Maria Arribere

Abstract The stabilization of the 18 R stress induced martensite in Cu–Zn–Al single crystals has been measured as a function of ageing time in differently prepared crystals. It is concluded that only small impurity contents of a concentration similar to that of the quenched-in vacancies can affect notably the stabilization kinetics.

The atmospheric pollution associated with the volcano Copahue activity was evaluated by analyzing the concentration of 33 elements including heavy metals in lichens. Fruticose thalli were collected between 7 and 18 km from the volcano crater, comprising a geothermal zone. Analytical data and geographic parameters were evaluated by Principal Component Analysis. Enrichment Factors was also calculated from elemental concentrations in the lichens. The Principal Components Analysis grouped the observations corresponding to the lichen samples in relation to the volcano crater distance, the thermal areas and the direction of the prevailing winds. The less impacted area by volcanic products presented a lower concentration of toxic elements (S and Hg) and a higher concentration of biological elements (Ca, K, Mg and Mn) than the other areas. All studied sites showed S and Se enrichments, even in the most distant areas from the volcano crater. The S concentrations in lichen recorded in areas of volcanic activity were higher for the volcanic complexes: Copahue-Caviahue and Puyehue-Cordón-Caulle (2800-12000 μg/g) than those reported for the rest of the world (600-2800 μg/g).

Mercury and heavy metal contents are monitored using lichens as a tool for evaluation of air pollution. Lichens allow the identification of zones with anthropic impact, pollution hotspots and natural sources of contamination like volcanic emissions. The concentration of mercury (Hg) semivolatiles and rare-earth elements (REEs) were measured in our case in fruticose lichen thalli and soils collected in an active volcanic area: the Copahue-Caviahue Volcanic Complex, in northern Patagonia, South America. The present research focus on Hg-release patterns and its association to elements such as sulphur (S) and bromine (Br). In order to discriminate the particulate from the gaseous forms the concentration ratios of elements to magnesium (Mg) were computed. The Hg vs. Br concentration linear regression, together with the Hg normalised concentration vs. volcano distance, suggest that Hg from volcanic origin may be oxidised changing to reactive forms in the ash plume. Total mercury concentration in fruticose lichens (0.207-0.331 μg g −1) in Copahue-Caviahue volcanic area were higher than those from several other volcanic areas in South America, USA and Italy (0.010-0.290 μg g-1). Nevertheless, the consequent deposition has not generated a net contamination in soils.

La actividad desarrollada en el campo de las lipasas vegetales es considerablemente menor que la que se lleva a cabo en el de las lipasas de mamíferos y de microorganismos, a pesar de la importancia que tiene el conocimiento de aquéllas, tanto para comprender su rol fisiológico como para analizar su posible aplicación en procesos biotecnológicos. En razón de ello, las semillas de oleaginosas deberían constituir la fuente de elección de lipasas vegetales, dado que los aceites representan su mayor sustrato energético. Por otra parte, su condición de cultivo intensivo asegura una fácil disponibilidad de material de bajo costo y elevada homogeneidad . Como ya ha sido mencionado, el girasol es la principal oleaginosa cultivada en nuestro país, correspondiendo a la Provincia de Buenos Aires más de la mitad de su producción. Sin embargo, más allá de algunos intentos aislados, la información de la que se dispone sobre el sistema lipolítico responsable de la movilización de los lípidos de re...

Through the last millennium, Patagonia has been affected by changing climate conditions and successive volcanic eruptions. Lake Tonček is a high-altitude lake in the Southern Volcanic Zone in the northern Patagonian Andes. We documented the responses of the subfossil chironomid community to the effects of successive volcanic and different conditions in a sedimentary sequence from this lake comprising the last 900 years. The community composition and structure (abundance, diversity, and richness) and the development of morphological anomalies in the chironomid mouthparts were evaluated throughout the core. Both climatic conditions and volcanism affected the chironomid community differentially. The chironomid community changed following short-term climate change patterns, being affecting not only by temperature changes but also by variations in the regional precipitation regime. Decreases in abundance and diversity were only observed in coarse volcanic layers. In these samples, we rec...

