Diffusion of HTO,Br, I,Cs, Sr and Co in a clay formation: Results and modelling from an in situ experiment in Opalinus Clay     

P. Wersin  J.M. Soler  L. Van Loon  J. Eikenberg  B. Baeyens  D. Grolimund  T. Gimmi  S. Dewonck 《Applied Geochemistry》2008

The migration of radioactive and chemical contaminants in clay materials and argillaceous host rocks is characterised by diffusion and retention processes. Valuable information on such processes can be gained by combining diffusion studies at laboratory scale with field migration tests. In this work, the outcome of a multi-tracer in situ migration test performed in the Opalinus Clay formation in the Mont Terri underground rock laboratory (Switzerland) is presented. Thus, 1.16 × 10⁵ Bq/L of HTO, 3.96 × 10³ Bq/L of ⁸⁵Sr, 6.29 × 10² Bq/L of ⁶⁰Co, 2.01 × 10⁻³ mol/L Cs, 9.10 × 10⁻⁴ mol/L I and 1.04 × 10⁻³ mol/L Br were injected into the borehole. The decrease of the radioisotope concentrations in the borehole was monitored using in situ γ-spectrometry. The other tracers were analyzed with state-of-the-art laboratory procedures after sampling of small water aliquots from the reservoir. The diffusion experiment was carried out over a period of one year after which the interval section was overcored and analyzed. Based on the experimental data from the tracer evolution in the borehole and the tracer profiles in the rock, the diffusion of tracers was modelled with the numerical code CRUNCH.  相似文献   

Improved mapping of schooling fish near the surface: comparison of abundance estimates obtained by sonar and echo integration     

Misund  Ole Arve; Aglen  Asgeir; Hamre  Johannes; Ona  Egil; Rottingen  Ingolf; Skagen  Dankert; Valdemarsen  John Willy 《ICES Journal of Marine Science》1996,53(2):383-388

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Crustal structure beneath the Mount Cameroon region derived from recent gravity measurements     

Severin Nguiya  Marcelin Mouzong Pemi  Alain Pierre Tokam  Évariste Ngatchou Heutchi  Willy Lemotio 《Comptes Rendus Geoscience》2019,351(6):430-440

In this study, the recent update of the gravity database with new measurements has raised the opportunity of improving the knowledge of the crustal structure beneath the large volcanic system called Mount Cameroon, and its implication in the regional tectonics. The multi-scale wavelet analysis method was applied to highlight the geologic features of the area, and their depths were estimated using the logarithmic power spectrum method. The results reveal a complex crustal structure beneath Mount Cameroon with high variation in the lateral distribution of crustal densities. The upper and lower crusts are intruded by dense materials originating from the mantle with less lateral extension. The trends of Tiko and Ekona faults along the intrusion suggest tectonic activities as deep as 25 km. The difference in mantle composition or temperature between the East and the West of the studied area is clearly seen in detailed wavelet images and agrees with a mantle origin for the Cameroon Volcanic Line.  相似文献   

Links between bacterial communities in marine sediments and trace metal geochemistry as measured by in situ DET/DGT approaches   总被引：1，自引：0，他引：1  

Gillan DC  Baeyens W  Bechara R  Billon G  Denis K  Grosjean P  Leermakers M  Lesven L  Pede A  Sabbe K  Gao Y 《Marine pollution bulletin》2012,64(2):353-362

Our current view about the relationship between metals and bacteria in marine sediments might be biased because most studies only use ex situ approaches to quantify metals. The aim of the present research was to compare ex situ and in situ methods of metal measurement (DET and DGT--diffusive equilibration or diffusive gradients in thin-films) and relate the results with two commonly used microbiological variables (bacterial biomass and bacterial diversity as revealed by DGGE). No previous studies have used such in situ approaches in microbial ecology. For biomass and most of the investigated trace metals (Ag, Cd, Sn, Cr, Ni, Cu, Pb, and Al) no significant correlations were found. The exceptions were Fe, Mn, Co, and As which behave like micronutrients. For bacterial diversity, no relevant relationships were found. We conclude that in situ methods are more adapted tools for microbial ecologists but that ex situ approaches are still necessary.  相似文献   

