Effect of galvanic distortions on the series and parallel magnetotelluric impedances and comparison with other responses     

Enrique Gómez-Treviño  Francisco Javier Esparza Hernández  José Manuel Romo Jones 《Geofísica Internacional》2013,52(2):135-152

The series and parallel impedances of the magnetotelluric tensor are appraised in relation to their relative immunity to galvanic electric distortions. The distorted responses are modeled using the Groom-Bailey decomposition of the tensor in terms of twist, shear, statics and strike direction. These four parameters and the undistorted responses are normally considered as unknowns, and are obtained from field data through the solution of an inverse problem. In the present work we use the decomposition as a forward model to simulate distorted sounding curves. Starting with undistorted 2-d te and tm responses, the tensor is distorted by assuming arbitrary values of twist, shear, static and strike direction. By default, both series and parallel responses are immune to the strike direction because they are invariants under rotation. In addition, series responses are immune to twist and shear and parallel responses only to twist. The dependence of the latter on shear is in the form of a real factor that shifts downwards the amplitude curves. On the other hand, the effect of statics on both series and parallel responses is more complicated than that on the impedance tensor because it cannot be accounted for by a simple shift of the curves. On the whole, there is a positive balance on the part of the series and parallel impedances over the te and tm responses because some of the distortions are filtered out by the invariants. It is shown that invariance is not sufficient to be immune to any of the distortions. The example chosen is Eggers’ eigenvalues, which are immune only to the by-the-fault strike direction. Invariance is not necessary either, as evidenced by the phase tensor, whose elements depend on strike but are immune to all distortions. The derivations are illustrated using soundings from the synthetic coprod2s1 and field-recorded coprod2 and bc87 data sets.  相似文献   

Hydrogeochemistry of fluoride in the Quequen river basin: natural pollutants distribution in the argentine pampa     

D. E. Martínez  O. M. Quiroz Londoño  H. E. Massone  P. Palacio Buitrago  L. Lima 《Environmental Earth Sciences》2012,65(2):411-420

Fluoride pollution is a widespread problem in Argentina, as it is in many areas of the World. Former investigations have demonstrated that the dissolution of volcanic glass disseminated in the loess-like sediments is the main source of fluoride in the Argentine pampas. Nevertheless, fluoride distribution is erratic and the factors controlling it are not yet well-known. A large amount of hydrochemical data collected in the Quequen Grande river catchment is used in order to contribute to the understanding of fluoride distribution and mobility in groundwater in the Argentine pampas. The Quequen Grande river catchment is 10,000 km². It extends between two low hills ranges of Precambrian metamorphic rocks and sedimentary Paleozoic rocks, filled by a thick sequence of Cenozoic sediments, mainly silts and silt-clayed, with sand layers. These sediments form a multilayer phreatic aquifer, which is recharged from precipitation infiltration, discharging through streams directly into the sea. Fluoride concentration in surface water (n = 353) ranges between 0 and 6.5 mg/l, with an average value of 2.14 mg/l. Groundwater concentration (n = 135) is from 0 up to 5.7 mg/l, with an average of 1.84 mg/l. Considering the statistic distribution of fluoride, two groups of samples can be determined. A dominant group between 0 and 3 mg/l, with a mean value around 1.5 mg/l, corresponding to samples widely distributed in the catchment; and a second one group with fluoride contents between 3 and 6 mg/l, corresponding to a smaller area in the central-west border. Two different sources are proposed. Volcanic glass dissolution is responsible for dominant values in the catchment, while the weathering of biotite from the Paleozoic bedrock can be assumed to account for the higher concentrations in the second group.  相似文献   

Sources and behavior of arsenic and trace elements in groundwater and surface water in the Poopó Lake Basin,Bolivian Altiplano     

Oswaldo Eduardo Ramos Ramos  Luis Fernando Cáceres  Mauricio Rodolfo Ormachea Muñoz  Prosun Bhattacharya  Israel Quino  Jorge Quintanilla  Ondra Sracek  Roger Thunvik  Jochen Bundschuh  Maria Eugenia García 《Environmental Earth Sciences》2012,66(3):793-807

