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41.
Assessment of groundwater quality and contamination problems ascribed to an abandoned uranium mine (Cunha Baixa region,Central Portugal) 总被引：2，自引：0，他引：2
The assessment of groundwater quality and its environmental implications in the region of the abandoned Cunha Baixa uranium
mine (Central Portugal) was carried out from 1995 to 2004. Shallow groundwater is the major water supply source for irrigation
in the neighbourhood of Cunha Baixa village. Water samples from the mine site as well as from private wells were collected
in order to identify the mining impact on water composition, the extent of contamination and the seasonal and temporal groundwater
quality variations. Some of the sampled private wells contain waters having low pH (<4.5–5) and high values of EC, TDS, SO4, F, Ca, Mg, Al, Mn, Ni, U, Zn and 226Ra. The wells located through the ESE–WSE groundwater flow path (1 km down gradient of the mining site) display the most contaminated
water. In the summer season, the levels of SO4, Al, Mn, and U were 50–120 times higher than those registered for uncontaminated waters and exceeded the quality limits for
irrigation purposes, presenting soil degradation risks. Nevertheless, this study indicates that groundwater contamination
suffered a small decrease from 1999 to 2004. The bioaccumulation of toxic metals such as Al, Mn, and U within the food chain
may cause a serious health hazard to the Cunha Baixa village inhabitants. 相似文献
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43.
A Multistep Methodology for Building a Stochastic Model of Gold Grades in the Disseminated and Complex Deposit of Casas Novas in Alentejo,Southern Portugal 
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下载免费PDF全文 This paper proposes a multistep approach for creating a 3D stochastic model of gold grades in a complex disseminated auriferous deposit located in the Alentejo region, southern Portugal. The approach involves the following steps: (i) the creation of a 3D low‐resolution vector object model of two geological domains that better discriminate gold grades; (ii) the definition of three intervals for gold grades (low, intermediate, and high values); (iii) the estimation of the probability of each grid block belonging to each interval constrained by the geological domains; (iv) the calculation of local conditional cumulative distribution functions (CCDFs) of gold grades, for each block, taking into account the geological domains and the borehole data; and finally (v) the simulation of images of gold grades. The results demonstrate the usefulness and accuracy of the proposed procedure, as they are in compliance with the conceptual model, the distribution laws are conditioned by the geological domains, and the transition of grades between domains is continuous. 相似文献
44.
In recent years some authors have given a certain amount of attention to towed seismic reflection acquisition systems. Based on some of these works we sought to design and test a system making use of currently available geophones instead of specifically designed sensors as employed in some previous works. Thus, bearing in mind that the geophone's characteristics are achieved in the conditions that they are originally designed to be employed in, i.e., coupled with a spike driven into the ground, we devoted our attention to some of the variables involved in the geophone's performance, namely the total weight, the effect of a spikeless geophone and the surfaces on which the geophone is placed. Previously, we had experimentally verified some variations in the signal response due to coupling geophones in different surface materials, such as hard soil, asphalt and concrete pavement and we noticed that these surface materials were in fact an important factor in the overall response. Hence, these materials, or as we also called them coupling agents, could be employed as a base material in the construction of a mobile seismic acquisition device composed of blocks of a certain size, on which the geophone would be then inserted and thus making it into a spikeless surface towable system. Therefore, various materials were tested in order to select one that could maintain a similar fidelity to that of the spike coupled geophone and thus contribute towards building a more time efficient and towable geophone and block system. Pinging tests revealed variations in the coupling frequency and damping characteristics of each coupling agent and from all of these tested materials one was selected for field comparative tests with the normally planted geophones with spike coupling. Finally a seismic reflection profile was acquired simultaneously with both systems, i.e., spike coupling versus cement block coupled geophones. This field test showed similar results in terms of signal levels and frequency content and therefore it was possible to observe the presence of the same reflectors and other seismic events in either of the time sections. With this experiment we propose not only a system that allows a time efficient seismic field operation but we also aim to encourage more research into the response dependency of the coupling agent of which the towable base block is made of. 相似文献
45.
An integrated 3D constant offset GPR and resistivity survey on a sealed landfill — Ilhavo,NW Portugal 总被引：1，自引：0，他引：1
Owing to their nature landfills are challenging targets for high resolution Near Surface Geophysics.Herein it is described an integrated high resolution geophysical survey over the Ilhavo landfill sealed about a decade ago.The first aim of the survey is to investigate the time evolution of the contamination plume of the landfill since operations stopped and sealing took place.The second, and main objective, is the study of the landfill itself, that is, to carry out a high resolution 3D geophysical survey over it in order to investigate the thickness and effectiveness of the top cover, the thickness and sealing conditions of the landfill bottom and, finally, to investigate its internal structure.To fulfill these objectives an integrated 3D constant offset GPR and resistivity survey was designed. The interpretation of the geophysical data was carried out together with local borehole and hydrogeological information, so that, the ambiguity and uncertainty of the interpretation was reduced considerably and the usefulness of the methods were assessed. 相似文献
46.
