La Caldera Research Articles

Tracking SARS-CoV-2 in rivers as a tool for epidemiological surveillance

The aim of this work was to evaluate if rivers could be used for SARS-CoV-2 surveillance. Five sampling points from three rivers (AR-1 and AR-2 in Arenales River, MR-1 and MR-2 in Mojotoro River, and CR in La Caldera River) from Salta (Argentina), two of them receiving discharges from wastewater plants (WWTP), were monitored from July to December 2020. Fifteen water samples from each point (75 in total) were collected and characterized physico-chemically and microbiologically and SARS-CoV-2 was quantified by RT-qPCR. Also, two targets linked to human contributions, human polyomavirus (HPyV) and RNase P, were quantified and used to normalize SARS-CoV-2 concentration, which was compared to reported COVID-19 cases. Statistical analyses allowed us to verify the correlation between SARS-CoV-2 and the concentration of fecal indicator bacteria (FIB), as well as to find similarities and differences between sampling points. La Caldera River showed the best water quality; FIBs were within acceptable limits for recreational activities. Mojotoro River's water quality was not affected by the northern WWTP of the city. Instead, Arenales River presented the poorest water quality; at AR-2 was negatively affected by the discharges of the southern WWTP, which contributed to significant increase of fecal contamination. SARS-CoV-2 was found in about half of samples in low concentrations in La Caldera and Mojotoro Rivers, while it was high and persistent in Arenales River. No human tracers were detected in CR, only HPyV was found in MR-1, MR-2 and AR-1, and both were quantified in AR-2. The experimental and normalized viral concentrations strongly correlated with reported COVID-19 cases; thus, Arenales River at AR-2 reflected the epidemiological situation of the city. This is the first study showing the dynamic of SARS-CoV-2 concentration in an urban river highly impacted by wastewater and proved that can be used for SARS-CoV-2 surveillance to support health authorities.

Dynamics of Stoichiometric Autotroph-Mixotroph-Bacteria Interactions in the Epilimnion.

Autotrophs, mixotrophs and bacteria exhibit complex interrelationships containing multiple ecological mechanisms. A mathematical model based on ecological stoichiometry is proposed to describe the interactions among them. Some dynamic analysis and numerical simulations of this model are presented. The roles of autotrophs and mixotrophs in controlling bacterioplankton are explored to examine the experiments and hypotheses of Medina-Sánchez, Villar-Argaiz and Carrillo for La Caldera Lake. Our results show that the dual control (bottom-up control and top-down control) of bacteria by mixotrophs is a key reason for the ratio of bacterial and phytoplankton biomass in La Caldera Lake to deviate from the general tendency. The numerical bifurcation diagrams suggest that the competition between phytoplankton and bacteria for nutrients can also be an important factor for the decrease of the bacterial biomass in an oligotrophic lake.

Geotechnical settings of volcanic residual soils and derived engineering problems in El Hierro Island (Spain)

Even today, studies about the properties and geotechnical behavior of volcanic residual soils are still scarce. Increasing the knowledge of this type of soil is important, since it has important economic and security repercussions in the infrastructures to be built in volcanic areas. This paper exposes the geotechnical data of volcanic residual soils acquired during the research investigation campaign carried out for the construction of the upper reservoir of El Hierro Hydro-Wind Plant (Gorona del Viento, S.A.) placed in the inactive crater La Caldera (El Hierro, Canary Islands). In this respect, and as per requirement of a geological study (geological mapping, geochemical analysis, and petrographic study), an exhaustive geotechnical investigation (rotary boreholes, dynamic penetrations of DPSH type, and trial pits) and geophysical surveys (seismic refraction and electrical tomography profiles) were carried out at this site, as well as numerous on-site and laboratory tests. The deficient geotechnical characteristics of these soils implied one of the main engineering problems addressed during the design and construction of the upper reservoir: the high risk of ground settlement. The exhaustive investigation through the combination of different techniques allowed to identify this geotechnical risk in advance and carry out a soil improvement using the most appropriate engineering technique.

