-XRF analysis using micro-focused synchrotron radiation. The complementary results showed that all flint-stones, even the most doubtful, presented abundant traces of Fe-sulphide, which were almost exclusively pyrite. Only sporadic indications towards the presence of trace amounts of marcasite and chalcopyrite were found. Furthermore, during the excavation, Fe-sulphide ore pieces were found in the same layer as the flint-stones. Geologically, these iron nodules appeared to be non-native to the setting in which they have been observed. The Fe-sulphide ore was also undoubtedly recognised as pyrite, indicating its potential use, conjointly with the flints, to kindle fire in a more efficient manner by the Neolithic populations at Lake Zurich more than 5000years ago.

Seasonal patterns of microcystin-producing and non-producing Planktothrix rubescens genotypes in a deep pre-alpine lake

The filamentous cyanobacterium Planktothrix rubescens produces secondary metabolites called microcystins (MC) that are potent toxins for most eukaryotes, including zooplankton grazers, cattle and humans. P. rubescens occurs in many deep and thermally stratified lakes throughout Europe. In Lake Zurich (Switzerland), it re-appeared in the 1970s concomitant with decreasing eutrophication. Since then, P. rubescens has become the dominant species in this major drinking water reservoir, where it forms massive metalimnetic blooms during late summer. These cyanobacteria harbor subpopulations of non-MC producers, but little is known about the environmental factors affecting the success of such genotypes. The non-MC-producing subpopulation of P. rubescens was studied using a quantitative real-time PCR (qPCR) assay on the MC synthetase (mcy) gene cluster that targets a deletion on the mcyH and mcyA genes, which inactivates MC biosynthesis. Two complementary qPCR assays were used to assess the total population abundance (based on the 16S rDNA gene) and the mcy gene copy number (based on a conserved region in the adenylation domain of the mcyB gene). The objective was to evaluate the seasonal patterns of the share of non-MC-producing filaments in the total P. rubescens population. The mcyHA mutants were present in low proportions (up to 14%) throughout the year. Their highest relative abundances occurred during the winter mixis, when total concentrations of P. rubescens were minimal. The MC deficient mutants seemed to better survive in sparse populations, possibly because of lower grazing pressure and a consequently reduced need for MC-mediated protection. Alternatively, the mutants might cope better with the sub-optimal, stressful pressure and light conditions during the winter mixis. Altogether, our results suggest that subtle trade-offs might seasonally determine the proportions of non-MC producers within P. rubescens populations.

Landscape opening and herding strategies: Carbon isotope analyses of herbivore bone collagen from the Neolithic and Bronze Age lakeshore site of Zurich-Mozartstrasse, Switzerland

Abstract Carbon isotope analysis (δ13C) was performed on collagen extracted from 54 domestic cattle (Bos taurus) and 20 red deer (Cervus elaphus) bones from the Neolithic (3913–2586 BC) and Bronze Age (1950–950 cal. BC) layers of the lakeshore site Zurich-Mozartstrasse located in the lower Lake Zurich basin, Switzerland. We observed shifts in the δ13C of both domestic cattle and red deer over two millennia. Mean δ13C values of red deer changed from −24.1 ± 0.7‰ to −22.5 ± 0.3‰, while mean δ13C values of domestic cattle showed minor changes from −22.7 ± 1.3‰ to −22.1 ± 0.3‰. Our data suggest that in the early 4th millennium BC the landscape was densely forested with red deer feeding in closed habitats and cattle grazing in more open landscapes. Forest was also a food resource for some young cattle as indicated by the lower δ13C values of non-adult relative to adult animals. This points to a greater diversity of herding strategies and feeding techniques compared to the later periods. The landscape was still rather forested towards the mid-3rd millennium BC, with no obvious changes in the habitat use of the large herbivores. However, the carbon isotopes suggest a clearly reduced forest cover in the 2nd millennium BC with red deer using similar open feeding grounds as domestic cattle. Our study demonstrates that the stable carbon isotope composition of archeological bone material from large herbivores can provide integrative constraints on paleoenvironmental and vegetation changes, prehistoric animal management and land-use.

Where Fantasy and Facts Meet: Fairy Science Books from 1870 to 1900

Natalie Ziarnik is the Head of the Children’s Department at the Ela Area Public Library District in Lake Zurich, Illinois. She is a member of the Hans Christian Andersen Nominating Committee.

