Fog harvesting: An alternative source of water supply on the West Coast of South Africa

Experiments conducted during the 1990s investigated the feasibility of using fog water to supplement existing water supplies in the arid west coast region of South Africa. Based on these results, a project was initiated aimed at implementing an operational fog water collection system to provide potable water to a small, water-poor rural community. A 70 m² fog water collector was subsequently erected on the crest of the hill located next to the mission station called Lepelfontein. The volume of water collected was measured by means of a water flow meter and a tipping bucket. An automatic weather station recorded rainfall, wind speed and direction. The data record spans the period September 1999–August 2001. This paper gives a brief overview of the methods used to select the experimental site and describes the design of the fog water collection system. This is followed by a detailed account of the water yields, the contribution of fog and rainfall to the total yield, the characteristics of wet events, the factors associated with water collection and water quality. On average, yields of around 4.6 l of water were collected per square metre of collecting surface per day with maximum daily yields approaching 4000 l. The quality of the water was excellent. It thus appears that fog water collection may have considerable potential as an alternative water source at many other locations on the west coast of South Africa. This revised version was published online in July 2006 with corrections to the Cover Date.     

The role of physical-biological coupling in the benthic boundary layer under megatidal conditions: The case of the dominant species of theAbra alba community in the Eastern Baie de Seine (English Channel)

Recent evidence has shown that postlarvae and juveniles of the most dominant species of theAbra alba community of the eastern Baie de Seine are able to re-enter the water column after larval settlement and undergo active and/or passive redistribution. However, few subtidal studies have been conducted to investigate and quantify the processes controlling the abundance of drifting postlarvae and juveniles. The purpose of this study was to verify the reproducibility or the variability of this phenomenon and to assess coupling between the intensity of drifting and that of bed shear stress, which is dependent on tidal currents, wave characteristics, and sediment features. This study was conducted in June and July 1995 at two sites in the bay, one located at the center of the muddy fine-sediment community and the other at its external border with the fine clean sands of theOphelia borealis community. At each site, suprabenthic sledge samples were taken during specific tidal conditions (low tide, slack water, and flood and ebb peaks) during a neap and a spring tide. Physical data (current velocity, turbidity, and suspended matter content) and meiobenthic samples were taken at the same time. Under megatidal conditions, drifting was a quantitatively important dispersal mechanism for at least 15 of the fine-sediment dominant species belonging to various groups such as polychaetes, molluscs (gastropods and bivalves), and echinoderms. The fluctuation in abundance of drifters was related to tidal range, tidal period, location of the site, and the recruitment dynamics. However, species differed strongly in theri response to hydrodynamical parameters. Three types of drifting species were observed: species that were only present in the water column (‘undet. cardiids’ and Mytilidae); species that were both drifting and present at the seaded (Abra alba, Phaxas pellucidus, Eteone picta, Mysella bidentata, Ophiura texturata, Owenia fusiformis, Pholoe minuta, Phyllodoce lineata, Pectinaria koreni, andSpisula subtruncata); species that were present at the seabed but did not drift during the sampling period (Acrocnida brachiata, Eteone longa, Eumida sanguinea, Glycinde normanni, Magelona mirabilis, Nemertean sp1,Nephtys sp.,Spiophanes bombyx, andTubulanus polymorphus). Each drifting pattern is related to eco-ethological species characteristics and may have very different consequences on population dynamics.     

Late Palaeozoic NE–SW ductile–brittle extension in the La Serre horst,eastern France

In the La Serre horst of the Alpine foreland, the pre-Triassic La Serre median fault zone separates a Late Devonian–Early Carboniferous granite from an ignimbrite of unknown age and from Permian deposits. Motion along this fault zone took place first in ductile conditions and then evolved in brittle conditions. Both ductile and brittle shear criteria indicate a top-NE normal-dextral displacement. Similar motions are reported along faults bounding Late Palaeozoic intramontane coal basins located in the Massif Central and correspond to a widespread NE–SW Late to Post-Orogenic extension that affected the Variscan basement during Late Carboniferous to Early Permian times. To cite this article: G. Coromina, O. Fabbri, C. R. Geoscience 336 (2004).     

