Re‐establishment of soil water repellency after destruction by intense burning in a Mediterranean heathland (SW Spain)

Soil water repellency has been conventionally considered as a fire‐induced effect, but an increasing number of studies have suggested that natural background repellency occurs in many soil types, and many of them have suggested that water repellency can be re‐established over time after being destroyed. An experimental fire was conducted to study changes of the soil surface during the first 18 months following intense burning. The main objectives of this paper are as follows: (1) to investigate in situ water repellency changes at three soil depths (0, 2 and 4 cm) immediately after burning; (2) to evaluate the medium‐term evolution of water repellency under field conditions; and (3) to outline the main hydrological consequences of these changes. Also, different water repellency tests (water drop penetration time, ethanol percentage test (EPT) and contact angle (CA) between water drops and the soil surface) were carried out for comparison purposes. Field experiments showed that soil water repellency was partly destroyed after intense burning. Changes were relatively strong at the soil surface, but diminished progressively with depth. Levels of water repellency were practically re‐established 18 months after burning. This suggests that water repellency in the studied area is not necessarily a consequence of fire, but can instead be a natural attribute. Finally, although limited in time, destruction of soil water repellency has important consequences for runoff flow generation and soil loss rates, and, indirectly, for water quality. Copyright © 2009 John Wiley & Sons, Ltd.     

Electron Density distribution and bonding in silicates

This paper summarizes the recent results of the investigation of bonding in silicates obtained by precision X-ray diffraction. The experimental electron density distribution is compared with theoretical electron density maps calculated for model silicate molecules. The characteristic features of the chemical bonds in ortho-, ring-, chain- and framework silicates are discussed.     

Mangrove ecology,aquatic primary productivity,and fish community dynamics in the Teacapán-Agua Brava Lagoon-Estuarine system (Mexican Pacific)

Aquatic primary productivity, mangrove ecology, and fish community dynamics were investigated in the Teacapán-Agua Brava lagoon-estuarine system, the most extensive mangrove ecosystem on the Pacific coast of Mexico with three species of mangroves distributed heterogeneously (Laguncularia racemosa, Rhizophora mangle, andAvicennia germinans). Tree density was 3,203 trees ha^?1 and basal area was 14.0 m² ha^?1. Litterfall was 1,417 g m^?2 yr^?1, characteristic of a productive riverine forest. The degradation constant forLaguncularia racemosa leaves varied from 1.71 to 4.7 yr^?1 and mean annual net aquatic productivity was 0.41 g C m^?3 d^?1. There were high concentrations of humic substances (up to 150 mg l^?1) early in the wet season. Seasonal variations of the above parameters seemed closely related to the ecology of fish populations. There were 75 fish species distributed in two principal assemblages associated with wet and dry seasons. Diversity and biomass analysis indicated 18 dominant species. Total biomass of the community in this coastal system was estimated at 10 g wet wt m^?2. The highest biomass occurred in the wet season. The most common fish species wereMugil curema, Achirus mazatlanus, Galeichthys caerulescens, Arius liropus, Diapterus peruvianus, Lile stolifera, Centropomus robalito, andEucinostomus sp., all of which have fishery importance. Primary productivity and fish community ecology are controlled by habitat characteristics, river discharge, and climatic seasonality.     

On the significance of aragonite occurrences in the Western Alps

Aragonite occurrences from two areas of the Western Alps are described. It is shown that aragonite has been formed under blueschist metamorphic conditions in the Western Vanoise, while it has been precipitated under sub-surface conditions in the Queyras region. An uplift (P, T) path of the aragonite-bearing rocks of the Western Vanoise is constructed using two independent methods: (1) temperature estimates using the Sr⁺⁺ content of aragonite in the successive veins and (2) the kinetics of the aragonitecalcite solid-state transition. The uplift (P, T) path has an unusual shape with an important temperature decrease (100° to 150° C for a pressure decrease of 0.2 GPa) following blueschists metamorphism (P=0.7 GPa, T=300° C). Thermal models show that this unusual (P, T) path of the Western Vanoise can be explained if one maintains a low temperature (between 125° and 175° C) at the base of the tectonic unit containing the aragonite-bearing rocks during part of its burial history, followed by the whole of its exhumation. A tectonic scenario is proposed to account for the observed and modelled (P, T) path.     

Karst in Gypsum and its environmental impact on the Middle Ebro Basin,Spain

The Middle Ebro Basin in characterised by strong evaporitic profiles from the Miocene period, and in which gypsum formations are predominant. These groups of easy solubility produce in many areas typically karstic landforms, although there are certain features specific to them. The generated landforms appear on the surface as different morphological types of doline, which very often develop on the alluvium deposited by the River Ebro and its affluents. On the agricultural land of the Peñaflor-Villamayor area the functional character of karst causes collapse dolines to appear after heavy storms, and these are constantly filled in by farmers. Motorways and roads that cross these areas, as also the industrial estates existing on the outskirts of Zaragoza, are affected by dissolution processes that bring about continual collapses. The infiltration of water from unlined canals causes the generation of numerous dolines along canal banks.     

