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151.
Loreto Donoso Rodrigo Romero Alberto Rondón Emmanuel Fernandez Pedro Oyola Eugenio Sanhueza 《Journal of Atmospheric Chemistry》1996,25(2):201-214
The levels of low molecular weight hydrocarbons were measured at pristine sites and rural locations affected by hydrocarbon emissions from oil and gas producing fields in Venezuela. At the clean sites, lower concentrations of C2 to C6 alkanes were observed, whereas, in comparison with remotes sites, very much higher levels were measured at the polluted sites. Alkenes present relatively high concentrations, with isoprene being the most abundant, all over the study region. The main sources of alkenes are likely to be natural, mainly from vegetation. The levels of alkanes recorded at the clean sites and the alkene levels found everywhere in the region are in agreement with the values reported for other clean sites in the tropics. The increase of ozone production capacity due to the anthropogenic emissions of alkanes from oil and gas fields was estimated. Due to the presence in the atmosphere of important amounts of naturally emitted isoprene, ethene and propene, which makes a substantial contribution to the reactivity of the hydrocarbon mixture, a small increase (<5%) was estimated to occur in the capacity of the ozone production at a regional scale during the rainy season. 相似文献
152.
Ian R. Calder G.S. Kariyappa N.V. Srinivasalu K.V. Srinivasa Murty 《Journal of Hydrology》1992,130(1-4):17-25
Flow rates calculated using the deuterium tracing method were compared with measurements of direct water uptake of excavated trees which had been inserted into water containers. Taking into account that the tracing method provides an estimate of the weighted mean flow rate over the period that the tracer pulse is present (the weighting factor is the relative concentration of the tracer as measured at the sampling point) agreement was obtained within the experimental error (about 10%) associated with the tracing method. 相似文献
153.
Numerical simulations show that water and oil/oily-contaminant migration are controlled by regional fluid-potential fields which may be modified locally by highly permeable lenses and buoyancy. In addition, fluid potentials are coupled to the distribution of oil/oily-contaminant via relative permeability and capillary-pressure curves. As saturation distributions evolve through space and time, so do the water and oil fluid-potential surfaces. The importance of capillary forces in oil contaminant migration and entrapment is illustrated by the fact that, in certain cases, lenses fill from above, even when the migrating fluid is lighter than water. Capillary forces operating in conjunction with lenticular reservoirs create excellent dynamic oil traps by allowing free passage of water, while retaining and concentrating oil. The analysis of oil (oily-contaminant) migration using numerical modeling and potentiometric-surface techniques is useful for the prediction of migration pathways and potential accumulation sites. On the other hand, identifying acatual accumulations from fluid-potential measurements (via inverse modeling) is not possible because fluid potentials are not uniquely dependent on saturation. 相似文献
154.
S. Jaskó 《Environmental Geology》1992,20(3):213-218
The study of Pleistocene and Holocene fluviatile deposits in river valleys is important for environmental protection. Well records allow the mapping of clay, sand, and gravel beds under recent valley floors. Such surveys can also locate active tectonic zones. This technique helps in assessing potential seismic hazards for large industrial sites.The study of fluviatile sediments under recent valley floors is relevant to environmental studies for another reason as well. The permeability characteristics of these formations have a decisive bearing on the spreading of various pollutants entering the rivers or the groundwater along the rivers. Thus, the knowledge of subsurface formations is essential for the siting of factories with dangerous products and deposits of hazardous waste.Fluviatile sediments along the Hungarian stretch of the Danube Valley have been explored by thousands of shallow boreholes. These allowed the geotectonical and hydrogeological study of sites for completed and planned dams and nuclear power stations and assessing potential environmental hazards. 相似文献
155.
Due to its physical and chemical properties, areas with a loess mantle of proper thickness favour arable farming. Loess as a parent material promotes the formation of soils of good structure, nutrient supply and water budget. The ongoing land evaluation project places particular emphasis on the consideration of parent material in its scoring system as soil and climatic parameters are assessed in conjunction with the grain size composition of subsurface material and soil texture.A test area most suitable for the presentation of the method seems to be a sandy alluvial fan with loess mantle and this circumstance allows the contrasting of the agroecological potentials of soils developed on the two parent materials of different nature.The favourable water storage properties of loess make this deposit particularly valuable under the conditions of climatic aridification. The geographical information system applied here is capable of simulating the agroecological potential changes caused by reduced precipitation, increased evaporation and dropping groundwater levels.The research for this paper was carried out as part of the MEDALUS II (Mediterranean Desertification and Land Use) collaborative research project. MEDALUS II was funded by the EC under its Environment Progamme, contract no. EV5V 0128/0166. A grant was also provided by the OTKA (Hungarian National Science Foundation), project no 1278. The support is gratefully acknowledged. 相似文献
156.