Equivocal Politics of Carnival

This article reflects on the political, social, and cultural institutionality of carnival in Uruguay and on its growing centrality as a means of expression and space of popular enunciation since the return to democracy in the 1980s. It also argues that the “field” of carnival is a site of constant negotiation with both the state and nongovernmental sources of power (economic groups, the media, churches, etc.) and can thus accommodate various political proposals, leading to constant symbolic-discursive reconfiguration. A detailed analysis of three carnivalesque performances belonging to the murga genre—La caldera de los diablos by Diablos Verdes (2003), Los Sueños by Agarrate Catalina (2005), and Creer o reventar by Don Timoteo (2014)—highlights how carnival has responded to, and has been reconfigured by, three recent circumstances: the apogee of neoliberalism and “the crisis of 2002,” the election of a “broad front” leftist government in 2005, and the end of this government’s second term in 2014.

Circunscripción taxonómica de Schinus pilifera (Anacardiaceae) y características reproductivas de una población de La Calderilla, Salta, Argentina

Schinus pilifera es un arbusto nativo del noroeste y centro de Argentina con amplia distribución en siete provincias y también en el sur de Bolivia. Es una especie muy polimórfica que ha sido dividida intra-específicamente en tres variedades: var. piliferus, var. boliviensis y var. cabrerae en base a caracteres de pubescencia y glabrescencia de sus hojas. No se encontró información sobre la variación morfológica, el sistema sexual y reproductivo de la especie. Los objetivos fueron obtener información morfológica general, del sistema reproductivo y analizar la validez de los taxones intraespecíficos. Se estudiaron colecciones de los herbarios LIL y MCNS además de herbarios virtuales BM, GH, MO y NY. Se realizaron nuevas colecciones en diferentes ambientes de las provincias de Salta y Tucumán a los fines de conocer y analizar la variación entre las poblaciones. Se estudiaron varios aspectos morfológicos y reproductivos de una población en La Calderilla, Departamento La Caldera (Salta) instalada en un antiguo lecho del río La Caldera a 1300 m snm. Se concluyó que los caracteres que definían a las variedades resultaron confusos por lo que fueron invalidadas y pasaron a la sinonimia. La especie es dioica. La polinización es ambófila.

Comprehensive population viability study of a rare endemic shrub from the high mountain zone of the Canary Islands and its conservation implications

Oceanic island ecosystems harbour many endemic plant and animal species, which are often threatened because they have only a few small populations. Many factors contribute to the biological viability of such populations, such as demography and population dynamics, breeding system and pollination ecology, seed dispersal and genetic variation. In a collaborative project, all these factors were studied in the rare endemic, predominantly monoecious shrub Bencomia exstipulata Svent. (Rosaceae), which grows exclusively in the national parks of El Teide (Tenerife) and La Caldera de Taburiente (La Palma). Demography was monitored through annual censuses of individual plants in a natural and an augmented population on Tenerife. The breeding system and reproductive success were studied through bagging and pollination experiments, and insect visitation censuses. Seed dispersal by animals was assessed using cafetaria experiments. With matrix projection models and stochastic simulations, we show that the Tenerife population was demographically stable. This was largely explainable by the high survival of adult individuals. Despite frequent germination, successful seedling recruitment was very rare. Male and female flowers occurred in separate inflorescences within individuals, although some inflorescences were mixed and some shrubs were entirely male or female. Despite frequent visits by honeybees, the species is predominantly wind pollinated. Insect-proof bags reduced seed set by 12.5%, and pollen-proof bags by 44%. Large quantities of airborne pollen were detected on unbagged sticky microscope slides, this was 56% reduced by insect-proof and 96% by pollen-proof bags. Hence, some self-pollination also seems to occur. Cafetaria experiments showed that the local lizards (Gallotia galloti Oudart) readily eat the fruits and that the seeds pass through their intestines unharmed and germinable. Since other dispersal vectors are unknown, saurochory seems the most likely mode of dispersal. Our study strongly suggests that the population of B. exstipulata on Tenerife is viable, and that there are no significant threats associated with its breeding system, pollination or seed dispersal. To alleviate the natural extinction risk typical of narrow endemics, five main conservation measures are proposed.

