Until recently, when solving ecological problems of gas industry in Russia, insufficient attention has been paid to the engeneering protection of objects located in areas of permafrost soils.
The economical development of central Yamal began in late 80's and is carried out, in the main, by individial sites confined to the areas of prospection and development of gas fields.
The development of gas fields went ahead of scientific evaluation of the development of such negative processes as gully channel erosiona: and under these circumstances, the organisation of full scale field investigation at the experimental grounds organised in the framework of the Yamal program of gas fields development, enlisting efforts of leading experts of VNIIGAZ, GGI, VNIIST, PNIIS was very advantageous.
The danger of development of gully and shore erosion is shown on the example of Bovanenkov gas condensate field. The quantitative indexes are indicated.
On the basis of the field observation data and mathematical models of the gully longitudinal profile development and erosion of river banks, prognostic maps were prepared, reflecting the dinamics of the erosion processes alteration in the period of the field operation.
Technical decisions on protection of objects and the territory of Bovanenkov gas condensate field from water erosion processes are presented.
In future, their practical approbation and adaptation to the natural condition of Yamal will allow to create the normative basis for prediction and monitoring of water erosion processes, designing, construction and operation of antierosion facilities, necessary for development of the Extreme Noth Gas fields.
The waters investigated have been sampled in two different areas of the Logudoro region (NW Sardinia, Italy) where Oligocene-Miocene volcanic formations occur. In the Bosa-Montresta area, the dominant rocks are ignimbrites (TR) containing feldspars, ±deeply altered mafic silicates, ±opaques, ±silica phases, ±glass. In the area Sindia-Pozzomaggiore, the dominant rocks are andesites consisting of plagioclase, clinopyroxene, orthopyroxene, opaques ±K-feldspar and microcrystalline groundmass. Secondary minerals related to hydrothermal activity and weathering include chlorite, smectite, kaolinite, calcite, silica phases and minor Fe, Mn-hydroxides, pure K-feldspar, illite, glauconite. In the waters, Mg is usually dominant over Ca (mole/l) and the (Na+K)/Cl ratio (mole/l) is comparable or higher (> 0.88) than in sea water. Most waters are very hard (> 180 mg/l) and thus not very good for drinking. The Mg/Cl ratio is significantly higher (> 0.17) than in sea water (0.097) also in samples with low salinity. Depending on the different mineralogy of the host roks and on the time of interaction, the waters exhibit variable chemical composition. The waters from TR show TDS and hardness ranging from 172 to 714 mg/l and from 28 to 314 mg/l respectively, and a prevalent Na+K and Cl character (Langelier's diagram); on the contrary, the waters from AN have higher TDS and hardness (375-661 and 158-372 mg/l respectively) and exhibit Ca+Mg and HCO3 character. The higher concentration of La, Ce and Al in the waters from TR in respect to the waters from AN is reasonably due to dissolution of silicate glass, which is present in TR and practically absent in AN. Equilibrium/disequilibrium conditions between the phases have been evaluated by log(Q/K), where Q represents the activity products of the components in water solution and K the equilibrium constant of the considered reaction. The waters are saturated in silica phases and sometimes in calcite; K-feldspar and gibbsite are unstable in respect to kaolinite; the stability relationships between kaolinite and smectite is uncertain. Total alkalinity and calcium distribution are determined not only by dissolution of calcite, but also by more complex interactions involving silicates. Low Ca vs total alkalinity in respect to values expected for calcite dissolution may be in part related to Ca exchange with clay minerals. As a consequence of water-soil interaction, the calculated partial pressure of CO2 is about 50 times higher than in the atmosphere.
