Geochemical behaviour and relative mobility of metals (Mn, Cd, Zn and Pb) in recent sediments of a retention pond along the A-71 motorway in Sologne, France

 Retention ponds have been dug along some of the motorways in France to minimize environmental pollution by keeping pollutants from spreading over the surrounding area. In the current work, eight core samples were collected from the bottom of a retention pond located along the A-71 motorway in Sologne to study the pollution of sediment by heavy metals and their diagenetic behaviour. The vertical concentration profiles of metals (Pb, Zn, Cd, Fe and Mn) in sediment as well as in interstitial water were determined. Especially in the case of the sediment, a sequential extraction method was employed to investigate how the movement of each metal is associated with the other metals and with other solid phases such as organic matter. In addition, to investigate the relative mobility of the metals, the distribution coefficients (K_D) were also determined. The concentrations of the metals were always found to be highest in the topmost layer of sediment. This so-called surface enrichment is caused by a substantial increase of the non-detrital fraction of these metals at the sediment surface. For instance, the accumulation of Pb and Zn is associated with the increase in the "fraction II" in the sequential extraction. The accumulation of Cd at the surface (0–2 cm) is partly due to the liberation of Cd from the particles during early diagenesis. However, the major factor contributing to the accumulation of Cd at the sediment surface is attributed to the dissolution of Cd from polluted roadside soil during the periods of rainstorms and its subsequent redeposition on the sediment surface after being carried to the retention pond. K_D values for Zn and Cd were found to decrease with depth, while K_D values for Pb increased. Based on the K_D values, the relative mobilities of the studied metals were determined to be as follows: Mn>Zn>Cd>Pb, for the upper layer, and Mn>Cd>Zn>Pb, for the layers below. Received: 28 October 1996 / Accepted: 21 November 1996     

Transition between the Okinawa trough backarc extension and the Taiwan collision: New insights on the southernmost Ryukyu subduction zone

Located between the Okinawa trough (OT) backarc basin and the collisional zone in Taiwan, the southernmost Ryukyu subduction zone is investigated. This area, including the southwestern portions of the OT and Ryukyu island arc (RA) and located west of 123.5° E, is named the Taiwan-Ryukyu fault zone (TRFZ). West of 123.5° E, the OT displays NNW-SSE structural trends which are different in direction from the ENE-WSW trending pattern of the rest of the OT. Using joint analysis of bathymetric, magnetic, gravity and earthquake data, three major discontinuities, that we interpret as right-lateral strike-slip faults (Faults A, B and C), have been identified. These faults could represent major decouplings in the southern portion of the Ryukyu subduction zone: each decoupling results in a decrease of the horizontal stress on the portion of the RA located on the eastern side of the corresponding fault, which allows the extension of the eastern side of OT to proceed more freely.We demonstrate that the 30° clockwise bending of the southwestern RA and the consecutive faulting in the TRFZ are mainly due to the collision of the Luzon arc with the former RA. After the formation of Fault C, the counterclockwise rotated portion of the ancient RA located west of the Luzon arc was more parallel to the Luzon arc. This configuration should have increased the contact surface and friction between the Luzon arc and the ancient RA, which could have reduced the northward subduction of the Luzon are. Thus, the westward component of the compressive stress from the collision of the Luzon arc should become predominant in the collisional system resulting in the uplift of Taiwan. Presently, because the most active collision of the Luzon arc has migrated to the central Taiwan (at about 23° N; 121.2° E), the southwestern OT has resumed its extension. In addition, the later resistent subduction of the Gagua ridge could have reactivated the pre-existing faults A and B at 1 M.y. ago and present, respectively. From 9 to 4 M.y., a large portion of the Gagua ridge probably collided with the southwestern RA. Because of its large buoyancy, this portion of the ridge resisted to subduct beneath the Okinawa platelet. As a result, we suggest that a large exotic terrane, named the Gagua terrane, was emplaced on the inner side of the present Ryukyu trench. Since that period, the southwestern portion of the Ryukyu trench was segmented into two parallel branches separated by the Gagua ridge: the eastern segment propagated westward along the trench axis while the western segment of the trench retreated along the trench axis.     