Denitrification and Biodiversity of Denitrifiers in a High-Mountain Mediterranean Lake.

Wet deposition of reactive nitrogen (Nr) species is considered a main factor contributing to N inputs, of which nitrate () is usually the major component in high-mountain lakes. The microbial group of denitrifiers are largely responsible for reduction of nitrate to molecular dinitrogen (N2) in terrestrial and aquatic ecosystems, but the role of denitrification in removal of contaminant nitrates in high-mountain lakes is not well understood. We have used the oligotrophic, high-altitude La Caldera lake in the Sierra Nevada range (Spain) as a model to study the role of denitrification in nitrate removal. Dissolved inorganic Nr concentration in the water column of la Caldera, mainly nitrate, decreased over the ice-free season which was not associated with growth of microbial plankton or variations in the ultraviolet radiation. Denitrification activity, estimated as nitrous oxide (N2O) production, was measured in the water column and in sediments of the lake, and had maximal values in the month of August. Relative abundance of denitrifying bacteria in sediments was studied by quantitative polymerase chain reaction of the 16S rRNA and the two phylogenetically distinct clades nosZI and nosZII genes encoding nitrous oxide reductases. Diversity of denitrifiers in sediments was assessed using a culture-dependent approach and after the construction of clone libraries employing the nosZI gene as a molecular marker. In addition to genera Polymorphum, Paracoccus, Azospirillum, Pseudomonas, Hyphomicrobium, Thauera, and Methylophaga, which were present in the clone libraries, Arthrobacter, Burkholderia, and Rhizobium were also detected in culture media that were not found in the clone libraries. Analysis of biological activities involved in the C, N, P, and S cycles from sediments revealed that nitrate was not a limiting nutrient in the lake, allowed N2O production and determined denitrifiers’ community structure. All these results indicate that denitrification could be a major biochemical process responsible for the N losses that occur in La Caldera lake.

Vulnerability of mixotrophic algae to nutrient pulses and UVR in an oligotrophic Southern and Northern Hemisphere lake

Nutrient inputs and ultraviolet radiation (UVR) are global factors affecting the structure and functioning of aquatic ecosystems, particularly clear-water ecosystems. We performed experiments in two model lakes highly exposed to UVR fluxes in order to test the effect that future increases in mineral nutrients transported by dust aerosol might exert on primary producers depending on the likelihood of atmospheric inputs. Lake La Caldera (Northern Hemisphere) has been receiving recurrent dust inputs from the Sahara Desert while lake Los Cántaros (Southern Hemisphere) has been less affected by dust aerosol. UVR × Nutrient synergistically stimulated primary production (PP), chlorophyll a (Chl a), with a smaller increase in phytoplanktonic biomass in La Caldera, but not in Los Cántaros, where nutrient addition unmasked the UVR inhibitory effect on phytoplankton. The proportional decrease of mixotrophic nanoflagellates (MNFs) after the nutrient pulse (in Los Cántaros) and the long-term decline of MNFs in La Caldera associated with the increase in aerosol-dust intrusions from the Sahara during the last 40 years suggest that a future scenario of intensified aerosol events from desert and desertified areas would not only reduce functional diversity with the decline of MNFs, but would ultimately alter the C flux towards the grazing chain in oligotrophic ecosystems.

