Magnetic monitoring of top soils of Merida (Southern Mexico)     

Bertha Aguilar Reyes  Francisco Bautista  Avto Goguitchaichvili  Ofelia Morton 《Studia Geophysica et Geodaetica》2011,55(2):377-388

This paper focuses on the study of the correlation between magnetic parameters with the level of contamination by heavy metals in urban soils. We report a magnetic investigation of urban soil samples from Merida, state of Yucatan, Southern Mexico. It appears that most of our samples contain ferrimagnetic minerals as the magnetic carriers, probably coming from the titanomagnetites/titanomaghemites series. This is inferred by the acquisition of isothermal remanent magnetization, which shows that most of samples are almost completely saturated at about 200 mT. The S₋₂₀₀ value (factor characterizing stability of remanent magnetization) is between 0.8 and 1.0, characteristic of ferrimagnetic minerals. The susceptibility vs. temperature measurements also point to some titanomaghemites and titanomagnetites as probable responsible for magnetization. On the other hand, measurements of magnetic susceptibility at high and low frequencies helped us to determine the high content of superparamagnetic grains in the majority of the samples, although not all of these showed high values of magnetic susceptibility. We found that the most contaminated samples by Pb and Zn showed the higher saturation isothermal remanent magnetization values, whereas the higher values in magnetic susceptibility correspond to samples contaminated by Cr. Finally, we noted that a high level in Sr decreases the magnetic susceptibility.  相似文献   

Approaching water management at watershed scale using distributed water balances in the Yanuncay River basins (Ecuador)     

Javier Fernández de Córdova  Juan Antonio Pascual Aguilar 《Environmental Earth Sciences》2014,71(1):53-60

In this study, the excess water generated during a 10-year period (1998–2008) in the upper and middle Yanuncay River basins is estimated. The distributed water balance method, which analyses the interaction between all the different parameters that form part of the water cycle in nature, was developed. To create the model, basic parameters such as rainfall, temperature, soil type and surface cover are required. Moreover, by using computer software such as Microsoft Office Excel and geographic information systems, it is possible to obtain monthly data showing the water excess and generate thematic maps which allow for an effective monitoring of the behaviour of the middle and upper Yanuncay River basins. This study takes the spatial variability of the various factors that influence the behaviour of a basin into account. This allows determining zones with greater water excess, which are areas that would need to be protected. The model can easily incorporate new data such as land use and surface cover (based on time frames) which would facilitate the comparison of different scenarios.  相似文献   

Vulnerability to environmental hazards in the Ciudad Juárez (Mexico)–El Paso (USA) metropolis: A model for spatial risk assessment in transnational context     

Timothy W. Collins  Sara E. Grineski  María de Lourdes Romo Aguilar   《Applied geography (Sevenoaks, England)》2009,29(3):448-461

The purpose of this paper is to present a geographic information system (GIS)-based method for mapping risk to environmental hazards. Framed by the hazards literature, the method has been developed to specifically overcome issues of data compatibility associated with transnational contexts. The approach is elaborated in reference to a project in which risk was spatially characterized, using a suite of biophysical and social indicators, for the Ciudad Juárez (Mexico)–El Paso (USA) metropolis. Results reveal clear spatial disparities in hazard vulnerability, both within and between the two cities, based on the differential allocation of selected risk factors. The case indicates that future international analyses will be advanced by the clear definition of concepts, the systematic mining of compatible variables, and the selection of valid risk indicators based on criteria that balance the need to incorporate contextual specificity with general comparability.  相似文献   

Altimetry with GNSS-R interferometry: first proof of concept experiment   总被引：1，自引：0，他引：1  

Antonio Rius  Oleguer Nogués-Correig  Serni Ribó  Estel Cardellach  Santi Oliveras  Enric Valencia  Hyuk Park  José Miguel Tarongí  Adriano Camps  Hans van der Marel  Roel van Bree  Bas Altena  Manuel Martín-Neira 《GPS Solutions》2012,16(2):231-241

The Global Navigation Satellite System Reflectometry (GNSS-R) concept was conceived as a means to densify radar altimeter measurements of the sea surface. Until now, the GNSS-R concept relied on open access to GNSS transmitted codes. Recently, it has been proposed that the ranging capability of the technique for ocean altimetric applications can be improved by using all the signals transmitted in the bandwidth allocated to GNSS, which includes open access as well as encrypted signals. The main objective of this study is to provide experimental proof of this enhancement through a 2-day experiment on the Zeeland Bridge (The Netherlands). In the experiment, we used a custom built GNSS-R system, composed of high gain GPS antennas, calibration subsystem, and an FPGA-based signal processor which implemented the new concepts, an X-band radar altimeter and a local geodetic network. The results obtained indicate that the new approach produces a significant improvement in GNSS-R altimetric performance.  相似文献   

Identification of groundwater quality trends in a chalk aquifer threatened by intensive agriculture in Belgium     

Jordi Batlle Aguilar  Philippe Orban  Alain Dassargues  Serge Brouyère 《Hydrogeology Journal》2007,15(8):1615-1627

The European Union (EU) has adopted directives requiring that Member States take measures to reach a “good” chemical status of water resources by the year 2015 (Water Framework Directive: WFD). In order to achieve the environmental objectives for groundwater, the identification and reversal of significant upward trends in pollutant concentrations are required. A very detailed dataset available for the Hesbaye chalk aquifer in Belgium is used to evaluate tools and to propose efficient methodologies for identifying and quantifying nitrate trends in groundwater. Results indicate that the parametric linear regression and the non-parametric Mann-Kendall tests are robust; however, the latter test seems more adequate as it does not require verification of the normality of the dataset and it provides calculated nitrate trends very comparable to those obtained using linear regression. From a hydrogeological point of view, results highlight a general upward trend in the whole groundwater basin. The extrapolation of the trend analysis results indicates that measures have to be taken urgently in order to avoid further major degradation of groundwater quality within the next 10–70 years. However, a good groundwater quality status cannot be expected in the Hesbaye aquifer for the 2015 EU WFD deadline.  相似文献   