Zinc (Zn) bioaccumulation and trophic transfer were analyzed in the food web of Lake Nahuel Huapi, a deep, unpolluted ultraoligotrophic system in North Patagonia. Benthic macroinvertebrates, plankton, and native and introduced fish were collected at three sites. The effect of pyroclastic inputs on Zn levels in lacustrine food webs was assessed by studying the impact of the eruption of Puyehue-Cordón Caulle volcanic complex (PCCVC) in 2011, by performing three sampling campaigns immediately before and after the PCCVC eruption, and after 2 years of recovery of the ecosystem. Zinc trophodynamics in L. Nahuel Huapi food web was assessed using nitrogen stable isotopes (δN). There was no significant increase of Zn concentrations ([Zn]) in L. Nahuel Huapi biota after the PCCVC eruption, despite the evidence of [Zn] increase in lake water that could be associated with volcanic ash leaching. The organisms studied exhibited [Zn] above the threshold level considered for dietary deficiency, reg...

Pomacea canaliculata is a mollusk potentially useful as a biomonitor species of freshwater quality. This work explores the ability of snail tissues and symbiotic corpuscles to bioconcentrate and depurate mercury, arsenic, and uranium. Adult snails cultured in metal-free reconstituted water were exposed for eight weeks (bioaccumulation phase) to water with Hg (2 μgL), As (10 μgL), and U (30 μgL) and then returned to the reconstituted water for other additional eight weeks (depuration phase). Elemental concentrations in digestive gland, kidney, symbiotic corpuscles and particulate excreta were determined by neutron activation analysis. The glandular symbiotic occupancy was measured by morphometric analysis. After exposure, the kidney showed the highest concentration of Hg, while the digestive gland accumulated mainly As and U. The subcellular distribution in symbiotic corpuscles was ∼71%, ∼48%, and ∼11% for U, Hg, and As, respectively. Tissue depuration between weeks 8 and 16 was vari...

Silver (Ag) is a pollutant of high concern in aquatic ecosystems, considered among the most toxic metallic ions. In lacustrine environments, contaminated sediments are a source of Ag for the food web. Chironomidae (Insecta: Diptera) are the most abundant, diverse, and representative insect groups in aquatic ecosystems. Chironomid larvae are closely associated to benthic substrates and link primary producers and secondary consumers. Given their trophic position and their life habits, these larvae can be considered the entry point for the transference of Ag, from the benthic deposit to the higher trophic levels of the food web. Previous studies in lakes from Nahuel Huapi National Park (Northern Patagonia) showed Ag enrichment over background levels (0.04-0.1 μg g(-1) dry weight) both in biota (bivalves and fish liver) and sediments from sites near human settlements. The aim of this study was to analyze the role of chironomids in the transference of Ag from the benthic reservoir of Lak...

Niche segregation between introduced and native fish in Lake Nahuel Huapi, a deep oligotrophic lake in Northwest Patagonia (Argentina), occurs through the consumption of different prey. Therefore, in this work we analyzed total mercury [THg] and methylmercury [MeHg] concentrations in top predator fish and in their main prey to test whether their feeding habits influence [Hg]. Results indicate that [THg] and [MeHg] varied by foraging habitat and they increased with greater percentage of benthic diet and decreased with pelagic diet in Lake Nahuel Huapi. This is consistent with the fact that the native creole perch, a mostly benthivorous feeder, which shares the highest trophic level of the food web with introduced salmonids, had higher [THg] and [MeHg] than the more pelagic feeder rainbow trout and bentho-pelagic feeder brown trout. This differential THg and MeHg bioaccumulation observed in native and introduced fish provides evidence to the hypothesis that there are two main Hg trans...

