Structural characterization of rockfall sources in Yosemite Valley from remote sensing data and field surveys

Yosemite Valley poses significant rockfall hazard and related risk due to its glacially steepened walls and approximately 4 million visitors annually. To assess rockfall hazard, it is necessary to evaluate the geologic structure that contributes to the destabilization of rockfall sources and locate the most probable future source areas. Coupling new remote sensing techniques (Terrestrial Laser Scanning, Aerial Laser Scanning) and traditional field surveys, we investigated the regional geologic and structural setting, the orientation of the primary discontinuity sets for large areas of Yosemite Valley, and the specific discontinuity sets present at active rockfall sources. This information, combined with better understanding of the geologic processes that contribute to the progressive destabilization and triggering of granitic rock slabs, contributes to a more accurate rockfall susceptibility assessment for Yosemite Valley and elsewhere.

Violence as a research object and intervention in the health field: an analysis from the production of the Research Group on Gender, Health and Nursingi

The study aimed to describe how violence is revealed in the production of the Research Group on Gender, Health and Nursing. This is a historical research of qualitative approach, which evaluated the production of the Research Group, through content analysis. The results show gender as a central category in determining violence and health practices. This aspect determines limitations on professional practices of coping, such as the invisibility of the problem. The female autonomy, the use of alcohol and drugs and social vulnerability play an important relation with the phenomenon and the bond is revealed as potentiality of health practices to address the problem. Conclusion: The gender perspective in nursing research is an innovative field and counter-hegemonic, a possibility to assume a meaning of praxis by transforming potential of understanding and modes of intervention in the phenomenon of gender violence.

Developing a Simple and Rapid Test for Monitoring the Heat Evolution of Concrete Mixtures for Both Laboratory and Field Applications, January 2006

Various test methods exist for measuring heat of cement hydration; however, most current methods require expensive equipment, complex testing procedures, and/or extensive time, thus not being suitable for field application. The objectives of this research are to identify, develop, and evaluate a standard test procedure for characterization and quality control of pavement concrete mixtures using a calorimetry technique. This research project has three phases. Phase I was designed to identify the user needs, including performance requirements and precision and bias limits, and to synthesize existing test methods for monitoring the heat of hydration, including device types, configurations, test procedures, measurements, advantages, disadvantages, applications, and accuracy. Phase II was designed to conduct experimental work to evaluate the calorimetry equipment recommended from the Phase I study and to develop a standard test procedure for using the equipment and interpreting the test results. Phase II also includes the development of models and computer programs for prediction of concrete pavement performance based on the characteristics of heat evolution curves. Phase III was designed to study for further development of a much simpler, inexpensive calorimeter for field concrete. In this report, the results from the Phase I study are presented, the plan for the Phase II study is described, and the recommendations for Phase III study are outlined. Phase I has been completed through three major activities: (1) collecting input and advice from the members of the project Technical Working Group (TWG), (2) conducting a literature survey, and (3) performing trials at the CP Tech Center’s research lab. The research results indicate that in addition to predicting maturity/strength, concrete heat evolution test results can also be used for (1) forecasting concrete setting time, (2) specifying curing period, (3) estimating risk of thermal cracking, (4) assessing pavement sawing/finishing time, (5) characterizing cement features, (6) identifying incompatibility of cementitious materials, (7) verifying concrete mix proportions, and (8) selecting materials and/or mix designs for given environmental conditions. Besides concrete materials and mix proportions, the configuration of the calorimeter device, sample size, mixing procedure, and testing environment (temperature) also have significant influences on features of concrete heat evolution process. The research team has found that although various calorimeter tests have been conducted for assorted purposes and the potential uses of calorimeter tests are clear, there is no consensus on how to utilize the heat evolution curves to characterize concrete materials and how to effectively relate the characteristics of heat evolution curves to concrete pavement performance. The goal of the Phase II study is to close these gaps.

MP2RAGE, a self bias-field corrected sequence for improved segmentation and T1-mapping at high field.