Resource versus consumer regulation of phytoplankton: testing the role of UVR in a Southern and Northern hemisphere lake

Models predict that phytoplankton is bottom-up regulated by resources and top-down controlled by consumers. However, how the strength of these controls varies with UV radiation (UVR) is not well known. In this study, we test the hypothesis that the phosphorus (P) content of phytoplankton affects the role that UVR exerts strengthening or weakening the resource and consumer control on distinct stoichiometric and functional phytoplankton traits. To accomplish this, we coupled field meso- and microcosms in a split-plot design using UVR treatments at the plot level and nutrients and zooplankton (presence/absence) at the subplot level, in two mountain lakes characterized by their P-sufficient (La Caldera) and P-deficient phytoplankton (Los Cantaros). We found that the addition of nutrients decreased phytoplankton C:P in both lakes, but enhanced primary production and chlorophyll a only under UVR in La Caldera. Also, the effects of zooplankton on phytoplankton varied between lakes and UVR conditions, and increased primary production and chlorophyll a under UVR in La Caldera, but not in Los Cantaros. These results suggest that differences in the stoichiometric aspects associated with the P content in phytoplankton play a key role in how UVR affects resource and consumer controls, with much weaker effects in P-deficient food webs.

Rising nutrient-pulse frequency and high UVR strengthen microbial interactions

Solar radiation and nutrient pulses regulate the ecosystem’s functioning. However, little is known about how a greater frequency of pulsed nutrients under high ultraviolet radiation (UVR) levels, as expected in the near future, could alter the responses and interaction between primary producers and decomposers. In this report, we demonstrate through a mesocosm study in lake La Caldera (Spain) that a repeated (press) compared to a one-time (pulse) schedule under UVR prompted higher increases in primary (PP) than in bacterial production (BP) coupled with a replacement of photoautotrophs by mixotrophic nanoflagellates (MNFs). The mechanism underlying these amplified phytoplanktonic responses was a dual control by MNFs on bacteria through the excretion of organic carbon and an increased top-down control by bacterivory. We also show across a 6-year whole-lake study that the changes from photoautotrophs to MNFs were related mainly to the frequency of pulsed nutrients (e.g. desert dust inputs). Our results underscore how an improved understanding of the interaction between chronic and stochastic environmental factors is critical for predicting ongoing changes in ecosystem functioning and its responses to climatically driven changes.

New species of Raphidascaris (Sprentascaris) (Nematoda: Anisakidae) inRineloricaria steinbachi (Actinopterygii: Loricariidae) from Northwest Argentina.

During a parasitological survey, we reported specimens of a new species of Raphidascaris (Sprentascaris) in Rineloricaria steinbachi from La Caldera River, province of Salta, Northwest Argentina. The new species, R. (S.) saltaensis sp. nov., is characterized by possessing 16 pairs of preanal papillae, lips with lateral protrusions and membranous elevations, and mature eggs rough-shelled with striations. This is the sixth species of the genus described in the Neotropical Region, and the second from Argentina. Rineloricaria steinbachi is reported as host of this nematode genus for the first time. A key to the species of Raphidascaris (Sprentascaris) in the Neotropical realm is provided. Also, zoogeographical and host information of the species, belonging to the subgenus Sprentascaris, is summarized.

Trophic models and short-term dynamic simulations for benthic-pelagic communities at Banco Chinchorro Biosphere Reserve (Mexican Caribbean): a conservation case