The ecology of pelagic freshwater methylotrophs assessed by a high-resolution monitoring and isolation campaign.

Methylotrophic planktonic bacteria fulfill a particular role in the carbon cycle of lakes via the turnover of single-carbon compounds. We studied two planktonic freshwater lineages (LD28 and PRD01a001B) affiliated with Methylophilaceae (Betaproteobacteria) in Lake Zurich, Switzerland, by a combination of molecular and cultivation-based approaches. Their spatio-temporal distribution was monitored at high resolution (n=992 samples) for 4 consecutive years. LD28 methylotrophs constituted up to 11 × 10(7) cells l(-1) with pronounced peaks in spring and autumn-winter, concomitant with blooms of primary producers. They were rare in the warm water layers during summer but abundant in the cold hypolimnion, hinting at psychrophilic growth. Members of the PRD01a001B lineage were generally less abundant but also had maxima in spring. More than 120 axenic strains from these so far uncultivated lineages were isolated from the pelagic zone by dilution to extinction. Phylogenetic analysis separated isolates into two distinct genotypes. Isolates grew slowly (μmax=0.4 d(-1)), were of conspicuously small size, and were indeed psychrophilic, with higher growth yield at low temperatures. Growth was enhanced upon addition of methanol and methylamine to sterile lake water. Genomic analyses of two strains confirmed a methylotrophic lifestyle with a reduced set of genes involved in C1 metabolism. The very small and streamlined genomes (1.36 and 1.75 Mb) shared several pathways with the marine OM43 lineage. As the closest described taxa (Methylotenera sp.) are only distantly related to either set of isolates, we propose a new genus with two species, that is, 'Candidatus Methylopumilus planktonicus' (LD28) and 'Candidatus Methylopumilus turicensis' (PRD01a001B).

Challenges and prospects for interpreting long‐term phytoplankton diversity changes in Lake Zurich (Switzerland)

Summary Analysing and interpreting long‐term phytoplankton time series present a number of challenges, arising from potential historical inconsistencies in data collection and taxonomic identification of organisms. In a previous paper, Pomati et al. (2012) found a remarkable increase in phytoplankton diversity that coincided with oligotrophication and warming of Lake Zurich over a 32‐year period. These findings were recently challenged on the basis of potential biases in detection limits and taxonomic classification over the time series (Straile, Jochimsen &amp; Kümmerlin, 2013). We agree that being cautious with long‐term phytoplankton data series is extremely important, but argue that the increase in richness detected in Lake Zurich cannot be due only to methodological bias. Following additional analysis of the Lake Zurich phytoplankton dataset, we found that the shift in taxon detection limits reported by Straile et al. (2013) is not supported by the data and stems from a rounding error in the calculation of density in the dataset available to those authors. We found a decline in the proportional abundance for common taxa, an increase in the annual prevalence of taxa and reduced community turnover over the time series. Taken together, the data clearly indicate a trend of decreasing dominance, while more taxa coexist simultaneously. We also argue that the taxonomic classification has been robust (at least at the family level) and propose a diagnostic plot that can help detect an unbiased signal of change in plankton richness through time. Straile et al. (2013) observed perfect synchrony in species occurrence between Lake Zurich and nearby Lake Walen. While we agree that such perfect synchrony in community composition can reflect a bias in the database compilation, it can also be an important ecological signal of changes in regional species pools that deserves further analysis. We conclude that the results of Pomati et al. (2012) are robust and not substantially undermined by the criticisms of Straile et al. (2013). More generally, it is indeed possible to extract meaningful signals of biodiversity change from long‐term phytoplankton monitoring datasets, provided there is a clear understanding of how the data have been sampled, recorded and analysed over the history of the time series.