The large spatial inhomogeneity in transmit B(1) field (B(1)(+)) observable in human MR images at high static magnetic fields (B(0)) severely impairs image quality. To overcome this effect in brain T(1)-weighted images, the MPRAGE sequence was modified to generate two different images at different inversion times, MP2RAGE. By combining the two images in a novel fashion, it was possible to create T(1)-weighted images where the result image was free of proton density contrast, T(2) contrast, reception bias field, and, to first order, transmit field inhomogeneity. MP2RAGE sequence parameters were optimized using Bloch equations to maximize contrast-to-noise ratio per unit of time between brain tissues and minimize the effect of B(1)(+) variations through space. Images of high anatomical quality and excellent brain tissue differentiation suitable for applications such as segmentation and voxel-based morphometry were obtained at 3 and 7 T. From such T(1)-weighted images, acquired within 12 min, high-resolution 3D T(1) maps were routinely calculated at 7 T with sub-millimeter voxel resolution (0.65-0.85 mm isotropic). T(1) maps were validated in phantom experiments. In humans, the T(1) values obtained at 7 T were 1.15+/-0.06 s for white matter (WM) and 1.92+/-0.16 s for grey matter (GM), in good agreement with literature values obtained at lower spatial resolution. At 3 T, where whole-brain acquisitions with 1 mm isotropic voxels were acquired in 8 min, the T(1) values obtained (0.81+/-0.03 s for WM and 1.35+/-0.05 for GM) were once again found to be in very good agreement with values in the literature.