Tjebbe M. Hepkema Huib E. de Swart Antonios Zagaris Matias Duran–Matute 《Ocean Dynamics》2018,68(4-5):439-455
In a tidal channel with adjacent tidal flats, along–channel momentum is dissipated on the flats during rising tides. This leads to a sink of along–channel momentum. Using a perturbative method, it is shown that the momentum sink slightly reduces the M2 amplitude of both the sea surface elevation and current velocity and favours flood dominant tides. These changes in tidal characteristics (phase and amplitude of sea surface elevations and currents) are noticeable if widths of tidal flats are at least of the same order as the channel width, and amplitudes and gradients of along–channel velocity are large. The M2 amplitudes are reduced because stagnant water flows from the flats into the channel, thereby slowing down the current. The M4 amplitudes and phases change because the momentum sink acts as an advective term during the fall of the tide, such a term generates flood dominant currents. For a prototype embayment that resembles the Marsdiep–Vlie double–inlet system of the Western Wadden Sea, it is found that for both the sea surface elevation and current velocity, including the momentum sink, lead to a decrease of approximately 2% in M2 amplitudes and an increase of approximately 25% in M4 amplitudes. As a result, the net import of coarse sediment is increased by approximately 35%, while the transport of fine sediment is hardly influenced by the momentum sink. For the Marsdiep–Vlie system, the M2 sea surface amplitude obtained from the idealised model is similar to that computed with a realistic three–dimensional numerical model whilst the comparison with regard to M4 improves if momentum sink is accounted for. 相似文献
47.
Isadora A.S. de Macedo Jose Jadsom S. de Figueiredo Matias C. de Sousa Murillo J.S. Nascimento 《Geophysical Prospecting》2020,68(4):1328-1340
Wavelet estimation and well-tie procedures are important tasks in seismic processing and interpretation. Deconvolutional statistical methods to estimate the proper wavelet, in general, are based on the assumptions of the classical convolutional model, which implies a random process reflectivity and a minimum-phase wavelet. The homomorphic deconvolution, however, does not take these premises into account. In this work, we propose an approach to estimate the seismic wavelet using the advantages of the homomorphic deconvolution and the deterministic estimation of the wavelet, which uses both seismic and well log data. The feasibility of this approach is verified on well-to-seismic tie from a real data set from Viking Graben Field, North Sea, Norway. The results show that the wavelet estimated through this methodology produced a higher quality well tie when compared to methods of estimation of the wavelet that consider the classical assumptions of the convolutional model. 相似文献
48.
Water quality monitoring could benefit from information derived from the newest generation of medium-resolution Earth observation satellites. The main objective of our study was to assess the suitability of both Landsat 8 and Sentinel-2A satellites for estimating and mapping of Secchi disk transparency (SDT), a common measurement of water clarity, in Cassaffousth Reservoir (Córdoba, Argentina). Ground observations and a dataset of four Landsat 8 and four Sentinel-2A images were used to create and validate models to estimate SDT in the reservoir. The selected algorithms were used to obtain graphic representations of water clarity. Slight differences were found between Landsat 8 and Sentinel-2 estimations. Thus, we demonstrated the suitability of both satellites for estimating and mapping water quality. This study highlights the importance of free and readily available satellite datasets in monitoring water quality, especially in countries where conventional monitoring programmes are either lacking or unsatisfactory. 相似文献
49.
Geography of crime research dates back to the early 1800s, most of which in English and in the context of the United States and Europe, but with a growing and significant literature studying the developing world. We contribute to this literature through an application of social disorganization theory in a Latin American context: Campinas, Brazil. We consider a number of property and violent crime types using census tracts as the spatial unit of analysis. Implementing a spatial regression method, we find support for social disorganization theory, but not as strong as similar studies in Europe and North America. However, because of the context of Campinas, Brazil, a different understanding of the local conditions proves to be important for understanding the geography of crime in this context. The implications of these results are discussed in the context of theoretical developments as well as crime prevention initiatives. 相似文献
50.
D. Dusunur J. Escartín V. Combier T. Seher W. Crawford M. Cannat S. C. Singh L. M. Matias J. M. Miranda 《Marine Geophysical Researches》2009,30(2):105-120
The crust at mid-ocean ridges is formed through a combination of magmatic and tectonic processes. Along slow-spreading ridges,
magmatism is inferred to be discontinuous and episodic, and lithospheric faulting may strongly interact with the melt supply
system. These interactions can be studied for the first time at the Lucky Strike segment along the Mid-Atlantic Ridge (MAR),
where a 3.4 km deep magma chamber (AMC) extending ~6 km along-axis is found at its centre (Singh et al. in Earth Planet Sci
Lett 246:353–366, 2006). With an array of ocean bottom seismometers we have detected along this ridge segment approximately 400 microseismic events
during a total of 6 days, and located 71 of them, whose local magnitudes ranged from 0.2 to 1.8. While most of the events
were concentrated at non-transform offset and inside corners, three events with well-constrained locations were detected beneath
the central volcano and at the edges of the AMC. Two of the microearthquakes, which occur in a brittle lithosphere and therefore
at temperatures lower than 750°C, are deeper than the AMC and therefore very steep thermal gradients both along- and across-axis.
Regionally seismicity deepens from ~6 km at the segment center to >10 km towards the ends. 相似文献