The migration and growth of protoplanets in protostellar discs   总被引：1，自引：0，他引：1  

Richard P. Nelson  John C. B. Papaloizou  Frédéric Masset  Willy Kley 《Monthly notices of the Royal Astronomical Society》2000,318(1):18-36

We investigate the gravitational interaction of a Jovian-mass protoplanet with a gaseous disc with aspect ratio and kinematic viscosity expected for the protoplanetary disc from which it formed. Different disc surface density distributions are investigated. We focus on the tidal interaction with the disc with the consequent gap formation and orbital migration of the protoplanet. Non-linear two-dimensional hydrodynamic simulations are employed using three independent numerical codes.
A principal result is that the direction of the orbital migration is always inwards and such that the protoplanet reaches the central star in a near-circular orbit after a characteristic viscous time‐scale of ∼10⁴ initial orbital periods. This is found to be independent of whether the protoplanet is allowed to accrete mass or not. Inward migration is helped by the disappearance of the inner disc, and therefore the positive torque it would exert, because of accretion on to the central star. Maximally accreting protoplanets reach about 4 Jovian masses on reaching the neighbourhood of the central star. Our results indicate that a realistic upper limit for the masses of closely orbiting giant planets is ∼5 Jupiter masses, if they originate in protoplanetary discs similar to the minimum-mass solar nebula. This is because of the reduced accretion rates obtained for planets of increasing mass.
Assuming that some process such as termination of the inner disc through a magnetospheric cavity stops the migration, the range of masses estimated for a number of close orbiting giant planets as well as their inward orbital migration can be accounted for by consideration of disc–protoplanet interactions during the late stages of giant planet formation.  相似文献   

Retrieval of chlorophyll and nitrogen in Norway spruce (Picea abies L. Karst.) using imaging spectroscopy     

Martin Schlerf  Clement Atzberger  Joachim Hill  Henning Buddenbaum  Willy Werner  Gebhard Schüler 《International Journal of Applied Earth Observation and Geoinformation》2010

The research evaluated the information content of spectral reflectance (laboratory and airborne data) for the estimation of needle chlorophyll (C_AB) and nitrogen (C_N) concentration in Norway spruce (Picea abies L. Karst.) needles. To identify reliable predictive models different types of spectral transformations were systematically compared regarding the accuracy of prediction. The results of the cross-validated analysis showed that C_AB can be well estimated from laboratory and canopy reflectance data. The best predictive model to estimate C_AB was achieved from laboratory spectra using continuum-removal transformed data (R²cv = 0.83 and a relative RMSEcv of 8.1%, n = 78) and from hyperspectral HyMap data using band-depth normalised spectra (R²cv = 0.90, relative RMSEcv = 2.8%, n = 13). Concerning the nitrogen concentration, we observed somewhat weaker relations, with however still acceptable accuracies (at canopy level: R²cv = 0.57, relative RMSEcv = 4.6%). The wavebands selected in the regression models to estimate C_AB were typically located in the red edge region and near the green reflectance peak. For C_N, additional wavebands related to a known protein absorption feature at 2350 nm were selected. The portion of selected wavebands attributable to known absorption features strongly depends on the type of spectral transformation applied. A method called “water removal” (WR) produced for canopy spectra the largest percentage of wavebands directly or indirectly related to known absorption features. The derived chlorophyll and nitrogen maps may support the detection and the monitoring of environmental stressors and are also important inputs to many bio-geochemical process models.  相似文献   

A heuristic probabilistic approach to estimating size-dependent mobility of nonuniform sediment     

Befekadu?Taddesse?WoldegiorgisEmail authorView author&#;s OrcID profile  Fu-Chun?Wu  Ann?Van?Griensven  Willy?Bauwens 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(6):1771-1782

This paper presents a heuristic probabilistic approach to estimating the size-dependent mobilities of nonuniform sediment based on the pre- and post-entrainment particle size distributions (PSDs), assuming that the PSDs are lognormally distributed. The approach fits a lognormal probability density function to the pre-entrainment PSD of bed sediment and uses the threshold particle size of incipient motion and the concept of sediment mixture to estimate the PSDs of the entrained sediment and post-entrainment bed sediment. The new approach is simple in physical sense and significantly reduces the complexity and computation time and resource required by detailed sediment mobility models. It is calibrated and validated with laboratory and field data by comparing to the size-dependent mobilities predicted with the existing empirical lognormal cumulative distribution function approach. The novel features of the current approach are: (1) separating the entrained and non-entrained sediments by a threshold particle size, which is a modified critical particle size of incipient motion by accounting for the mixed-size effects, and (2) using the mixture-based pre- and post-entrainment PSDs to provide a continuous estimate of the size-dependent sediment mobility.  相似文献   

