Drivers of atmospheric deposition of polycyclic aromatic hydrocarbons at European high-altitude sites

Arellano L., Fernández P., Van Drooge B.L., Rose N.L., Nickus U., Thies H., Stuchlík E., Camarero L., Catalan J., Grimalt J.O. (2018) Drivers of atmospheric deposition of polycyclic aromatic hydrocarbons at European high-altitude sites. Atmospheric Chemistry and Physics. 18: 16081-16097.
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Doi: 10.5194/acp-18-16081-2018

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Polycyclic aromatic hydrocarbons (PAHs) were analysed in bulk atmospheric deposition samples collected at four European high-mountain areas, Gossenköllesee (Tyrolean Alps), Redon (Central Pyrenees), Skalnate Pleso (High Tatra Mountains), and Lochnagar (Grampian Mountains) between 2004 and 2006. Sample collection was performed monthly in the first three sites and biweekly in Lochnagar. The number of sites, period of study and sampling frequency provide the most comprehensive description of PAH fallout in high mountain areas addressed so far. The average PAH deposition fluxes in Gossenköllesee, Redon and Lochnagar ranged between 0.8 and 2.1 μgm-2 month-1, and in Skalnate Pleso it was 9.7 μgm-2 month-1, showing the influence of substantial inputs from regional emission sources. The deposited distributions of PAHs were dominated by parent phenanthrene, fluoranthene and pyrene, representing 32 %-60% of the total. The proportion of phenanthrene, the most abundant compound, was higher at the sites of lower temperature, Gossenköllesee and Skalnate Pleso, showing higher transfer from gas phase to particles of the more volatile PAHs. The sites with lower insolation, e.g. those located at lower altitude, were those with a higher proportion of photooxidable compounds such as benz[a]anthracene. According to the data analysed, precipitation is the main driver of PAH fallout. However, when rain and snow deposition were low, particle settling also constituted an efficient driver for PAH deposition. Redon and Lochnagar were the two sites receiving the highest amounts of rain and snow and the fallout of PAH fluxes was related to this precipitation. No significant association was observed between long-range backward air trajectories and PAH deposition in Lochnagar, but in Redon PAH fallout at higher precipitation was essentially related to air masses originating from the North Atlantic, which were dominant between November and May (cold season). In these cases, particle-normalised PAH fallout was also associated with higher precipitation as these air masses were concurrent with lower temperatures, which enhanced gas to particle partitioning transfer. In the warm season (June-October), most of the air masses arriving at Redon originated from the south and particle deposition was enhanced as consequence of Saharan inputs. In these cases, particle settling was also a driver of PAH deposition despite the low overall PAH content of the Saharan particles. In Gossenköllesee, the site receiving lowest precipitation, PAH fallout was also related to particle deposition. The particle-normalised PAH fluxes were significantly negatively correlated to temperature, e.g. for air masses originating from central and eastern Europe, showing a dominant transfer from gas phase to particles at lower temperatures, which enhanced PAH fallout, mainly of the most volatile hydrocarbons. Comparison of PAH atmospheric deposition and lacustrine sedimentary fluxes showed much higher values in the latter case of 24-100 μgm-2 yr-1 vs. 120-3000 μgm-2 yr-1. A strong significant correlation was observed between these two fluxes, which is consistent with a dominant origin related to atmospheric deposition at each site. © 2018 IEEE Transactions on Mobile Computing. All rights resered.

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Experimental evidence of the quantitative relationship between the prokaryote ingestion rate and the food vacuole content in mixotrophic phytoflagellates

Ballen-Segura M., Catalan J., Felip M. (2018) Experimental evidence of the quantitative relationship between the prokaryote ingestion rate and the food vacuole content in mixotrophic phytoflagellates. Environmental Microbiology Reports. 10: 704-710.
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Doi: 10.1111/1758-2229.12696

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The verification that many phytoflagellates ingest prokaryotes has changed the view of the microbial loop in aquatic ecosystems. Still, progress is limited because the phagotrophic activity is difficult to quantify in natural assemblages. Linking the food vacuole content in protist with the ingestion rate of prokaryotes would provide a crucial step forward. In this study, using the catalysed reporter deposition – fluorescence in situ hybridization protocol (CARD-FISH), which allows the visualization of labelled prokaryotes inside protists without relying on incubation procedures, we experimentally relate the food vacuole content of prokaryotes (Vc) to the population-averaged ingestion rates (Ir) estimated using bacteria-size fluorescent microspheres. The two variables relate according to the equation Ir = 7.52 Vc 0.9, which indicates a prokaryote half-life of about 6 min in the protist vacuole. Five mixotrophic flagellate species from natural and culture populations were evaluated seven times during 24 h; they provided a broad range of average vacuole content (0.01 to 2.02 prokaryote protist−1) and ingestion rates (0.18 to 23 prokaryote protist−1 h−1). Consequently, the relationship found can be applied to quantify the mixotrophy activity in a large variety of field and experimental studies. © 2018 Society for Applied Microbiology and John Wiley & Sons Ltd

