Functional ecology of microbial freshwater communities from Byers Peninsula (Livingston Island, Antarctica)

This thesis studies the microbial communities inhabiting freshwater ecosystems of Byers Peninsula (Livingston Island, Antarctica). This is an ice-free area of around 60 km2 that holds numerous lakes, ponds, rivers and wetlands. As a deglaciated region, the functioning of aquatic ecosystems is very closely linked with the surrounding land. So, when snow melting occurs during summer, interactions with the catchment become more intense, and coincide with enhanced biological activity. We conducted a systematic survey in the most representative lakes during some consecutive austral summers between 2002 and 2006. Most of these lakes are located on a plateau, where the landform facilitates water retention and they show well-defined surface outlets. According to their nutrient concentrations and the phytoplankton biomass, these lakes range merely from ultra-oligotrophic to oligotrophic. Our surveys have revealed the existence of a large standing stock of mosses (Drepanocladus longifolius) at the bottom of some of them, thus suggesting that primary production could mainly be allocated in the benthic compartment. On the other hand, the shallow lagoons located in coastal areas usually show bigger catchments, which are largely covered by mosses cushions and plants. These coastal lagoons have a higher nutrient content due to the inputs of elephant seals (Mirounga leonina) dwelling in their vicinities, and somewhat greater salinity due to more exposure to sea spray. Bacterial abundances vary broadly among lakes (0.5 to 6.5 x 106 cell mL-1), thus also underlying this inland-coastal gradient of productivity. Still, these bacterial abundances are greater than is expected for these nutrient-poor lakes. We also performed a multivariate analysis that reveals other factors such as the lakes’ morphometry to explain the more subtle differences in their trophic status. In general, all the lakes hold a few species and apparently exhibit a simple food web dominated by microbial communities. The only relevant metazoan species we found are the copepod Boeckella poppei and the fairy shrimp Branchinecta gaini. Besides, the former is the only species to present a significant role in the pelagic part. Our surveys describe microbial communities dominated by small flagellates species (both colourless and plastidic forms), amoebae and a few ciliates species. These last species are mainly composed of the euplanktonic ciliate Balanion planctonicum, with densities in Lake Limnopolar of up to 2.8x103 ind L-1, just after the ice cover retreat. Otherwise, phytoplankton is composed mainly of diatoms, chrysophytes, picocyanobacteria and chlorophytes. However, these assemblages may be incidental since some species originate from the catchment or are resuspended from the benthos when turbulence in the lake increases. One of our aims was to test the basic principles of the functional ecology in these simple environments. These lakes support plankton in truncated pelagic food webs, where the copepod B.poppei is the capstone predator. A strong trophic connection exists, however, between copepods and the microbial loop. We present a conceptual model of the ecological functioning of one of these lakes, Lake Limnopolar, located on the plateau, which we have adopted as a model study lake. By means of manipulative experiments, we demonstrate the potential existence of a trophic cascade in its pelagic food web. It is mediated by a strong top-down regulation of protozoa populations by copepods, which indirectly benefits pico-sized organisms (both autotrophic and heterotrophic). The experiments showed that these trophic pathways are mainly channelized through ciliates, whose abundance declined markedly in response to increased copepod densities. The selective grazing of protists over picoplankters furthermore favours a shift in the bacterial size structure. Our observations also advocate the incorporation into this food web modelling of an effective recycling of nutrients driven by these copepods. In this sense, we conjecture that a translocation of nutrients from lake’s bottom to surface waters could be mediated by the copepods’ diel vertical migration. The analysis of the isotopic carbon fractionation occurring in Lake Limnopolar indicated that B.poppei profits mainly from pelagic resources. Besides, the liquid chromatography (HPLC) analysis of taxa-specific carotenoids revealed the ability of this copepod to produce a redistribution of the relative abundances of pelagic algal