Effect of the environment on the hydrochemical characteristics of an alluvial aquifer following an exceptional multiyear drought (Mediterranean Seashore,Hérault,France): Part II—Climatology and agronomy     

Jean-Claude Grillot  Isabelle Chaffaut  Moumtaz Razack 《Environmental Geology》1988,11(2):163-173

The hydrochemical evolution of an alluvial groundwater located along the Mediterranean seashore is analyzed with respect to its agricultural and climatic environment, including degree of saturation of the soil; types of cultures, chemical fertilizers and phytosanitary treatments; selective irrigations of the cultivated areas; precipitations. It is shown that the environmental effect on the groundwater's vulnerability depends on two groups of factors:

1. Transfers from surface to groundwater of nitrates, chlorides, sulfates, and potassium, which are governed by: (a) the climatic conditions before the agricultural activities begin, (b) the kinds of agricultural activities and their distribution in time with respect to a given climatic context. Phenomena of retention of and/or rapid diffusion are related to the sedimentary heterogeneities of the reservoir and to the differences of temperatures between irrigation waters and precipitations.
2. Cationic exchanges related to the presence of clays of Montmorillonite-Kaolinite type.

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The tropospheric distribution of formaldehyde during TROPOZ II     

D. W. Arlander  D. Brüning  U. Schmidt  D. H. Ehhalt 《Journal of Atmospheric Chemistry》1995,22(3):251-269

A series of 149 measurements of the HCHO mixing ratio were made between 0 and 10 km altitude and 70° N to 60° S latitude during TROPOZ II. The data show a vertical decrease of the HCHO mixing ratio with altitude at all latitudes and a broad latitudinal maximum in the HCHO mixing ratio between 30° N and 30° S at all altitudes. The measured mixing ratios of HCHO are considerably higher than those expected from CH₄ oxidation alone, but agree broadly with the average latitude by altitude distribution of HCHO derived by a 2D model including emissions of C₁–C₇ hydrocarbons. A number of the regional scale deviations of the measured HCHO distribution from the average modelled one can be explained in terms of the local wind field.  相似文献   

Bestimmung gelöster und suspendierter Schwermetalle in der Elbe     

Prof. Dr. Lutz Brügmann 《Ocean Dynamics》1990,43(3):127-135

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Experimental study of aluminum speciation in fluoride-rich supercritical fluids   总被引：2，自引：0，他引：2  

Boris TagirovJacques Schott  Jean-Claude HarrichourryStefano Salvi 《Geochimica et cosmochimica acta》2002,66(11):2013-2024

The solubility of the albite-paragonite-quartz mineral assemblage was measured as a function of NaCl and fluorine concentration at 400°C, 500 bars and at 450°C, 500 and 1000 bars. Decreasing Al concentrations with increasing NaCl molality in F-free fluids of low salinity (mNaCl < 0.01) demonstrates that Al(OH)₄⁻ dominates Al speciation and is formed according to the reaction 0.5 NaAl₃Si₃O₁₂H_2(cr)+2 H₂O = 0.5 NaAlSi₃O_8(cr)+Al(OH)₄⁻+H⁺. Log K results for this reaction are −11.28 ± 0.10 and −10.59 ± 0.10 at 400°C, 500 bars and 450°C, 1000 bars, respectively. Upon further salinity increase, Al concentration becomes constant (at 400°C, 500 bars) or even rises (at 450°C, 1000 bars). The observed Al behavior can be explained by the formation of NaAl(OH)₄⁰_(aq) or NaAl(OH)₃Cl_(aq)⁰. The calculated constant for the reaction Al(OH)₄⁻+Na⁺=NaAl(OH)₄⁰_(aq) expressed in log units is equal to 2.46 and 2.04 at 400°C, 500 bars and 450°C, 1000 bars, respectively. These values are in good agreement with the predictions given in Diakonov et al. (1996). Addition of fluoride at m(NaCl) = const = 0.5 caused a sharp increase in Al concentration in equilibrium with the albite-paragonite-quartz mineral assemblage. As fluid pH was also constant, this solubility increase indicates strong aluminum-fluoride complexation with the formation of NaAl(OH)₃F_(aq)⁰ and NaAl(OH)₂F₂⁰_(aq), according to 0.5 NaAl₃Si₃O₁₂H_2(cr)+Na⁺+HF_(aq)⁰+H₂O = 0.5 NaAlSi₃O_8(cr)+ NaAl(OH)₃F_(aq)⁰+H⁺, log K = −5.17 and −5.23 at 400°C and 450°C, 500 bars, respectively, and 0.5 NaAl₃Si₃O₁₂H_2(cr)+Na⁺+2 HF_(aq)⁰ = 0.5 NaAlSi₃O_8(cr)+NaAl(OH)₂F₂⁰_(aq)+H⁺, log K = −2.19 and −1.64 at the same P-T conditions. It was found that temperature increase and pressure decrease promote the formation of Na-Al-OH-F species. Stability of NaAl(OH)₂F₂⁰_(aq) in low-density fluids also increases relative to NaAl(OH)₃F_(aq)⁰. These complexes, together with Al(OH)₂F_(aq)⁰ and AlOHF₂⁰_(aq), whose stability constants were calculated from the corundum solubility measured by Soboleva and Zaraisky (1990) and Zaraisky (1994), are likely to dominate Al speciation in metamorphic fluids containing several ppm of fluorine.  相似文献   