Banco Chinchorro is the largest reef in the Mexican Caribbean. Historically, spiny lobster, queen conch and over 20 other reef species have been exploited here. Multispecies intervention management from an ecosystem perspective has been developed in this area; however, an assessment of the effects of such practices on ecosystem health is required. Five quantitative trophic models were constructed using Ecopath with Ecosim. The results show that, in terms of biomass, benthic autotrophs are the dominant group in all communities. Ecosystem Network Analysis indices showed that Cueva de Tiburones was the most mature, developed, complex and healthy subsystem, but, El Colorado and La Baliza were the subsystems most resistant to disturbances. The fisheries mainly concentrate on primary (La Baliza and Cueva de Tiburones sites) and secondary consumers (La Caldera, Chancay, and El Colorado). The greatest propagation of direct and indirect effects, estimated by Mixed Trophic Impacts and Ecosim simulations, were generated by the benthic autotrophs, small benthic epifauna, benthic-pelagic carnivorous fish and benthic carnivorous fish, among others. In contrast, the System Recovery Time showed different patterns among subsystems, indicating several compartments that reduce resilience. Considering the structure, dynamics, trophic functioning and ecosystem health of Banco Chinchorro, its ecological heterogeneity highlights the need for the design of a specific (by subsystem) management strategy, particularly because different species or functional groups present greater sensitivity to human interventions in each community.

Changes in the phytoplankton-bacteria coupling triggered by joint action of UVR, nutrients, and warming in Mediterranean high-mountain lakes

From an extensive study, we determined that heterotrophic bacterial production (HBP) variance in Sierra Nevada (Spain) lakes was explained mainly by excretion of organic carbon by algae (EOC), underlining a bacterial dependence on algal carbon. Subsequently, we studied how the interaction among global change factors such as ultraviolet radiation (UVR), nutrient inputs, and increased temperature affected this phytoplankton-bacteria coupling through in situ factorial experiments in two model high-mountain lakes, La Caldera, and Las Yeguas. Bacterioplankton were more sensitive than phytoplankton because the joint action of increased temperature and nutrient-addition unmasked an inhibitory UVR effect on HBP while reducing the inhibitory UVR effect on primary production (PP) (in La Caldera) or augmenting the net PP values (in Las Yeguas). The interaction among the three factors had a different effect on phytoplankton-bacteria coupling depending on the lake. Thus, in the colder lake (La Caldera), EOC was not adequate to meet the bacterial carbon demand (BCD), leading to a mismatch in phytoplankton-bacteria coupling. Contrarily, in the warmer lake (Las Yeguas), the phytoplankton-bacteria coupling was accentuated by the interaction among the three factors, with EOC exceeding BCD. These contrasting responses of phytoplankton-bacteria coupling may affect the microbial loop development, becoming reinforced in warmer and less UVR-transparent high-mountain lakes, but weakened in colder and more UVR-transparent high-mountain lakes, with implications in the C-flux of these sentinel ecosystems in a scenario of global change.