groups because of a differential grazing pressure. For instance, this indicates that chlorophytes (e.g. Ankistrodesmus antarcticus) , but not diatoms and chrysophytes, are favoured when copepods abound. In some periods however, we found that copepods mainly retreated to deep layers, suggesting nektobenthic behaviour. Here, we agree with those observations indicating a certain phenotypic plasticity of this species, in such a way that its feeding mode may vary depending on environmental conditions. In contrast, isotopic fractionation clearly revealed that Branchinecta gaini exploits benthic resources, thus demonstrating a niche segregation between the two dominant metazoans in the lake. We demonstrate that ice dynamics is very much subject to variations due to the year-to-year meteorological variability of the region. We observed, for instance, inter-summer differences in the ice-out timing of 55 or 25 days. We demonstrate that this local variability could be an important factor to explain the limnological dynamics. Therefore, further attention has to be paid to the fact that these year-to-year variations may be large and may thus complicate the explanation of long-term variations attributed to climate change, unless we better understand such dynamics. We partially studied the gains and losses of heat in the lake, and observed differences either with or without a frozen cover. During the ice-free periods, if solar radiation is low, the lake loses sensible heat by the shear produced by wind, although this occurs with some delay. On the other hand, density-driven currents dominate when the lake is to be ice-covered. Seasonal changes in the phytoplankton community structure occur in Lake Limnopolar in relation to ice dynamics. When the lake is ice-covered, light availability is greatly limited and nutrients diffusion is restricted because of the high water column stability. During this period, autotrophic picoplankters, both picocyanobacteria and picoprasinophytes, which usually play a minor role, account for up to around 50% of the total phytoplankton biomass at sub-surface layers. By contrast, greater abundances of larger phytoplankton (chrysophytes and diatoms) and bacteria take place with the onset of ice melting and coincide with increases in nutrients, turbulence and light availability. In other respects, and along the trophic gradient previously defined among the lakes, the relative role of autotrophic picoplankters increases as nutrient content decreases. In general, pelagic primary production is very low in the lakes from Byers; however, the plankton’s heterotrophic component is relatively abundant for such low productive rates. In relation to this, our studies suggest that the benthic communities which flourish in the surrounding areas of the lakes (principally microbial mats) could be a source of allochthonous inputs of organic carbon, as the isotopic fractionation also suggests, thus contributing to fuel bacterial production. This organic carbon may also originate from the benthic mosses growing within the lake. In this sense, an in-depth study into this subject is necessary because, if bacteria are mainly subsidised by allochthonous carbon, the idea that low-productive systems tend to be net heterotrophic is reinforced. The dissolved organic carbon (DOC) concentrations in the oligotrophic lakes of Byers Peninsula were around 1 mg L-1, which seems high enough to sustain bacterial growth. The results indicate that bacteria may compete with phytoplankton for mineral nutrients, which hypothetically may occur if nutrients availability is notably scarce. We also examined the taxonomic and physiological diversity of the benthic microbial communities at the site. For this purpose, we conducted a multi-approach study of three representative microbial mats at the site. Two of the mats (soil and pond mats) were located on the central plateau, whereas the third one (stream mat) was located in the coastal area of the South Beaches on the edge of streams. The microscopic and pigment analyses revealed that the stream mat was dominated by diatoms (genera Navicula, Fragilaria, Stauroneis, Nitzschia, Gomphonema and Pinnularia), whereas the mats’ characteristics of the plateau (soil and pond mats) were dominated by cyanobacteria (Leptolyngbya sp., Oscillatoria spp., Phormidium spp., Porphyrosiphon sp., Nostoc sp.). The photosynthetic activity of the three mats is comparable to that observed in similar Antarctic communities, yet relies on the local factors where they grow. The soil and pond mats were distributed over moist soils and at the bottom of