The geothermal area on Reykjanes, Iceland has been investigated mineralogically. The temperature within the studied area is very variable from 30–300° C. Mineral zones corresponding to the temperature conditions in the area are found. Accidental changes in the geothermal system are also reflected in the mineralogy by formation of anhydrite. Changes in temperature conditions in the field are indicated by epidote occurrence at 40° C and retrograd formation of montmorillonite. 相似文献
157.
Micron-scale iron-distribution patterns in sphalerite grains derived from two contrasting mineral assemblages of the Nagybörzsöny hydrothermal ore deposits (high temperature stockwork and low temperature veins), were determined with electron microprobe, pointcounter and continuous chart-recorder measurements along radial profiles. A significant oscillation of iron-content ranging from 8.1 to 18 per cent for stockwork and 4.3 to 15.8 per cent for veins took place during crystal growth. Homogeneous crystal cores are characteristic for vein-filling, while replacement occurring in deeper levels of the stockwork results in mosaic cores. Frequent oscillation of iron content is relevant to top-sections of the ore bodies, copious supply being recorded in recurring shells, whereas scanty, unilateral ones produce crescents arranged in onion-like structure.
Zusammenfassung Bestimmungen der Eisenverteilung wurden an Zinkblendekörnern aus zwei verschiedenen Mineralparagenesen (Hochtemperatur-Stockwerk und Gangfüllungen niederiger Bildungstemperatur) der hydrothermalen Erzlagerstätte Nagybörzsöny im Mikronbereich durch Elektronen-Mikrosonde-Messungen (Punktzählung und kontinuierliche Band-Registrierung) entlang radialer Profile vorgenommen. Bedeutende Schwankungen des Eisengehaltes (8,1–18% für das Stockwerk und 4,3–15,8% für die Gänge) wurden registriert. Homogene Kristallkerne kennzeichnen die Gangfüllungen, wogegen in tieferen Horizonten des Stockwerks Verdrängungen zur Bildung von Kristallen mit Mosaik-Kernen führen. Allgemein ist in den Gipfel-Partien der Erzkörper Fluktuation des Eisengehaltes häufig. Gleichmäßiger Nachschub während des Kristallwachstums führte zu ringförmigen Zonen gleicher Eisengehalte, spärlicher oder einseitiger dagegen zu halbmondförmigen Hüllen mit Zwiebelstruktur.相似文献
158.
Reference is hereby made to the characteristics of seismic recordings of volcanic origin as obtained at the Vesuvian Observatory up to date. The new seismic equipment recently put into operation and consisting of four three-component seismographs set up on the slopes of the Vesuvius Great Cone is also described. The characteristics of the records obtained by the above said equipment are hereby explained and related to the activity of the volcano. 相似文献
159.
We report preliminary results from a series of numerical simulations of the reduced magnetohydrodynamic equations used to describe the dynamics of magnetic loops in active regions of the solar corona. A stationary velocity field is applied at the photospheric boundaries to imitate the driving action of granule motions. A turbulent stationary regime is reached, characterized by a broadband power spectrum Ek approximately k-3&solm0;2 and heating rate levels compatible with the energy requirements of active region loops. A dimensional analysis of the equations indicates that their solutions are determined by two dimensionless parameters: the Reynolds number and the ratio between the Alfvén time and the photospheric turnover time. From a series of simulations for different values of this ratio, we determine how the heating rate scales with the physical parameters of the problem, which might be useful for an observational test of this model. 相似文献
160.
Diego Gómez Pablo Salvador Julia Sanz Mikhail Urbazaev José Luis Casanova 《地理信息系统科学与遥感》2020,57(6):813-829
ABSTRACT The climate in southern Iceland has warmed over the last 70 years, resulting in accelerated glacier dynamics at the Solheimajoküll glacier. In this study, we compare glacier terminus locations from 1973 to 2018, to changes in climate across the study area, and we derive ice-surface velocities (2015–2018) from satellite remote-sensing imagery (Sentinel-1) using the offset-tracking method. There have been two regional temperature trends in the study period: cooling (1973–1979) and warming (1980–2018). Our results indicate a time lag of about 20 years between the onset of glacier retreat (?53 m/year since 2000) and the inception of the warming period. Seasonally, the velocity time series suggest acceleration during the summer melt season since 2016, whereas glacier velocities during accumulation months were constant. The highest velocities were observed at high elevations where the ice-surface slope is the steepest. We tested several scenarios to assess the hydrological time response to glacier accelerations, with the highest correlations being found between one and 30 days after the velocity estimates. Monthly correlation analyses indicated inter-annual and intra-annual variability in the glacier dynamics. Additionally, we investigate the linkage between glacier velocities and meltwater outflow parameters as they provide useful information about internal processes in the glacier. Velocity estimates positively correlate with water level and negatively correlate with water conductivity between April and August. There is also a disruption in the correlation trend between water conductivity and ice velocity in June, potentially due to a seasonal release of geothermal water. 相似文献