Will the river Irtysh survive the year 2030? Impact of long-term unsuitable land use and water management of the upper stretch of the river catchment (North Kazakhstan)

The Irtysh river basin all the way from river spring in China across Kazakhstan as far as the Russian part of Siberia is among the most ecologically endangered and affected regions on our planet. The study provides a summary of the historical reasons for anthropological interventions in this area, which began with the construction of plants of the military—industrial complexes in the forties of the last century during World War II. These plants have a major share in extreme high concentrations of heavy metals in surface as well in groundwaters locally. The Semipalatinsk nuclear polygon plays a specific role as a source of contamination of local waters. The release of top secret data enabled us to gain knowledge about serious problems related to high radioactivity of groundwaters, which should spread uncontrollably through a system of secondary fissures activated by nuclear blasts. Another serious problem in this region is the quantitative aspect of contamination. Model simulations of water balance indicate that large industrial development in the spring area in China and continuously increasing water consumption in Kazakhstan may lead to desiccation of the lower stretch of this large river in Siberia during the summer months of 2030.     

Observations of the North Equatorial Current,Mindanao Current,and Kuroshio current system during the 2006/07 El Niño and 2007/08 La Niña

Two onboard observation campaigns were carried out in the western boundary region of the Philippine Sea in December 2006 and January 2008 during the 2006/07 El Niño and the 2007/08 La Niña to observe the North Equatorial Current (NEC), Mindanao Current (MC), and Kuroshio current system. The NEC and MC measured in late 2006 under El Niño conditions were stronger than those measured during early 2008 under La Niña conditions. The opposite was true for the current speed of the Kuroshio, which was stronger in early 2008 than in late 2006. The increase in dynamic height around 8°N, 130°E from December 2006 to January 2008 resulted in a weakening of the NEC and MC. Local wind variability in this region did not appear to contribute to changes in the current system.     

A novel approach for estimating karst groundwater recharge in mountainous regions and its application in Switzerland

A pragmatic and simple approach for estimating the groundwater recharge of karst aquifers in mountainous regions by extrapolation of the hydrological regimes of gauged and well‐documented systems is presented. Specific discharge rates are derived using annual precipitation and spring measurements by taking into account catchment size and elevation, which are assumed to be the dominant factors. Reference sites with high data reliability are used for calibration and regional extrapolation. This is performed with normalized values employing spatial precipitation deviations and correlation with the elevation of the catchment areas. A tiered step procedure provides minimum and maximum normalized gradients for the relationship between recharge quantity and elevation for karst regions. The normalized recharge can therefore be obtained and extrapolated for any location using the spatial precipitation variability to provide an estimate of annual groundwater recharge. The approach was applied to Switzerland (approximately 7500 km² of karst terrain situated between 200 and over 4000 m a.s.l.) using annual precipitation data from meteorological stations for the years 2000 to 2011. Results show that the average recharge rates of different Swiss karst domains range from 20 to 46 L/km²s, which corresponds to an infiltration ratio between 0.6 and 0.9 of total precipitation. Despite uncertainties inherent in the approach, these results provide a benchmark for renewable karst groundwater resources in Switzerland of about 8.4 km³/year. The approach can be applied to any other mountainous karst region, that is, where a clear relationship between elevation, precipitation and recharge can be assumed. Copyright © 2015 John Wiley & Sons, Ltd.     

Atténuation de l'intensité macrosismique pour la France métropolitaine : importance de l'intensité épicentrale

The main result of this work is to show that macroseismic intensity decay with distance strongly depends on the epicentral intensity. An attenuation law that takes this parameter into account is proposed for Metropolitan France, from the analysis of SISFRANCE macroseismic database. Such a model significantly reduces the difference between observed and theoretical intensities. A map of the attenuation variations is also set up for Metropolitan France. No major site effects are observed, but at a broad scale, young Alpine regions display a stronger attenuation than old Hercynian regions. To cite this article: P. Arroucau et al., C. R. Geoscience 338 (2006).     

Crystal morphologies in pillow basalts: implications for mid-ocean ridge processes

We present the results of a detailed petrological study of a sparsely phyric basalt (MAPCO CH98-DR11) dredged along the Mid-Atlantic Ridge (30°41′N). The sample contains microphenocrysts of olivine that display four different rapid-growth morphologies. Comparison of these morphologies with those obtained in dynamic crystallization experiments allows us to constrain the thermal history of the sample. The dendritic morphology (swallowtail, chain and lattice olivine) is directly related to the final quenching during magma–seawater interaction. In contrast, the three other morphologies, namely the complex polyhedral crystal, the closed hopper and the complex swallowtail morphology result from several cycles of cooling–heating (corresponding to a maximum degree of undercooling of 20–25°C) during crystal growth. These thermal variations occurred before eruption and are interpreted to be the result of turbulent convection in a small magmatic body beneath the ridge. The results suggest that the Mid-Atlantic Ridge is underlain by a mush zone that releases batches of liquid during tectonic segregation. Aphyric basalts are emitted during eruptions controlled by the tectonic activity, whereas phyric basalts correspond to small fractions of magma from the mush zone mobilized by reinjections of primitive magmas.     