Despite located far from point sources of Hg pollution, high concentrations were recorded in plankton from the deep oligotrophic Lake Nahuel Huapi, located in North Patagonia. Native and introduced top predator fish with differing feeding habits are a valuable economic resource to the region. Hence, Hg and Se trophic interactions and pathways to these fish were assessed in the food web of this lake at three sites, using stable nitrogen and carbon isotopes. As expected based on the high THg in plankton, mercury did not biomagnify in the food web of Lake Nahuel Huapi, as most of the THg in plankton is in the inorganic form. As was observed in other aquatic systems, Se did not biomagnify either. When trophic pathways to top predator fish were analyzed, they showed that THg biomagnified in the food chains of native fish but biodiluted in the food chains of introduced salmonids. A more benthic diet, typical of native fish, resulted in higher [THg] bioaccumulation than a more pelagic or mixed diet, as in the case of introduced fish. Se:THg molar ratios were higher than 1 in all the fish species, indicating that Se might be offering a natural protection against Hg toxicity.

Chironomid communities were studied in a sediment core collected from Lake Moreno Oeste, located in Nahuel Huapi National Park. A major change in midge assemblages occurred at ∼AD 1760, which was characterized by a decrease of “cold taxa” including Polypedilum sp.2 and Dicrotendipes, and an increase of “warm taxa” including Apsectrotanypus and Polypedilum sp.1. These taxa are likely related to climatic conditions concurrent with the end of a cold period at ∼AD 1500-1700 and the beginning of a drying climate at ∼AD 1740-1900 in northern Patagonia. Coarse tephra layers had low midge diversity; however they did not disrupt the climatic trend as the community recovered rapidly after the event. Since AD 1910, after the increase in suburban housing, fish introduction, and the construction of a road, there was an increase in the relative abundances of taxa typically associated with the littoral zone, such as Parapsectrocladius, Riethia, Apsectrotanypus, and some Tanytarsini morphotypes. Th...

ABSTRACT Los depósitos de cenizas volcánicas son excelentes marcadores estratigráficos y cronológicos ya que pueden ser dispersados a cientos de kilómetros de su fuente. Sin embargo, su correlación puede ser problemática. Si bien la mayoría de los estudios basan estas correlaciones en análisis geoquímicos de roca total, las partículas volcánicas juveniles poseen gran heterogeneidad en cuanto a la forma de los fragmentos, textura y composición de la matriz y las fases minerales. Trabajos previos en niveles volcánicos identificados en una secuencia del lago Nahuel Huapi permitieron identificar los productos de la erupción del año 1960 del sistema Cordón Caulle, presentando una gran variabilidad en el tipo de partículas volcánicas juveniles identificadas, como pómez blanca, marrón, escorias y trizas vítreas, con variaciones en la composición de roca total de cada tipo de partícula. Con esta información como base, en el presente trabajo se presentan los primeros análisis morfológicos, texturales y composicionales de los diferentes productos juveniles con el objeto de identificar el origen de las variaciones morfológicas y de geoquímica de roca total de las mismas. Los resultados permitieron asociar dichas diferencias a variaciones en el contenido de cristales y tamaño, forma y distribución de vesículas. Dicha variación, a su vez, fue relacionada a procesos de fraccionamiento previos a la erupción de 1960 del sistema Cordón Caulle, generando información de valiosa utilidad para el uso de estos niveles como marcadores cronoestratigráficos.

RESUMEN INTRODUCCIÓN: el contenido mineral de las hojas usadas en infusiones cambia de acuerdo con el grado de madurez de las partes vegetales incluidas o con las condiciones climáticas del área de crecimiento de la planta e incluso puede mostrar ...