The aquifer system of Sado's Basin is located in Portugal in the Sado's Cenozoic Basin, which is limited at SE by the Messejana Fault and at NW by the Tejo's inferior valley fault system. The soils that fulfil this basin date from Palaeocene to Quaternary. The Palaeocene is composed by clay sandstones, limestones and conglomerates, follows the Miocene that was originated by a transgress movement and is constituted by four formations: Guizo's Valley formation, Alcácer do Sal formation, Esbarrondadoiro formation and Alvalade formation. The composition of these formations is mainly by conglomerates, sandstones and some clay levels (Pimentel, 1997). These formations which are the most relevant from the hydrological point of view, originate a complex system of stratified reservoir separated by confined or semiconfined layers. Analysis performed in various number of boreholes lead to a physical and chemical characterisation of subterranean water and quality, have been observed that its electric conductivity and pH assume median values of 360 mS/cm and 6, respectively. These values of pH and electric conductivity have a correlation of 0.507, which could indicate the influence of another factors besides mineral dissolution in the water mineralization. The Stiff's diagram had permitted to classify waters as principally calcium bicarbonate and sodium bicarbonate. But exists some cases of calcium or sodic chloride Waters which are resultant from antropic contamination. With these diagrams we can also know that the waters with lower mineralization are explored in the marine miocene formations at higher depth. Also, quality diagram for humans consume classified, generally, waters as acceptable, which is notice by the minute values of sulphate and nitrate. It was only detected some cases of unacceptable waters that were related with cattle-breeding activities. Using HIDSPEC software (Carvalho, 1989) we obtained values of rSO4/rCl, rMg/rCa, rK/rNa, rCl/rHCO3, rNa/rCa e rNa/rCa+Mg that showed a possible groundwater flow. These kind of hydrochemical values indicate the region with lower and higher salt concentrations, which shows possible recharge or discharge areas (Custódio & Llammas, 1976). With this information it was possible identify an area with a divergent chemical evolution, that could be related with the Valverde Horst and that will be confirmed with piezometric and geophysical data. This investigation is part of the Study of the Alentejo's Groundwater Resources (ERHSA) and has the goal for knowledge of the hydrochemical and hydrodynamics characteristics of this aquifer system.
Pimentel N, PhD tesis to FCUL- Terciário da Bacia do Sado, 381, (1997).
Carvalho MRE, Master Tesis- HIDSPEC, um programa de especiação e calculo de equílibrios água-rocha, (1993).
Custodio E, Llamas MR, Hidrologia Subterranea, Vol I e II, 463, (1976).
The Meskala area represent a key sector for understanding the architectural frame of Essaouira basin. This basin corresponds to the most subsiding area of the Atlantic Atlas. The aquifer system of the Creatace includes: i) dolomitics limestones and dolomies of Senonian; ii) fissured and karstified limestones of the Turonian; iii) Shelly limestone of the cenomanian. The lack of impermeable formations with important thickens make this aquifer to be considered as a multilayred system. The aquifer properties of this system are linked to the existence of discontinuities within those formations. The discontinuities are represented by the stratification planes, by the fracturations and also by the development of karstification phenomenon. The analysis of the elevations of summit level surface and the keen analysis of the drainage pattern was made. This enables the recognition of discontinuities, in relation with deep tectonics structures. In this way the stratigraphic correlation of bore hole lead us to confirm the existence of those faulted structure (with variable vertical displacements). Certain faults can be detected which correspond to structures known from field geology (N30, N120 and N160 oriented sets). Those ones corresponds to the hercynian trend which have controlled the architectural frame of Essaouira basin. It's a matter of Horst and Graben structure compatible with N-S constraint. A such architecture presents a direct implications on the hydrogeology of the cretaceous aquifer.
The papers deals with some problems of modeling and predicting concentration of emergency liquid hydrocarbon leakage in two-dimensional and one- dimensional regions of complex form. Lakes and rivers with tributaries can be cited as investigation objects. The formulation and method of solution of parabolic equation of mathematical physics for two-dimensional flow under arbitrary initial and boundary conditions for regions of complex form are given in linear approximation.