Nucleation and growth of metamorphic minerals in contact aureoles

THESIS ABSTRACT Nucleation and growth of metamorphic minerals are the consequence of changing P-T-X-conditions. The thesis presented here focuses on processes governing nucleation and growth of minerals in contact metamorphic environments using a combination of geochemical analytics (chemical-, isotope-, and trace element composition), statistical treatments of spatial data, and numerical models. It is shown, that a combination of textural modeling and stable isotope analysis allows a distinction between several possible reaction paths for olivine growth in a siliceous dolomite contact aureole. It is suggested that olivine forms directly from dolomite and quartz. The formation of olivine from this metastable reaction implies metamorphic crystallization far from equilibrium. As a major consequence, the spatial distribution of metamorphic mineral assemblages in a contact aureole cannot be interpreted as a proxy for the temporal evolution of a single rock specimen, because each rock undergoes a different reaction path, depending on temperature, heating rate, and fluid-infiltration rate. A detailed calcite-dolomite thermometry study was initiated on multiple scales ranging from aureole scale to the size of individual crystals. Quantitative forward models were developed to evaluate the effect of growth zoning, volume diffusion and the formation of submicroscopic exsolution lamellae (<1 µm) on the measured Mg-distribution in individual calcite crystals and compare the modeling results to field data. This study concludes that Mg-distributions in calcite grains of the Ubehebe Peak contact aureole are the consequence of rapid crystal growth in combination with diffusion and exsolution. The crystallization history of a rock is recorded in the chemical composition, the size and the distribution of its minerals. Near the Cima Uzza summit, located in the southern Adamello massif (Italy), contact metamorphic brucite bearing dolomite marbles are exposed as xenoliths surrounded by mafic intrusive rocks. Brucite is formed retrograde pseudomorphing spherical periclase crystals. Crystal size distributions (CSD's) of brucite pseudomorphs are presented for two profiles and combined with geochemistry data and petrological information. Textural analyses are combined with geochemistry data in a qualitative model that describes the formation periclase. As a major outcome, this expands the potential use of CSD's to systems of mineral formation driven by fluid-infiltration. RESUME DE LA THESE La nucléation et la croissance des minéraux métamorphiques sont la conséquence de changements des conditions de pression, température et composition chimique du système (PT-X). Cette thèse s'intéresse aux processus gouvernant la nucléation et la croissance des minéraux au cours d'un épisode de métamorphisme de contact, en utilisant la géochimie analytique (composition chimique, isotopique et en éléments traces), le traitement statistique des données spatiales et la modélisation numérique. Il est montré que la combinaison d'un modèle textural avec des analyses en isotopes stables permet de distinguer plusieurs chemins de réactions possibles conduisant à la croissance de l'olivine dans une auréole de contact riche en Silice et dolomite. Il est suggéré que l'olivine se forme directement à partir de la dolomie et du quartz. Cette réaction métastable de formation de l'olivine implique une cristallisation métamorphique loin de l'équilibre. La principale conséquence est que la distribution spatiale des assemblages de minéraux métamorphiques dans une auréole de contact ne peut pas être considérée comme un témoin de l'évolution temporelle d'un type de roche donné, puisque chaque type de roche suit différents chemins de réactions, en fonction de la température, la vitesse de réchauffement et le taux d'infiltration du fluide. Une étude thermométrique calcite-dolomite détaillée a été réalisée à diverses échelles, depuis l'échelle de l'auréole de contact jusqu'à l'échelle du cristal. Des modèles numériques quantitatifs ont été développés pour évaluer l'effet des zonations de croissance, de la diffusion volumique et de la formation de lamelles d'exsolution submicroscopiques (<1µm) sur la distribution du magnésium mesuré dans des cristaux de calcite individuels. Les résultats de ce modèle ont été comparés ä des échantillons naturels. Cette étude montre que la distribution du Mg dans les grains de calcite de l'auréole de contact de l'Ubehebe Peak (USA) résulte d'une croissance cristalline rapide, associée aux processus de diffusion et d'exsolution. L'histoire de cristallisation d'une roche est enregistrée dans la composition chimique, la taille et la distribution de ses minéraux. Près du sommet Cima Uzza situé au sud du massif d'Adamello (Italie), des marbres dolomitiques à brucite du métamorphisme de contact forment des xénolithes dans une intrusion mafique. La brucite constitue des pseudomorphes rétrogrades du périclase. Les distributions de taille des cristaux (CSD) des pseudomorphes de brucite sont présentées pour deux profiles et sont combinées aux données géochimiques et pétrologiques. Les analyses textorales sont combinées aux données géochimiques dans un modèle qualitatif qui décrit la formation du périclase. Ceci élargit l'utilisation potentielle de la C5D aux systèmes de formation de minéraux controlés par les infiltrations fluides. THESIS ABSTRACT (GENERAL PUBLIC) Rock textures are essentially the result of a complex interaction of nucleation, growth and deformation as a function of changing physical conditions such as pressure and temperature. Igneous and metamorphic textures are especially attractive to study the different mechanisms of texture formation since most of the parameters like pressure-temperature-paths are quite well known for a variety of geological settings. The fact that textures are supposed to record the crystallization history of a rock traditionally allowed them to be used for geothermobarometry or dating. During the last decades the focus of metamorphic petrology changed from a static point of view, i.e. the representation of a texture as one single point in the petrogenetic grid towards a more dynamic view, where multiple metamorphic processes govern the texture formation, including