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991.
There is an exceptionally rich aquatic fauna in the epikarst, the skin of karst. High species richness in the epikarst, coupled
with its special vulnerability as the first point of entry of nearly all toxic spills, makes its protection especially important.
The epikarst fauna may also be an useful tool in tracing the potential route of pollutants. Copepods in epikarst have extremely
local distributions, and their body size is such that they are largely at the mercy of directional flows. In a series of caves
in southwest Slovenia and West Virginia, a significant fraction of the copepod species occur in less than 100 m of linear
extent. This suggests a pattern of highly restricted lateral flow under normal conditions and the distribution of copepods
could potentially be used to trace water movement. Under high flow conditions as would often be the case with toxic spill,
mounding of water may increase the lateral radius of flow. Nevertheless, copepods may be useful tracers. 相似文献
992.
María Gabriela García Ondra Sracek Diego Sebastián Fernández Margarita del Valle Hidalgo 《Environmental Geology》2007,52(7):1261-1275
The concentration of arsenic measured in groundwater from three aquifers in the study area located in the Eastern Tucuman
province, Argentina, mostly depends on the lithology, but the spatial and temporal variations of concentrations seem to be
also controlled by pH changes, climatic factors, and human perturbations. The highest concentrations of As (more than 1,000 μg
L−1) were found in the shallow aquifer, made of As-rich loess, while the lowest concentrations were measured in the deep confined
aquifer, consisting of alternating layers of alluvial sands/gravels and clays. Intermediate values were measured in the semiconfined
aquifer made of the fluvial sediments deposited in the Salí River valley, that alternate in the upper part of the sedimentary
sequence with layers of loess. Because most of As in the loess is considered to be adsorbed onto Fe-oxyhydroxide coatings,
the increase of pH in the flow direction (west-east) leads to increasing arsenic concentrations towards the eastern border
of the study area. The decomposition of organic wastes poured into the Salí River or associated with local and diffuse sources
of contamination in the eastern part of the study area depletes dissolved oxygen, which leads to the reductive dissolution
of Fe and Mn oxyhydroxides, and to the subsequent release of the adsorbed and co-precipitated As. This process mainly affects
shallow groundwater and the upper part of the semiconfined aquifer. Geochemical and hydrological data also suggest that rising
water table levels at the end of the wet season may also lead to reductive dissolution of As-rich Fe oxyhydroxides in the
shallow aquifer. 相似文献
993.
The distribution of platinum group elements (PGEs) in massive sulfides and hematite–magnetite±pyrite assemblages from the
recently discovered basalt-hosted Turtle Pits hydrothermal field and in massive sulfides from the ultramafic-hosted Logatchev
vent field both on the Mid-Atlantic Ridge was studied and compared to that from selected ancient volcanic-hosted massive sulfide
(VHMS) deposits. Cu-rich samples from black smoker chimneys of both vent fields are enriched in Pd and Rh (Pd up to 227 ppb
and Rh up to 149 ppb) when compared to hematite–magnetite-rich samples from Turtle Pits (Pd up to 10 ppb, Rh up to 1.9 ppb).
A significant positive correlation was established between Cu and Rh in sulfide samples from Turtle Pits. PGE chondrite-normalized
patterns (with a positive Rh anomaly and Pd and Au enrichment), Pd/Pt and Pd/Au ratios close to global MORB, and high values
of Pd/Ir and Pt/Ir ratios indicate mafic source rock and seawater involvement in the hydrothermal system at Turtle Pits. Similarly
shaped PGE chondrite-normalized patterns and high values of Pd/Pt and Pd/Ir ratios in Cu-rich sulfides at Logatchev likely
reflect a similar mechanism of PGE enrichment but with involvement of ultramafic source rocks. 相似文献
994.
995.