A technological cycle includes the following stages:selection of physical and mathematical model; development of numerical algorithm; program preparation; and analysis of computational results. An important feature of the above stages is their interrelation. The computational experiment begins with the selection of mathematical problem. For solving a complex of water quality problems an information system was developed. The system consists of the following blocks: partial differential equations describing the distribution of contamination in water; solution methods - numerical (explicit and implicit) and analytical; qualitative features of physical and mechanical process of contaminants distribution in water; data bank of solved problems results; databank of terms of water quality; finite elements library; library of standard regions for automation of input initial data; data bank of physical and chemical properties; standards for results presentation.
Mathematical monitoring in which instrumental monitoring is taken as basis is presently of particular interest. The following methods are used for designing, operating and predicting water quality management: mathematical modeling, numerical simulation and analysis of response functions. The computation results of some problems are given.
In order to solve the problem of liquid hydrocarbon concentration the turbulent diffusion equation is used. The equation describes the law of conservation of matter and is based on the following assumptions: liquid is incompressible; Re number is so high that one may reject the molecular effect of diffusion; and a quantity of matter evolved in time unit per unit volume is very small and its influence on turbulence can be neglected. The paper describes general formulation, algorithm and parabolic equation of mathematical physics for two-dimensional flow under arbitrary initial and boundary conditions for complex form regions.
The equations describe the distribution of liquid hydrocarbons in water based on two-dimensional flow of liquid. The method of differential assumptions was used for studying the convergence of explicit two-layer two-dimensional finite element schemes for internal nodes of uniform triangle and rectangular nets, i.e. on seven and nine node models. A complex of programs for solving two-dimensional problem with regard to liquid flow velocity in rivers with tributaries is presented. The complex is written on Fortran-90 language. The mathematical model of a river with tributaries is used for predicting water quality in case of emergency accidents. Deterministic models are also used. The complex system is divided into simple subsystems which can be easily used on modern computers.
The analysis of algorithm and method was performed with the help of response functions. The following response of functions are used: half-period sinusoid; delta-function; and Heaviside function. Sinusoidal and Rectangular functions are used as periodic. To assess the accuracy and validity of the developed procedure its results were compared with the other methods.
The nature of fluids contained in deep sedimentary basins is intimately linked with basin formation and evolution. In basins containing petroleum or natural gas, this information can be critical to developing a plan of field exploitation. We have developed and tested a protocol for studying the chemical and chlorine stable isotope composition of waters contained in "dry" oil. We chose the Gyda basin in the North Sea as our test field from which we received samples biweekly over a period of 18 months. The Gyda basin is of Late Jurassic age, containing a sandstone reservoir which overlies a salt dome by several hundred meters. Oil emplacement is thought to have started ~40 Ma ago, with the main stage occurring ~10 Ma. Principal component analysis of our data shows that we have three distinct fluids in the basin which differ in salinity, interelement ratios, and chlorine stable isotope composition. Fluid inclusion data suggests that a mixture of fluids was trapped in the reservoir concurrently with the oil. The systematic way in which the formation waters were sampled during production is consistent with the fluid inclusion data; there are two fluids present in the oil zone, while the third probably resides in a aquifer just below the oil-bearing formation. The composition of the waters in the oil zone varies from salty (~50,000 ppm Cl) to nearly fresh (<200 ppm Cl). The third formation water contains almost 200,000 ppm Cl, and is similar to water sampled during test drilling. The chlorine stable isotope composition of these waters show that they are not directly related to seawater. Chemical and isotope data show that none of the formation waters have been in diffusional contact since emplacement, supporting the hypothesis that crude oil is an excellent barrier to diffusion. The primary source of interaction between water masses occurs now, primarily during oil production. Chlorine isotope data for the two salty formation waters differ by ~1 per mille, both being depleted in the heavier Cl isotope relative to seawater. We are currently modelling the origin of the fluids using a combination of the chemical and isotopic data.
In the Eastern Carpathians and Harghita Mountains of Romania structural investigations and studies about the regional distribution of chemically distinct superficial fluid discharges let to the description of regional-scale fluid flow systems.