ponds. Unlike the stream mat, these two mats exhibited the sheath pigment scytonemin, a higher content of exopolymeric substances (EPS) and some elemental disequilibrium (C:N:P), thus suggesting great environmental stress. The areal carbon uptake (mainly through oxygenic photosynthesis) in the three mats ranged from 2.7 to 4.2 μg C cm-2 h-1, being these higher in the stream mat. The profiles with microelectrodes showed maximum photosynthetic activity at the sub-surface layers, which moreover revealed a more balanced stoichiometry than at the surface layers. Nitrogen uptakes also varied among mats. N2 fixation only occurred in the mats from the plateau, and was notably higher in the soil mats. In contrast, the areal assimilation rates of combined forms (nitrate and ammonium) were higher in the stream mat. The other benthic communities we studied are the different phototrophic biofilms which flourish in streams. Our study particularly focused on several biofilms revealing a restricted distribution within a waterfall that formed a canyon downstream. We observed up to five different communities there, whose position responded to the selective stresses exerted by stream flow and moisture. In our opinion, there is a trade-off between water current (i.e., water renewal) and nutrient availability to explain the biofilms distribution. Accordingly, the exopolymeric substances (EPS) content, stoichiometry (C:N:P) and pigment composition of the biofilms demonstrated a distinct nutritional status. Occurrence of functionally competent biofilms of chlorophytes (Ulothrix sp.) was restricted to the central stream channel, which likely indicates adaptation to faster flow events. The communities dominated by cyanobacteria (Oscillatoria spp., Phormidium cf. autumnale, Leptolyngbya sp.) were, in contrast, more diverse and appeared in a wide range of environmental conditions. The dominant diatoms in these biofilms were Fragilaria capucina s.l., Nitzschia cf. gracilis, Nitzschia inconspicua, Chamaepinnularia gerlachei, Planothidium delicatulum y Gomphonema sp., being the later related with biofilms subjected to higher drought stress. The areal photosynthetic rates (mainly oxygenic) in the biofilms ranged from 0.7 to 3.4 μg C cm-2 h-1. Greater activities were comparable to those observed in other maritime Antarctic locations, whereas the lower values obtained in the more stressed biofilms fall in the same range observed for the cyanobacterial communities of the continental region. We also assessed if the competitive interactions based on resource utilisation could explain the structure of the photosynthetic community in the microbial mats. Thus, a fully factorial nitrate and phosphorus addition experiment was conducted with the stream mat, which revealed that phosphorus fertilisation favours the growth of non-heterocystous cyanobacteria in relation to diatoms. Our experimental handling did not generate a detectable accretion of mat; however, the balanced nutrients availability improved phototrophic activity. As far as we know, this is the first attempt to study the effects of inorganic nutrient additions on the structure and function of an Antarctic microbial mat. Our findings demonstrate that biotic interactions may play a key role in structuring these aquatic food webs despite strong physical control, at least when physical stressors are temporarily relaxed. This idea contrasts partly with the general contention that ecosystems in extreme environments lack biotic control. We have certainly observed that ice dynamics and water column stability greatly explain plankton succession; nevertheless, community size structure and the occurrence of metazoan zooplankton may also explain plankton dynamics. As regards microbial mats, our enrichment experiment with stream mats also suggests that a shift in regional nutrients dynamics might alter the metabolic equilibrium of these microbial communities. The freshwater ecosystems at this site are not affected by direct anthropic stressors, but are disturbed by climate or natural eutrophication processes. Accordingly, they can be effective sentinels for climate change as they are highly sensitive and integrate information about the processes occurring in the catchment. Monitoring and experimental activities should then continue in Byers to conduct an in-depth study into the consequences of climate change on both local and global scales. The knowledge acquired by this limnological study furthermore stresses the idea of establishing this Antarctic location as an international reference site for research into polar regions