Taxonomic aggregation does not alleviate the lack of consistency in analysing diversity in long‐term phytoplankton monitoring data: a rejoinder to Pomati et al. (2015)

Summary Long‐term phytoplankton monitoring provides an important resource for studying the effects of environmental change on communities and testing ecological hypotheses. However, because of identification difficulties, maintaining consistency in the data over long periods is extremely difficult. It is usually assumed that consistency is improved when only one taxonomist is responsible throughout, and/or when data are aggregated to a coarser taxonomic level. Neither assumption has been critically tested. We address the comment of Pomati et al. (2015) on our earlier Opinion paper (Straile et al, 2013) and test these assumptions with the long‐term data from Lake Zurich. We show that aggregation to coarser taxonomic levels does not improve data set consistency because: (i) the proportional effect of misclassification is unlikely to be reduced by lumping taxa since the fewer misclassifications affect the dynamics of an overall lower number of taxa, that is the proportional effect is constant, and (ii) because changes in detection limits will affect all taxonomic levels proportionally. We also show that, although a single taxonomist supervised phytoplankton recordings, data consistency is undermined by: (i) learning via exchange with other taxonomists and participation in taxonomic workshops, and (ii) a reduction in detection limits of species, presumably due to an increase in the number of taxonomists (allowing an increased processing time per sample). As a consequence of (i) a reduction in detection limits, (ii) the confirmed taxonomic learning and (iii) the failure of taxonomic aggregation to improve consistency, our new evidence strengthens the view that there are consistency problems in the Lake Zurich data set, and the need for a critical review of the conclusions of Pomati et al. (2012) and Matthews &amp; Pomati (2012).

Post-glacial rock avalanches in the Obersee Valley, Glarner Alps, Switzerland

The geological record of prehistoric rock avalanches provides invaluable data for assessing the hazard posed by these rare but destructive mass movements. Here we investigate two large rock avalanches in the Obersee valley of the Glarner Alps, Switzerland, providing detailed mapping of landslide and related Quaternary phenomena, revised volume estimates for each event, and surface exposure dating of rock avalanche deposits. The Rautispitz rock avalanche originated from the southern flank of the Obersee valley, releasing approximately 91 million m3 of limestone on steeply-dipping bedding planes. Debris had maximum horizontal travel distance of ~5000m, a fahrboeschung angle (relating fall height to length) of 18°, and was responsible for the creation of Lake Obersee; deposits are more than 130m thick in places. The Platten rock avalanche encompassed a source volume of 11 million m3 sliding from the northern flank of the Obersee valley on similar steeply-dipping limestone beds (bedrock forms a syncline under the valley). Debris had a maximum horizontal travel distance of 1600m with a fahrboeschung angle of 21°, and is more than 80m thick in places. Deposits of the Platten rock avalanche are superposed atop those from the Rautispitz event at the end of the Obersee valley where they dam Lake Haslensee. Runout for both events was simulated using the dynamic analysis code DAN3D; results showed excellent match to mapped deposit extents and thickness and helped confirm the hypothesized single-event failure scenarios. 36Cl cosmogenic nuclide surface exposure dating of 13 deposited boulders revealed a Younger Dryas age of 12.6±1.0ka for the Rautispitz rock avalanche and a mid-Holocene age of 6.1±0.8ka for the Platten rock avalanche. A seismological trigger is proposed for the former event due to potentially correlated turbidite deposits in nearby Lake Zurich.

Plastic pollution in Swiss surface waters: nature and concentrations, interaction with pollutants

Environmental contextPlastic, and particularly microplastic, pollution is a growing environmental concern worldwide. Research regarding marine environments has led to a substantial increase in knowledge, yet little is known as regards the situation in freshwater environments. Although the occurrence of microplastics was demonstrated in Lake Geneva in 2012, the present research aims at confirming this pollution and expanding the data set for other lakes and environments of Switzerland. AbstractMarine microplastic (&lt;5mm) water pollution has met growing public and scientific interest in the last few years. The situation in freshwater environments remains largely unknown, although it appears that they play an important role as part of the origin of marine pollution. Apart from the physical impacts on biota, chemical effects are to be expected as well, especially with smaller particles. This study aims at assessing plastic abundance in Lakes Geneva, Constance, Neuchâtel, Maggiore, Zurich and Brienz, and identifying the nature of the particles, potential ingestion by birds and fishes, and the associated pollutants. Lake surface transects and a few rivers were sampled using a floating manta net, and beach sediments were analysed. Plastics were sorted by type (fragments, pellets, cosmetic beads, lines, fibres, films, foams) and composition (polypropylene, polyethylene, polystyrene, etc.); fish and water birds were dissected to assess their potential exposure, and analyses were conducted on the hydrophobic micropollutants adsorbed to the microplastics as well as some potentially toxic additives they contained. Evidence of this pollution is shown for all lakes, microplastics of all types and diverse composition having been found in all samples. Birds and fish are prone to microplastic ingestion, and all the tested chemicals (both adsorbed micropollutants and contained additives) were found above the detection limit, and often the quantification limit. The sources and their respective contribution need to be confirmed and quantified, and the ecotoxicological effects need further investigation. Other questions remain open, including the transport and fate of plastic particles in the environment.