The chemistry of the fluid and gas occurrences (water with CO2, H2S, NaCl, HCO3-, hydrocarbons, methan) is an important indicator of their source area. It is possible to demonstrate a good correlation between the composition of the fluids, their regional distribution with respect to the geologic structures, and the structural correlation with expected source rocks in depth (p.ex. lower Cretaceous and Oligocene black shales or Miocene evaporites). Isotopic data of Berner & Stüben (work in progress) and geologic considerations make it possible to distinguish fluids originating from superficial precipation (whole working area) and from diagenese/very low grade metamorphism (hydrocarbons, area of flysch nappes and foreland basin) and to prove the inflow of fluids and gases of mantle origin (area of Neogene/Quaternary volcanism).
From the totality of the data and the large-scale structure of the Eastern Carpathians it is possible to define several hydrologically significant aquifers (p.ex. Oligocene Kliwa sandstone, Miocene Doftana molasse) and to deduce a large-scale fluid flow. The increased precipitations in the topographically high areas of the East Carpathians and the Harghita mountains lead to a forced convection of groundwater, whose flow is strongly influenced by the geological structures. Cold surface water from these topographically high areas move down to the low-lying foreland areas respectively Quaternary intramontanous basins, where they rise back to the surface. From the distribution of the hydrocarbon occurrences and zones of artesic water it is possible to confine these areas of upwelling fluids. These areas are partly connected with an increased heat flow. Minor advection of mantle fluids and gases in the area of young volcanism is probably connected with faults related to the Quaternary intramontanous basins between Covasna and Brasov.
Sines Meso-cenozoic Basin is located at W coast of South Portugal. This region has an important industrial area, and three major villages: Sines, Santiago do Cacém and Vila Nova de Santo André, with Agriculture and Cattle Breeding confined on the oriental Boundary of the area.Mesozoic rocks are mainly composed by dolomite limestones (liasic rocks) and, limestones, oolitic limestones and calciclastic limestones (Dogger and Malm) (Inverno et al, 1993). Lying-over exists miocene's calcareous sandstones, and finally clay and sand of Pliocene. Palaeozoic rocks corresponds to the E Boundary of the basin (Oliveira, 1984). In the major part of the basin don't exist limestone's and dolomite's outcrops, because those are covered by cenozoic sediments. These outcrops are present only on a N-S line between Santiago do Cacém and Melides (Inverno et al, 1993). When we analyse the distribution of water chemical facies, we conclude that calcium-magnesium ones are present on the eastern area as well as at Vila Nova de Santo André region. The presence of dolomite rocks on the oriental area explains the magnesium enrichment, as shows the values of rMg2+/rCa2+ (Aprox. 1). Nevertheless, the presence of magnesium-calcium bicarbonate waters near Vila Nova de Santo André is harder to explain, due the relative level of uncertainty of knowledge about the presence of dolomite rocks under the cenozoic sediments. At the moment available data indicate only the existence of limestones under cenozoic. Water samples from bore-holes exploiting Miocene and Pliocene are mainly calcium- sodium bicarbonate ones. Although some have a magnesium enrichment. This could be due a hydraulic connection between liasic dolomites and cenozoic deposits across Deixa-o-Resto Fault. At Ribeira de Moinhos, near Sines, waters are calcium bicarbonate, with enrichment in chloride and sodium. In general, the carbonate rocks have a primordial role ion the hydrogeochemical evolution of groundwater, as it shows by the high value of correlation coefficient between Electric Conductivity and Permanent Hardness of groundwater (r=0.9). To confirm piezometric data that gives us a groundwater flow from E to W we observed what kind the spatial behaviour of the ratio rCl-/rHCO-3. According with Custodio et al(1976) this ratio grows as the groundwater flow advances. The lowest values presents at E, growing to W, confirming the piezometric data. Finally, the quality of water to drink has been polluted, with a big growing of Nitrate during last decade due a human activity, especially Cattle Breeding. The highest values of Nitrate and location of these cattle breeding sites almost a totally coincidence and worst, both coincides with the regional recharge area of the aquifer. Finally the objective of this study, as well as the ERHSA project, is a complete characterisation of groundwater chemistry and hydrodynamic of each aquifer.