Spectrophotometric methods for the determination of photosynthetic pigments in stratified lakes : a critical analysis based on comparisons with HPLC determinations in a model lake

High-performance liquid chromatography (HPLC) is an accurate method for photosynthetic pigment analysis; however, spectrophotometric equations are also frequently used for pigment quantification in aquatic systems. Here, we present a critical analysis of the most-used spectrophotometric equations by comparing the results obtained using these equations with unambiguous HPLC determinations. The study was performed in Lake La Cruz (central Spain). In this meromictic lake with strong thermal stratification, photosynthetic populations occur in different, vertically stratified layers. Eukaryotic algae and picocyanobacteria are mostly located in oxic layers, whereas purple sulphur bacteria grow at the oxic-anoxic interface and below, and green sulphur bacteria occur primarily in deeper anoxic layers. This broad diversity of photosynthetic microorganisms involves a complex mixture of photosynthetic pigments that often exhibit overlapping absorption spectra. We tested spectrophotometric equations using samples that represented the entire range of spatial and temporal variability of the lake. For chlorophyll-a, the best correlations with all tested equations were observed for oxic layers. Regardless of where the sample was obtained, the best fit for chlorophyll-a was produced by the equation of Overmann & Tilzer, which is specifically designed to handle mixtures of chlorophyll-a and bacteriochlorophyll-d from green sulphur bacteria. Trichromatic equations for determining chlorophyll-b and -c exhibited strong interferences in anoxic waters, whereas in the upper layers of the lake, concentrations of these pigments were usually below the detection limit, restricting the use of these equations. The equations of Takahashi & Ichimura for bacterial pigments slightly overestimated both bacteriochlorophyll-a and -d by approximately 10 % and underestimated bacteriochlorophyll-c by nearly 23 %, although for bacteriochlorophyll-d, the correlation was better than those obtained using the dichromatic equations of Parkin & Brock and Overmann & Tilzer, respectively. Total carotenoid abundance can be assessed with the equation designed for this purpose by Strickland & Parsons (1972); however, the accuracy of the results differs with depth and is strongly biased by the presence of the bacterial carotenoid okenone. On the other hand, dual-wavelength carotenoid-to-chlorophyll-a ratios (430/665 and 480/665) only produced acceptable results in the epilimnion, with the occurrence of the bacterial carotenoid okenone in the microaerobic and anoxic layers again producing significant interference. Additionally, the wide variation with depth of the carotenoid composition undermined the validity of these dual-wavelength ratios. In conclusion, our findings indicate that a complete and unambiguous study of photosynthetic pigments in highly stratified lakes with overlapping populations of phototrophic microorganisms requires the use of HPLC techniques. Anyway, our results demonstrate that chlorophyll-a and bacteriochlorophyll-a and -d can be directly measured in oxic and anoxic layers, respectively, using spectrophotometric methods with an error lower than 10 %. However, according to our results, chlorophyll-b and -c and bacteriochlorophyll-c cannot be accurately estimated by spectrophotometric methods in stratified lakes.La cromatografía líquida de alta eficacia (HPLC) es un método preciso para el análisis de pigmentos fotosintéticos, sin embargo las ecuaciones espectrofotométricas todavía se usan frecuentemente en sistemas acuáticos. En este trabajo mostramos un análisis crítico de algunas de estas ecuaciones comparando los resultados obtenidos con las determinaciones más precisas realizadas por HPLC. El estudio se realizó tomando como modelo la Laguna de La Cruz (centro de España). En este lago meromíctico, que además presenta una fuerte estratificación térmica estival, las poblaciones de microorganismos fotosintéticos se sitúan verticalmente estratificadas en diferentes capas. Mientras que las algas eucariotas y las picocianobacterias se localizan en las capas óxicas, las bacterias púrpuras del azufre crecen en la interfase óxico-anóxica y por debajo de esta y a las bacterias verdes del azufre se localizan en capas anóxicas más profundas. Esta amplia diversidad de microorganismos fotosintéticos implica una compleja mezcla de pigmentos fotosintéticos en los extractos, los cuales a menudo muestran espectros de absorción que se superponen. Hemos ensayado las ecuaciones espectrofotométricas con muestras que abarcan toda la variabilidad espacial y temporal del lago. Para la clorofila-a encontramos buenas correlaciones en las capas óxicas para la mayoría de las ecuaciones ensayadas. Sin embargo, la ecuación que mejor funciona en general para la determinación de la concentración de clorofila-a, independientemente del origen de la muestra, es la dada por Overmann & Tilzer, que está diseñada específicamente para mezclas de clorofila-a con bacterioclorofila-d de bacterias verdes del azufre. Las ecuaciones tricromáticas para la determinación de clorofila-b y c presentaron fuertes interferencias en aguas anóxicas, mientras que en las capas superiores del lago las concentraciones se encontraron normalmente por debajo del límite de detección, lo que restringía la posibilidad de uso de estas ecuaciones. Las ecuaciones de Takahashi & Ichimura (1970) para pigmentos bacterianos sobreestimaban tanto la concentración de bacterioclorofila-a como la d, aproximadamente en un 10 %, y subestimaban la concentración de bacterioclorofila-c casi en un 23 %; si bien para la determinación de bacterioclorofila-d la correlación fue mejor que la obtenida por las ecuaciones dicromáticas de Parkin & Brock y de Overmann & Tilzer. La abun- dancia de carotenos totales puede ser estimada por la ecuación de Strickland & Parsons (1972) diseñada para este propósito, sin embargo la precisión en los resultados difiere con la profundidad y se ve tremendamente sesgada por la presencia del caroteno bacteriano okenona. Por otro lado, las relaciones caroteno/clorofila-a basada en medidas a doble longitud de onda (430/665 y 480/665) solo mostraban resultados aceptables en el epilimnion, ya que en otras capas la aparición de carotenos bacterianos como la okenona produce interferencias significativas. Además, la gran variación en profundidad de la composición de carotenos socava la validez de estas relaciones fundamentadas en medidas a doble longitud de onda. En conclusión, nuestros resultados indican que el estudio de los pigmentos fotosintéticos completo y sin ambigüedades en lagos fuertemente estratificados y consolapamiento de sus poblaciones de organismos fototróficos requiere del uso de HPLC. Sin embargo, nuestros resultados también demuestran que las concentraciones de clorofila-a y bacterioclorofila-a y d pueden ser directamente medidas, tanto en profundidades óxicas como anóxicas, usando ecuaciones espectrofotométricas con un error inferior a un 10 %. Por el contrario, de acuerdo con nuestros resultados ni la concentración de clorofila-b y c, ni la de bacterioclorofila-c pueden ser estimadas con precisión por métodos espectrofotométricos en lagos estratificados