Une méthode de quantification de la dégradation d'un escarpement de faille au cours des cycles climatiques du Quaternaire : la faille de Jobourg (Nord Cotentin,France)Quantification of a fault-scarp degradation through Quaternary: the Jobourg fault (North Cotentin,France)     

Marianne Font  Jean-Louis Lagarde  Daniel Amorese  Jean-Pierre Coutard  Jean-Claude Ozouf 《Comptes Rendus Geoscience》2002,334(3):171-178

The degradation of the Jobourg fault-scarp occurred by cryoclastic processes in a periglacial environment during a part of Quaternary time. An attempt of quantification indicates a bulk scarp erosion of about 39 m³ m^?2, while the head accumulated at the bottom of the fault scarp only represents 4.6 m³ m^?2. To cite this article: M. Font et al., C. R. Geoscience 334 (2002) 171–178.  相似文献   

Four thousand years of atmospheric lead pollution in northern Europe: a summary from Swedish lake sediments   总被引：8，自引：7，他引：8  

M.-L. Bränvall  R. Bindler  O. Emteryd  I. Renberg 《Journal of Paleolimnology》2001,25(4):421-435

This paper presents a large palaeolimnological study of the pre-industrial and industrial history of atmospheric lead pollution deposition in Sweden. Both lead concentrations and ²⁰⁶Pb/²⁰⁷Pb ratios have been analysed in 31 lakes covering most of Sweden, plus one lake in north-west Russia. Four of the lakes have varved (annually-laminated) sediments. Isotope analysis is a sensitive and effective method to distinguish pollution lead from natural catchment lead and to detect early pollution influence, because the ²⁰⁶Pb/²⁰⁷Pb ratio in unpolluted background sediments in Sweden was > 1.3, while that of lead from pollution, derived from ores and coal, was < 1.2. The sediments show a consistent picture of past temporal changes in atmospheric lead pollution. These changes include: the first traces of pollution 3,500-3,000 yrs ago; a pollution peak in Greek-Roman Times (about 0 AD); lower lead fall-out between 400 and 900 AD; a significant and permanent increase in atmospheric lead fall-out from about 1000 AD; an increase with the Industrial revolution; a major increase following World War II; the maximum peak in the 1970s; and decreasing fall-out over the last decades. The four varved sediments provide high-resolution records of atmospheric pollution. They reveal pollution peaks about 1200 and 1530 AD which match the history of metal production in Europe. According to the varve records the lead pollution level in the late 1990s had decreased beneath the level of the 1530s. The pollution level 1200 AD was about 35% of the 1980s, when lead pollution was still near its all time high. About 50% of the total accumulated atmospheric lead pollution deposition through time was deposited in the pre-industrial period. The sediments also show a consistent picture of the geographic distribution of atmospheric lead deposition over time, with higher deposition in south Sweden and declining levels to the north, which supports the hypothesis that the main sources of pre-industrial atmospheric lead pollution in Sweden were cultural areas in mainland Europe and Great Britain.  相似文献   

Volcanic edifice stability during cryptodome intrusion     

Franck Donnadieu  Olivier Merle  Jean-Claude Besson 《Bulletin of Volcanology》2001,63(1):61-72

Limit equilibrium analyses were applied to the 1980 Mount St. Helens and 1956 Bezymianny failures in order to examine the influence on stability of structural deformation produced by cryptodome emplacement. Weakening structures associated with the cryptodome include outward-dipping normal faults bounding a summit graben and a flat shear zone at the base of the bulged flank generated by lateral push of the magma. Together with the head of the magmatic body itself, these structures serve directly to localize failure along a critical surface with low stability deep within the interior of the edifice. This critical surface, with the safety coefficient reduced by 25-30%, is then very sensitive to stability condition variation, in particular to the pore-pressure ratio (r_u) and seismicity coefficient (n). For r_u=0.3, or n=0.2, the deep surface suffers catastrophic failure, removing a large volume of the edifice flank. In the case of Mount St. Helens, failure occurred within a material with angle of friction ~40°, cohesion in the range 10⁵-10⁶ Pa, and probably significant water pore pressure. On 18 May 1980, detachment of slide block I occurred along a newly formed rupture surface passing through the crest of the bulge. Although sliding of block I may have been helped by the basal shear zone, significant pore pressure and a triggering earthquake were required (r_u=0.3 and n=0.2). Detachment of the second block was guided by the summit normal fault, the front of the cryptodome, and the basal shear zone. This occurred along a deep critical surface, which was on the verge of failure even before the 18 May 1980 earthquake. The stability of equivalent surfaces at Bezymianny Volcano appears significantly higher. Thus, although magma had already reached the surface, weaker materials, or higher pore pressure and/or seismic conditions were probably required to reach the rupture threshold. From our analysis, we find that deep-seated sector collapses formed by removing the edifice summit cannot generally result from a single slide. Cryptodome-induced deformation does, however, provide a deep potential slip surface. As previously thought, it may assist deep-seated sector collapse because it favors multiple retrogressive slides. This leads to explosive depressurization of the magmatic and hydrothermal systems, which undermines the edifice summit and produces secondary collapses and explosive blasts.  相似文献   