non-equilibrium processes. This thesis tries to advance our understanding on the processes governing nucleation and growth of minerals in contact metamorphic environments and their dynamic interplay by using a combination of geochemical analyses (chemical-, isotope-, and trace element composition), statistical treatments of spatial data and numerical models. In a first part the thesis describes the formation of metamorphic olivine porphyroblast in the Ubehebe Peak contact aureole (USA). It is shown that not the commonly assumed succession of equilibrium reactions along a T-t-path formed the textures present in the rocks today, but rather the presence of a meta-stable reaction is responsible for forming the olivine porphyroblast. Consequently, the spatial distribution of metamorphic minerals within a contact aureole can no longer be regarded as a proxy for the temporal evolution of a single rock sample. Metamorphic peak temperatures for samples of the Ubehebe Peak contact aureole were determined using calcite-dolomite. This geothermometer is based on the temperature-dependent exchange of Mg between calcite and dolomite. The purpose of the second part of this thesis was to explain the interfering systematic scatter of measured Mg-content on different scales and thus to clarify the interpretation of metamorphic temperatures recorded in carbonates. Numerical quantitative forward models are used to evaluate the effect of several processes on the distribution of magnesium in individual calcite crystals and the modeling results were then compared to measured field. Information about the crystallization history is not only recorded in the chemical composition of grains, like isotope composition or mineral zoning. Crystal size distributions (CSD's) provide essential information about the complex interaction of nucleation and growth of minerals. CSD's of brucite pseudomorphs formed retrograde after periclase of the southern Adamello massif (Italy) are presented. A combination of the textural 3D-information with geochemistry data is then used to evaluate reaction kinetics and to constrain the actual reaction mechanism for the formation of periclase. The reaction is shown to be the consequence of the infiltration of a limited amount of a fluid phase at high temperatures. The composition of this fluid phase is in large disequilibrium with the rest of the rock resulting in very fast reaction rates. RESUME DE LA THESE POUR LE GRAND PUBLIC: La texture d'une roche résulte de l'interaction complexe entre les processus de nucléation, croissance et déformation, en fonction des variations de conditions physiques telles que la pression et la température. Les textures ignées et métamorphiques présentent un intérêt particulier pour l'étude des différents mécanismes à l'origine de ces textures, puisque la plupart des paramètres comme les chemin pression-température sont relativement bien contraints dans la plupart des environnements géologiques. Le fait que les textures soient supposées enregistrer l'histoire de cristallisation des roches permet leur utilisation pour la datation et la géothermobarométrie. Durant les dernières décennies, la recherche en pétrologie métamorphique a évolué depuis une visualisation statique, c'est-à-dire qu'une texture donnée correspondait à un point unique de la grille pétrogénétique, jusqu'à une visualisation plus dynamique, où les multiples processus métamorphiques qui gouvernent 1a formation d'une texture incluent des processus hors équilibre. Cette thèse a pour but d'améliorer les connaissances actuelles sur les processus gouvernant la nucléation et la croissance des minéraux lors d'épisodes de métamorphisme de contact et l'interaction dynamique existant entre nucléation et croissance. Pour cela, les analyses géochimiques (compositions chimiques en éléments majeurs et traces et composition isotopique), le traitement statistique des données spatiales et la modélisation numérique ont été combinés. Dans la première partie, cette thèse décrit la formation de porphyroblastes d'olivine métamorphique dans l'auréole de contact de l'Ubehebe Peak (USA). Il est montré que la succession généralement admise des réactions d'équilibre le long d'un chemin T-t ne peut pas expliquer les textures présentes dans les roches aujourd'hui. Cette thèse montre qu'il s'agirait plutôt d'une réaction métastable qui soit responsable de la formation des porphyroblastes d'olivine. En conséquence, la distribution spatiale des minéraux métamorphiques dans l'auréole de contact ne peut plus être interprétée comme le témoin de l'évolution temporelle d'un échantillon unique de roche. Les pics de température des échantillons de l'auréole de contact de l'Ubehebe Peak ont été déterminés grâce au géothermomètre calcite-dolomite. Celui-ci est basé sur l'échange du magnésium entre la calcite et la dolomite, qui est fonction de la température. Le but de la deuxième partie de cette thèse est d'expliquer la dispersion systématique de la composition en magnésium à différentes échelles, et ainsi d'améliorer l'interprétation des températures du métamorphisme enregistrées dans les carbonates. Des modèles numériques quantitatifs ont permis d'évaluer le rôle de différents processus sur la distribution du magnésium dans des cristaux de calcite individuels. Les résultats des modèles ont été comparés aux échantillons naturels. La composition chimique des grains, comme la composition isotopique ou la zonation minérale, n'est pas le seul témoin de l'histoire de la cristallisation. La distribution de la taille des cristaux (CSD) fournit des informations essentielles sur les interactions entre nucléation et croissance des minéraux. La CSD des pseudomorphes de brucite retrograde formés après le périclase dans le sud du massif Adamello (Italie) est présentée dans la troisième partie. La combinaison entre les données textorales en trois dimensions et les données géochimiques a permis d'évaluer les cinétiques de réaction et de contraindre les mécanismes conduisant à la formation du périclase. Cette réaction est présentée comme étant la conséquence de l'infiltration d'une quantité limitée d'une phase fluide à haute température. La composition de cette phase fluide est en grand déséquilibre avec le reste de la roche, ce qui permet des cinétiques de réactions très rapides.