The primary factors that control the concentration of total reduced (inorganic) sulfide in coastal sediments are believed
to be the availability of reactive iron, dissolved sulfate and metabolizable organic carbon. We selected nine sites in shallow
(<3 m), close to sub-tropical, estuaries and bays along the central Texas coast that represented a range in sediment grain
size (a proxy for reactive iron), salinity (a proxy for dissolved sulfate), and total organic carbon (a proxy for metabolizable
organic carbon). Based on these parameters a prediction was made of which factor was likely to control total reduced sulfide
at each site and what the relative total reduced sulfide concentration was likely to be. To test the prediction, the sediments
were analyzed for total reduced sulfide, acid volatile sulfide, and citrate dithionate-extractable, HCl-extractable and total
Fe in the solid phase. Using solid-state gold–mercury amalgam microelectrodes and voltammetry, we determined pore water depth
profiles of Fe(II) and ΣH2S and presence or absence of FeS(aq). At five of the nine sites the calculated degree of sufildization of citrate dithionite-reactive-iron was close to or greater
than 1 indicating that rapidly reactive iron was probably the limiting factor for iron sulfide mineral formation. At one site
(salinity = 0.9) dissolved Fe(II) was high, ΣH2S was undetectable and the total reduced sulfide concentration was low indicating sulfate limitation. At the last three sites
a low degree of sulfidization and modest total reduced (inorganic) sulfide concentrations appeared to be the result of a limited
supply of metabolizable organic carbon. Fe(II)–S(-II) clusters (FeS(aq)) were undetectable in 10 out of 12 bay sediment profiles where ΣH2S was close to or below detection limits, but was observed in all other porewater profiles. Acid volatile sulfide, but not
total reduced sulfide, was well correlated with total organic carbon and ranged from being undetectable in some cores to representing
a major portion of total reduced sulfide in other cores. Although predicted controls on total reduced sulfide were good for
very low salinity water or sandy sediments, they were only right about half the time for the other sediments. The likely reasons
for the wrong predictions are the poor correlation of total organic carbon with grain size and differing fractions of metabolizable
organic carbon in different sedimentary environments. Differences in sediment accumulation rates may also play a role, but
these are difficult to determine in this region where hurricanes often resuspend and move sediments. This study demonstrates
the need to examine more complex and often difficult to determine parameters in anoxic “normal marine” sediments if we are
to understand what controls the concentration and distribution of sulfides. 相似文献
996.
997.
Partitioning,bioavailability and origin of heavy metals from the Nador Lagoon sediments (Morocco) as a basis for their management 总被引:2,自引:0,他引:2
Nador Lagoon sediments show low trace element concentrations, and, in relation to the lagoon geochemical baseline, only some
anomalies for As, Cd, Cu and Pb in the NW of the lagoon deserve to be outstanding. The distribution of major, minor and trace
elements in the lagoon allows a breakdown in four zones. Between “Beni Ensar” and “Atelouane” (zone A), a quite confined zone
rich in organic matter and S, the most important trace-element anomalies (As, Cd, Co, Cu, Mn, Pb, Zn) were found, mainly around
industry and old mining activities. In the surrounding of the city of Nador (zone B), the anomalies correspond to Mn, Cu and
Zn. The coastal barrier and Kebdana channel (zone C) show moderately concentrations of Cd, Cr and Ni at specific sites. The
less polluted area is the SE of the lagoon (zone D), with no outstanding anomaly. In lagoon sediments, metal bioavailability
is very low. The metal partitioning patterns show that Cu, Pb and Zn present a low availability because they are bounded to
the residual, non-mobile phases of the sediments. Only in some sites, the fraction was associated with organic matter, which
could be liberated easily. Arsenic is concentrated in both the residual phases and the organic matter, the latter being more
available. Cadmium is mainly concentrated in some samples in the interchangeable fraction, which could be considered as a
potentially toxic element because it is easily released. Concerning the origin of these trace elements, those found in zone A
correspond mostly to a natural source by weathering of mount Gourougou volcanic rocks (As, Co, Cu, Pb and Zn), and to an anthropogenic
origin (Cd) owing to the presence of industry and old mines. In zone B, contributions of Cu and Zn enter the lagoon through
soil weathering and river-borne, and as anthropogenic pollution from urban wastes. In zone C the most important pollutant
is Cd deduced to be of anthropogenic origin from the close industry and intensive agriculture area. In spite of the intense
socio-economic activities developed in the Nador Lagoon (agriculture, industry, fishing, tourism) trace element concentrations
in the sediments are low and with scarce bioavailability. Only the NW sector is relativity polluted because of geogenic features. 相似文献
998.
Compaction localization in the Earth and the laboratory: state of the research and research directions 总被引:1,自引:1,他引:1
Localized compaction in porous rocks is a recently recognized phenomenon that has been shown to reduce permeability dramatically.
Consequently, the phenomenon is relevant to a variety of technologies involving fluid injection or withdrawal. This article
summarizes current understanding of localized compaction and impediments to further progress. The article is based on discussions
at a small workshop on localized compaction sponsored by the Office of Science, U. S. Department of Energy. 相似文献
999.