On the water and energy cycles in the Tropics

The water and energy cycles are major elements of the Earth climate. These cycles are especially active in the intertropical belt where satellites provide the most suitable observational platform. The history of Earth observations of the water cycle and of the radiation budget viewed from space reveals that the fundamental questions from the early times are still relevant for today's research. The last 2 decades have seen a number of milestones regarding the documentation of rainfall, mesoscale convective systems (MCS), water vapour and radiation at the top of the atmosphere (TOA). Beyond dedicated missions that provided enhanced characterizations of some elements of the atmospheric water cycle and field campaigns that allowed the gathering of validation data, the advent of the long record of meteorological satellites lead to new questioning on the homogenisation of the data time series, etc. The use of this record to document the tropical climate brought new results of the distribution of humidity and reinforced the understanding of some robust features of the African monsoon. Challenges for the immediate future concerns the deepening of the understanding of the role of cloud systems in the monsoon circulation, the downscaling of the documentation of the water and energy cycle at the scale of these cloud systems, the research of better adequation between the users and the satellite estimate of rainfall and finally a much needed methodological effort to build exploitable time series for the estimation of climatic trends in the water and energy cycle in the Tropics. The required observations to address these challenges are rapidly presented with emphasis on the upcoming Megha-Tropiques (MT) mission.     

Some critiques of the big bang cosmology

Still more shocking than the metaphysical assumption of some initial singularity, is the constant insistence upon the so-called cosmological principle of “homogeneity” and “isotropy” of the Universe. Observations do contradict this principle. And to me, the inhomogeneous, fractal at least on a certain scale range, of the distribution of matter is in itself an important cosmological fact, hitherto almost neglected. Moreover difficultties as to the applicability of the second principle of thermodynamics, observations of abnormal redshifts, etc., are casting large doubts not only upon the standard cosmological models, but even on the interpretation of the observed redshift as due solely to a universal expansion.     

Soho Contribution to Prominence Science

We present the main current issues concerning prominence studies. We recall the large range of plasma parameters found in prominences which makes the work of the MHD modeler more difficult. We also summarize the capabilities of the SOHO instrumentation. We present and discuss the most recent SOHO results concerning the determination of temperature, densities, and velocities. We put some emphasis on the different morphologies observed, the diagnostic capabilities of the Lyman lines profiles when accompanied by improved non-LTE modeling, and the information gathered from the first prominence oscillations measured from space. We also make an account of eruptive prominences. We finally discuss what could be done with present and future SOHO data to improve our understanding of prominences.     

Evaluation of mineral substrates for in situ iron removal from groundwater

Calcium carbonate-based materials (CCBM) have been found to remove Fe(II) and other divalent metal cations from aqueous solution and thus have the potential for incorporation into remediation systems to remove Fe(II) from groundwater at landfills. Research was conducted to examine the ability of a range of CCBM to remove Fe(II) and assess the mechanism of removal. Different CCBM (limestone, concrete, dolomite, marble), as well as gypsum, witherite, and quartz sand, were tested for their ability to remove Fe(II) from water using batch tests conducted under anaerobic conditions. Limestone (specific surface area of approximately 0.46 m²/g) was found to have the best removal effectiveness, and the final Fe(II) concentration was reduced from 50 to <0.01 mg/L. Kinetics experiments conducted over a 72 h period indicated that the removal process of Fe(II) by CCBM was a two-step process. The first step is rapid sorption of Fe(II) onto the CCBM surfaces within the first hour, and the second step is relatively slow co-precipitation of iron-containing solids formed through various chemical reactions. The two best performing CCBM (limestone and concrete) were evaluated for their removal ability based on media particle size (diameters of 3–5, 7–10, 15–25, and 40–50 mm) and revealed statistically significant (p < 0.01) increases in Fe(II) removal for each particle size class examined. SEM analysis of reacted materials revealed visible precipitates on the reactive material surface; XRD analysis was not able to detect crystalline Fe minerals on limestone surface.     

Mutual relationships in neighborhood socioeconomic change

In this article, we investigate the factors that lead to changes in the socioeconomic complexion of urban neighborhoods along four critical dimensions: crime, youth social distress, home ownership, and economic conditions. We argue that the dynamics of these dimensions are better apprehended simultaneously considering their potential mutual relationships and we propose a cross-lagged panel model approach within a structural equation modeling framework. Neighborhoods in Charlotte, North Carolina, are used as a case study, and change is modeled at several time lags throughout the 2000–2010 decade. Findings indicate that the model performs well and that it offers a very promising avenue for modeling the socioeconomic changes of neighborhoods that accounts for complex longitudinal effects as well as spatial dependencies. Specifically, it shows that lower human capital manifested by a decline in youth indicators is significant in explaining subsequent increases in crime and declines in economic indicators. Also, the predominance of housing stock constructed in the 1950s and 1960s is a significant trigger of declines across all neighborhood indicators. Finally, spatial spillover effects between neighborhoods are found to be short-lived and dissipate after a few years.     