Splitting rivers at their seams: bifurcations and avulsion

River bifurcations are critical but poorly understood elements of many geomorphological systems. They are integral elements of alluvial fans, braided rivers, fluvial lowland plains, and deltas and control the partitioning of water and sediment through these systems. Bifurcations are commonly unstable but their lifespan varies greatly. In braided rivers bars and channels migrate, split and merge at annual or shorter timescales, thereby creating and abandoning bifurcations. This behaviour has been studied mainly by geomorphologists and fluid dynamicists. Bifurcations also exist during avulsion, the process of a river changing course on a floodplain or in a delta, which may take 102103 years and has been studied mainly by sedimentologists. This review synthesizes our current understanding of bifurcations and brings together insights from different research communities and different environmental settings. We consider the causes and initiation of bifurcations and avulsion, the physical mechanisms controlling bifurcation and avulsion evolution, mathematical and numerical modelling of these processes, and the possibility of stable bifurcations. We end the review with some open questions. Copyright (c) 2012 John Wiley & Sons, Ltd.

Finite horizon bargaining and the consistent field

This paper explores the relationships between noncooperative bargaining games and the consistent value for non-transferable utility (NTU) cooperative games. A dynamic approach to the consistent value for NTU games is introduced: the consistent vector field. The main contribution of the paper is to show that the consistent field is intimately related to the concept of subgame perfection for finite horizon noncooperative bargaining games, as the horizon goes to infinity and the cost of delay goes to zero. The solutions of the dynamic system associated to the consistent field characterize the subgame perfect equilibrium payoffs of the noncooperative bargaining games. We show that for transferable utility, hyperplane and pure bargaining games, the dynamics of the consistent fields converge globally to the unique consistent value. However, in the general NTU case, the dynamics of the consistent field can be complex. An example is constructed where the consistent field has cyclic solutions; moreover, the finite horizon subgame perfect equilibria do not approach the consistent value.

Microfabrics in carbonate mylonites along a large-scale shear zone (Helvetic Alps)

Carbonate mylonites with varying proportions of second-phase minerals were collected at positions of increasing metamorphic grade along the basal thrust of the Morcles nappe (Helvetic nappes, Switzerland). Variations of temperature, stress, and strain rate, changes in chemistry of solid and fluid phases, and differing degrees of strain localization and annealing were tracked by measuring the shapes, mean sizes, and size distributions of both matrix and second-phase grains, as well as crystal preferred orientation (CPO) of the matrix. Field structures suggest that strain rate was constant along the fault. The mean and distribution of the calcite grain sizes were affected most profoundly by temperature: Increased temperature, presumably accompanied by decreased stress, correlated with larger mean sizes and wider size distributions. At a given location, the matrix grains in mylonites with more second-phase particles are, on average, smaller, have narrower size distributions, and have more elongate shapes. For example, mylonites with 50 vol.% of second phases have matrix grain sizes half that of pure mylonites. Changes in calcite chemistry and the presence of synkinematic fluids seemed to influence microfabric only weakly. Temporal variations in conditions, such as exhumation-induced cooling, apparently provoke changes in temperature, stress, and strain rate along the nappe. These changes result in further strain localization during retrograde conditions and cause the grain size to be reduced by an additional 50%. The matrix CPO strengthens with increasing temperature or strain, but weakens and rotates with increasing second-phase content, These fabric changes suggest differing rates of grain growth, grain size reduction, and development of CPO owing to variations in the deformation conditions and, perhaps, mechanisms. To interpret natural mylonite structures or to extrapolate mechanical data to natural situations requires careful characterization of the microfabric, and, in particular, second-phase minerals. (c) 2007 Elsevier B.V, All rights reserved.