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Digital long-term topoclimate surfaces of the Pyrenees mountain range for the period 1950–2012

Batalla M., Ninyerola M., Catalan J. (2018) Digital long-term topoclimate surfaces of the Pyrenees mountain range for the period 1950–2012. Geoscience Data Journal. 5: 50-62.
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Doi: 10.1002/gdj3.52

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Long-term climate data accounting for high-spatial variability and detailed topographic effects are crucial for research and management in complex terrains such as mountain ranges. Here, we introduce the Pyrenean Digital Climate Atlas based on data from around 400 weather stations located across the range during the 1950–2012 period. Average monthly, seasonal, and annual temporal resolutions are provided for 30-m spatial resolution surfaces. Local heterogeneity was considered, integrating meteorological station data, high-quality terrain information (altitude, latitude, distance to the sea, and solar potential radiation) and multivariate regression modelling in a Geographical Information System. Climate surfaces of air temperature (minimum, maximum, and mean) and precipitation were obtained and used to derive maps of bioclimatic interest such as potential evapotranspiration, water availability, and growing degree-days. Metadata are provided in XML standard format (ISO 19139) with all the usual fields and quality indicators for each map, with an RMSE ranging from 0.7 to 1.2°C and 11 to 15 mm for air temperature and precipitation maps respectively. The Atlas is available in GeoTIFF format at the ZENODO repository. Open Practices: This article has earned an Open Data badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at DOI 10.5281/zenodo.1186639. Learn more about the Open Practices badges from the Center for Open Science: https://osf.io/tvyxz/wiki. © 2018 The Authors. Geoscience Data Journal published by Royal Meteorological Society and John Wiley & Sons Ltd.

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High planktonic diversity in mountain lakes contains similar contributions of autotrophic, heterotrophic and parasitic eukaryotic life forms

Ortiz-Álvarez R., Triadó-Margarit X., Camarero L., Casamayor E.O., Catalan J. (2018) High planktonic diversity in mountain lakes contains similar contributions of autotrophic, heterotrophic and parasitic eukaryotic life forms. Scientific Reports. 8: 0-0.
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Doi: 10.1038/s41598-018-22835-3

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A rich eukaryotic planktonic community exists in high-mountain lakes despite the diluted, oligotrophic and cold, harsh prevailing conditions. Attempts of an overarching appraisal have been traditionally hampered by observational limitations of small, colorless, and soft eukaryotes. We aimed to uncover the regional eukaryotic biodiversity of a mountain lakes district to obtain general conclusions on diversity patterns, dominance, geographic diversification, and food-web players common to oligotrophic worldwide distributed freshwater systems. An unprecedented survey of 227 high-altitude lakes comprising large environmental gradients was carried out using Illumina massive tag sequencing of the 18S rRNA gene. We observed a large Chrysophyceae dominance in richness, abundance and novelty, and unveiled an unexpected richness in heterotrophic phagotrophs and parasites. In particular, Cercozoa and Chytridiomycota showed diversity features similar to the dominant autotrophic groups. The prominent beta-dispersion shown by parasites suggests highly specific interactions and a relevant role in food webs. Interestingly, the freshwater Pyrenean metacommunity contained more diverse specific populations than its closest marine oligotrophic equivalent, with consistently higher beta-diversity. The relevance of unseen groups opens new perspectives for the better understanding of planktonic food webs. Mountain lakes, with remarkable environmental idiosyncrasies, may be suitable environments for the genetic diversification of microscopic eukaryotic life forms. © 2018 The Author(s).

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Denitrification Temperature Dependence in Remote, Cold, and N-Poor Lake Sediments

Palacin-Lizarbe C., Camarero L., Catalan J. (2018) Denitrification Temperature Dependence in Remote, Cold, and N-Poor Lake Sediments. Water Resources Research. 54: 1161-1173.
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Doi: 10.1002/2017WR021680