Investigation of drainage basin geometry near an anomalously straight reach of the Big Black River,Mississippi, USA     

Zachary A. Musselman  Alex Aguilar 《自然地理学》2016,37(2):169-187

Drainage basin geometry was analyzed in the lower portion of the Big Black River, Mississippi. The study was centered on a reach of the Big Black River that encompasses an anomalous straight reach (ASR) and has morphometric characteristics that differ from those of upstream and downstream reaches. The study area was divided into three reaches, defined by alluvial valley and active floodplain width, sinuosity, and slope. Tributary streams with confluences in the three study reaches were investigated for evidence of surface tilting, and channel and valley slopes and sinuosity were measured. The average stream channel and valley slopes within the middle reach are nearly double those of the upper and lower reaches. Lateral stream migration within the tributary basins was quantitatively analyzed by measuring the asymmetry factor (AF) and transverse topographic symmetry factor (T) indices. While AF results suggest minimal to no lateral migration within the tributaries, the T results show some shifting. The results are inconclusive regarding the possible effect of neotectonic activity in the study area near the ASR. The mean southward migration may indicate a preferred migration direction relative to the general dip of the coastal plain and plunge of the Mississippi Embayment.  相似文献   

Seasonal variation in the structure of three Mediterranean algal communities in various light conditions     

Ruth Martí  Maria J. Uriz  Enric Ballesteros  Xavier Turon 《Estuarine, Coastal and Shelf Science》2005,64(4):613-622

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Comments on ‘numerical simulation of a random sea: a common error and its effect upon wave group statistics by M.J. Tucker,T.G. Challenor and D.J.T. Carter’     

Josep R. Medina  José Aguilar 《Applied Ocean Research》1985,7(2):113-114

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A paleomagnetic and rock-magnetic study of a neogene lava flow sequence in La Gomera (Canary Islands,Spain)     

Anna Caccavari  Manuel Calvo-Rathert  Avto Goguitchaichvili  Vicente Soler  Bertha Aguilar Reyes 《Studia Geophysica et Geodaetica》2010,54(4):547-560

We present rock-magnetic and paleomagnetic results obtained on samples belonging to a Neogene sequence of 11 successive lava flows and a dyke from La Gomera (Canary Islands, Spain). Analysis of thermomagnetic curves allows to distinguish three types of samples: (i) Type H samples with low-Ti titanomagnetite as the only carrier of remanence; (ii) type M samples with a main intermediate Curie-temperature phase (T_C = 450°C) and low-Ti titanomagnetite; (iii) type L curves with a low Curie-temperature phase (T_C = 120 to 200°C) and an intermediate Curie-temperature phase (T_C = 400°C). Analysis of hysteresis parameters suggests that the grain size of most studied samples corresponds to pseudo single-domain particles, which can be also interpreted as a mixture of single-domain and multi-domain particles. Paleomagnetic experiments reveal only a single paleomagnetic component. Characteristic remanence of all studied lava flows and the dyke shows reverse polarity. The mean direction of the whole sequence is D = 188.2°, I =−35.4° (k = 46.9; α₉₅ = 6.4°) and the calculated paleomagnetic pole yields a longitude λ= 150.7° and a latitude ϕ= 78.8° (k = 59.4; A₉₅ = 5.7°). Secular variation is analysed through the scatter of virtual geomagnetic poles (VGP). A VGP angular scatter S_B = 5.9 with an upper confidence limit S_up = 8.0 and a lower confidence limit S_low = 4.6 are obtained. This scatter is clearly smaller than the average for this latitude obtained for the last 5 Ma. The studied lava flows were probably emitted in a relatively short time interval.  相似文献   

Benzene Dynamics and Biodegradation in Alluvial Aquifers Affected by River Fluctuations     

J. Batlle‐Aguilar  B. Morasch  D. Hunkeler  S. Brouyère 《Ground water》2014,52(3):388-398

The spatial distribution and temporal dynamics of a benzene plume in an alluvial aquifer strongly affected by river fluctuations was studied. Benzene concentrations, aquifer geochemistry datasets, past river morphology, and benzene degradation rates estimated in situ using stable carbon isotope enrichment were analyzed in concert with aquifer heterogeneity and river fluctuations. Geochemistry data demonstrated that benzene biodegradation was on‐going under sulfate reducing conditions. Long‐term monitoring of hydraulic heads and characterization of the alluvial aquifer formed the basis of a detailed modeled image of aquifer heterogeneity. Hydraulic conductivity was found to strongly correlate with benzene degradation, indicating that low hydraulic conductivity areas are capable of sustaining benzene anaerobic biodegradation provided the electron acceptor (SO₄^2–) does not become rate limiting. Modeling results demonstrated that the groundwater flux direction is reversed on annual basis when the river level rises up to 2 m, thereby forcing the infiltration of oxygenated surface water into the aquifer. The mobilization state of metal trace elements such as Zn, Cd, and As present in the aquifer predominantly depended on the strong potential gradient within the plume. However, infiltration of oxygenated water was found to trigger a change from strongly reducing to oxic conditions near the river, causing mobilization of previously immobile metal species and vice versa. MNA appears to be an appropriate remediation strategy in this type of dynamic environment provided that aquifer characterization and targeted monitoring of redox conditions are adequate and electron acceptors remain available until concentrations of toxic compounds reduce to acceptable levels.  相似文献