Carbon metabolic rates and GHG emissions in different wetland types of the Ebro Delta

Deltaic wetlands are highly productive ecosystems, which characteristically can act as C-sinks. However, they are among the most threatened ecosystems, being very vulnerable to global change, and require special attention towards its conservation. Knowing their climate change mitigating potential, conservation measures should also be oriented with a climatic approach, to strengthen their regulatory services. In this work we studied the carbon biogeochemistry and the specific relevance of certain microbial guilds on carbon metabolisms of the three main types of deltaic wetlands located in the Ebro Delta, north-eastern Spain, as well as how they deal with human pressures and climate change effects. We estimated the metabolic rates of the main carbon-related metabolisms (primary production and respiration) and the resulting carbon and global warming potential balances in sites with a different salinity range and trophic status. With the results obtained, we tried to define the influence of possible changes in salinity and trophic level linked to the main impacts currently threatening deltaic wetlands, on the C-metabolisms and GHG emissions, for a better understanding of the mitigating capacity and their possible enhancement when applying specific management actions. Metabolic rates showed a pattern highly influenced by the salinity range and nutrients inputs. Freshwater and brackish wetlands, with higher nutrient inputs from agricultural runoff, showed higher C-capture capacity (around 220–250 g C m-2 y-1), but also higher rates of degradative metabolisms (aerobic respiration and CH4 emissions). Contrastingly, the rates of C-related metabolisms and C-retention of Salicornia-type coastal salt marshes were lower (42 g C m-2 y-1). The study of the microbial metacommunity composition by the16S RNA gene sequencing revealed a significant higher presence of methanogens in the salt marsh, and also higher metabolic potential, where there was significantly more organic matter content in sediment. Salinity inhibition, however, explained the lower respiration rates, both aerobic and anaerobic, and prevented higher rates of methanogenesis despite the major presence of methanogens. Conservation measures for these wetlands would require, overall, maintaining the sediment contributions of the river basin intending to overcome the regression of the Delta and its salt marshes in a climate change scenario. Particularly, for reducing degradative metabolisms, and favour C-retention, nutrient inputs should be controlled in freshwater and brackish wetlands in order to reduce eutrophication. In salt marshes, the reduction of salinity should be avoided to control increases in methanogenesis and CH4 emissions.info:eu-repo/semantics/publishedVersio

Bacterioplankton Community Composition Along Environmental Gradients in Lakes From Byers Peninsula (Maritime Antarctica) as Determined by Next-Generation Sequencing

