Current status,distribution, life cycle and ecology ofRhithrogena germanica Eaton, 1885 in Switzerland: Preliminary results (Ephemeroptera,Heptageniidae)

Rh. germanica is a European species that, due to human impacts, has progressively disappeared from its original territories and is now considered rare. In SwitzerlandRh. germanica has disappeared from the Aare, Broye and Kleine Emme rivers and is actually found in a limited reach of the River Rhine and some of its tributaries (Limmat, Sihl, Thur and Töss rivers).Rh. germanica is a univoltine species, hatching probably in summer. The emergence occurs from February to the beginning of April. It takes place on the water surface. Laboratory observations have shown that the subimaginal stage lasts four days.Rh. germanica occurs on different substrate types, ranging from stones and cobbles to pebbles and gravel. The larvae are more abundant in zones of erosion with coarse and porous sediments than in depositional zones with fine sediments and silts. They are most abundant in riffles with water velocities from 20 to 150 cm/sec. The species tolerates moderately organic-polluted waters.The particular strategy concerning growth and emergence ofRh. germanica is also discussed.     

Training Image Free High-Order Stochastic Simulation Based on Aggregated Kernel Statistics

Mathematical Geosciences - A training image free, high-order sequential simulation method is proposed herein, which is based on the efficient inference of high-order spatial statistics from the...     

Experimental and numerical evaluation of single-layer covers placed on acid-generating tailings

This study focuses on the reclamation work being performed on two former acid-generating tailings sites, located in Quebec, Canada. At both sites, the tailings were partially oxidized due to extended exposure, and the pore water is acidic. The reclamation solution applied to control acid mine drainage is a monolayer cover, made of non acid-generating tailings in one case and a till in the other. The goal of this project was to assess the response of the tailings-cover systems under various conditions. Tailings samples were collected in situ and characterized in the laboratory. Large column tests were conducted to evaluate the hydrogeological and geochemical behaviour of the covered tailings following wetting and drying cycles. The instrumented columns were designed to reproduce some of the existing site conditions and provide representative results for longer term analyses. Volumetric water content, suction, and oxygen concentrations were also monitored over time. The experimental data were used to validate different numerical models including those constructed with Vadose/W (GeoSlope Int.). Additional simulations were conducted under field conditions to evaluate the effect of various influence factors such as the depth of the water table, climatic conditions and the thickness of the cover. The combination of experimental and numerical results show how the behaviour and efficiency of a monolayer cover placed over reactive tailings depend on these factors, highlighting the importance of hydrogeological properties and water table depth. In many instances, the cover materials were prone to desaturation, especially when the water table was deeper than about 2 m below the tailings-cover interface. These results tend to indicate that relatively thin monolayer covers would not be able to prevent oxygen ingress under some of the conditions observed in the field. Desaturation of the cover and/or reactive tailings is due to a combination of drainage and evaporation. In such cases, increasing the thickness of the monolayer cover only has a limited effect. A discussion follows on the practical implications of these laboratory experiments and the numerical simulations for field design of reclamation measures at these two tailings impoundments.     

The World Karst Aquifer Mapping project: concept,mapping procedure and map of Europe

Karst aquifers contribute substantially to freshwater supplies in many regions of the world, but are vulnerable to contamination and difficult to manage because of their unique hydrogeological characteristics. Many karst systems are hydraulically connected over wide areas and require transboundary exploration, protection and management. In order to obtain a better global overview of karst aquifers, to create a basis for sustainable international water-resources management, and to increase the awareness in the public and among decision makers, the World Karst Aquifer Mapping (WOKAM) project was established. The goal is to create a world map and database of karst aquifers, as a further development of earlier maps. This paper presents the basic concepts and the detailed mapping procedure, using France as an example to illustrate the step-by-step workflow, which includes generalization, differentiation of continuous and discontinuous carbonate and evaporite rock areas, and the identification of non-exposed karst aquifers. The map also shows selected caves and karst springs, which are collected in an associated global database. The draft karst aquifer map of Europe shows that 21.6% of the European land surface is characterized by the presence of (continuous or discontinuous) carbonate rocks; about 13.8% of the land surface is carbonate rock outcrop.