An experiment was performed to assess the feasibility of using transplantedProtousnea magellanica (Mont.) Krog thalli as a bioindicator of atmosphericheavy metal contamination. The thalli were collected for pristine areas ofNahuel Huapi National Park and transplanted back in the same site and at differentlocations at Bariloche city. One year later, the thalli were collected andtheir elemental contents were analyzed by instrumental

... ELSEVIER Earth and Planetary Science Letters 133 (1995) 47-57 EPSL Rare earth geochemistry in sediments of the Upper Manso River Basin, Rio Negro, Argentina Gabriela Roman Ross *'1, S. Ribeiro Guevara 2, MA Arribere 2 Comisi6n Nacional de Energia At6mica, Centro ...

Vegetation associated with lacustrine systems in Northern Patagonia was studied for heavy metal and trace element contents, regarding their elemental contribution to these aquatic ecosystems. The research focused on native species and exotic vascular plant Salix spp. potential for absorbing heavy metals and trace elements. The native species studied were riparian Amomyrtus luma, Austrocedrus chilensis, Chusquea culeou, Desfontainia fulgens, Escallonia rubra, Gaultheria mucronata, Lomatia hirsuta, Luma apiculata, Maytenus boaria, Myrceugenia exsucca, Nothofagus antarctica, Nothofagus dombeyi, Schinus patagonicus, and Weinmannia trichosperma, and macrophytes Hydrocotyle chamaemorus, Isöetes chubutiana, Galium sp., Myriophyllum quitense, Nitella sp. (algae), Potamogeton linguatus, Ranunculus sp., and Schoenoplectus californicus. Fresh leaves were analyzed as well as leaves decomposing within the aquatic bodies, collected from lakes Futalaufquen and Rivadavia (Los Alerces National Park), and lakes Moreno and Nahuel Huapi (Nahuel Huapi National Park). The elements studied were heavy metals Ag, As, Cd, Hg, and U, major elements Ca, K, and Fe, and trace elements Ba, Br, Co, Cr, Cs, Hf, Na, Rb, Se, Sr, and Zn. Geochemical tracers La and Sm were also determined to evaluate contamination of the biological tissues by geological particulate (sediment, soil, dust) and to implement concentration corrections.

The ratios of Rb to Cs contents were studied in five fish species from seven lakes located in the Patagonia Andean Range, Argentina in order to trace fish diet. The species studied were native velvet catfish (Diplomistes viedmensis) and creole perch (Percichthys trucha), and exotic brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvenilus fontinalis). Rainbow trout specimens from two farms were also studied, as well as fish food items and native mussels (Diplodon chilensis). Rb and Cs concentrations were determined by instrumental neutron activation analysis. A positive correlation of Cs concentration in the muscle of velvet catfish with fish length was observed, probably associated with the long biological half-life of this element in this species, whereas the Rb concentration remained constant, hence inhibiting the use of Rb-Cs ratios as a tracer in this case. Seasonal variations observed for rainbow trout and Cs concentration background bias in one of the lakes studied are also a limiting factor to the use of Rb-Cs ratios as a diet tracer. Rb-Cs ratios allowed clear differentiation of rainbow trout raised in farms from the natural specimens that lived in the same environment, in agreement with Rb-Cs ratios determined in both diets. Rb-Cs ratios in rainbow trout showed significant differences between Rivadavia and Futalaufquen lakes compared to Moreno and Nahuel Huapi lakes, which could be associated with a higher participation of plankton in the diet in the first case. No relevant variations in Rb-Cs ratios of brown trout were observed, probably because of the similarity in the diet.

Mercury is released to the environment from natural and anthropogenic sources, and through atmospheric transport is distributed globally. Lake Futalaufquen (42.8°S) is an oligotrophic lake located in Los Alerces National Park (Northern Patagonia), providing a remote and unpolluted study system. A lacustrine sedimentary sequence revealed 1600years of Hg deposition, identifying natural baselines and marked peaks not correlated with long-range atmospheric transport. Organic matter and catchment erosion were discarded as Hg drivers. Natural background, pre-1300CE Hg concentrations, ranged between 27 and 47ngg(-1) (accumulation rates from 8 to 15μgm(-2)y(-1)). From 1300CE on, the Hg background profile did not follow the generally increasing Hg pattern observed in both Southern and Northern Hemisphere since pre-industrial times. It was not until the last century that a 1.6-fold increase is observed in the Hg accumulation rate, considered among the lowest increments in southern South Ameri...

