Temporal variability of suspended sediment sources in an alpine catchment combining river/rainfall monitoring and sediment fingerprinting

Influence of the rainfall regime on erosion and transfer of suspended sediment in a 905‐km² mountainous catchment of the southern French Alps was investigated by combining sediment monitoring, rainfall data, and sediment fingerprinting (based on geochemistry and radionuclide concentrations). Suspended sediment yields were monitored between October 2007 and December 2009 in four subcatchments (22–713 km²). Automatic sediment sampling was triggered during floods to trace the sediment origin in the catchment. Sediment exports at the river catchment outlet (330 ± 100 t km^‐2 yr^‐1) were mainly driven (80%) by widespread rainfall events (long duration, low intensities). In contrast, heavy, local and short duration storms, generated high peak discharges and suspended sediment concentrations in small upstream torrents. However, these upstream floods had generally not the capacity to transfer the sediment down to the catchment outlet and the bulk of this fine sediment deposited along downstream sections of the river. This study also confirmed the important contribution of black marls (up to 70%) to sediment transported in rivers, although this substrate only occupies c. 10% of the total catchment surface. Sediment exports generated by local convective storms varied significantly at both intra‐ and inter‐flood scales, because of spatial heterogeneity of rainfall. However, black marls/marly limestones contribution remained systematically high. In contrast, widespread flood events that generate the bulk of annual sediment supply at the outlet were characterized by a more stable lithologic composition and by a larger contribution of limestones/marls, Quaternary deposits and conglomerates, which corroborates the results of a previous sediment fingerprinting study conducted on riverbed sediment. Copyright © 2012 John Wiley & Sons, Ltd.     

Spatial Variability of Sampling: Grid Size Impact on Atmospheric Metals and Trace Elements Deposition Mapping with Mosses

This paper deals with the spatial heterogeneity structure and the influence of the precision of moss data on results interpretation as real spatial variations of atmospheric heavy metal deposition. Different sizes of map mesh net (unit I of 30 × 30 km, unit II of 10 × 10 km, unit III of 3 × 3 km) have divided an area of 90 × 90 km. The protocol used is a nested design with three levels and random draws. The statistical method of components of variance analysis estimates the associated variability for each mesh size. Our results show the poor precision of this biological tool for map purposes on a little scale (unit III). Furthermore, the high residual variance of As, Ba, Cd, Co, Cu, La, Ti, and U hides the spatial variations associated with mesh sizes. In order to obtain useful maps, it should be reasonable to use a 30 × 30 km mesh size, or even larger, to build spatial variation maps of Pb, Sb and with more caution for Cu, Sr, Rb and Zn. For V, As and Cd, the residual variability of moss data was too important to guarantee any spatial origin to the mapped variations. The cost–benefit study shows that the sampling effort has to be concentrated on unit I of 30 × 30 km to optimize future campaigns, and with a particular stress on the sampling repetitions for Cu, Pb, and Sb.     

The sedimentary coastal basin of Togo: example of a multilayered aquifer still influenced by a palaeo-seawater intrusion

In Togo, the hydrogeology of the sedimentary coastal aquifers along the Gulf of Guinea has been studied for the last three decades to define the recharge processes and the origin and evolution of the salinity. Isotope hydrology and fluid geochemistry suggest that the current recharge of all aquifers, both confined and unconfined, occurs through the crystalline basement and the Plio-Quaternary deposits. Two main groundwater mineralization processes are observed: the first one, in recharge areas, is due to farming, village and city life and concerns unconfined aquifers (crystalline basement, Continental Terminal and Quaternary sediments); the second one is a mixing process between recent freshwater and fossil saline water still present in the deep confined aquifers inland, several kilometers away from the coast. Brackish water was trapped in low-permeability lenses of confined aquifers (Eo-Palaeocene and Maastrichtian) during the Quaternary, in periods of low recharge, notably during the last glacial maximum (LGM), and has not yet been flushed out. Hydrodynamic simulations indicate that, at that time, the aquifers experienced a maximum seawater intrusion as far as 20–22 km inland, depending on the palaeo-recharge value at the outcrops.     