Oliveira, JT, Cominicações serviços geológicos, IGM, Tomo 65, 151.168, (1979).
Inverno C, Manuppella G, Zbyszewski, Pais J, Ribeiro ML, Carta Geológica 1:50 000, IGM, 42-C, (1993).
Custodio E, Llamas MR, Hidrologia Subterranea, Vol I e II, 463, (1976).
Stable isotopes (18O and 13C), tritium (3H) and radiocarbon (14C) have been used in conjunction with chemical data to evaluate recharge mechanisms, groundwater residence time and palaeohydrology within the multilayer and confined Miocene aquifer of Carpentras-Valreas. This small sedimentary basin area is almost 1000 km2 and the thickness of the aquifer reaches 600 meters near to the center. The Miocene confined aquifer consists of sands and sandstones interbeded with clays and marls. Miocene sediments overlay Cretaceous sandstones in the northern section of the basin, and potentially karstified Cretaceous limestones in the southern portion. The multilayer structure of the aquifer entail intricate groundwater flows which complicate the understanding of the system. The Miocene aquifer is an important water ressource for the communities and agricultural activities in the Vaucluse and declining potentiometric levels in the system are of concern for the long-term sustainability of the resource.
This study is based on 2 sampling campaigns carried out in november 1997 and august 1998, and also includes bibliographic data from studies performed over the past decade on the same area. 18O composition for all groundwater samples recently collected ranges from -6.3‰ to -8.55‰ and can be divided into 2 groups : on the one hand 18O values close to the actual regional mean annual-weighted composition of meteoric waters (close to -6.7‰), on the other hand, significantly depleted values close to -8‰. Measured radiocarbon concentrations (21 samples) range gradually from 1 pcm in the center of the basin to about 86 pcm on the border (tritium bearing waters, corresponding to the recharge area). The Fontes & Garnier model (1979) provides a 14C age up to 29500 years for the groundwaters from the center of the basin.
Confined old groundwaters from the center of the basin are significantly depleted in 18O with respect to younger groundwaters, and may have been recharged under different climatic conditions from actual waters. The depletion in the 18O isotopic composition of groundwater which occurs between 13000 and 20000 years B.P. can be caused by lower temperature at the time of the recharge. Old groundwaters (20000 to 29500) are isotopically lighter than younger groundwaters by up to 1.5 ‰. Using the following temperature- relationship, 18O = 0.55‰°C-1 (Dansgaard, 1964), this shift would represent a decrease in recharge temperature of approximately 3°C. This value is consistent with previous studies carried out in other western european regions (Bath et al., 1979 ; Blavoux et al., 1993) and points out the transition from the Late Glacial to Holocene (Rosanski et al., 1997).
Bath AH et al., IAEA, Neuherberg Symposium, 545-568, (1979).
Blavoux B et al., IAEA, Vienna Symposium, 293-305, (1993).
Dansgaard W, Tellus, XVI, 436-468, (1964).
Fontes JC & Garnier JM, Water Resources Research, 15, 399-413, (1979).
Rosanski Ket al, Hydrological Sciences Journal, 42, 725-745, (1997).
Remote sensing presents an invaluable tool in fields where spatial information is required. For example, many solutions of hydrological parameter modelling problems need area wide or spatially distributed input data in order to replace single local measurements. For topics like land use evaluation or digital elevation model calculation, remote sensing techniques have proved their potential. For other subjects, like soil moisture or roughness parameter values, image processing techniques are still under investigation.
Sensors working in the visible and infrared domain are not suited for soil moisture quantification due to unfavorable signal to noise ratio. On the other hand, microwave sensors (especially active microwaves) are sensitive to surface properties (vegetation cover, soil moisture, roughness, soil type) and imaging configuration (local incidence angle, polarization, frequency). These properties define the radar imagery as an appropriate instrument for retrieving the spatial distribution of bio-physical parameters. This work focuses on the problem of separation and thus extraction of interrelated parameters, namely moisture and roughness, from a series of radar images.