Water management in semiarid and arid catchments such as the Poopó Lake Basin requires improved understanding of the complex behavior of the various contaminants, which affect the drinking water quality and considered as crucial for sustainable development of the region. Mechanisms of arsenic (As) release in the surface and groundwater were studied. Hydrochemical data for surface water (4 samples) and groundwater (28 samples) were collected in a small watershed in the Poopó catchment at the highland of the Bolivian Andes (Altiplano). All of them show high electrical conductivity values and moderately oxidizing conditions. The surface water contains high concentration of sulfate and the trace elements As, Zn and Pb in the zone affected by acid mine drainage. There is a large variability of the concentration of As and of the trace elements in the groundwater in the five different regions within the Poopó catchment. The metal concentrations sensitive to changes of redox state and results of speciation modeling suggest that As (V) is a predominant aqueous species, which conforms to the prevailing oxidizing conditions in the shallow groundwater environment. Two generalized trends for As distribution were identified in groundwater: (a) high concentrations are found in the arid zone (100–250 μg/L) in the southern (region III) and in the northwestern (region V) regions, and (b) low concentrations (<50 μg/L) are found in the remaining part of the basin (region I, II and IV). However, the spatial distribution within these regions needs to be investigated further. A conclusion from the present study is that there are multiple sources of As as well as other trace elements (such as Cd, Mn and Zn) in the Poopó Lake Basin. Among the sources and the processes which led to the mobility of As and other trace metals in the region are: (a) weathering of sulfide minerals, (b) oxidation of pyrite and/or arsenopyrite in mineralized areas and (c) desorption from hydrous ferric oxide (HFO) surfaces. In non-mining areas, volcanic ash is suggested to be a significant source of As.  相似文献   

Response of single benthic metrics and multi-metric methods to anthropogenic pressure gradients, in five distinct European coastal and transitional ecosystems   总被引：4，自引：0，他引：4  

Borja A  Barbone E  Basset A  Borgersen G  Brkljacic M  Elliott M  Garmendia JM  Marques JC  Mazik K  Muxika I  Magalhães Neto J  Norling K  Rodríguez JG  Rosati I  Rygg B  Teixeira H  Trayanova A 《Marine pollution bulletin》2011,62(3):499-513

In recent times many benthic indices have been proposed to assess the ecological quality of marine waters worldwide. In this study we compared single metrics and multi-metric methods to assess coastal and transitional benthic status along human pressure gradients in five distinct environments across Europe: Varna bay and lake (Bulgaria), Lesina lagoon (Italy), Mondego estuary (Portugal), Basque coast (Spain) and Oslofjord (Norway). Hence, 13 single metrics (abundance, number of taxa, and several diversity and sensitivity indices) and eight of the most common indices used within the European Water Framework Directive (WFD) for benthic assessment were selected: index of size spectra (ISS), Benthic assessment tool (BAT), Norwegian quality index (NQI), Multivariate AMBI (M-AMBI), Benthic quality index (BQI), (Benthic ecosystem quality index (BEQI), Benthic index based on taxonomic sufficiency (BITS), and infaunal quality index (IQI). Within each system, sampling sites were ordered in an increasing pressure gradient according to a preliminary classification based on professional judgement. The different indices are largely consistent in their response to pressure gradient, except in some particular cases (i.e. BITS, in all cases, or ISS when a low number of individuals is present). Inconsistencies between indicator responses were most pronounced in transitional waters (i.e. IQI, BEQI), highlighting the difficulties of the generic application of indicators to all marine, estuarine and lagoonal environments. However, some of the single (i.e. ecological groups approach, diversity, richness) and multi-metric methods (i.e. BAT, M-AMBI, NQI) were able to detect such gradients both in transitional and coastal environments, being these multi-metric methods more consistent in the detection than single indices. This study highlights the importance of survey design and good reference conditions for some indicators. The agreement observed between different methodologies and their ability to detect quality trends across distinct environments constitutes a promising result for the implementation of the WFD’s monitoring plans. Moreover, these results have management implications, regarding the dangers of misclassification, uncertainty in the assessment, use of conflicting indices, and testing and validation of indices.  相似文献   

Estrogen pollution in a highly productive ecosystem off central-south Chile     

Bertin A  Inostroza PA  Quiñones RA 《Marine pollution bulletin》2011,62(7):1530-1537