Dynamique et modélisation des crues dans le bassin du Mono à Nangbéto (Togo/Bénin)

Résumé

Les inondations des dernières années en Afrique de l’Ouest rendent nécessaire la prévision hydrologique pour réduire la vulnérabilité des populations. Nous avons étudié la dynamique des crues dans le bassin du Mono en amont du barrage de Nangbéto (Togo et Bénin) par des méthodes statistiques et déterministes. L’augmentation des précipitations au cours de la décennie 1990 et la mise en eau du barrage de Nangbéto en 1988 ont modifié le régime du Mono, dont les débits d’étiages ont augmenté. Les débits entrants et sortants du barrage sont équivalents, même lors des crues. Les maximums annuels des débits entrants peuvent être modélisés par une distribution des valeurs extrêmes (GEV) de type Fréchet, tandis que ceux des débits sortants, suivent une loi GEV de type Weibull (bornée). Le mécanisme dominant de génération des crues dans le bassin est la montée progressive des eaux associée à l’augmentation de la saturation des sols. L’analyse des débits de crue entre 1988 et 2010 n’a pas montré d’augmentation de la magnitude ou de la fréquence des crues. Le modèle GR4J reproduit bien les débits de crues en période calage, mais ces critères de performance se dégradent lorsque l’on s’en éloigne. Dans ces conditions, l’utilisation de ce modèle pour évaluer les risques futurs de crues serait hasardeuse et il est nécessaire d’envisager d’autres types d’approches.     

Zooplankton community structure in a highly turbid environment (Charente estuary,France): Spatio-temporal patterns and environmental control

Zooplankton assemblages were studied from January 2007 to January 2008 along the salinity gradient of the Charente estuary (France). A Lagrangian survey was performed monthly at five sampling stations defined by salinity (freshwater, 0.5, 5, 15 and 25) in order to collect zooplankton and measure the main environmental parameters (concentrations of suspended particulate matter, particulate organic carbon, chlorophyll a and phaeopigments). A combination of multivariate cluster analysis, species indicator index and canonical correspondence analysis was used to relate the spatio-temporal patterns of the zooplankton assemblages with environmental drivers. The estuary was divided into three different zones by means of environmental parameters while four zooplankton assemblages were identified along the salinity gradient. The Charente estuary appeared as one of the most turbid systems in Europe, with suspended particulate matter (SPM) concentration reaching 3.5 g l⁻¹ in the Maximum Turbidity Zone (MTZ). Algal heterotrophy and microphytobenthos resuspension from the wide mudflats could be responsible for the relatively high chlorophyll a concentrations measured within this MTZ. Salinity and SPM affected significantly the spatial distribution of zooplankton species while temperature and river flow seemed to control their temporal variations. From a zooplanktonic viewpoint, the highly turbid Charente estuary seemed to match an “ecotone–ecocline” model: the succession of species assemblages along the salinity gradient matched the concept of ecocline while the MTZ, which is a stressful narrow area, could be considered as an ecotone. Although such ecoclinal characteristics seemed to be a general feature of estuarine biocenoses, the ecotone could be more system-specific and biological compartment-specific.     

Coupled ‘storm‐flood’ depositional model: Application to the Miocene–Modern Baram Delta Province,north‐west Borneo

The Miocene to Modern Baram Delta Province is a highly efficient source to sink system that has accumulated 9 to 12 km of coastal–deltaic to shelf sediments over the past 15 Myr. Facies analysis based on ca 1 km of total vertical outcrop stratigraphy, combined with subsurface geology and sedimentary processes in the present‐day Baram Delta Province, suggests a ‘storm‐flood’ depositional model comprising two distinct periods: (i) fair‐weather periods are dominated by alongshore sediment reworking and coastal sand accumulation; and (ii) monsoon‐driven storm periods are characterized by increased wave‐energy and offshore‐directed downwelling storm flow that occur simultaneously with peak fluvial discharge caused by storm precipitation (‘storm‐floods’). The modern equivalent environment has the following characteristics: (i) humid‐tropical monsoonal climate; (ii) narrow (ca <100 km) and steep (ca 1°), densely vegetated, coastal plain; (iii) deep tropical weathering of a mudstone‐dominated hinterland; (iv) multiple independent, small to moderate‐sized (10² to 10⁵ km²) drainage basins; (v) predominance of river‐mouth bypassing; and (vi) supply‐dominated shelf. The ancient, proximal part of this system (the onshore Belait Formation) is dominated by strongly cyclical sandier‐upward successions (metre to decametre‐scale) comprising (from bottom to top): (i) finely laminated mudstone with millimetre‐scale silty laminae; (ii) heterolithic sandstone–mudstone alternations (centimetre to metre‐scale); and (iii) sharp‐based, swaley cross‐stratified sandstone beds and bedsets (metre to decimetre‐scale). Gutter casts (decimetre to metre‐scale) are widespread, they are filled with swaley cross‐stratified sandstone and their long axes are oriented perpendicular to the palaeo‐shoreline. The gutter casts and other associated waning‐flow event beds suggest that erosion and deposition was controlled by high‐energy, offshore‐directed, oscillatory‐dominated, sediment‐laden combined flows within a shoreface to delta front setting. The presence of multiple river mouths and exceptionally high rates of accommodation creation (characteristic of the Neogene to Recent Baram Delta Province; up to 3000 m Ma⁻¹), in a ‘storm‐flood’‐dominated environment, resulted in a highly efficient and effective offshore‐directed sediment transport system.