Graphitization in a high-pressure,low-temperature metamorphic gradient: a Raman microspectroscopy and HRTEM study

The graphitization of carbonaceous material (CM) in a high-pressure metamorphic gradient is characterized along a cross section in the Schistes Lustrés formation, Western Alps. Along this 25-km cross section, both the CM precursor and the host-rock lithology are homogeneous, and the prograde evolution of the pressure-temperature metamorphic conditions from the lower blueschist-facies (13 kbar, 330 °C) to the eclogite-facies (20 kbar, 500 °C) is tightly constrained by literature data. Raman microspectroscopy shows that at the micrometre scale, this process is progressive and continuous with increasing metamorphic grade, and that the structure of CM is very sensitive to temperature variations. At the nanometre scale (HRTEM), the CM is composed of a mixture of a microporous phase and an onion-ring like phase, both known as non-graphitizing under the effect of temperature at ambient pressure. The HP-LT graphitization produces structurally and microtexturally heterogeneous CM. With increasing metamorphic grade, the graphitization of the two types of CM proceeds up to the triperiodic graphite stage because of microtextural and structural changes that are specific to each type of CM. The microporous material is progressively transformed into graphite through a macroporous transitional stage. In this case, graphitization mainly occurs on the pore walls as a result of pore growth. In the case of concentric onion-ring like material, graphitization occurs in the regions with the largest radius of curvature, i.e. on the outer part of the ring. In comparison with 1-bar experiments, pressure seems to induce microtextural changes, which allows the subsequent structural modifications of the starting material.     

Display-sites selection by houbara bustard (Chlamydotis [undulata] macqueenii) in Mori, Xinjiang, People''s Republic of China

Display-site selection by houbara bustards was studied in Mori, Xinjiang, China during the breeding seasons from April to June 2000. Most of the habitats chosen for displaying were short sub-shrubby and open areas close to high shrub patches. The displaying males clearly prefer low covered areas and avoid densely covered and high vegetation sites. The vegetation density and number of plant species at display sites were significantly lower from that at randomly selected sites. The average distance to the closest shrub patch was significantly shorter at display sites than at random sites. Plant species richness, vegetative density, vegetative cover and distance to the shrub patches are possibly the most important factors that determined the display-sites selection of houbara bustard.     

An improved index of environmental quality for Swiss rivers based on benthic invertebrates

A total of 1424 samples of benthic invertebrates, collected in 56 rivers of western Switzerland (canton of Vaud), was used to improve the RIVAUD (Rivers of Vaud) index of environmental quality. This index, described for the first time in 1989, was based on total number of taxa and on number of taxa intolerant of pollution (Plecoptera, Heptageniidae, and Trichoptera with a case). The 1995 version of RIVAUD, called RIVAUD 95, presented a larger range of values (0–20) than the previous one (0–10), to describe more precisely the variations of environmental quality. According to RIVAUD 95, the environmental quality of Swiss rivers increased with the altitude of sampling sites because anthropogenic impacts decreased along the same gradient. This altitudinal pattern was used to define classes of environmental quality which can be adapted to the rivers of other regions.     

Experimental modelling of thin-skinned shortening around magmatic intrusions

Magmatic intrusions can trigger thin-skinned compression of the adjacent sedimentary cover by three processes: (a) gravity gliding away from the topographic dome resulting from the ascending magma; (b) fluid push from the rear resulting from forceful intrusion then lateral spreading of the magma; and (c) increased loading by volcanic accumulation. The applicability of the first two mechanisms, gravity gliding and fluid push, was tested using dynamically scaled experiments. Model results help to elucidate the kinematics and structural evolution of thrusts and folds formed by such processes and determine which geological parameters control the deformation style. The results show that the presence of a weak layer within the sedimentary overburden is essential to form thrust and fold belts around the intrusion. Experiments suggest that although gravity gliding can dominate the early stages of deformation, most of the deformation is caused by lateral spreading of the fluid magma pushing the adjacent sedimentary rocks. Models also suggest that true laccoliths can form only if the sedimentary section comprises a basal low-viscosity stratum. Comparison with natural examples allows the evaluation of the applicability of experimental results.     

Water quality in rivers of western Switzerland: Application of an adaptable index based on benthic invertebrates

Water quality was estimated from 205 samples of benthic invertebrates collected between 1982 and 1986 in 51 rivers of western Switzerland (canton of Vaud). Each sample consisted of the combined list of taxa resulting from one spring sample pooled with one summer sample. Water quality was indicated by total number of taxa and number of taxa intolerant of pollution: i. e. Heptageniidae, Plecoptera, and Trichoptera with a case. Six classes of values were delimited for each of these two variables by cluster analysis. Values from zero to five were attributed to each class. The index of water quality was computed by adding these two values in each sample. According to this index, good water quality was indicated by 42% of samples. This index can be adapted to other rivers because its components are easily modified.