ABSTRACT Neutron capture resonance integrals of the reactions 79Br(n, )80Brm, 79Br(n, )80Brg, 81Br(n, )82Brm, 81Br(n, )82Brg, and 81Br(n, )82Brm+g have been measured under 1-mm-thick cadmium covers inside the core of the RA-6 research reactor. The measured values are, respectively, (29.2 ± 3.1) b, (86.1 ± 8.9) b, (40.9 ± 2.3) b, (5.1 ± 1.1) b, and (46.8 ± 2.3) b. Resonance integrals of the reactions 79Br(n, )80Brm and 81Br(n, )82Brm were also measured by a direct method using the gamma ray from the isomeric transition. The results are (30.3 ± 2.6) b and (42.7 ± 4.0) b, respectively. All measured resonance integrals are referred to the standard value (1562 ± 48) b, corresponding to the reaction 197Au(n, )198Au. Spectrum unfolding with the STAY'SL code showed the 1/E behavior of the neutron energy spectrum in the epithermal range. Good agreement was found between the results of this work and others published in the literature. Perturbations of epithermal activation due to the presence of cadmium covers are discussed and corrected in the cases where differential cross-section data are available.

In regions with limited knowledge of the historical volcanic record, like remote areas in the Andean Southern Volcanic Zone, the definition of reliable age-depth models for lake sequences represents a valuable tool for tephra layers dating. In Lake Futalaufquen (42.8 S), Northern Patagonia, a short sedi-mentary sequence was extracted after the AD 2008 Chait en eruption with the purpose to analyze the records of volcanic eruptions at these poorly studied latitudes. The sequence was dated by 210 Pb, 137 Cs, and 14 C techniques. Five tephras were identified for the last 1600 years, restricted to the last 5 centuries. Sedimentology, morphology, and geochemical properties allowed the characterization of the tephras and their correlation with tephras recently identified proximal to the sources, mainly from Chait en and Huequi volcanoes, and Michinmahuida accessory cones, representing the first distal records reported of these tephras. Furthermore, tephras modeled ages obtained by the sequence age-depth model shrink the ages for the volcanic events, like a potential cycle of activity from Michinmauida accessory cones during AD 1530 ± 55, one eruption from Huequi volcano at AD 1695 ± 50, and a possible recent eruption from Chait en at AD 1775 ± 40. Additionally, the work contributes to improve the regional volcanic records knowledge, basic for volcanic hazard assessment.

Volcanic eruptions are recognized sources of toxic elements to freshwater, including arsenic (As). In order to study the short term changes in the bioaccumulation of naturally occurring As by aquatic organisms in Lake Nahuel Huapi (Argentina), located close to the Puyehue-Cordón Caulle volcanic complex (PCCVC), we described As concentrations at different trophic levels and food web transfer patterns in three sites of the lake prior to the last PCCVC eruption (June 2011), and compared As concentrations in biota before and after the eruption. The highest As concentrations and greater variations both between sites and position in the water column, were observed in phytoplankton (3.9-64.8 µg g(-1) dry weight, DW) and small zooplankton (4.3-22.3 µg g(-1) DW). The pattern of As accumulation in aquatic organisms (whole body or muscle) was: primary producers (phytoplankton) > scrapper mollusks (9.3-15.3 µg g(-1) DW) > filter feeding mollusks (5.4-15.6 µg g(-1) DW) > omnivorous invertebrates (0.4-9.2 µg g(-1) DW) > zooplankton (1.2-3.5 µg g(-1) DW) > fish (0.2-1.9 µg g(-1) DW). We observed As biodilution in the whole food web, and in salmonids food chains, feeding on fish prey; but biomagnification in the food chain of creole perch, feeding on benthic crayfish. The impact of the 2011 PCCVC eruption on the As levels of biota was more evident in pelagic-associated organisms (zooplankton and planktivorous fish), but only in the short term, suggesting a brief high bioavailability of As in water after ash deposition. In benthic organisms As variations likely responded to shift in diet due to coverage of the littoral zone with ashes.

