Isotope measurements and ground water flow modeling using MODFLOW for understanding environmental changes caused by a well field in semiarid Brazil     

Luiz Alberto Ribeiro Mendonça  Horst Frischkorn  Marlúcia Freitas Santiago  Josué Mendes Filho 《Environmental Geology》2005,47(8):1045-1053

Measurements of the environmental isotopes carbon-14 and oxygen-18 and of the electrical conductivity in ground water, together with MODFLOW-88 (DOS) simulations of pumping tests, were used to achieve a detailed understanding of the functioning of an aquifer in the area of a well field. The methodology was applied in the sedimentary basin of the Cariri region, in the south of Ceará State in Brazil. Localized hydraulic connections between adjacent aquifer units could be detected, and mixing ratios for the contributions from the units involved were determined. Cone of depression simulations for a three-year drought period revealed well interference and a drastic lowering of the piezometric level, thereby explaining the hydrogeologic changes and transformations in vegetation that were observed in the area of the well field. The combined use of the modeling tools and the geochemical field observations is shown to provide more detailed insight into the conceptual model of the groundwater flow system.  相似文献   

Burying processes carried out by a mobile transversal dunefield, Paracuru County, State of Ceará, Brazil     

João Wagner Alencar Castro 《Environmental Geology》2005,49(2):214-218

The migration of dunes and the consequent burying of the city of Paracuru by a transversal dunefield with perpendicular ridges oriented to the dominant windstream have been investigated. Overlapping aerial photographs taken during different flights have been used as a reference. Two sediment transportation directions were identified: the first is fed by the prevailing easterly winds; the second corresponds to the secondary southeasterly winds. With the maintenance of current wind conditions and pluvial precipitation, dunes will bury part of Paracuru town in approximately 120 years. Within this context, the geological evolution model that was applied proved to be satisfactory for the comprehension of sediment transportation mechanisms along the transversal dunes. Considering the prognosis in relation to Paracuru and its urban growth towards the dunefield, it is necessary to continue to study aeolian dynamics, aiming to develop support for the elaboration of future projects directed towards environmental management of the area.  相似文献   

There’s nothing inherent about scale: political ecology, the local trap, and the politics of development in the Brazilian Amazon     

J. Christopher Brown  Mark Purcell 《Geoforum》2005,36(5):607-624

This paper argues that research in political ecology would benefit from more explicit and careful attention to the question of scale and scalar politics. Although political ecologists have extensively considered scale as a methodological question, they have yet to develop an explicit theoretical approach to scale as an object of inquiry. We highlight one principal drawback to this underdeveloped approach to scale: what we call “the local trap” in which political ecologists assume that organization, policies, and action at the local scale are inherently more likely to have desired social and ecological effects than activities organized at other scales. Over the past 10 years or so, an increasingly sophisticated literature on scale has been developing among scholars in geography working in the political economy tradition. This literature has argued that scale is socially produced rather than ontologically given. Therefore, there is nothing inherent about any scale, and so the local scale cannot be intrinsically more desirable than other scales. We suggest that a greater engagement with this scale literature offers political ecology a theoretical way out of the local trap. As a first approximation of the kind of scalar analysis we advocate, we present a case study that examines the scalar politics that have shaped environmental change in the Brazilian Amazon.  相似文献   

Lead in food and soil from a mining area in Brazil and human exposure     

Talita Lammoglia Bemardino R Figueiredo Alice M. Sakuma M.L. Buzzo I.A. Okada C.S. Kira 《中国地球化学学报》2006,25(B08):66-66

During the last century, several lead mines and a metal smelter were in production in the Upper Ribeira Valley, southeastern Brazil. After fifty years of activity, the refinery was shut down in November 1995 and, thereafter the last mines in production were closed. Since 1998, a multidisciplinary research group has carried out an ambitious investigation among the population of five municipalities in the Ribeira Valley （sampled population of 472 children and 523 adults） to assess the human exposure to lead. The highest blood lead levels were found among the population of two villages in the vicinity of the smelter where soil and indoor-dust are highly contaminated. During the present study, the lead contents of several food species that are part of local population diet were investigated. Greens, vegetables, corn, chicken eggs and cow milk, were sampled in two occasions, July 2004 and February 2005. The analytical procedures included burning of organic matter, pre-concentration of lead and, finally, determination by AAS using background correction. The quantification limit was 0.05 μg/g Pb. Soil samples were also collected and analyzed by X-ray fluorescence spectroscopy with a quantification limit of 2 μg/g Pb. The results are very impressing since 100% of greens, vegetables and eggs yielded lead concentrations exceeding the upper limits established by Brazilian regulations whereas milk and maize samples presented lead contents below the regulated limit of 0.05 μg/g Pb. Lead concentrations in soil varied between 156 and 1292 μg/g Pb, resembling the results of previous studies and far exceeding the threshold of 200 μg/g Pb indicated as the intervention value. Lead contents in some species vary consistently with lead concentrations in soils, however, other factors may account for the bioavailability of lead and its intake by plants, like the soil pH, its cationic exchange capacity, clay and organic matter contents, characteristics of the plant species itself, climate, among others.  相似文献   

Stable Isotope Investigations on the Granulite Facies Terrains of Brazil: A Review     