J. P. Cárcomo Lobo Ferreira Maria da Conceição Cunha A. G. Chachadi Kai Nagel Catarina Diamantino Manuel Mendes Oliveira 《Hydrogeology Journal》2007,15(6):1147-1155
Using the hydrogeological and socio-economic data derived from a European Commission research project on the measurement,
monitoring and sustainability of the coastal environment, two optimization models have been applied to satisfy the future
water resources needs of the coastal zone of Bardez in Goa, India. The number of tourists visiting Goa since the 1970s has
risen considerably, and roughly a third of them go to Bardez taluka, prompting growth in the tourist-related infrastructure
in the region. The optimization models are non-linear mixed integer models that have been solved using GAMS/DICOPT++ commercial
software. Optimization models were used, firstly, to indicate the most suitable zones for building seaside resorts and wells
to supply the tourist industry with an adequate amount of water, and secondly, to indicate the best location for wells to
adequately supply pre-existing hotels. The models presented will help to define the optimal locations for the wells and the
hydraulic infrastructures needed to satisfy demand at minimum cost, taking into account environmental constraints such as
the risk of saline intrusion.
Résumé A l’aide de données hydrogéologiques et socio-économiques, dérivées d’un projet de recherche de la Commission Européenne sur l’étude, la surveillance et la durabilité de l’environnement c?tier, deux modèles d’optimisation ont été appliqués en vue de satisfaire les besoins futurs en ressources en eau de la zone c?tière de Bardez au Goa en Inde. Le nombre de touristes qui visitent le Goa depuis les années 70 a considérablement augmenté et environ un tiers d’entre eux se rend à Bardez taluka, ce qui encourage la croissance des infrastructures liées au tourisme dans la région. Les modèles d’optimisation sont des modèles non linéaires mixtes en nombres entiers qui ont été résolus en utilisant le logiciel commercial GAMS/DICOPT++. Les modèles d’optimisation ont été utilisés pour indiquer premièrement les zones les plus appropriées pour construire des stations balnéaires et des puits pour approvisionner en quantité d’eau suffisante l’industrie touristique, et deuxièmement pour indiquer la meilleure localisation de puits pour l’alimentation des h?tels préexistants. Les modèles présentés aideront à définir les localisations optimales des puits et des infrastructures hydrauliques nécessaires à la satisfaction de la demande à un co?t minimum, tout en prenant en compte les contraintes environnementales, tel que le risque d’intrusion saline.
Resumen Se han aplicado dos modelos de optimización en base a datos socio-económicos e hidrogeológicos derivados de un proyecto de investigación de la Comisión Europea sobre medición, monitoreo y sostenibilidad del ambiente costero para satisfacer las necesidades futuras de recursos hídricos de la zona costera de Bardez en Goa, India. El número de turistas que visita Goa desde la década de 1970′s ha subido considerablemente y cerca de un tercio de ellos van a Bardez taluka impulsando el crecimiento en la infraestructura turística de la región. Los modelos de optimización son modelos de números enteros mixtos no-lineales que se han resuelto usando el programa comercial GAMS/DICOPT++. Los modelos de optimización se usaron, primero para indicar las zonas más adecuadas para la construcción de centros de diversión en las márgenes del océano y pozos para abastecer la industria turística con una adecuada cantidad de agua, y segundo, para indicar la mejor localización de pozos para el abastecimiento de hoteles pre-existentes. Los modelos que se presentan ayudarán a definir las localizaciones óptimas para los pozos y las infraestructuras hidráulicas necesarias para satisfacer la demanda al mínimo costo, tomando en consideración restricciones ambientales tal como el riesgo de intrusión salina.相似文献
1000.
Facies reconstructions are used in hydrogeology to improve the interpretation of aquifer permeability distribution. In the absence of sufficient data to define the heterogeneity due to geological processes, uncertainties in the distribution of aquifer hydrofacies and characteristics may appear. Geometric and geostatistical methods are used to understand and model aquifer hydrofacies distribution, providing models to improve comprehension and development of aquifers. However, these models require some input statistical parameters that can be difficult to infer from the study site. A three-dimensional reconstruction of a kilometer scale fine-grain dominated Cenozoic alluvial fan derived from more than 200 continuously cored, closely spaced, and regularly distributed wells is presented. The facies distributions were reconstructed using a genetic stratigraphic subdivision and a deterministic geostatistical algorithm. The reconstruction is only slightly affected by variations in the geostatistical input parameters because of the high-density data set. Analysis of the reconstruction allowed identification in the proximal to medial alluvial fan zones of several laterally extensive sand bodies with relatively higher permeability; these sand bodies were quantified in terms of volume, mean thickness, maximum area, and maximum equivalent diameter. These quantifications provide trends and geological scenarios for input statistical parameters to model aquifer systems in similar alluvial fan depositional settings. 相似文献