RESUMEN Se discute la posibilidad de utilizar germanio como monitor de las componentes térmica y epitérmica del flujo neutrónico y como comparador en el análisis por activación paramétrico. Se comentan las ventajas e inconvenientes asociados a su empleo y se efectúa la comparación con el zirconio, en términos del error relativo de las determinaciones. Su empleo como monitor de flujo integral, incluyendo la componente rápida del flujo neutrónico, es también discutido. Se presentan los datos correspondientes a las mediciones de factores k 0 para las transiciones gamma más importantes de 75 Ge y 77 Ge y los resultados del análisis de materiales de referencia, empleando al germanio como monitor de flujo y comparador en forma simultánea. I. INTRODUCCIÓN La factibilidad de utilizar monitores de flujo y comparadores elementales bi o multiisotópicos ha sido ya demostrada y aplicada para los métodos paramétricos de análisis por activación en reactores nucleares. Así, se ha propuesto el uso d...

Keywords: k 0-neutron activation analysis CRM production ERM-EB530 Microhomogeneity Al–0.1%Au Inter-comparison Reliable certified reference materials (CRM) are required for neutron dosimetry in k 0-neutron activation analysis (k 0-NAA). In the past, levitation melting was employed to produce highly homogeneous alloys used in the production of CRMs. This publication describes a novel and more efficient way of processing such alloys using the example of an Al–Au alloy, the evaluation of the efficacy with respect to achieving homogeneity and avoiding micro-and macrosegregation and the final certification of the Au mass fraction. First, Al–5% Au alloy was melted by arc melting and then diluted into Al–0.1% Au with high purity Al in a resistance furnace under the protection of high purity argon gas. The as-casted Al–0.1% Au was then heat-treated at about 635 °C for 48 h. No significant macrosegregation and no intermetallic phase (AuAl 2) were observed in the heat-treated alloy. Using this approach , a new CRM for gold mass fraction in Al–0.1% Au was produced in the form of wires and foils (ERM-EB530A, B and C). The relative uncertainty from gold inhomogeneity in the material was assessed using a randomised block design and inductively coupled plasma optical emission spectrometry (ICP-OES) and was found to be 0.3%. The characterisation of the gold mass fraction was performed by an interlaboratory comparison of expert laboratories. Sixteen laboratories participated using instrumental neutron activation analysis (197 Au(n,γ) 198 Au), fire assay and ICP-OES. Alternative INAA reactions (197 Au(n,2n) 196 Au) and calibration strategies were tested but not retained for the characterisation study as they did not meet the strict performance criteria set for the study. After evaluation of homogeneity and characterisation, the Au mass fraction in ERM-EB530A, B and C was certified to be 1005 ± 7 mg/kg (k = 2), which is a lower uncertainty than for previous similar materials. This demonstrates the suitability of the new production route, which should also be applicable to other binary alloys required for neutron dosimetry.

Increased chromium (Cr) and arsenic (As) concentrations in mussels Diplodon chilensis from lakes Nahuel Huapi and Moreno were associated with human settlements. Higher proportions of benthic/littoral preys in diets were reported to be positively correlated with higher [Cr] in fish from Lake Moreno, whereas biodilution trends of Cr, cobalt (Co) and As were reported in the whole biota of the same lake. We hypothesized that benthic/littoral preys could also be important in the Cr pathway to top predator fish from other regional lakes (TPFOL) sharing the same species assemblages, and that TPFOL could bioaccumulate more Cr, Co and As when feed on preys from lower trophic levels. The objective of the present work is to compare Cr, Co and As pathways and bioaccumulation trends described in Lake Moreno with those of TPFOL. Trace elements concentrations were measured in muscles of brown trout Salmo trutta, rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis and creole perch ...