Modèle hydrologique du Lac Tchad

Résumé

Le Lac Tchad est modélisé par un bilan de volume donnant ses niveaux et superficies de plans d'eau en fonction d'apports et pertes: débit des tributaires; pluie; évaporation; infiltration. Il est représenté par trois réservoirs (cuvette nord et archipel connectés à la cuvette sud) dont les niveaux de plan d'eau, distincts en période d'apports déficitaires (situation actuelle), sont confondus en période excédentaire (situation avant 1973). Suite aux observations de terrain, la cuvette nord est représentée avec un “réservoir sol” devant être rempli pour que l'eau puisse apparaître en surface. Le modèle utilise sept paramètres optimisés: intensité d'infiltration; profondeur du “réservoir sol”; quatre paramètres d’échange entre réservoirs; niveau de fond de l'archipel. Grâce aux données mesurées au sol ou par satellite (débits, précipitations, évaporation, niveaux et superficie de plans d'eau) il est calé sur la période 1970–1996 et validé sur la période 1956–2008.

Citation Bader, J.-C., Lemoalle, J. & Leblanc, M. (2011) Modèle hydrologique du Lac Tchad. Hydrol. Sci. J. 56(3), 411–425.     

The Multiscale TROPIcal CatchmentS critical zone observatory M-TROPICS dataset I: The Nyong River Basin,Cameroon

Simultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modelling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented in the past 25 years, only a few are located in the humid Tropics despite the importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents, size of river systems, etc. Since 1994, weathering and erosion processes and fluxes have been investigated at both local (experimental watershed) and regional scales in the Nyong River Basin (Cameroon) which belongs to the Critical Zone Observatories network named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Cameroon are: (1) rainfall; (2) air temperature, air relative humidity, wind speed and direction, and global radiation; (3) stream and river water level; (4) pH, electrical conductivity, water temperature and suspended particulate matter (SPM) concentration; (5) major ion, alkalinity and dissolved organic carbon (DOC) concentrations. The dataset already contributed to describe the water partitioning in these tropical humid watersheds, to better understand the factors controlling chemical weathering and physical erosion in tropical ecosystems, particularly the role of organic matter. The dataset also contributed to calculate elemental weathering fluxes and saprolite production rate and to propose denudation rates on tropical cratonic landscapes. Hydrological modelling allowed quantification of the geographical water sources contributing to streamflow. DOC data were used to determine greenhouse-gas emissions and carbon budgets from African inland waters. However, long-term solute concentrations at the outlet of a small tributary of the Nyong River exhibit non-stationary behaviour over the last 26 years. The processes governing those fluctuations are not yet fully understood and might be related to changes in the hydrological regime, land-cover and land-use. The latter highlights the need for longer time-series and continued support for CZOs particularly in the humid tropics.     

Crustal features of the northeastern South China Sea: insights from seismic and magnetic interpretations

We interpret seven two-dimensional deep-penetration and long-offset multi-channel seismic profiles in the northernmost South China Sea area, which were collected by R/V Marcus G. Langseth during the TAIwan GEodynamics Research (TAIGER) project in 2009. To constrain the crustal characteristics, magnetic inversion and forward magnetic modeling were also performed. The seismic results clearly show tilted faulting blocks in the upper crust and most of the fault plane connects downward to a quasi-horizontal detachment as its bottom in the south of the Luzon-Ryukyu transform plate boundary. North of the plate boundary, a small-scale failed rifted basin (minimum 5 km in crustal thickness) with negative magnetization probably indicates an extended continental origin. Significant lower crustal material (LCM) was imaged under a crustal fracture area which indicated a continent and ocean transition origin. The thickest LCM (up to 6.5 km) is located at magnetic isochron C15 that is probably caused by the magma supply composite of a Miocene syn-rift volcanic event and Pliocene Dongsha volcanic activity for submarine volcanoes and sills in the surrounding area. The LCM also caused Miocene crustal blocks to be uplifted reversely as 17 km crustal thickness especially in the area of magnetic isochron C15 and C16. In addition, the wide fault blocks and LCM co-existed on the magnetic striped area (i.e. C15–C17) in the south of the Luzon-Ryukyu transform plate boundary. Magnetic forward modeling suggests that the whole thick crustal thickness (>12 km thick) needs to be magnetized in striped way as oceanic crust. However, the result also shows that the misfit between observed and synthetic magnetic anomaly is about 40 nT, north of isochron C16. The interval velocity derived from pre-stack time migration suggests that the crust is composed of basaltic intrusive upper crust and lower crustal material. The crustal nature should refer to a transition between continent and ocean. Thus, the magnetic reversals may be produced in two possible ways: basaltic magma injected along the crustal weak zone across magnetic reversal epoch and because some undiscovered ancient piece of oceanic crust existed. The crustal structure discrimination still needs to be confirmed by future studies.