While the presence of steroid estrogens in the environment has become a major environmental and health concern, their occurrence in coastal sediments remains poorly characterized. In this study, we measured the levels of three natural (estrone, 17β-estradiol, estriol) and one synthetic (17α-ethinylestradiol) estrogens in 54 coastal sediment samples collected from nine locations off central-southern Chile. Steroid estrogens were found in every sample. Remarkably high levels of 17α-ethinylestradiol were detected, reaching up to 48.14 ng/g dry weight. As a result, the global estrogenic loads were estimated to be high at all sites. Interestingly, they were found to correlate with the size of human populations served by sewage plants. Our study indicates that 17α-ethinylestradiol may accumulate in coastal sediments. The possible impact of this highly potent synthetic estrogen on the biota of the marine ecosystem off central-south Chile and on human health remains an open question.  相似文献   

Latitudinal variation in the aerial/aquatic ratio of oxygen consumption of a supratidal high rocky‐shore crab     

Marco A. Lardies  José Luis Muñoz  Kurt A. Paschke  Francisco Bozinovic 《Marine Ecology》2011,32(1):42-51

The colonisation of the terrestrial environment by crustaceans is more apparent in tropical latitudes because of the high diversity of semi‐terrestrial and terrestrial crabs. However, in temperate regions there are also great numbers of crustaceans that inhabit ecological niches at the water–air interface. Grapsidae crabs (Decopoda) are especially important in studies of water‐to‐land transition as the family contains species occupying the intertidal and adjacent regions. A way to evaluate the ability of intertidal invertebrates to breathe air is to measure the aerial/aquatic oxygen consumption ratio. The objective of this study was to test the effect of thermal variation on the aquatic and aerial metabolism. We selected as study model the decopoda crab Cyclograpsus cinereus Dana and utilised five populations of the species spread over 2000 km along the Chilean coast. To determine the compensation capacity in respiration with respect to latitude, we evaluated metabolic rate at the same temperature in a common garden design in the laboratory, to examine the extent to which variation in crab physiology is environmentally determined. Whereas in our study, m_b (body mass) varied significantly with latitude, the difference in mass‐independent metabolism both in air and water persisted, indicating that observed differences in MR (Metabolic Rate) were not an effect of differences in body size. We demonstrated that C. cinereus is able to breath oxygen from air and water as expected for an amphibious crab. Almost all the studied populations of C. cinereus show a aerial/aquatic metabolism ratio near 1. The pattern found indicates an increase in metabolic rate, both aerial and aquatic, in low latitudes and therefore does not support the latitudinal compensation hypothesis for temperate habitats. Finally, these kinds of studies are required to make the necessary link between ecological physiology and macroecology and to help develop a global understanding of organismal function in marine systems.  相似文献   

Trace elements in Holocene sediments of the southern Doñana National Park (SW Spain): historical pollution and applications     

M. I. Carretero  M. Pozo  F. Ruiz  J. Rodríguez Vidal  L. M. Cáceres  M. Abad  J. M. Muñoz  F. Gómez  J. M. Campos  M. L. González-Regalado  M. Olías 《Environmental Earth Sciences》2011,64(5):1215-1223

The multidisciplinary analysis of core sediments from Doñana National Park, south Spain, permits to delimitate both the paleoenvironmental changes and the geochemical evolution of this area during the Holocene. In a first phase (10–6.5 kyr cal), this area was occupied by freshwater/brackish marshes with periodical alternation of dry periods and humid intervals. In a second phase, these marshes were inundated during the Flandrian transgression (~6.5 kyr cal), with the deposition of bioclastic sands. The third phase (6.5–3.6 kyr cal) is characterized by the transition to an old lagoon, with unpolluted, bottom sediments. The geochemical concentrations of these clayey sediments can be used as a geochemical background for present-day and future environmental evaluations of this area. In the following 600 years approximately, two tsunamis caused the partial infilling of this area with bioclastic, marine sediments. In the interval comprised between these two tsunamis, this lagoon was polluted with heavy metals derived from historical mining activities. This environmental contamination represents one of the oldest evidences of mining pollution in the world (>3 kyr cal BP).  相似文献   