A survey of trace element contents in fish muscle and liver was performed in different lakes of two northern Patagonian national parks: Nahuel Huapi and Los Alerces national parks. The aim of the work was to obtain the first set of reference data on elements that are not liable to be disturbed by human activities and to identify compositional patterns related to the species and site of collection. The species studied are native creole perch and velvet catfish and exotic brown trout, rainbow trout, and brook trout. The elements analyzed are Br, Cs, Fe, Rb, Se, Na, and Zn. Trace elements in muscle of brown trout, rainbow trout, and creole perch showed statistical patterns that allow one to identify the national park of origin, as well as which of the lakes (Traful, Espejo Chico, or the Nahuel Huapi-Moreno system) of the Nahuel Huapi National Park from which they come. Contents in the liver provide similar but less clear patterns than contents in muscle; however, in some particular cas...

The ratios of Rb to Cs contents were studied in five fish species from seven lakes located in the Patagonia Andean Range, Argentina in order to trace fish diet. The species studied were native velvet catfish (Diplomistes viedmensis) and creole perch (Percichthys trucha), and exotic brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvenilus fontinalis). Rainbow trout specimens from two farms were also studied, as well as fish food items and native mussels (Diplodon chilensis). Rb and Cs concentrations were determined by instrumental neutron activation analysis. A positive correlation of Cs concentration in the muscle of velvet catfish with fish length was observed, probably associated with the long biological half-life of this element in this species, whereas the Rb concentration remained constant, hence inhibiting the use of Rb-Cs ratios as a tracer in this case. Seasonal variations observed for rainbow trout and Cs concentration background bias in one of the lakes studied are also a limiting factor to the use of Rb-Cs ratios as a diet tracer. Rb-Cs ratios allowed clear differentiation of rainbow trout raised in farms from the natural specimens that lived in the same environment, in agreement with Rb-Cs ratios determined in both diets. Rb-Cs ratios in rainbow trout showed significant differences between Rivadavia and Futalaufquen lakes compared to Moreno and Nahuel Huapi lakes, which could be associated with a higher participation of plankton in the diet in the first case. No relevant variations in Rb-Cs ratios of brown trout were observed, probably because of the similarity in the diet.

ABSTRACT Los depósitos de cenizas volcánicas son excelentes marcadores estratigráficos y cronológicos ya que pueden ser dispersados a cientos de kilómetros de su fuente. Sin embargo, su correlación puede ser problemática. Si bien la mayoría de los estudios basan estas correlaciones en análisis geoquímicos de roca total, las partículas volcánicas juveniles poseen gran heterogeneidad en cuanto a la forma de los fragmentos, textura y composición de la matriz y las fases minerales. Trabajos previos en niveles volcánicos identificados en una secuencia del lago Nahuel Huapi permitieron identificar los productos de la erupción del año 1960 del sistema Cordón Caulle, presentando una gran variabilidad en el tipo de partículas volcánicas juveniles identificadas, como pómez blanca, marrón, escorias y trizas vítreas, con variaciones en la composición de roca total de cada tipo de partícula. Con esta información como base, en el presente trabajo se presentan los primeros análisis morfológicos, texturales y composicionales de los diferentes productos juveniles con el objeto de identificar el origen de las variaciones morfológicas y de geoquímica de roca total de las mismas. Los resultados permitieron asociar dichas diferencias a variaciones en el contenido de cristales y tamaño, forma y distribución de vesículas. Dicha variación, a su vez, fue relacionada a procesos de fraccionamiento previos a la erupción de 1960 del sistema Cordón Caulle, generando información de valiosa utilidad para el uso de estos niveles como marcadores cronoestratigráficos.