For this purpose, in Spring 1997, the Experimental Airborne Synthetic Aperture Radar (ESAR) of DLR Oberpfaffenhofen twice acquired multipolarization and multifrequency radar image data over a 3 km x 4 km agricultural catchment in the South West of Germany. At the same time, field measurements of samples of surface roughness, volumetric and gravimetric soil moisture have been performed on several representative agricultural fields.
After geometric and radiometric correction, the radar image data have been introduced into inversion models. The semi-empirical DUBOIS-model has been applied, because of its main advantage to tolerate sparsely vegetated ground surface and to estimate soil moisture within narrow error limits. In this paper, a review of this model will be described by adapting the empirically determined algorithm coefficients. The results produced up to now show a better agreement with the ground truth measurements. Indeed, the soil moisture in the 0 to 15 cm surface layer and the roughness estimation could be reduced to 3.5 vol-% and 0.2 cm RMS error limits respectively. In a second part, other parameters will be proposed for integration into the model in order to improve the results further.
The metamorphism of snow to glacier ice is characterised by the transitional material firn which, from a hydrological point of view, behaves as a porous medium. In the accumulation area of a glacier, meltwater infiltrates the surface snow or firn and percolates through the porous layer until it reaches the firn-ice transition, defined as the level where firn becomes impermeable to water. Above this transition a water-saturated layer or aquifer is formed.
We investigated the drainage of the firn aquifer through tracer tests and water level measurements. We injected dissoved salt (NaCl) into the firn aquifer and measured electrical conductivity (EC) in surrounding boreholes. From these measurements we were able to calculate flow velocity in the aquifer. In addition, we measured EC profiles in different boreholes to determine the depth of the porous firn. We used two different fluorescent dye tracers, Fluorescein and Rhodamine B. 5 kg of Fluorescein, dissolved in 100 l of water, was injected into the firn aquifer through a bore hole and 12 kg of Rhodamine B, also dissolved in 100 l of water, was sprayed on the firn surface. Water samples were taken in surrounding boreholes and at the terminus of the glacier about 3 km from the injection site.
Measurements of spatial variations of the firn water-table level and observations of drainage from the aquifer into crevasses lead us to the conclusion that crevasses play a major role in the drainage of the firn aquifer if they are connected to the englacial drainage system. The depth of the firn-ice transition was determined to be 20-21.5 m below the glacier surface based on the EC profiles measured in boreholes. The dye-tracer test showed, that dye injected into the firn aquifer reached the terminus of the glacier about 6 days after injection whereas dye which was sprayed on the firn surface emerged at the proglacial stream after 10 days. Assuming that both tracers travelled the same way through the glacier drainage system, the time lag of the two dyes can be used to estimate percolation velocity in the unsaturated part of the firn layer. With a time lag of four days and a percolation distance (from surface down to the water saturated layer) of 20 m, percolation velocity is estimated to be 0.21 m h-1. The investigation of drainage characteristics of the firn area of Storglaciären is the first step in understanding the influence of hydrological processes in the firn area on the hydrology of the whole glacier. We can quantify the delay of run-off from a glacier basin and the temporal water storage within the glacier. This will lead to the development of a process-based model for glacier drainage which will incorporate water flow in the firn layer as well as flow through the englacial and subglacial drainage system.
Rare Earth element (REE) analyses were obtained from river waters sampled along the Moselle River (NE France), from its source in the Vosges Mountains to the south of the city of Nancy, over a distance of ca. 150 km. Samples were filtered to 0.45 microns, acidified with distilled nitric acid and stored in acid cleaned teflon bottles prior to the REE analysis, using ICP-MS. The river flows over three different rock types, from granites and gneisses in the source region, to sandstones in the middle, and finally over limestones for the last 70 km. The chemistry of some major cations (Si, Al, Ca, Fe, Mg) and trace elements (Sr, Li) in the water samples seems to be controled by the catchment rocks.