Nonsense and Unmusic

First thing. Without nonsense there is no sense. Without sense there is no nonsense. Without sense there is no sense. Without nonce there is no once. Without out end there is no begin in. Without redundancy the waves would surge in one direction only. Second thing. I want to play a language game with you, a game that starts with a passage from a story by Jorge Luis Borges, concerning a man with an absolutely perfect memory: Me dijo que hacia 1886 habla discurrido un sistema original de numeration y que en muy pocos dlas habla rebasado el veinticuatro mil. [...] En lugar de siete mil trece, decia (por ejemplo) Maximo Perez; en lugar de siete mil catorce, El Ferrocarril; otros eran Luis Melian Lafinur, Olimar, azufre, los bastos, la ballena, el gas, la caldera, Napoleon, Agustin de Vedia. En lugar de quinientos, decia nueve. [...] Yo trate de explicarle que esa rapsodia de voces inconexas era precisamente lo contrario de un sistema de numeration. Le dije que decir 365 era decir tres centenas, seis decenas, cinco unidades: analisis que no existe en los numeros El Negro Timoteo o manta de carne. Funes no me entendio o no quiso entenderme. He told me that in 1886 he had thought up his own original numbering system, and that in a very few days he had gone past the number 24,000. [...] Instead of 7013 he would say, for example, Maximo Perez; instead of 7014 he would say The Railroad; other were Luis Melian Lafinur, Olimar, sulfur, the saddle pads, the whale, the gas, the cooking pots, Napoleon, Agustin de Vedia. Instead of 500 he would say nine. [...] I tried to explain to him that this rhapsody of disconnected words was precisely the opposite of numbering system. I told him that to say 365 was to say three hundreds, six tens, five ones; an analysis that doesn't exist in the numbers The Negro Timoteo or meat blanket. Funes didn't understand me or didn't want to understand me. The game is to reverse Borges's premise: to imagine a language that consists entirely of numbers, by taking the Oxford English Dictionary and assigning to each of its more than 200,000 words. (171,476 words in current use, and 47,156 obsolete words, in the second edition.) So aardvark would be word number 10; zymurgy would have a very high number. If a new word were added to the language we could place it with decimal point 1, or 2, and so forth, added to the number of the word preceding it in the alphabet. Plurals and verb tense and and moods could be indicated by pronouncing a suffix such as plus or tilde or backslash after the word-number. So speech would consist of a string of numbers. It would take a long time to say a sentence, but if signifiers are perfectly arbitrary, it would be as easy to use as our normal version of the English language, for two people with a lot of time on their hands. And it would have the advantage that you write could poems with indeterminate words, such as 86, x5y, thereby creating a new form of discourse unavailable in standard English. But normal forms of nonsense, in the Jabberwocky or Finnegans Wake manner, would be impossible: you couldn't create a portmanteau between lithe and slimy, because you can't elide two in the way that you can elide two words. And there is no reason why the phonetic aspect of the word couldn't erode away into almost nothing: as became the common medium of speech, you would need no sounds except those needed to pronounce the numbers. Eventually the word aardvark wouldn't exist; there would only be 10, meaning an ant-eating snouted African beast. But ant, and eating, and snouted, and African, and beast, would also exist only as numbers. Maybe all connection between the and the concepts they were designed to represent would ultimately become wispy to the verge of non-being, and language would become Jacques Derrida's dream system, self-enclosed, hermetically sealed. …

DOS NUEVOS REGISTROS DE HELECHOS PARA EL NOROESTE ARGENTINO

Cacharani, D. A.; M. Ramos & O. G. Martinez. Two new fern records from Northwestern Argentina. Darwiniana, nueva serie 2(2): 277-283. Adiantum peruvianum (Pteridaceae) and Serpocaulon polystichum (Polypodiaceae) are recorded for the first time for Argentina in this paper. These new records were collected during trips to La Caldera and Chicoana department in Salta province. The diagnostic characters are described and illustrated, a keys for identification of species and distribution map are provided.

Strategies to optimize monitoring schemes of recreational waters from Salta, Argentina: a multivariate approach.

Several recreational surface waters in Salta, Argentina, were selected to assess their quality. Seventy percent of the measurements exceeded at least one of the limits established by international legislation becoming unsuitable for their use. To interpret results of complex data, multivariate techniques were applied. Arenales River, due to the variability observed in the data, was divided in two: upstream and downstream representing low and high pollution sites, respectively, and cluster analysis supported that differentiation. Arenales River downstream and Campo Alegre Reservoir were the most different environments, and Vaqueros and La Caldera rivers were the most similar. Canonical correlation analysis allowed exploration of correlations between physicochemical and microbiological variables except in both parts of Arenales River, and principal component analysis allowed finding relationships among the nine measured variables in all aquatic environments. Variable's loadings showed that Arenales River downstream was impacted by industrial and domestic activities, Arenales River upstream was affected by agricultural activities, Campo Alegre Reservoir was disturbed by anthropogenic and ecological effects, and La Caldera and Vaqueros rivers were influenced by recreational activities. Discriminant analysis allowed identification of subgroup of variables responsible for seasonal and spatial variations. Enterococcus, dissolved oxygen, conductivity, E. coli, pH, and fecal coliforms are sufficient to spatially describe the quality of the aquatic environments. Regarding seasonal variations, dissolved oxygen, conductivity, fecal coliforms, and pH can be used to describe water quality during dry season, while dissolved oxygen, conductivity, total coliforms, E. coli, and Enterococcus during wet season. Thus, the use of multivariate techniques allowed optimizing monitoring tasks and minimizing costs involved.