This study comprises the first attempt to describe the planktonic bacterial communities of lakes from Byers Peninsula, one of the most significant limnological districts in the Maritime Antarctica, leveraging next-generation sequencing (NGS) technologies. For the survey, we selected 7 lakes covering the environmental gradient from inland to coastal lakes, some of them sampled both in surface and deep waters. Analysis provided just over 85,000 high quality sequences that were clustered into 864 unique Zero-radius Operational Taxonomic Units (ZOTUs) (i.e., 100% sequence similarity). Yet, several taxonomic uncertainties remained in the analysis likely suggesting the occurrence of local bacterial adaptations. The survey showed the dominance of the phyla Proteobacteria and Bacteroidetes. Among the former, the Gammaproteobacteria class, more specifically the order Betaproteobacteriales, was the dominant group, which seems to be a common trend in nutrient-limited Antarctic lakes. Most of the families and genera ubiquitously detected belonging to this class are indeed typical from ultra-oligotrophic environments, and commonly described as diazotrophs. On the other hand, among the members of the phylum Bacteroidetes, genera such as Flavobacterium were abundant in some of the shallowest lakes, thus demonstrating that also benthic and sediment-associated bacteria contributed to water bacterial assemblages. Ordination analyses sorted bacterial assemblages mainly based on the environmental gradients of nutrient availability and conductivity i.e., salinity. However, transient bacterial associations, that included the groups Clostridiaceae and Chloroflexi, also occurred as being forced by other drivers such as the influence of the nearby fauna and by the airborne microorganisms. As we intended, our NGS-based approach has provided a much greater resolution compared to the previous studies conducted in the area and confirmed to a large extent the previously obtained patterns, thus reinforcing the view of Byers as a hotspot of microbial biodiversity within Antarctica. This high microbial diversity allows the use of these aquatic ecosystems and their bacterial assemblages as sentinels for the monitoring of adaptive responses to climate change in this rapidly warming area

Preliminary results of a vaginal constraint for reducing G2 late vaginal complications after postoperative brachytherapy in endometrial cancer: A proepective analysis

Purpose: To evaluate the preliminary results of the use of 68 Gy EQD2(α/β=3 Gy) as a dose limit to the lowest dose in the most exposed 2 cm3 of the vagina in order to reduce G2 late vaginal problems in postoperative endometrial carcinoma (EC). Methods: From November 2016 to October 2019, 69 postoperative EC patients receiving vaginal brachytherapy (VBT) ± external beam radiotherapy (EBRT) were prospectively analyzed. The median EBRT dose was 45 Gy (range: 44-50.4 Gy), 1.8-2 Gy/day, 5 fractions(Fr)/week. VBT was administered with the following schedule: 1Fr of 7 Gy after EBRT and 2 daily Fr × 7.5 Gy in exclusive VBT. The dose was prescribed at 0.5 cm from the applicator surface with an active length of 2.5 cm; 56 patients were treated with vaginal cylinders (49-3.5 cm, 6-3 cm, and 1-2.5 cm) and 13 with the colpostat technique. The overall VBT dose was adjusted to meet the vaginal restriction of < 68 Gy EQD2(α/β=3 Gy) at 2 cm3. Late toxicity was prospectively assessed using RTOG scores for bladder and rectum, and the objective LENT-SOMA criteria for vagina. Results: With a median follow-up of 31.0 months, no vaginal-cuff recurrences were found. Late toxicity: only 1G1(1.4%) rectal toxicity; 21G1(30.4%) and 3G2(4.3%) vaginal complications. Only one (1.4%) of 3 G2 manifested as vaginal shortening. Conclusions: In postoperative EC patients treated with VBT, only one developed G2 vaginal stenosis with the use of 68 Gy EQD2(α/β=3 Gy) as a dose constraint. These preliminary results seem to indicate the value of this dose limit for reducing G2 vaginal stenosis. Nonetheless, these findings should be confirmed in a larger number of patients with longer follow-up. Keywords: Brachytherapy; Postoperative endometrial cancer; Vaginal complications; Vaginal constraint

Aquatic ecosystems in Byers Peninsula, Livingston Island. An Antarctic Noah’s Ark in a changing world

第6回極域科学シンポジウム[OB] 極域生物圏11月17日（火）　統計数理研究所 セミナー室1（D305

Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins

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.Peer reviewe

In Situ Bioremediation Techniques to Reduce Total Organic Matter Oversaturation of Fluvial Sediments: An Experimental Study