Slump debris flows in the Akovolwo Mountains area of Benue State,Nigeria

In September 1979, rain-induced complex landslides occurred in two separate localities along the slopes of the Akovolwo Mountains near Jato-Aka in the Kwande Local Government area of Benue State, Nigeria.The two movements developed on bedrock slopes covered by a veneer of colluvium and (or) residuum no more than 1.5 to 2m deep. Each started as a slump and graduated into a debris flow. The slump, extending downhill a short distance away from the head scarp, had been reconstituted into a debris flow as the initial movement (sliding movement) of the soil mass caused remoulding of the saturated moving mass into viscous debris-laden mud. The resulting mass moved partly along a pre-existing mountain stream channel and partly along a fresh channel it cleared in the savanna forest. At the break of slope, the mass of boulders was dumped and a trail of smaller fragments littered the channels towards the Katsina-Ala River.     

Les minéralisations stratiformes à F-Ba de Hammam Zriba,Jebel Guébli (Tunisie nord orientale): l'apport des études d'inclusions fluides à la modélisation génétique

Résumé Le gîte de H. Zriba-J. Guebli (réserves: 5 millions de tonnes à 15–35% CaF₂) est constitué pour l'essentiel d'amas stratoïdes encaissés dans des formations phosphatifères argileuses et carbonatées, d'âge Campanien inférieur. Quatre formations minéralisées (Mo, Fr, F₂ et F₃) ont été distinguées. La plus ancienne (formation Mo) ne contient pas de fluorine; elle est à dominante quartzeuse ou barytique avec quelques sulfures. Le minerai à fluorine rubanée (formation F₁) est le plus important sous l'angle économique. Trois types d'inclusions fluides ont été observés dans la fluorine: 1) d'abondantes inclusions aqueuses, 2) de rares inclusions gazeuses et 3) de fréquentes inclusions à hydrocarbures liquides jaunes, fluorescentes en éclairage U.V. Les études microthermométriques montrent une augmentation des températures d'homogénéisation (100 à 130°C dans la fluorine F₁, 150–185°C dans la fluorine F₃) avec augmentation parallèle de la salinité des solutions piégées. On propose un modèle de mise en place de la fluorine par voie épigénétique à partir de solutions semblables aux eaux de formation des champs pétrolifères, suivi par des remaniements liés à des circulations hydrothermales récentes.

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In the H. Zriba-J. Guebli mine (5 millions tons of ore with 15%–35% CaF₂) the ore deposits are mostly stratiform bodies hosted by lower-Campanian clay-carbonate sediments with significant phosphate contents. Four successive ore formations are apparently fluorite-free and either quartz-rich or barite-rich with minor amounts of sulfides. The fluorine rubannée (formation F₁) is the main economic ore. Three major fluid inclusions types have been observed in fluorite: (1) abundant aqueous inclusions, (2) rare gas inclusions, and (3) usually yellow oil-bearing inclusions with intense UV fluorescence. In microthermometric investigations on primary aqueous inclusions a general increase in the homogenization temperature from about 100°C to 130°C in fluorite F₁ up to 150°–185°C in fluorite F₃ with a simultaneous increase in salinity was observed. Finally, fluorite crystallized epigenetically in formation-water-type brines; the last geodic filling by fluorite F₃ is tentatively related to Miocene hydrothermal circulation.

     

Experimental Petrology of Melilite Nephelinites

Experimental study of natural melilite nephelinite lavas ofintermediate K/Na ratio at low pressure (fo₂ reveals the presenceof a peritectic ‘point’ of distributary type (1090?C)for liquids saturated with leucite, nepheline, and spinel. Withdecreasing temperature on the olivine + melilite cotectic, botholivine and melilite react with such liquids to produce high-calciumpyroxene at the peritectic. Both the olivine + high-calciumpyroxene and melilite + high-calcium pyroxene cotectics arestable at temperatures below the peritectic. Olivines coexistingwith such liquids are much more magnesian than those in comparabletholeiitic liquids. The olivine-liquid Fe-Mg distribution coefficient is a monotonically increasing function of silica activity over the composition range spannedby melilite nephelinite, ugandite, alkali basalt, and tholeiitebasalt liquids. The analogous Fe-Mg distribution coefficientfor melilite and liquid is effectively constant , while that for high-calcium pyroxene and liquidis highly dependent on the chemistry of high-calcium pyroxene(cf., Sack & Carmichael, 1984). Pseudoternary liquidus projectionsof multiply saturated liquids coexisting with nepheline, leucite,and spinel (?olivine?high-calcium pyroxene?melilite) have beenprepared to facilitate graphical analysis of the evolution oflava compositions during hypabyssal cooling. Major element chemicalanalyses and petrographic features of lavas from Mt. Nyiragongo,East Africa and Oahu, Hawaii (e.g., Denaeyer et al., 1965; Wilkinson& Stolz, 1983) confirm the validity of these diagrams andthe systematics established from the experimental data. ^*Reprint requests to R.O. Sack