APPLICATION OF RESPONSE SURFACE METHODOLOGY (RSM) FOR CULTURE CONDITIONS AND BIOMASS PRODUCTION OF PSYCHROPHILIC MICROALGAE ISOLATED FROM HIGH MOUNTAINS LAKE DURING THE ICE-FREE SEASON

Many studies on cold environments have been developed over the past two decades. High mountain freshwater presents high variability of nutrients and chemico-physical parameters, showing variations of pH, oxygen concentration, metals and temperature throughout the year. National Park of Sierra Nevada (Granada, Spain) (37°032 N 03°182 W), has almost 40 lakes that are reported to be both endemic and oligotrophic. However, very little information about their microbial diversity can be found in literature. In this work, a Response Surface Methodology (RSM) was used to find best nutritional conditions for the isolation of psychrophilic microalgae from La Caldera Lake. The results showed that best culture medium, was the Rodriguez-Lopez medium (RL); data were adjusted to a quadratic prediction model reporting a biomass concentration over 600 mg/L at 10 and 20oC. In this paper, the diversity of culturable freshwater microalgae in the La Caldera Lake was observed by PCR using specific primers for eukaryotic 18S rRNA genes. Samples were taken in early July and late Agust, 2011. In July presence of strains belonging to the Eustigmatophyceae, Bacillariophyceae, Trebouxiophyceae, Chlorophyceae and Scenedesmaceae families were found. In August, only microalgae from the Eustigmatophyceae, Trebouxiophyceae, Chlorophyceae and Scenedesmaceae families were found. An individual culture of each isolated strain was carried out. Microalgae S21 had phylogenetic similitude with Chlorophyceae, and showed best growth being biomass concentration in RL 393.73 mg/L and 128.52 mg/L at 20oC and 10oC, respectively. Moreover, specific growth rates (µ max ), 0.25/h and 0.13/h at 20oC and 10oC, respectively, were detected for strain S21.

Bacterial Communities’ Structure in a High mountain lake during the ice-free season: cultural and PCR-TGGE investigations

La Caldera” is a high mountain lake located in Sierra Nevada, Spain. For its position andcharacteristics it is considered as an important “sensor” for global changes. Water samples were collectedduring the ice-free season in order to observe changes in the bacterial community structure. Experiments were carried out complementing culture and culture-independent methods. Strong variations of the bacterialcommunities were recorded along the sampling period in particular regarding number and phylogeneticrelationships of the microorganisms detected. At the season beginning, bacterial counts were rather high butstrains belonged only to β- and γ-Proteobacteria. By contrast, in the middle of the season, possibly due toexternal inputs, total number of bacteria decreased but other phylogenetic groups, such as α–proteobacteria, Actinobacteria and Firmicute appeared. On the whole, Proteobacteria were the dominant microbiota. Bacterial diversity and presence of most abundant species were analysed by PCR-TGGE. Sequencing of TGGE bandsconfirmed that prevalent Bacteria populations were evolutively close to Proteobacteria with predominance of α- and β-Proteobacteria. Analysis of diversity and functional organization suggested that “La Caldera” bacterial microbiota, typical of oligotrophic and/or extreme environments with low habitability, was characterized by a community organized in an adequate distribution of dominant and resilient species. Although rather specialized, the community presented a sufficient functionality and flexibility to react to changing and stressing conditions. However, along the ice-free season, the community evolved showing more specialized populations with less adaptation abilities. This is the first work complementing cultural and cultural-independent methods for the “La Caldera” lake.