Environmental and climatic conditions at a potential Glacial refugial site of tree species near the Southern Alpine glaciers. New insights from multiproxy sedimentary studies at Lago della Costa (Euganean Hills, Northeastern Italy)     

Petra Kaltenrieder  Claudio A. Belis  Simone Hofstetter  Brigitta Ammann  Cesare Ravazzi  Willy Tinner   《Quaternary Science Reviews》2009,28(25-26):2647-2662

It has been hypothesized that refugia of thermophilous tree species were located in Northern Italy very close to the Alps, though, this hypothesis has yet to be tested thoroughly. In contrast to Central and Southern Italy with its relative wealth of data, only a few fragmentary records are currently available from Northern Italy for the last Glacial (Würm, Weichselian). Our new study site Lago della Costa lies adjacent to the catchment of the megafans of the Alpine forelands and the braided rivers of the Northeastern Po Plain that have so far inhibited the recovery of continuous Glacial and Late-Glacial records. We analyze pollen, plant macrofossils, charcoal and ostracods to reconstruct the vegetation, fire and lake history for the period 33,000–16,000 cal. BP. We compare our data with Glacial records from Southern Europe to discuss similarities and dissimilarities between these potential refugial areas. A comparison with independent paleoclimatic proxies allows to assess potential linkages between environmental and climatic variability. New macrofossil and pollen data at Lago della Costa unambiguously document the local persistence of boreal tree taxa such as Larix decidua and Betula tree species around the study site during the last Glacial. The regular occurrence of pollen of temperate trees in the organic lake sediments (fine-detritus calcareous gyttja) suggests that temperate taxa such as Corylus avellana, Quercus deciduous, Tilia, Ulmus, Fraxinus excelsior, Carpinus, Abies alba and Fagus sylvatica, most likely survived the Last Glacial Maximum (LGM) at favorable sites in the Euganean Hills. The percentage values of temperate trees are comparable with those from Southern Europe (e.g. Monticchio in Southern Italy). We conclude that the Euganean Hills were one of the northernmost refugial areas of temperate taxa in Europe. However, the relative and absolute abundances of pollen of temperate trees are highly variable. Pollen-inferred declines of temperate tree communities (e.g. Quercetum mixtum) and low ostracod-inferred water levels at Lago della Costa correspond to the cold Heinrich events H-2 (LGM; 23,000–19,000 cal. BP) and H-3 (around 28,000 cal. BP), as recorded in the marine sediments of the North Atlantic. Similar patterns of significant temperate tree population collapses during cold Heinrich events are recorded at southern Mediterranean sites (e.g. Monticchio and the Alboran Sea). These findings suggest close linkages between Northern Atlantic and South-Central European climates during the past Glacial.  相似文献   

A fluid inclusion reconnaissance study of the Huanuni tin deposit (Bolivia), using LA-ICP-MS micro-analysis   总被引：1，自引：0，他引：1  

Barbara Müller  Rolf Frischknecht  Terry Seward  Christoph Heinrich  Willy Camargo Gallegos 《Mineralium Deposita》2001,36(7):680-688

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High atmospheric nitrogen deposition events over the North Sea   总被引：2，自引：0，他引：2  

L. Spokes  T. Jickells  A. Rendell  M. Schulz  A. Rebers  W. Dannecker  O. Krüger  M. Leermakers  W. Baeyens 《Marine pollution bulletin》1993,26(12):698-703

Atmospheric circulation patterns over the North Sea occasionally result in episodes of high concentrations of various contaminants. Synergistic chemical effects can act to enhance the deposition of nitrogen during these events resulting in highly episodic nitrogen inputs to the North Sea. Two such episodes are described and their causes interpreted. The problems of devising sampling strategies to quantify these events and assess their effects on phytoplankton communities are discussed.  相似文献