Staying With the Tension: “Estranged Intimacy” and Gendered Expectations in the Field

The position of the anthropologist in the field is discussed, in this article, as a position of “estranged intimacy”, that is to say, the anthropologist occupies an ambiguous position of becoming intimately involved whilst concurrently standing back. This definition derives from reflections upon fieldwork, conducted in the north of Portugal, with Cape Verdean migrant young women and their experiences as mothers. The article discusses two aspects related to the fieldwork. Firstly, the way in which diverse strategies of establishing relations in the field placed me in a position of “estranged intimacy” which reconfigured the meanings I had initially attributed to the term “Cape Verdean women”. Secondly, how becoming unexpectedly involved in a situation of intense conjugal conflict led me to reconsider my understanding of Cape Verdean gender relations. Both cases demonstrate how the endeavour to produce analytical and ethnographical knowledge was shot through with an unstable mix of detachment and involvement and how coming up against the unexpected may contribute towards the reconfiguration of ethnographic knowledge, in this specific case, with regard to the dynamics of gender relations.

An in vivo ultrahigh field 14.1 T (1) H-MRS study on 6-OHDA and α-synuclein-based rat models of Parkinson's disease: GABA as an early disease marker.

The detection of Parkinson's disease (PD) in its preclinical stages prior to outright neurodegeneration is essential to the development of neuroprotective therapies and could reduce the number of misdiagnosed patients. However, early diagnosis is currently hampered by lack of reliable biomarkers. (1) H magnetic resonance spectroscopy (MRS) offers a noninvasive measure of brain metabolite levels that allows the identification of such potential biomarkers. This study aimed at using MRS on an ultrahigh field 14.1 T magnet to explore the striatal metabolic changes occurring in two different rat models of the disease. Rats lesioned by the injection of 6-hydroxydopamine (6-OHDA) in the medial-forebrain bundle were used to model a complete nigrostriatal lesion while a genetic model based on the nigral injection of an adeno-associated viral (AAV) vector coding for the human α-synuclein was used to model a progressive neurodegeneration and dopaminergic neuron dysfunction, thereby replicating conditions closer to early pathological stages of PD. MRS measurements in the striatum of the 6-OHDA rats revealed significant decreases in glutamate and N-acetyl-aspartate levels and a significant increase in GABA level in the ipsilateral hemisphere compared with the contralateral one, while the αSyn overexpressing rats showed a significant increase in the GABA striatal level only. Therefore, we conclude that MRS measurements of striatal GABA levels could allow for the detection of early nigrostriatal defects prior to outright neurodegeneration and, as such, offers great potential as a sensitive biomarker of presymptomatic PD.

Promoting rule compliance in daily-life: Evidence from a randomized field experiment in the public libraries of Barcelona

We study how to promote compliance with rules in everyday situations. Having access to unique data on the universe of users of all public libraries inBarcelona, we test the effect of sending email messages with dierent contents.We find that users return their items earlier if asked to do so in a simple email.Emails reminding users of the penalties associated with late returns are more effective than emails with only a generic reminder. We find differential treatmenteffects by user types. The characteristics we analyze are previous compliance,gender, age, and nationality.

The impact of gender composition on team performance and decision-making: Evidence from the field

We investigate whether the gender composition of teams affect theireconomic performance. We study a large business game, played in groups ofthree, where each group takes the role of a general manager. There are twoparallel competitions, one involving undergraduates and the other involvingMBAs. Our analysis shows that teams formed by three women aresignificantly outperformed by any other gender combination, both at theundergraduate and MBA levels. Looking across the performancedistribution, we find that for undergraduates, three women teams areoutperformed throughout, but by as much as 10pp at the bottom and by only1pp at the top. For MBAs, at the top, the best performing group is two menand one woman. The differences in performance are explained bydifferences in decision-making. We observe that three women teams are lessaggressive in their pricing strategies, invest less in R&D, and invest more insocial sustainability initiatives, than any other gender combination teams.Finally, we find support for the hypothesis that it is poor work dynamicsamong the three women teams that drives the results.