Salt damage and microclimate in the Postumius Tomb, Roman Necropolis of Carmona, Spain     

D. Benavente  S. Sanchez-Moral  A. Fernandez-Cortes  J. C. Cañaveras  J. Elez  C. Saiz-Jimenez 《Environmental Earth Sciences》2011,63(7-8):1529-1543

The necropolis of Carmona (Seville, Spain) is one of the most significant Roman burial sites in southern Spain used during the first and second centuries ad. Of its more than 600 tombs, the Postumius Tomb is one of the best examples of a tomb affected by severe salt damage. To define safe microclimatic conditions for its conservation, environmental parameters were recorded from June 2007 to April 2009, both inside and outside the tomb, and mineralogical, textural, petrophysical, and durability characterization studies of the host-rock were made. Experimental tests revealed a high susceptibility to salt deterioration of a host-rock (calcarenite) with low mechanical properties and a complex porous medium that favors salt weathering, water condensation, and capillary rise. The analysis of the weathered material showed the presence chiefly of gypsum (CaSO₄·2H₂O), thenardite (Na₂SO₄) and halite (NaCl) in the tomb of Postumius, with alteration that was more intensive in spring and autumn, and less so during summer months. Salt damage activity was calculated by quantifying the number of transitions of crystallization–dissolution of saline phases. The calculated seasonality for water condensation and salt damage is coeval. The host-rock alteration is in accord with the estimated salt decay, and was more intensive in spring and autumn and less so during summer. The seasonality of halite transitions is similar to that of the sodium sulfate system, which suggests that salt weathering is produced by the two types of salts. By combining different methodological approaches (pore structure, water condensation, salt and environmental conditions), it is possible to explain why salt crystallization occurs in a tomb with hygrometric conditions that are not suitable for this process to occur. These methodological approaches are also used to other rock-decaying processes, such as the development of microorganisms, clay swelling and calcite dissolution by NaCl- and CO₂-rich pore waters, and can be used to predict safe threshold microclimatic conditions that minimize all rock-decaying processes.  相似文献   

Territorial dynamics and boundary effects in a protected area of the Central Iberian Peninsula     

Paloma de las Heras  Paloma Fernández-Sañudo  Nieves López-Estébanez  María José Roldán 《Central European Journal of Geosciences》2011,3(1):1-11

We analysed the main changes in land use over a 21 year period within the perimeter of a Protected Natural Area (PNA) and outside this perimeter. The area is characterised by its Mediterranean mid-mountain landscape and its piedmont, which extends almost as far as the city of Madrid. We employed cartography of land use and plant formation from 1980 and 2001. We identified land uses and their changes in this time period in order to determine the principal territorial dynamics (scrub encroachment, urban development, forest encroachment, new pastures and new crops). Subsequently, we performed a comparative analysis between the changes inside and those outside the protected area. The results show that there is a boundary effect between the protected area and the surrounding zone, which is more notable in the areas where urban development has intensified. This kind of research serves to establish whether or not a PNA contributes to protecting and conserving natural resources as compared to what occurs in the unprotected surrounding area, which tends to be subjected to more aggressive dynamics.  相似文献   

Development of the POLCOMS–WAM current–wave model     

R. Bolaños  P. Osuna  J. Wolf  J. Monbaliu  A. Sanchez-Arcilla 《Ocean Modelling》2011,36(1-2):102-115

The continuous research and improvement of ocean modelling helps to provide a more sustainable development of coastal and offshore regions. This paper focuses on ocean modelling at the NW Mediterranean using the POLCOMS–WAM model with new developments. The Stokes’ drift effect on currents has been included and the distribution of surface stress between waves and currents has also been considered. The system is evaluated in the NW Mediterranean and an evaluation of different forcing terms is performed. The temperature and salinity distributions control the main patterns of the Mediterranean circulation. Currents are typically small and therefore the modification of waves due to the effect of currents is minimal. However, the wave induced currents, mainly caused by a modified wind drag due to waves, produce changes that become an important source of mass transport. POLCOMS was able to reproduce the main Mediterranean features, its coupling with WAM can be a very useful tool for ocean and wave modelling in the Mediterranean and other shelf seas.  相似文献