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111.
M. Alazard A. Boisson J-C. Maréchal J. Perrin B. Dewandel T. Schwarz M. Pettenati G. Picot-Colbeaux W. Kloppman S. Ahmed 《Hydrogeology Journal》2016,24(1):35-57
The recharge flow paths in a typical weathered hard-rock aquifer in a semi-arid area of southern India were investigated in relation to structures associated with a managed aquifer recharge (MAR) scheme. Despite the large number of MAR structures, the mechanisms of recharge in their vicinity are still unclear. The study uses a percolation tank as a tool to identify the input signal of the recharge and uses multiple measurements (piezometric time series, electrical conductivity profiles in boreholes) compared against heat-pulse flowmeter measurements and geochemical data (major ions and stable isotopes) to examine recharge flow paths. The recharge process is a combination of diffuse piston flow and preferential flow paths. Direct vertical percolation appears to be very limited, in contradiction to the conceptual model generally admitted where vertical flow through saprolite is considered as the main recharge process. The horizontal component of the flow leads to a strong geochemical stratification of the water column. The complex recharge pattern, presented in a conceptual model, leads to varied impacts on groundwater quality and availability in both time and space, inducing strong implications for water management, water quality evolution, MAR monitoring and longer-term socio-economic costs. 相似文献
112.
Spatial and temporal dynamics of bacterial contamination in South France coastal rivers: focus on in‐stream processes during low flows and floods
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Y. Chu M. G. Tournoud C. Salles P. Got J. L. Perrin C. Rodier A. Caro M. Troussellier 《水文研究》2014,28(8):3300-3313
Faecal indicator bacteria (thermotolerant coliform and faecal streptococci) were enumerated in a Mediterranean coastal river to evaluate bacterial contamination levels in relation to hydrological conditions, to estimate delivery of bacterial loads to transitional and coastal waters (Thau lagoon) and to identify bacterial sources of pollution and their contribution to the bacterial flow. Results showed that (1) in low flow conditions, mean bacterial concentrations were higher than EU guidelines for bathing waters; (2) floods had higher concentrations of indicator bacteria than low flows; (3) low flow conditions represented a negligible proportion of bacterial loads compared with high flow and flood periods; (4) during medium and low flow conditions, bacteria were stored in riverbed fine sediments forming in‐stream stores that may be flushed during floods; (5) the first flush effect was highlighted during an early autumn flood as was the role of in‐stream stores during the course of the flood; and (6) point sources that continuously feed the river are contributing to the pool of bacteria accumulated in the riverbed sediment. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
113.
Adriane Commin-Fischer Gilles Berger Mireille Polvé Michel Dubois Paul Sardini Daniel Beaufort Milton Formoso 《Journal of South American Earth Sciences》2010,29(3):751-760
The filling process of amethyst-bearing geodes from Serra Geral Formation basalts, Brazil, is investigated by different methods performed on the SiO2 filling phases. Image analysis of quartz–amethyst deposits suggests a single growing mechanism ruled by geometric selection of randomly oriented crystals. Microthermometry of fluid inclusions reveals formation temperature lower than 100 °C, probably lower than 50 °C, and fluid salinity as high as 3 mass% NaCl eq. Composition in REE and trace-elements measured by ICP-MS on acid-digested or laser-ablated samples indicates a common genesis for amethyst, quartz and chalcedony, as well as the absence of significant variations from one geode to another. 87Sr/86Sr data on chalcedony shows that both the host basalt or the Botucatu sandstone are possible silica sources. These data, combined with thermo-kinetic considerations, permit us to discuss the filling process. We argue in favor of the contribution of a mineralized fluid of hydrothermal origin producing a regional silica source which decreased with time. The observed mineral sequence is related to the depletion of silica in the solution. 相似文献
114.
The main aim of this study was to estimate the influence of the seasonal variations of the Danube River particulate organic matter (POM) inputs on the Black Sea surface seawater POM and upper layer of sediments along the Romanian coast. Ratios of carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) stable isotopes allowed differentiating river and marine organic matter sources. Danube River POM presented significantly lower average values of delta(13)C (-27.52+/-0.88 per thousand) and delta(15)N (4.88+/-1.45 per thousand) than seawater POM (delta(13)C=-24.70+/-2.37 per thousand and delta(15)N=6.75+/-1.96 per thousand), whereas surface sediment presented average values similar to seawater POM (delta(13)C=-24.02+/-2.39 per thousand and delta(15)N=7.29+/-2.16 per thousand). Stable isotope values showed that the Danube River influence on marine ecosystems decreased from the North to the South of the Romanian coast. Strong seasonal variations of C and N isotopic signatures were observed in all compartments studied with generally higher values in spring when the river was flooding. 相似文献
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Summary Wind speeds in extra-tropical latitudes are known to be approximately Weibull distributed. Hence a Weibull distribution fitted
to all available data is often used to predict extreme winds. The most extreme values then, however, have little influence
on the estimated parent Weibull distribution, and the accuracy of the extreme value predictions obtained in this manner may
be questioned. In the present paper such a “Weibull method” is compared to a method based on statistical extreme value theory,
“the annual maxima method”. The comparison is based on 30 years of 10 minute wind speed averages measured hourly at 12 meteorological
stations located at airports in Sweden. Results show that the Weibull method generates incorrect estimates of the tails of
the distributions of wind speeds and of the distribution of yearly maximum wind speed, and that serial dependence of individual
measurements has to be taken into account. In addition, it is inherent in the Weibull method that it does not provide any
confidence bounds for the estimates. The annual maxima method avoids these problems. The measurements were rounded, first
to entire knots, and then to m/s. A further, “technical”, result is that if this rounding were disregarded in the estimation
procedure, then the computed standard errors of the parameter estimates would be erroneously low. Hence, if rounding is done,
it should be taken into account in the estimation procedure. We also believe this to be a clear indication that rounding of
the data decreases estimation accuracy. 相似文献
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119.
Michle BOUROT-DENISE Urbain WENMENGA Mireille CHRISTOPHE 《Meteoritics & planetary science》1998,33(Z4):A181-A182
Abstract— Two H4–5 meteorite showers have been reported to have fallen at one month intervals in the Guenie-Gao area, but eyewitness accounts are imprecise. Though subtle mineralogical differences are found between stones with different 21Ne content, these differences are insufficient to confirm that two meteorite falls had occurred. 相似文献
120.
Mireille Christophe Michel-Levy 《Earth and Planetary Science Letters》1976,30(1):143-150
Finely divided products, making a black carbonaceous crust, have coated the chondrules in space. After their agglomeration, a white silica and alumina rich deposit has accumulated between them. Crystalline debris that are found outside the chondrules must not be confounded with the black and white products, which are the only constituents of the low-temperature matrix. These debris are broken chondrules but do not necessarily result from shock effects. Many of them are indeed very fragile, because they are very porous: they contain primary cavities (voids in the crystals, druses) and secondary ones because of selective leaching of part of the glass. The chemical elements leached out of the chondrules may have been reconcentrated in the matrix. 相似文献