An in situ experiment was performed in sediments of River Magro (east Spain) in order to evaluate the usefulness of microbial bioremediation, both bioaugmentation and biostimulation, as a tool for reducing the excessive organic matter (OM) content in dammed river stretches due to historical wastewater spilling. The study had a prospective approach focused on the application of a biologically active commercial product (BAP), consisting of a mix of bacterial strains, ectoenzymes, and nutrients, where a range of concentrations and temporal dosages of the product were experimentally assayed in situ. They were further combined with the addition of potential organic enhancers, such as acetate, as well as of inhibitors of specific microbial guilds. On the other hand, inorganic electron acceptors for the anaerobic respiration of the organic matter were additionally amended. In additional assays, the BAP additions were combined with inorganic nutrients amendments, or even the latter were tested alone. These combinative treatments aimed at exploring the possible enhancement of synergistic or antagonistic interactions among the amended compounds, as well as the eventual effect of growth limiting factors. The single BAP additions of 50 g/m3 led to OM reductions of up to 17%, and significant removals of nitrogen or phosphorus were additionally observed by increasing or by fractioning the BAP dosage, respectively. However, a better response using the same amount of the BAP was obtained by supplementing it with sodium acetate. In this case, reductions of the OM content reached up to 35% of the accumulated OM, thus indicating that a complementary stimulus is still necessary to run out barriers towards the final steps of the anaerobic OM digestion. This treatment was also linked to the strongest significant drop in the TP content of the sediments. Neither the addition of inorganic electron acceptors nor inorganic nutrients improved the results, or they were even antagonistic of the degradative potential of the BAP product. Apparently, the occurrence of acetoclastic microorganisms, which was demonstrated by high throughput DNA-sequencing, was critical for the optimal OM reductions in the sediments. This exploratory study demonstrates that the applicability of BAPs can be extended to cover the remediation of fluvial ecosystems, and support the complementarity of different bioremediation strategies

Proyecto de mejora energética en el tren de precalentamiento de crudo en una refinería

Treball Final de Grau en Enginyeria en Tecnologies Industrials. Codi: ET1040. Curs acadèmic: 2019/2020El objetivo principal de este proyecto es proponer diferentes mejoras de eficiencia energética en el tren de precalentamiento de crudo y desarrollar la mejor propuesta de entre todas ellas de una forma justificada. Dicho proyecto está situado en las instalaciones de la refinería de Castellón, situada en la costa mediterránea, más concretamente en el polígono industrial El Serrallo. En primer lugar, se ha realizado una auditoría parcial de la instalación para identificar los consumos energéticos más importantes y la cantidad de emisiones a la atmósfera. Una vez analizada la instalación, los consumos energéticos más significativos son los que se producen en el horno de proceso aguas abajo de la torre de destilación fraccionada. En segundo lugar, para seleccionar una solución se han propuesto diferentes medidas novedosas de eficiencia energética y se ha realizado un estudio económico para comprobar qué alternativa es la más viable de todas. Posteriormente, después de elegir la opción más conveniente económicamente para la empresa, se ha definido al detalle y se ha aportado toda la información necesaria para llevar a cabo el proyecto. Además, este proyecto cuenta con un plan de protección contra incendios específico para la zona de la refinería donde se va a llevar a cabo la mejora de la instalación. Finalmente, se ha desarrollado una solución técnicamente viable para reutilizar un calor residual de la torre de destilación fraccionada y aprovecharlo en el tren de precalentamiento de crudo, para conseguir ahorros en términos económicos y por consiguiente reducir las emisiones a la atmósfera debido al ahorro de combustible. Dicha solución se basa en la instalación de dos intercambiadores carcasa-tubo en serie para realizar el intercambio de calor.The main objective of this project is to propose different energy efficiency improvements in the crude oil preheating train and to develop the best proposal among them in a justified way. This project is located in the facilities of the Castellón refinery, located on the Mediterranean coast, more specifically in the El Serrallo industrial estate. Firstly, a partial audit of the installation has been carried out to identify the most important energy consumption and the amount of emissions into the atmosphere. Once the installation has been analyzed, the most significant energy consumption is produced in the process furnace downstream of the fractional distillation tower. Secondly, in order to select a solution, different innovative energy efficiency measures have been proposed and an economic study has been carried out to see which alternative is the most viable of all. Later, after choosing the most economically convenient option for the company, it has been defined in detail and all the necessary information to carry out the project has been provided. In addition, this project has a specific fire protection plan for the area of the refinery where the improvement of the facility will be carried out. Finally, a technically viable solution has been developed to reuse waste heat from fractional distillation tower and use it in the crude oil preheating train, to achieve savings in economic terms and consequently reduce emissions into the atmosphere due to fuel savings. This solution is based on the installation of two shell-and-tube exchangers in series to carry out the heat exchange.L’objectiu principal d'aquest projecte és proposar diferents millores d'eficiència energètica al tren de precalentament de cru i desenvolupar la millor proposta d'entre totes elles d'una forma justificada. Aquest projecte està situat en les instal·lacions de la refineria de Castelló, situada en la costa mediterrània, més concretament en el polígon industrial El Serrallo. En primer lloc, s'ha realitzat una auditoria parcial de la instal·lació per a identificar els consums energètics més importants i la quantitat d'emissions a l'atmosfera. Una vegada analitzada la instal·lació, els consums energètics més significatius són els que es produeixen en el forn de procés aigües avall de la torre de destil·lació fraccionada. En segon lloc, per a seleccionar una solució s'han proposat diferents mesures noves d'eficiència energètica i s'ha realitzat un estudi econòmic per a comprovar quina alternativa és la més viable de totes. Posteriorment, després de triar l'opció més convenient econòmicament per a l'empresa , s'ha definit al detall i s'ha aportat tota la informació necessària per a dur a terme el projecte. A més, aquest projecte compta amb un pla de protecció contra incendis específic per a la zona de la refineria on es durà a terme la millora de la instal·lació. Finalment, s'ha desenvolupat una solució tècnicament viable per a reutilitzar una calor residual de la torre de destil·lació fraccionada i aprofitar-lo al tren de precalentament de cru, per a aconseguir estalvis en termes econòmics i per consegüent reduir les emissions a l'atmosfera a causa de l'estalvi de combustible. Aquesta solució es basa en la instal·lació de dos intercanviadors carcassa-tub en sèrie per a realitzar l'intercanvi de calor