Interactive effects of vertical mixing, nutrients and ultraviolet radiation: in situ photosynthetic responses of phytoplankton from high mountain lakes in Southern Europe

Abstract. Global change, together with human activities, has resulted in increasing amounts of organic material (including nutrients) that water bodies receive. This input further attenuates the penetration of solar radiation, leading to the view that opaque lakes are more "protected" from solar ultraviolet radiation (UVR) than clear ones. Vertical mixing, however, complicates this view as cells are exposed to fluctuating radiation regimes, for which the effects have, in general, been neglected. Furthermore, the combined impacts of mixing, together with those of UVR and nutrient inputs are virtually unknown. In this study, we carried out complex in situ experiments in three high mountain lakes of Spain (Lake Enol in the National Park Picos de Europa, Asturias, and lakes Las Yeguas and La Caldera in the National Park Sierra Nevada, Granada), used as model ecosystems to evaluate the joint impact of these climate change variables. The main goal of this study was to address the question of how short-term pulses of nutrient inputs, together with vertical mixing and increased UVR fluxes modify the photosynthetic responses of phytoplankton. The experimentation consisted in all possible combinations of the following treatments: (a) solar radiation: UVR + PAR (280–700 nm) versus PAR (photosynthetically active radiation) alone (400–700 nm); (b) nutrient addition (phosphorus (P) and nitrogen (N)): ambient versus addition (P to reach to a final concentration of 30 μg P L−1, and N to reach N:P molar ratio of 31); and (c) mixing: mixed (one rotation from surface to 3 m depth (speed of 1 m 4 min−1, total of 10 cycles)) versus static. Our findings suggest that under ambient nutrient conditions there is a synergistic effect between vertical mixing and UVR, increasing phytoplankton photosynthetic inhibition and excretion of organic carbon (EOC) from opaque lakes as compared to algae that received constant mean irradiance within the epilimnion. The opposite occurs in clear lakes where antagonistic effects were determined, with mixing partially counteracting the negative effects of UVR. Nutrient input, mimicking atmospheric pulses from Saharan dust, reversed this effect and clear lakes became more inhibited during mixing, while opaque lakes benefited from the fluctuating irradiance regime. These climate change related scenarios of nutrient input and increased mixing, would not only affect photosynthesis and production in lakes, but might also further influence the microbial loop and trophic interactions via enhanced EOC under fluctuating UVR exposure.

Epiclastic deposits associated with large-scale landslides and the formation of erosive calderas in oceanic islands: The example of the La Palma Island (Canary Archipelago)

The growth and evolution of the La Palma Island has frequently been punctuated by high magnitude mass-wasting events triggered by gravitational collapses of volcanic edifices and by the erosion of the Caldera de Taburiente. These episodes are evidenced by voluminous debris accumulations in the submarine vicinity of the island and the presence of six very-coarse epiclastic units in the geological record of the island. In this paper we study these epiclastic units in order to characterize their stratigraphic architecture and facies associations, and the mechanisms involved in the transport and emplacement of the material associated with large failures and the erosion of volcanic edifices. Emphasis is also placed on characterising the temporal sequence of processes that have occurred on the island and discussing the origin of the Caldera de Taburiente.Three of the units described — La Cumbrecita Breccias and Megabreccias, La Pared de la Caldera Breccias and Conglomerates and La Viña Breccias – are overlying the detachment surfaces of the Santa Cruz de La Palma, Playa de la Veta and Cumbre Nueva landslides, respectively. They mainly represent the products of debris avalanches and debris flows with subordinate stream-flows filling the scars of the landslides. Unit 4, Las Angustias Breccias and Conglomerates, is interpreted as debris-flow or lahar deposits generated by landslides during the growth of the Bejenado Volcano. The uppermost units, the Tazacorte Conglomerates and El Riachuelo Conglomerates, represent water-laid deposits related to the excavation and erosion of the Caldera de Taburiente, and the incision of a valley between the Bejenado Volcano and the Cumbre Nueva scarp, respectively.Our results provide new and valuable data about cyclic events of construction–destruction of volcanic edifices worldwide, and their related processes and deposits.