Historical records of short lived (140Ba, 131I, 103Ru and 95Zr+95Nb) and long-lived (137Cs and 90Sr) fission products by fallout measurements performed in Argentina since 1959 were analyzed in order to define the main characteristics of 137Cs fallout time evolution in the Nahuel Huapi National Park, Patagonia, Argentina. Sedimentary cores were sampled from Lake Nahuel Huapi and Lake Morenito, which are

Native mussels, Diplodon chilensis, were sampled from four lakes in Nahuel Huapi National Park, Northern Patagonia, Argentina in order to evaluate heavy-metal distribution in the region and to assess the contribution of this compartment of the trophic web to their circulation in the food chain. The concentration of potential pollutants Ag, As, Cr, Hg, Sb, and Se, and other nine elements of interest (Ba, Br, Ca, Co, Cs, Fe, Na, Sr, and Zn) were determined in Diplodon chilensis pooled samples. Digestive glands were analyzed separately from soft tissues. Geological tracers Sc, Ta, Th, and rare earth elements were also determined in order to discriminate lithophile contributions. Elemental concentrations of Ba, Br, Fe, Sr, Se, and Zn in total soft tissues samples do not show significant differences among sampling sites. Arsenic and Cr contents in total soft tissues and digestive gland pooled samples are higher in sampling points close to zones with human settlements. Silver contents in samples collected in Lake Nahuel Huapi were higher than in the other lakes studied, and up to 50-fold higher than the sample collected in Lake Traful, considered as the reference. Mercury highest concentration values measured in total soft tissues pooled samples from lakes Nahuel Huapi and Moreno were found to be similar to those observed in other reported Hg contamination situations, and they are three to five times higher than those of the reference samples collected in Lake Traful.

Abstract. Trace metals (Sb, As, Br, Cs, Co, Cr, Ag and Hg), rare earth elements (Ce, Eu, La, Lu, Sm, Tb and Yb), and Sc. were analysed in suspended load and in two sediment cores from Lake Nahuel Huapi, Nahuel Huapi National Park, Patagonia, Argentina, by using ...

The incorporation and trophic transfer of total and methyl mercury (THg, MeHg) were examined in three size classes of plankton (10-53, 53-200, and >200 μm size range) and a small planktivorous fish, Galaxias maculatus, from the large multi-branched Lake Nahuel Huapi (North Patagonia, Argentina). Three sites representing a large range of lake benthic-pelagic structures (based on depth and shoreline characteristics) and precipitation regimes were sampled. Nitrogen and carbon stable isotopes (δ(15)N, δ(13)C) were analyzed to assess Hg trophodynamics. Selenium concentrations were determined together with THg in order to consider its potential effect on Hg trophodynamics. High THg concentrations (0.1-255 µg g(-1) dry weight (DW)) were measured in plankton, largely in inorganic form (MeHg: 3-29 ng g(-1) DW, 0.02-7% of THg, in the two larger size classes). A trend of increasing THg concentrations, varying in two to three orders of magnitude, with decreasing plankton size was associated with precipitation measured prior to each sampling event. Passive adsorption of dissolved Hg(2+) from wet deposition and runoff is considered to be the principal Hg uptake mechanism at the base of the pelagic food web. Despite the initially high THg uptake in the smaller plankton classes, the transfer to G. maculatus, and consequently to the entire food web, is likely limited due to low proportion of MeHg to THg in plankton. Furthermore, evidence of G. maculatus with benthic feeding habits having higher impact on MeHg trophic transfer compared to the same species with more pelagic (e.g., zooplankton) feeding habits, was observed. Although there is a high THg uptake in plankton, limited amounts are incorporated in the entire food web from the pelagic compartment.