REE concentrations in samples varies from 1 to a few tens of ppt, which are similar to concentrations reported in the litterature for river waters having pH varying from 7 to 8.5. In terms of concentrations normalised to Al, enrichment factors relative to shales calculated for La and Nd range from 7 (near the source region) and drop to 1 for the sample having the highest pH (8.5). This feature is coherent with the solubility of light-REE in fonction of the pH. In contrast, Ce enrichments vary between 1 and 2 for pH values of 7-7.5 (source region) and increase to 3 at pH of 8.5. When normalized to shales, the samples show enrichment in heavy-REE relative to light-REE, with (La/Yb)N varying between 0.18 and 0.03. The normalized profils display also negative Ce anomalies for all the samples, which anomalies vary from 0.2 to 0.8 when defined as: Ce anomaly = 3*(Ce)n/(2*(La)n+(Nd)n). The Ce anomaly correlate positively with Fe and Ca concentrations and also with the lithology of the catchment rocks, i.e. the anomaly tends to fade out in water flowing onto carbonate rocks. Futhermore, waters having the most important Ce anomaly (0.2-0.6) display the lowest pH values (7-7.5), whereas those having light Ce anomaly (0.7-0.8) tend to have pH higher than 7.5. The correlation between the Ce anomaly and pH observed for the Moselle waters is the opposite to what someone would expect considering the measured values obtained for large rivers and estuaries. A positive correlation between the Ce anomaly and pH was also observed for in the Alsace plainrivers and the Rhine River (carbonate-rich waters) just East of the Vosges Mountains (Tricca, 1997). This implies that the chemistry of secondary phases such as colloidal material may play a major role for REE fractionation, specially in carbonate-rich river waters.
Tricca A, Doctor Dissertation/Strasbourg, (1997).
Stable environmental isotopes, abundance of majors ions and chemical composition of atmospheric depositions have been observed on the western part of the Mediterranean basin since 1997. We use a network including 10 stations located in the seaside countries, managed by the University of Avignon for 2 years, and data provided by the International Atomic Energy Agency network since 1965. Two approaches have been carried out to show spatial and temporal variations of precipitations isotopic content: a daily sampling on 10 stations for 4 months each year and an other one on Avignon during 2 years.
In order to show spatial variations during an atmospheric disturbance, we have collected daily samples at the 10 stations of our network on October, November, March and April (the most rainy months of the Mediterranean area) to link variations of the mediterranean precipitations isotopic content to the trajectories of air masses and to the stations locations. Study of oxygen-18 and deuterium daily values at each station allows to precise phenomena (such as continental effect in connection with meteorological data, altitude effect, refill over the mediterranean sea), which may entail isotopic content variations. Then we can define a typology of precipitations isotopic content evolution related to air masses'back trajectories.
On the other hand, a daily sampling is done on Avignon since march 1997 to underline the importance of origins and trajectories of air masses in the determination of precipitation isotopic content and in the knowledge of the input function of regional aquifers. Theses data show a relation between precipitations (isotopes, chemistry and atmospheric depositions), air masses (origins and trajectories) and meteorological parameters (temperature, amount of precipitation and air humidity). We have defined 5 main air masses trajectories : mediterranean (21% of events), north atlantic (16%), central atlantic (26%), mixing between mediterranean and north atlantic (18%), and mixing between mediterranean and central atlantic (19%). So the discrimination between mediterranean air masses influence enriched in heavy isotopes (mean precipitation isotopic value = -4.69‰) and atlantic ones relatively depleted (mean precipitation isotopic value = -6.34‰) is possible. According to the whole period mean weighted isotopic value of -4.80‰ on Avignon, the weight of mediterranean precipitations in the recharge of regional aquifers seems to be more important than atlantic one.
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