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The reservoir size and pathway rates of the nitrogen (N) cycle have been deeply modified by the human enhancement of N fixation, atmospheric emissions, and climate warming. Denitrification (DEN) transforms nitrate into nitrogenous gas and thus removes reactive nitrogen (Nr) back to the atmospheric reservoir. There is still a rather limited knowledge of the denitrification rates and their temperature dependence across ecosystems; particularly, for the abundant cold and N-poor freshwater systems (e.g., Arctic and mountain lakes). We experimentally investigated the denitrification rates of mountain lake sediments by manipulating nitrate concentration and temperature on field collected cores. DEN rates were nitrate limited in field conditions and showed a large potential for an immediate DEN increase with both warming and higher Nr load. The estimated activation energy (Ea) for denitrification at nitrate saturation was 46 ± 7 kJ mol−1 (Q10 1.7 ± 0.4). The apparent Ea increased with nitrate (μM) limitation as Ea = 46 + 419 [NO2 −]−1. Accordingly, we suggest that climate warming may have a synergistic effect with N emission reduction to readjusting the N cycle. Changes of nitrate availability might be more relevant than direct temperature effects on denitrification. © 2018. American Geophysical Union. All Rights Reserved.

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Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors

Palacin-Lizarbe C., Camarero L., Catalan J. (2018) Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors. Journal of visualized experiments : JoVE. : 0-0.
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Doi: 10.3791/58553

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Denitrification is the primary biogeochemical process removing reactive nitrogen from the biosphere. The quantitative evaluation of this process has become particularly relevant for assessing the anthropogenic-altered global nitrogen cycle and the emission of greenhouse gases (i.e., N2O). Several methods are available for measuring denitrification, but none of them are completely satisfactory. Problems with existing methods include their insufficient sensitivity, and the need to modify the substrate levels or alter the physical configuration of the process using disturbed samples.This work describes a method for estimating sediment denitrification rates that combines coring, acetylene inhibition, and microsensor measurements of the accumulated N2O. The main advantages of this method are a low disturbance of the sediment structure and the collection of a continuous record of N2O accumulation; these enable estimates of reliable denitrification rates with minimum values up to 0.4-1 µmol N2O m-2 h-1. The ability to manipulate key factors is an additional advantage for obtaining experimental insights. The protocol describes procedures for collecting the cores, calibrating the sensors, performing the acetylene inhibition, measuring the N2O accumulation, and calculating the denitrification rate. The method is appropriate for estimating denitrification rates in any aquatic system with retrievable sediment cores. If the N2O concentration is above the detection limit of the sensor, the acetylene inhibition step can be omitted to estimate the N2O emission instead of denitrification. We show how to estimate both actual and potential denitrification rates by increasing nitrate availability as well as the temperature dependence of the process. We illustrate the procedure using mountain lake sediments and discuss the advantages and weaknesses of the technique compared to other methods. This method can be modified for particular purposes; for instance, it can be combined with 15N tracers to assess nitrification and denitrification or field in situ measurements of denitrification rates.

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Diatom species variation between lake habitats: implications for interpretation of paleolimnological records

Pla-Rabés S., Catalan J. (2018) Diatom species variation between lake habitats: implications for interpretation of paleolimnological records. Journal of Paleolimnology. 60: 169-187.
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Doi: 10.1007/s10933-018-0017-0

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A sample of a sediment record contains diatom species that have grown in disparate habitats and eventually accumulated in a deep part of the lake. The original habitats may differ in substrate, depth location, and availability of resources. Identifying the species characteristic of each habitat should improve our ecological and environmental interpretation of the sediment record by distinguishing habitat specific responses. With this aim, we studied the benthic diatom communities of a deep oligotrophic lake across several habitats. The main source of variation in the diatom composition was the substrate type; particularly, sediment biofilms. Depth was the second factor. The thermocline defined a shift in diatom communities that also included changes in the dominant lifeforms. A third factor was the mesoscale heterogeneity (i.e., rock sides). Although most species were present in many habitats, characteristic species were identified for all the main habitats and used for an improved interpretation of the deep sediment record. Appropriate standardization showed increasing species richness and diversity from epilimnetic epilithic samples to hypolimnetic sediment samples. We estimate that more than 5000 valve counts are required for appropriate comparisons. Consequently, in sediment records with lower counts per sample, one has to amalgamate samples—losing temporal resolution—to achieve reliable analyses of diversity changes over time. Deep sediment samples are representative of the gamma-diversity of the lake diatom metacommunity, which result from the local alpha diversity of the habitats and the beta-diversity of the variability in composition among them. This double source of diversity has to be taken into account when using the sediment record for estimating lake biodiversity changes. On the other hand, we show that an estimation of the spatial (habitat) heterogeneity of a reconstructed environmental variable can be achieved using subsets of species characteristic of each habitat. We demonstrate the procedure by reconstructing the pH fluctuations during the last 200 years in several habitats from a single sediment record. The results are coherent with the expected differences between predominantly trophogenic or tropholithic habitats. © 2018, Springer Science+Business Media B.V., part of Springer Nature.

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