SwissParam: a fast force field generation tool for small organic molecules.

The drug discovery process has been deeply transformed recently by the use of computational ligand-based or structure-based methods, helping the lead compounds identification and optimization, and finally the delivery of new drug candidates more quickly and at lower cost. Structure-based computational methods for drug discovery mainly involve ligand-protein docking and rapid binding free energy estimation, both of which require force field parameterization for many drug candidates. Here, we present a fast force field generation tool, called SwissParam, able to generate, for arbitrary small organic molecule, topologies, and parameters based on the Merck molecular force field, but in a functional form that is compatible with the CHARMM force field. Output files can be used with CHARMM or GROMACS. The topologies and parameters generated by SwissParam are used by the docking software EADock2 and EADock DSS to describe the small molecules to be docked, whereas the protein is described by the CHARMM force field, and allow them to reach success rates ranging from 56 to 78%. We have also developed a rapid binding free energy estimation approach, using SwissParam for ligands and CHARMM22/27 for proteins, which requires only a short minimization to reproduce the experimental binding free energy of 214 ligand-protein complexes involving 62 different proteins, with a standard error of 2.0 kcal mol(-1), and a correlation coefficient of 0.74. Together, these results demonstrate the relevance of using SwissParam topologies and parameters to describe small organic molecules in computer-aided drug design applications, together with a CHARMM22/27 description of the target protein. SwissParam is available free of charge for academic users at www.swissparam.ch.

Dispersion of natural arsenic in the Malcantone watershed, Southern Switzerland: field evidence for repeated sorption-desorption and oxidation-reduction processes

In recent years, elevated arsenic concentrations have been found in waters and soils of many, countries, often resulting in a health threat for the local population. Switzerland is not an exception and this paper deals with the release and subsequent fate of arsenic in a 200-km(2) mountainous watershed, characterized by crystalline silicate rocks (gneisses, schists, amphibolites) that contain abundant As-bearing sulfide ore deposits, some of which have been mined for iron and gold in the past. Using analytical methods common for mineralogical, ground water and soil studies (XRD, XRF, XAS-XANES and -EXAFS, electron microprobe, extraction, ICP, AAS with hydride generator, ion chromatography), seven different field situations and related dispersion processes of natural arsenic have been studied: (1) release by rock weathering, (2) transport and deposition by water and ice; (3) release of As to the ground and surface water due to increasing pH; (4) accumulation in humic soil horizons; (5) remobilization by reduction in water-saturated soils and stagnant ground waters; (6) remobilization by using P-rich fertilizers or dung and (7) oxidation, precipitation and dilution in surface waters. Comparison of the results with experimental adsorption studies and speciation diagrams from the literature allows us to reconstruct and identify the typical behavior of arsenic in a natural environment under temperate climatic conditions. The main parameters identified are: (a) once liberated from the primary minerals, sorption processes on Fe-oxy-hydroxides dominate over Al-phases, such as Al-hydroxides or clay minerals and limit the As concentrations in the spring and well waters between 20 and 300 mug/l. (b) Precipitation as secondary minerals is limited to the weathering domain, where the As concentrations are still high and not yet too diluted by rain and soils waters. (c) Although neutral and alkaline pH conditions clearly increase the mobility of As, the main factor to mobilize As is a low redox potential (Eh close or below 0 mV), which favors the dissolution of the Fe-oxy-hydroxides on which the As is sorbed. (d) X-ray absorption spectroscopy (XAS) of As in water-logged humic forest soils indicates that the reduction to As III only occurs at the solid-water interface and that the solid contains As as As V (e) A and Bh horizons of humic cambisols can effectively capture As when As-rich waters flow through them. Complex spatial and temporal variation of the various parameters in a watershed results in repeated mobilization and immobilization of As, which continuously transports As from the upper to the lower part of a watershed and ultimately to the ocean. (C) 2004 Elsevier B.V. All rights reserved.