     

The early Cretaceous orogen-scale Dabieshan metamorphic core complex: implications for extensional collapse of the Triassic HP–UHP orogenic belt in east-central China

International Journal of Earth Sciences - The Dabieshan massif is famous as a portion of the world’s largest HP–UHP metamorphic belt in east-central China that was built by the Triassic...     

The zircon evidence of temporally changing sediment transport—the NW Gondwana margin during Cambrian to Devonian time (Aoucert and Smara areas,Moroccan Sahara)

International Journal of Earth Sciences - Detrital zircon provenance studies are an established tool to develop palaeogeographic models, mostly based on zircon of siliciclastic rocks and isotope...     

Water solubility in haplogranitic melts coexisting with H2O-H2 fluids

The water solubility in haplogranitic melts (normative composition Ab₃₉Or₃₂Qz₂₉) coexisting with H₂O-H₂ fluids at 800 and 950 °C and 1, 2 and 3 kbar vapour pressure has been determined using IR spectroscopy. The experiments were performed in internally heated pressure vessels and the hydrogen fugacity (f _H2) was controlled using the double capsule technique and oxygen buffer assemblages (WM and IW). Due to the limited lifetimes of these oxygen buffers the water solubility was determined from diffusion profiles (concentration-distance profiles) measured with IR spectroscopy in the quenched glasses. The reliability of the experimental strategy was demonstrated by comparing the results of short- and long-duration experiments performed with pure H₂O fluids. The water solubility in Ab₃₉Or₃₂Qz₂₉ melts equilibrated with H₂O-H₂ fluids decreases progressively with decreasing f _H2O, as f _H2 (or X _H2) increases in the fluid phase. The effect of H₂ on the evolution of the water solubility is similar to that of CO₂ or another volatile with a low solubility in the melt and can be calculated in a first approximation with the Burnham water solubility model. Recalculation of high temperature water speciation for AOQ melts coexisting with H₂O-H₂ fluids at 800 °C, 2 kbar suggests that the concentrations of molecular H₂O are proportional to f _H2O (calculated using available mixing models), indicating Henrian behaviour for the solubility of molecular H₂O in haplogranitic melts. Received: 29 June 1998 / Accepted: 10 March 1999     

The production of cosmogenic nuclides in stony meteoroids by galactic cosmic‐ray particles

Abstract— We present a purely physical model for the calculation of depth‐ and size‐dependent production rates of cosmogenic nuclides by galactic cosmic‐ray (GCR) particles. besides the spectra of primary and secondary particles and the excitation functions of the underlying nuclear reactions, the model is based on only one free parameter—the integral number of gcr particles in the meteoroid orbits. We derived this value from analysis of radionuclide data in Knyahinya. We also show that the mean GCR proton spectrum in the meteoroid orbits has been constant over about the last 10 Ma. For the major target elements in stony meteoroids, we present depth‐ and size‐dependent production rates for ¹⁰Be, ¹⁴C, ²⁶Al, ³⁶Cl, and ⁵³Mn as well as for the rare gas isotopes ³He, ²⁰Ne, ²¹Ne, ²²Ne, ³⁶Ar, and ³⁸Ar. The new data differ from semi‐empirical estimates by up to a factor of 4 but agree within ～20% with results obtained by earlier parametric or physical approaches. The depth and size dependence of the shielding parameter ²²Ne/²¹Ne and the correlations ²⁶Al vs. ¹⁰Be, ²⁶Al vs. ⁵³Mn, ¹⁰Be/²¹Ne vs. ²²Ne/²¹Ne, and ³⁶Ar vs. ³⁶Cl for deciphering preatmospheric sizes, shielding depths, terrestrial residence times, and exposure histories are also discussed.