A novel ion-exclusion chromatography–mass spectrometry method to measure concentrations and cycling rates of carbohydrates and amino sugars in freshwaters

The concentrations of free neutral carbohydrates and amino sugars were determined in freshwater samples of distinct matrix complexity, including meso-, eu- and dystrophic lakes and ponds, using high-performance ion-exclusion chromatography (HPIEC) coupled to mass spectrometry (MS). In contrast to other methods, our approach allowed the quantification of free neutral carbohydrates and amino sugars at low nM concentrations without derivatization, de-salting or pre-concentration. New sample preparation procedures were applied prior to injection employing syringe and hollow fiber filtration. Analytes were separated on a strong cation exchange resin under 100% aqueous conditions using 0.1% formic acid as a mobile phase. To minimize background noise in MS, analytes were detected in a multiple reaction monitoring scan mode with double ion filtering. Detection limits of carbohydrates and amino sugars ranged between 0.2 and 2nM at a signal-to-noise ratio >5. Error ranged between 1 and 12% at 0.5–500nM levels. Using a stable isotope dilution approach, both the utilization and recycling of glucose in Lake Zurich was observed. In contrast, N-acetyl-glucosamine was equally rapidly consumed but there was no visible de novo production. The simple and rapid sample preparation makes our protocol suitable for routine analyses of organic compounds in freshwater samples. Application of stable isotope tracers along with accurate measures of carbohydrate and amino sugar concentrations enables novel insights into the compound in situ dynamics.

Ménage-à-trois: The Amoeba Nuclearia sp. from Lake Zurich with its Ecto- and Endosymbiotic Bacteria

We present a fascinating triad relationship between a eukaryotic amoeba and its two bacterial symbionts. The morphological characteristics of the amoeba allowed for a confident assignment to the genus Nuclearia (Opisthokonta, Nucleariidae), but species identification resulted in an ambiguous result. Sequence analysis indicated an affiliation to the species N. thermophila, however, several morphological features contradict the original description. Amoebal isolates were cultured for several years with their preferred food source, the microcystin-producing harmful cyanobacterium Planktothrix rubescens. Symbioses of the amoeba with ecto- and endosymbiotic bacteria were maintained over this period. Several thousand cells of the ectosymbiont are regularly arranged inside a layer of extracellular polymeric substances produced by the amoeba. The ectosymbiont was identified as Paucibacter toxinivorans (Betaproteobacteria), which was originally isolated by enrichment with microcystins. We found indications that our isolated ectosymbiont indeed contributed to toxin-degradation. The endosymbiont (Gammaproteobacteria, 15-20 bacteria per amoeba) is enclosed in symbiosomes inside the host cytoplasm and represents probably an obligate symbiont. We propose the name "Candidatus Endonucleariobacter rarus" for this bacterium that was neither found free-living nor in a symbiotic association. Nucleariidae are uniquely suited model organisms to study the basic principles of symbioses between opisthokonts and prokaryotes.

Seasonal growth potential of rare lake water bacteria suggest their disproportional contribution to carbon fluxes.

We studied the seasonal growth potential of opportunistic bacterial populations in Lake Zurich (Switzerland) by a series of grazer-free dilution culture assays. Pronounced shifts in the composition of the bacterial assemblages were observed within one doubling of total cell numbers, from initially abundant Actinobacteria to other fast-growing microbial lineages. Small populations with growth potentials far above community average were detected throughout the year with striking seasonal differences in their respective taxonomic affiliations. Members of Cytophaga-Flavobacteria (CF) were disproportionally proliferating only during phytoplankton blooms in spring and summer, while Beta- and Gammaproteobacteria showed superior growth at all other occasions. Growth rates of Alphaproteobacteria and esp. Sphingomonadaceae were significantly correlated to water temperatures and were far above community average in summer. Within the genus Flavobacterium, two species-like populations showed a tendency for fast growth in most experiments, while four others were exclusively proliferating either during a spring or during a summer phytoplankton bloom. Their high growth potentials but low in situ abundances hint at a tight control by bacterivorous grazers and at a consequently accelerated carbon flux to higher trophic levels.