Globalizing urban resilience

Urban resilience, a new urban development and governance agenda, is being rolled out from the top down by a network of public, private, non-profit sector actors forming a global urban resilience complex: producing norms that circulate globally, creating assessment tools rendering urban resilience technical and managerial, and commodifying urban resilience such that private sector involvement becomes integral to urban development planning and governance. The Rockefeller Foundation's 100 Resilience Cities Program is at the center of this complex, working with the World Bank, global consultants, NGOs, and private sector service providers to enroll cities, develop and circulate urban resilience assessment tools, and create a market catalyzed by the notion of a resilience dividend. Notwithstanding the claim of this program being open and inclusive, aspects of its initial operationalization in Jakarta suggest that urban resilience assessment tools preempt alternative understandings of urban resilience and marginalizing voices of the city's most vulnerable populations.     

Comparing the atmosphere to a bathtub: effectiveness of analogy for reasoning about accumulation

Understanding the process of accumulation is fundamental to recognising the magnitude and speed of emissions reduction required to stabilise atmospheric CO₂ and, hence, global temperature. This research investigated the effectiveness of analogy for building understanding of accumulation among non-experts. Two studies tested the effects of analogy and graphical information on: (1) performance on a CO₂ stabilisation task; and (2) preferred level of action on climate change. Study 1 was conducted with a sample of undergraduate students and Study 2, with a sample of the Australian public. In the student sample, analogical processing significantly improved task performance when information about emission rates was presented in text but not when it was presented in graph format. It was also associated with greater preference for strong action on climate change. When tested with the public, analogy and information format independently influenced task performance. Furthermore, there was a marginal effect of education such that the analogy especially might have helped those with at least high school attainment. Our results show that analogy can improve non-experts’ understanding of CO₂ accumulation but that using graphs to convey emissions rate information is detrimental to such improvements. The results should be of interest to climate change communicators, advocates, and policy-makers.     

Summer air temperature,reconstructions from the last glacial stage based on rodents from the site Taillis-des-Coteaux (Vienne), Western France

The oxygen isotope composition of phosphate from tooth enamel of rodents (δ¹⁸O_p) constitutes a valuable proxy to reconstruct past air temperatures in continental environments. This method has been applied to rodent dental remains from three genera, Arvicola sp., Microtus sp. and Dicrostonyx sp., coming from Taillis-des-Coteaux, Vienne, France. This archaeological site contains an exceptionally preserved sedimentary sequence spanning almost the whole Upper Palaeolithic, including seven stratigraphic layers dated from 35 to 17 cal ka BP. The abundant presence of rodent remains offers the opportunity to quantify the climatic fluctuations coeval of the various stages of human occupation of the site. Differences between δ¹⁸O_p values of Arvicola sp. and Microtus sp. teeth are interpreted as the result of heterochrony in tooth formation as well as differences in ecology. Mean δ¹⁸O_p values of Microtus sp. are preferentially used to reconstruct summer air temperatures, which range from 16.0 ± 3.7 to 19.1 ± 3.1°C throughout the sedimentary sequence; however, the highest variability is observed during the last glacial maximum.     

Surface chemistry and structural properties of mackinawite prepared by reaction of sulfide ions with metallic iron

Tetragonal FeS_1−x mackinawite, has been synthesized by reacting metallic iron with a sodium sulfide solution and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), transmission Mössbauer spectroscopy (TMS) and X-ray photoelectron spectroscopy (XPS). Based on XRD and TEM analyses, synthetic mackinawite exhibits crystallization and is identical to the natural mineral. Unit cell parameters derived from XRD data are a = b = 0.3670 nm and c = 0.5049 nm. The bulk Fe:S ratio derived from the quantitative dispersive energy analysis is practically 1. XPS analyses, however, showed that mackinawite surface is composed of both Fe(II) and Fe(III) species bound to monosulfide. Accordingly, monosulfide is the dominant S species observed at the surface with lesser amount of polysulfides and elemental sulfur. TMS analysis revealed the presence of both Fe(II) and Fe(III) in the mackinawite structure, thus supporting the XPS analysis. We propose that the iron monosulfide phase synthesized by reacting metallic iron and dissolved sulfide is composed of Fe(II) and S(-II) atoms with the presence of a weathered thin layer covering the bulk material that consists of both Fe(II) and Fe(III) bound to S(-II) atoms and in a less extent of polysulfide and elemental sulfur.