Clay-rich deposits are usually considered as hard materials to be eroded by wind. Data from both surface monitoring and field survey at the dry-up bottom of Aiby Lake present that clay-rich lacustrine deposits are easily broken down and eroded away by wind in the seasonal alternation process under the natural arid environment, and are the significant source of air dust. The surface of the clay-rich deposits is broken and softened by the freezing-and-thawing action in winter season and/or by salt and alkali action with precipitation. Impact of wind-input particles and plow of plant branches with wind force drive the clay-rich sediments moving. Wind picks up the clay pebbles and repeats the impaction further-ward onto the dry-up surface. Tremendous fine materials, including soft salts, are contributed to air dust, and transported in long distance.
Interaction of groundwater with As-bearing rocks has been proposed as one of three main sources of arsenic at Zimapán valley,
México. The complexity of the geology and hydrogeology of the valley make it difficult to identify the natural causes of arsenic
poisoning. Samples from the different rock outcrops and water from wells tapping various rock formations were analyzed. The
rocks from mineralized areas contained higher concentrations of arsenic with respect to the same formations in non-mineralized
areas. The arsenic minerals arsenopyrite, scorodite, and tennantite were identified in some rock samples. Higher temperature
and lower Eh values were found for those wells containing more arsenic. The physicochemical characteristics of these naturally
polluted well waters could be produced by arsenopyrite oxidation. The geochemical model PHREEQCI was used to perform the inverse
modeling of two wells located along the same fault. Arsenopyrite oxidation and scorodite dissolution appear to be the geochemical
processes producing the natural pollution according to the model. The release and transport of arsenic mainly occur through
fractures within the cretaceous limestones where the most productive wells are drilled. The presence of arsenic should be
expected also in other formations near mineralized zones in the Zimapán Valley. Field determinations of Eh and T could be
used to detect potentially polluted wells.
Received: 29 April 1999 / Accepted: 18 July 2000 相似文献
A model based on numerical solutions, which allows for solving the dispersion equation under variable recharge and velocity conditions, is developed to simulate solute transport in conduit flow aquifers during flow recession periods. As an example, the evolution of a tracer in the little known karst conduit that links the sinking stream of Oma valley to the Olalde spring is investigated in the karstic region of Santa Eufemia-Ereñozar (Basque Country, Spain). The model, with different hypothetical structures, allows for obtaining series of tracer breakthrough curves, which are fitted to experimental data using an optimization algorithm. These results, although they can be used to simulate the tracer evolution between the two points considered, do not allow for determining the internal structure and spatial disposition of contributions in the aquifer. 相似文献
A semi-numeric method by Herrera, Jiménez and Ruggeri is used to study the evolution of general relativistic spheres in the free streaming radiation approximation when specific contraction schemes are imposed and for particular oscillatory radiation profiles. On one hand, the emerging radiation is studied for oscillating contracting spheres, on the other, the variation of the boundary surface is analyzed when a pulsating profile is provided. We considered three particular equations of state previously studied. It is found that the oscillatory frequency of the surface for the equations of state considered coincide with the frequency of the oscillation for the radiation profile. 相似文献
The effects of the thermal conduction on the linear stability analysis of an optically thin plasma with metallicity Z = 1 and including chemical relaxation time effects, is carried out. Generally, a further stabilizing effect on the unstable modes and an increasing of the damping of stable modes appear for disturbances with values of wave number large enough. However, the oscillating mode appearing at low temperature remain unaffected by the thermal conduction. 相似文献
We present 190 astrometric positions of comet Halley and 46 positions of comet Giacobini-Zinner obtained at Fabra Observatory during the 1985/1986 campaign by the astrometric network of the International Halley Watch. 相似文献
In gully erosion, the detached soil can be transported over long distances along the landscape. The eroded material can be redistributed and/or deposited on the soil surface along the landscape and then eventually be buried by newly eroded and deposited sediment. There can be significant variability of the soil conditions (e.g., texture and moisture content) over which the eroded material travels. The eroded material can be detected through the use of magnetic tracers attached to or mixed with the eroded soil. In this study we evaluated the degree to which the magnetic signal of the magnetite is conditioned by (i) burial depth of tracer, (ii) condition of soil covering the tracer and (iii) tracer concentration. In the laboratory containers were filled with a specific soil. In the filling process, a 0.5-cm layer of a soil–magnetite mixture was interspersed in the soil profile at a certain depth. Experiments encompassed three different soil–tracer concentrations (1000:1, 200:1, 100:1), four burial depths of tracer (0 cm, 3 cm, 5 cm and 10 cm from soil surface), and two different soils. In each case, the magnetic susceptibility was measured with a susceptometer. Experiments were repeated with different soil moisture contents. If the tracer is located under the soil surface, a minimum soil–tracer concentration of 200:1 is required for its correct detection. The intensity of the magnetic signal decreases dramatically with the vertical distance of the tracer from the soil surface. The maximum detection depth for the tracer's magnetic signal is strongly dependent on the natural magnetic susceptibility of the soil, which masks the tracer's signal. Variation in soil moisture content does not significantly affect the magnetic signal. For extensive field studies, the soil–tracer volume to be handled would be very high and therefore, it is necessary to explore new tracer application techniques. 相似文献