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991.
Assessing rapid environmental change using geoindicators 总被引:1,自引:1,他引:1
A. R. Berger 《Environmental Geology》1997,32(1):36-44
Geoindicators are high-resolution measures of short-term (<100 years) surface or near-surface changes in earth processes,
and phenomena that are significant for environmental monitoring and assessment. They are based on standard concepts and procedures
and can be used to track changes in fluvial, coastal, desert, mountain, permafrost and other terrestrial areas. Geoindicators
assess both catastrophic events and those that are more gradual, but evident within a human lifespan. Most deal with changes
on the landscape (0.1–10 km) and meso-scales (10–100 km), but some, such as relative sea level and volcanic unrest, have regional
and global dimensions. Some are complex and costly to measure, others are relatively simple and easy to apply. Geoindicators
can also be used to unravel trends over the past few centuries and longer through paleoenvironmental research, thus providing
the important baselines against which human-induced and natural stresses can be better understood. Geoindicators have been
designed by the International Union of Geological Sciences as an aid to state-of-the-environment reporting and long-term ecological
monitoring.
Received: 26 July 1996 / Accepted: 1 November 1996 相似文献
992.
The Bengal basin, Bangladesh, represents one of the most densely populated recent floodplains of the world. The sediment
flux through the basin is one of the highest on a global scale. A significant portion of this sediment load find its sink
in the basin itself because of its lower elevation and frequent flooding. The textural, mineralogical and chemical nature
of the sediments thus have an important bearing on the environmental quality of the basin as well as for the Bay of Bengal.
The sediment load of the Ganges-Brahmaputra-Meghna (GBM) river system consists exclusively of fine sand, silt and clay at
their lower reaches within the Bengal basin, Bangladesh, and is deposited under uniformly fluctuating, unidirectional energy
conditions. The sediments have a close simitarity in grain size with the sediments of the surrounding floodplain. The mineral
assemblage is dominated by quartz and feldspars. Illite and kaolinite are the major clay minerals, and occur in almost equal
proportion in bed sediments. The heavy mineral assemblage is dominated by unstable minerals which are mostly derived from
high-rank metamorphic rocks. The characteristic smaller grain-size, i.e. having large surface-to-mass ratios, and the mineralogy
of sediments suggests that they are susceptible to large chemical adsorptive reactions and thus could serve as a potential
trap for contaminants. However, the sediments of the GBM river system in the Bengal basin, Bangladesh, shows lower concentration
of Pb, Hg and As, and a marginally higher value for Cd as compared to that of standard shale. Considering population density
and extensive agricultural practice in the basin, the sediments can in the long run become contaminated.
Received: 9 November 1994 · Accepted: 18 June 1996 相似文献
993.
994.
Effects of geology and human activity on the dynamics of salt-water intrusion in three coastal aquifers in southern Spain 总被引:4,自引:0,他引:4
Mathematical modelling of salt-water intrusion processes in three aquifers on the southern coast of Spain (Río Verde, Río
Vélez and Castell de Ferro) reveals that, although all three systems are subject to the same climate and seasonal over-exploitation,
geological and human factors have very different effects on the dynamics of contamination. In the Río Verde aquifer, the most
important influence is the high volume of extractions occurring during the dry season; in Río Vélez, the intrusion is strongly
controlled by infiltration of water from the river to the aquifer, and, in the Castell de Ferro system, an intensely karstified
carbonate massif lying in contact with both the sea water and the detrital aquifer represents the main entrance point for
influx of sea water and subsequent washing of the aquifer. We have undertaken a mathematical simulation of various possible
measures to counteract intrusion, according to the specific characteristics of the process in each aquifer. These measures
include artificial recharge, use of natural recharge from the river as a hydraulic barrier, and the construction of a low-permeability
barrier.
Received: 5 December 1995 · Accepted: 12 April 1996 相似文献
995.
996.
A bivariate meta-Gaussian density for use in hydrology 总被引:3,自引:0,他引:3
K. S. Kelly R. Krzysztofowicz 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(1):17-31
Convenient bivariate densities found in the literature are often unsuitable for modeling hydrologic variates. They either
constrain the range of association between variates, or fix the form of the marginal distributions. The bivariate meta-Gaussian
density is constructed by embedding the normal quantile transform of each variate into the Gaussian law. The density can represent
a full range of association between variates and admits arbitrarily specified marginal distributions. Modeling and estimation
can be decomposed into i) independent analyses of the marginal distributions, and ii) investigation of the dependence structure.
Both statistical and judgmental estimation procedures are possible. Some comparisons to recent applications of bivariate densities
in the hydrologic literature motivate and illustrate the model. 相似文献
997.
998.
The separation of the influence of nutrients and climate on the varve time-series of baldeggersee, Switzerland 总被引:7,自引:2,他引:7
The varve data-set from a freeze-core taken in the deepest part of Baldeggersee was subjected to different multivariate statistical
analyses in order to estimate the amount of variance in the varve thickness measures explicable by past climate and by the
trophic state of the lake. A comparison of two different time-periods (1902 to1992 versus 1920 to 1980) revealed that the
lake restoration programme since 1982 has had a significant impact on the formation of the seasonal layers. Results of the
partitioning of the variance in the varve thickness measures showed that about two thirds of the variance are unexplained
by a climate and trophic state model and that trophic state explains 6%, whereas climate accounts for about 28% of the variance
before the effect of lake restoration had a strong impact on the varves. Among the climate parameters the amount of annual
precipitation is a strong predictor for explaining the thickness of both dark layer and total couplet thickness, whereas summer
precipitation is important for the thickness of the light layer. 相似文献
999.
—An algorithm has been developed to compute the dispersive and dissipative seismic response using FUTTERMAN’S (1962) third attenuation-dispersion relationship. In the computation, frequency-dependent velocity and quality factor Q have been used but in the case of the nondispersive synthetic seismogram, frequency-independent velocity has been used. The model’s parameters are density, phase velocity, quality factors and thicknesses of the layers. Dispersive and nondispersive synthetic seismograms have been computed with and without absorption for a layered earth geological model. Fast Fourier transform (FFT) technique has been adopted for converting the frequency domain response into the time domain. The frequency spacing, Δf = 0.976?Hz, has been considered to avoid the aliasing effect. The results have revealed changes in the reflected waveforms in the frequency domain as well as in the time domain for absorption and dispersion cases. It is also concluded that dispersion reduces the arrival time and this effect is increasing with the travel time. The effect of constant Q on the seismic response has also been studied. 相似文献
1000.
K. Holub 《Pure and Applied Geophysics》1997,150(3-4):435-450
—Mining-induced seismicity associated with longwall face operations in the Ostrava- Karviná coal mines, Czech Republic, has
been investigated in order to establish the conditions leading to a focal zone generation. The study, based on macroseismic
and instrumental observations, proved that seismicity is influenced by natural as well as mining conditions. The first group
includes the influence of faults, washouts and red beds, while the second one is represented by shaft and/or crosscut safety
pillars and various types of remnant pillars. All the cases discussed show that many focal zones are generated in overstressed
strata as a consequence of interaction of natural conditions and/or old workings with the active coal face.
Received June 18, 1996, accepted March 10, 1997 相似文献