Limnology and Aquatic Microbial Ecology of Byers Peninsula: A Main Freshwater Biodiversity Hotspot in Maritime Antarctica

Here we present a comprehensive review of the diversity revealed by research in limnology and microbial ecology conducted in Byers Peninsula (Livingston Island, South Shetland Islands, Antarctica) during the last two decades. The site constitutes one of the largest ice-free areas within the Antarctic Peninsula region. Since it has a high level of environmental protection, it is less human-impacted compared to other sites within the South Shetland archipelago. The main investigations in Byers Peninsula focused on the physical and chemical limnology of the lakes, ponds, rivers, and wetlands, as well as on the structure of their planktonic and benthic microbial communities, and on the functional ecology of the microbial food webs. Lakes and ponds in Byers range along a productivity gradient that extends from the less productive lakes located upland to the eutrophic coastal lakes. Their planktonic assemblages include viruses, bacteria, a metabolically diverse community of protists (i.e., autotrophs, heterotrophs, and mixotrophs), and a few metazooplankton species. Most of the studies conducted in the site demonstrate the strong influence of the physical environment (i.e., temperature, availability of light, and water) and nutrient availability in structuring these microbial communities. However, top-down biotic processes may occur in summer, when predation by zooplankton can exert a strong influence on the abundance of protists, including flagellates and ciliated protozoa. As a consequence, bacterioplankton could be partly released from the grazing pressure exerted by these protists, and proliferates fueled by external nutrient subsidies from the lake&rsquo;s catchment. As summer temperatures in this region are slightly above the melting point of water, biotic processes, such as those related to the productivity of lakes during ice-free periods, could become even more relevant as warming induced by climate change progresses. The limnological research carried out at the site proves that Byers Peninsula deserves special attention in the framework of the research in extreme environments. Together with nearby sites, such as Signy Island, Byers Peninsula comprises a featuring element of the Maritime Antarctic region that represents a benchmark area relative to the global distribution and diversity of aquatic microorganisms