Lithium isotopes in large rivers reveal the cannibalistic nature of modern continental weathering and erosion

The erosion of major mountain ranges is thought to be largely cannibalistic, recycling sediments that were deposited in the ocean or on the continents prior to mountain uplift. Despite this recognition, it has not yet been possible to quantify the amount of recycled material that is presently transported by rivers to the ocean. Here, we have analyzed the Li content and isotope composition (View the MathML source) of suspended sediments sampled along river depth profiles and bed sands in three of the largest Earth's river systems (Amazon, Mackenzie and Ganga–Brahmaputra rivers). The View the MathML source values of river-sediments transported by these rivers range from +5.3 to −3.6‰ and decrease with sediment grain size. We interpret these variations as reflecting a mixture of unweathered rock fragments (preferentially transported at depth in the coarse fraction) and present-day weathering products (preferentially transported at the surface in the finest fraction). Only the finest surface sediments contain the complementary reservoir of Li solubilized by water–rock interactions within the watersheds. Li isotopes also show that river bed sands can be interpreted as a mixture between unweathered fragments of igneous and sedimentary rocks. A mass budget approach, based on Li isotopes, Li/Al and Na/Al ratios, solved by an inverse method allows us to estimate that, for the large rivers analyzed here, the part of solid weathering products formed by present-day weathering reactions and transported to the ocean do not exceed 35%. Li isotopes also show that the sediments transported by the Amazon, Mackenzie and Ganga–Brahmaputra river systems are mostly sourced from sedimentary rocks (>60%) rather than igneous rocks. This study shows that Li isotopes in the river particulate load are a good proxy for quantifying both the erosional rock sources and the fingerprint of present-day weathering processes. Overall, Li isotopes in river sediments confirm the cannibalistic nature of erosion and weathering

Microbial metagenomes from three aquifers in the Fennoscandian shield terrestrial deep biosphere reveal metabolic partitioning among populations

Microorganisms in the terrestrial deep biosphere host up to 20% of the earth's biomass and are suggested to be sustained by the gases hydrogen and carbon dioxide. A metagenome analysis of three deep subsurface water types of contrasting age (from &lt;20 to several thousand years) and depth (171 to 448 m) revealed phylogenetically distinct microbial community subsets that either passed or were retained by a 0.22 mu m filter. Such cells of &lt;0.22 mu m would have been overlooked in previous studies relying on membrane capture. Metagenomes from the three water types were used for reconstruction of 69 distinct microbial genomes, each with &gt;86% coverage. The populations were dominated by Proteobacteria, Candidate divisions, unclassified archaea and unclassified bacteria. The estimated genome sizes of the &lt;0.22 mu m populations were generally smaller than their phylogenetically closest relatives, suggesting that small dimensions along with a reduced genome size may be adaptations to oligotrophy. Shallow 'modern marine' water showed community members with a predominantly heterotrophic lifestyle. In contrast, the deeper, 'old saline' water adhered more closely to the current paradigm of a hydrogen-driven deep biosphere. The data were finally used to create a combined metabolic model of the deep terrestrial biosphere microbial community.Supplementary information available for this article at http://www.nature.com/ismej/journal/v10/n5/suppinfo/ismej2015185s1.html</p

Multiple introductions and environmental factors affecting the establishment of invasive species on a volcanic island

Invasive species pose significant challenges to local biodiversity and ecosystem function, especially on islands. Understanding the factors affecting the establishment of invasive species and how these relate to their genetic background is crucial to improve our ability to manage biological invasions. Here, we performed a phylogeographic study of two cosmopolitan megascolecid earthworms of Asian origin: Amynthas gracilis and Amynthas corticis at 38 localities on S~ao Miguel Island in the Azores archipelago (Portugal). Samples from putative source populations in China, Taiwan, Malaysia, as well as ‘outlier’ populations in USA, Mexico, Brazil and Spain were also included, resulting in a total of 565 earthworms genotyped at the mitochondrial cytochrome oxidase I (COI) and 16S ribosomal RNA genes. Soils were characterised for elemental composition, water holding capacity, organic matter content, texture and pH, and some habitat features were recorded. Both species showed a wide distribution across S~ao Miguel and their abundances were negatively associated, suggesting spatial segregation/competition, with the parthenogenetic A. corticis being relatively more successful. The presence of multiple mitochondrial lineages within each species, one of them found exclusively in the Azores, suggests a complex invasion history. Environmental factors affected the establishment of the different lineages, with metal concentrations, topographical elevation and the degree of human influence being differently linked to their abundances. Lineage diversity was negatively correlated with metal concentrations. These results emphasise the importance of genetically characterising invasive species to better understand their invasion patterns

The Chernobyl fallout in France, critical review measurement-results obtained at that time and lessons learned for crisis management [Les retombées de l'accident de Tchernobyl en France: analyse critique des mesures effectuées à l'époque sur le territoire national et enseignements pour la gestion de crise]