River incision and vegetation dynamics in cut-off channels   总被引：1，自引：0，他引：1  

Gudrun Bornette  Claude Amoros  Jean-Claude Rostan 《Aquatic Sciences - Research Across Boundaries》1996,58(1):31-51

The consequences of river incision on ecosystems dynamics in cut-off channels were hypothesized to be 1) the reduction of river backflows and overflows of the river in the former channels; 2) the reduction of seepage flows from the river and drainage into the channels; 3) the drainage of the hillslope aquifer by the former channels. The subsequent changes of aquatic plant communities should be 1) the terrestrialization of the higher part of former channels and 2) their change into more oligotraphent ones if the hillslope aquifer is poorer in nutrients than the river. In those reaches where the river bed is aggraded, river backflows in the cut-off channel should increase, as should overflows and seepage, and more eutraphent species should develop. Changes in aquatic vegetation were studied over a ten-year period in four cut-off channels supplied by a nutrient-poor hillslope aquifer and a nutrient-rich river. Two of them were located in an incised reach of the river, one in an aggraded reach and one (reference) in a reach that was neither aggraded nor incised. The vegetation of the reference channel exhibited only minor changes over the ten-year period, indicating that the successional trend is not perceptible at the time scale of the study, and thus that any change observed in the other channels can be ascribed to river incision or aggradation. Terrestrialization expected in the channels located in the incised reach clearly progressed in the downstream parts, but was inhibited by groundwater supplies in the upper parts. As expected, oligotraphent communities progressed or remained dominant in the upper part. The channel located in the aggraded reach of the river exhibited the highest floristic changes. As expected, eutraphent communities progressed in this channel, but unexpectedly, terrestrialization also progressed in the upstream part. Alternative explanations are: 1) aggradation could have instigated more backflows and overflows without modifying significantly the mean water-level and 2) more frequent water overflows could have favoured alluvial deposition and thus terrestrialization.  相似文献   

Atmospheric effects from post-nuclear fires     

Paul J. Crutzen  Ian E. Galbally  Christoph Brühl 《Climatic change》1984,6(4):323-364

During a large nuclear war, the atmosphere would be loaded with huge quantities of pollutants, which are produced by fires in urban and industrial centers, cultivated lands, forests and grasslands. Especially detrimental are the effects of light absorbing airborne particles. An analysis of the amounts of the various types of fuels which could burn in a nuclear war indicates that more than 10¹⁴ g of black smoke could be produced by fires started by the nuclear explosions. Due to this, the penetration of sunlight to the earth's surface would be reduced greatly over extended areas of the northern hemisphere, maybe even globally. This could temporarily cause extreme darkness in large areas in midlatitudes and reduce crop growth and biospheric productivity.This situation would last for several weeks and cause very anomalous meteorological conditions. Much solar radiation would be absorbed in the atmosphere instead of at the earth's surface. The land areas and lower atmosphere would, therefore, cool and the overlying atmosphere warm, creating strong vertical thermal stability in a highly polluted atmosphere. For extended periods and in large parts of the world, weather conditions would be abnormal. The resulting cold, probably freezing, temperatures at the ground would interfere severely with crop production during the growing season and cause extreme conditions for large sections of the biosphere. The combination of lack of sunlight, frost and other adverse meteorological conditions would add enormously to the already huge problems of the survivors.  相似文献   

Les derniers stades de la cristallisation du filon à fluorite et barytine de Chavaniac (Haute-Loire,France) d'après des études d'inclusions fluides et solides     

Colette Derré  Jean-Claude Touray 《Mineralium Deposita》1971,6(4):292-301

Résumé L'étude des inclusions fluides des minéraux de fin de cristallisation (principalement fluorite et barytine) du filon de Chavaniac, montre une diminution de la température et de la salinité. La fluorite a commencé à se déposer vers 140°C±10°C dans une solution renfermant 20% en poids en équivalents NaCl. La température de formation de la barytine était de 40°C au plus et les solutions diluées renfermaient parfois en émulsion des hydrocarbures liquides. On a pu établir des relations entre succession paragénétique, phases de fracturation, et les résultats précédents.

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Fluid inclusion studies in end-crystallisation minerals from Chavaniac mine (mainly fluorite and baryte) show that temperature and salinity fell during crystallisation. Crystallisation of fluorite began at around 140°C±10°C, in a solution containing about 20% NaCl. The temperature of formation of baryte never exceeded 40°C and the dilute solutions sometimes contained emulsified hydrocarbons. Relations have been established between paragenetic succession, fracture phases, and the above results.

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