The Chernobyl fallout in France, critical review measurement-results obtained at that time and lessons learned for crisis management. Seventeen years after, all data of radioactivity measurements made in the environment at the time of Chernobyl accident by the various official French organisations have been listed and reassessed. These data were appropriate to evaluate within a short period of time, the radiological consequences of the accident fallout for a large part of the French population. However, because the effect of rain was not taken into consideration, these data did not enabled a correct evaluation of the contamination of foodstuff in some parts of the Eastern France where radioactive deposition were exceeding the regional mean value. For instance, despite the large analytical capability devoted to sensitive foodstuff measurements as milk, no focus was placed on the consumption of Corsica goat and sheep milk which could have lead to thyroid doses for children significantly higher that estimated mean values for Eastern France. Nowadays, the experience gained by IRSN would permit to better optimise the measurement distribution and to better assimilate data produced. However, to achieve this optimisation, we still need to carry on the radioecological sensitivity analysis of the different geographical compartments of the French territory, analysis eventually guiding any sample strategy. © 2004 EDP Sciences

Les retombées de l'accident de Tchernobyl en France : analyse critique des mesures effectuées à l'époque sur le territoire national et enseignements pour la gestion de crise

Dix sept ans après l'accident de Tchernobyl, toutes les données de mesure de la radioactivité dans l'environnement faites à l'époque par les différents services de l'État ont été collationnées et validées. Ces données étaient appropriées pour évaluer dans des délais satisfaisants, les conséquences des retombées de cet accident pour la grande majorité de la population française. En revanche, elles ne permettaient pas, du fait de l'absence de prise en compte de l'importance des précipitations, d'évaluer la contamination des produits alimentaires locaux dans les régions de l'Est de la France où les dépôts ont été très supérieurs aux moyennes. Ainsi, la capacité de mesure mobilisée à la suite de cet accident n'a pu être focalisée sur des productions sensibles telles que les laits de brebis et de chèvre en Corse dont la consommation a pu conduire à des doses à la thyroïde des enfants significativement supérieures aux moyennes estimées pour l'Est de la France. Aujourd'hui, l'expérience de l'IRSN permettrait de mieux optimiser l'utilisation des moyens de mesures et de mieux assimiler les données produites. Toutefois cette optimisation ne pourra être complète sans que soit conduite l'analyse préalable de la sensibilité radioécologique des différentes composantes géographiques du territoire français qui doit guider toute stratégie d'échantillonnage

International safety standards and supporting projects related to demonstrating the safety of radioactive waste disposal facilities

The paper elaborates on the international safety standards related to demonstrating the safety of radioactive waste disposal and provides on overview of the intercomparaison and harmonization projects presently underway

Long-term flux of Chernobyl-derived 137Cs from soil to French rivers: A study on sediment and biological indicators

Sediment and aquatic plants were collected annually since the early 1990s in the main French rivers, upstream of nuclear power plants. These time series were used in order to assess the parameters of a compartmental model describing the Chernobyl-derived 137Cs flux from soil to rivers. In order to reduce the dispersal of 137Cs measured activities in sediment samples due to the granulometric heterogeneity, a correction method was set up using sediment test-fractions artificially enriched with specific diameter particles. The method was based on 137Cs affinity for fine particles, especially clays, and thus clay and fine silt contents of each sample was analysed. Corrected sediment data showed (1) that the method efficiently reduced the variability; and (2) that 137Cs activities in French rivers decreased with a half-life of 4 to 6 years since 1987 (after correction by radioactive decay). A similar half-life value was obtained for aquatic plants pointing out that this half-life is related to the gradual decay of the flux from soil to rivers, not to the indicator itself. Comparing our results with similar ones published by other authors, it appeared possible that this kinetic varies with the time period over which the study is conducted, the longer the period the lower is the kinetic. © 2003 Elsevier Science Ltd. All rights reserved

Influence des retombées de l'accident de Tchernobyl sur l'activité en

Avec des dépôts de 137Cs dépassant quelquefois 20 000 Bq m-2, certains coteaux de la vallée du Rhône ont été assez fortement touchés par les retombées de l'accident de Tchernobyl. C'est le cas à Cornas (Ardèche) près de Valence et à Vinsobres (Vaucluse) au nord de Vaison-la-Romaine. La vigne occupe dans ces régions l'essentiel des surfaces agricoles, pour la production d'un vin réputé. Cette étude montre que les conséquences des retombées de l'accident de Tchernobyl pour les vins de la vallée du Rhône ont été visibles mais très faibles. L'activité en 137Cs du vin produit en 1986 n'a pas atteint 1 Bq/l. Ces conséquences très limitées sont dues à la date des dépôts qui sont intervenus début mai 1986, alors que les vignes développaient à peine leurs premières feuilles. Depuis 1986, l'activité en 137Cs du vin a fortement décru jusqu'à revenir en 2000 à un niveau proche de celle d'avant l'accident : quelques millibecquerels par litre. Le césium ajouté aux sols, dans des proportions pourtant importantes, se trouve essentiellement dans les 20 premiers centimètres et est peu disponible pour les racines de la vigne

Zn isotopic fractionation during complexation with organic matter

International audienc