S.S. Iyer  A. Choudhuri  J.S.F. Barbosa 《Gondwana Research》1998,1(3-4):393-402

Stable isotope data from three areas in the granulite facies terrains of Brazil are assembled and discussed. All the three areas (Jequié, Guaxupé and São José do Rio Pardo) are from the São Francisco Craton. The carbon isotope composition of the fluid inclusion CO₂ in the Archean granulite terrain of Jequié indicate the participation of two distinct sources, an upper mantle source and an internal source of Archean organic matter. The isotope data may be interpreted in terms of the granulite genesis due to the intrusion of magma in the lower crust. The singularly uniform carbon isotope data for CO₂ fluid inclusion of plutonic granulites is a clear indication of the magmatic addition of CO₂-rich volatiles from deeper crustal sources. In the São José do Rio Pardo area sulfur and carbon isotope data of scapolites from the granulites imply the derivation of volatiles from internal sources. The whole rock oxygen isotope data of the amphibolite and granulite facies gneisses from Guaxupé indicate a small scale variation of d¹⁸O values, compatible with the chemical data, suggesting the preservation of pre-metamorphic oxygen isotope composition. The isotope data of the granulites from São Francisco Craton indicate non-pervasive fluid flow during metamorphism.  相似文献   

A comparison between natural and anthropogenic emissions of the reduced sulfur compounds H2S, COS, and CS2 in a tropical industrialized region     

J. Dippell  W. Jaeschke 《Journal of Atmospheric Chemistry》1996,25(3):251-270

Extensive ambient concentration and flux measurements have been performed in the heavily polluted region of Cubatão/Brazil. Substantial contribution of anthropogenic sources to the local reduced sulfur burden has been observed. As a result of this atmospheric sulfur burden average gas exchange between vegetated soils and the atmosphere shows net deposition. Based mainly on own field measurements a local budget for H₂S, COS, and CS₂ has been made up in order to calculate anthropogenic emissions. All major sources and sinks in the chosen atmospheric reservoir (24×20×1 km) have been taken into account. Due to the small reservoir size fluxes across its boundaries are dominant sources and sinks. The differences between outflux and influx therefore account for the unknown anthropogenic emissions which have been determined to be 80±10 (H₂S), 66±15 (COS), and 29±6 Mmol year^-1 (CS₂). Other sources and sinks like natural emissions, chemical conversion, and dry deposition turned out to be of minor importance on a local scale. In fact, inside the investigated reservoir natural emissions were below 0.5% of anthropogenic emissions. Anthropogenic emissions of H₂S, COS, and CS₂ quantified in this work have been compared with global emission estimates for these compounds made by other authors. We conclude that global anthropogenic emissions of reduced sulfur compounds especially of COS and CS₂ are currently under-estimated.  相似文献   

Tropospheric chemical composition measurements in Brazil during the dry season   总被引：3，自引：0，他引：3  

P. J. Crutzen  A. C. Delany  J. Greenberg  P. Haagenson  L. Heidt  R. Lueb  W. Pollock  W. Seiler  A. Wartburg  P. Zimmerman 《Journal of Atmospheric Chemistry》1985,2(3):233-256

Field measurement programs in Brazil during the dry seasons in August and September 1979 and 1980 have demonstrated the large importance of the continental tropics in global air chemistry. Many important trace gases are produced in large amounts over the continents. During the dry season, much biomass burning takes place, especially in the cerrado regions, leading to a substantial emission of air pollutants, such as CO, NO _x , N₂O, CH₄ and other hydrocarbons. Ozone concentrations are enhanced due to photochemical reactions. The large biogenic organic emissions from tropical forests play an important role in the photochemistry of the atmosphere and explain why CO is present in such high concentrations in the boundary layer of the tropical forest. Carbon monoxide production may represent more than 3% of the net primary productivity of the tropical forests. Ozone concentrations in the boundary layer of the tropical forests indicate strong removal processes. Due to atmospheric supply of NO _x by lightning, there is probably a large production of O₃ in the free troposphere over the Amazon tropical forests. This is transported to the marine-free troposphere and to the forest boundary layer.  相似文献   

Teleconnections between the rainfall over Northeast Brazil and the winter circulation of Northern Hemisphere     

Rao  V. Brahmananda  de Brito  José Ivaldo B. 《Pure and Applied Geophysics》1985,123(6):951-959

Linear correlation coefficients are calculated between the geopotential heights for the winter months (December, January, and February) at 700 mb in the Northern Hemisphere and the March rainfall over Northeast Brazil. Isolines of correlation coefficients showed interesting patterns and regions of significantly high correlation. The occurrence of PNA pattern is interpreted as a connection between the Northern Hemisphere winter circulation and NE Brazil rainfall through El Niño—Southern oscillation phenomena. The negative center over North-West United States in the PNA pattern also has a direct relationship to the NE Brazil rainfall. Further studies are needed to substantiate and understand the teleconnections noted here.  相似文献   

巴西Paraná和Bahia地区滑石矿床的地质特征与成因模式     

Antonio Carlos GONDIM  蒋少涌 《岩石学报》2004,20(4)

本文总结了巴西两个最重要的滑石产地,Parana和Bahia区中滑石矿床的地质特征,并探讨了这些矿床的可能成因。巴西的滑石在世界滑石储量与产量中占有十分重要的地位。巴西Parana和Bahia区的滑石矿主要产于前寒武纪地体中。尽管该区的滑石具有不同的地质产状,与变质火山岩和变质沉积岩共生的滑石最为重要。其他类型的滑石,如与镁铁质-超镁铁质岩共生的、在花岗岩与白云质大理岩接触带的、在花岗岩体中呈包体或顶垂体状的、则相对不重要。在巴西与岩浆活动有关的滑石矿化主要发生在前寒武纪(Bahia区)和白垩纪(Parana区)。滑石的成因模式主要有两类:一为与岩浆热液有关的热液交代成矿模式,另一是起源于盆地热卤水的变质流体交代成矿模式。其中后一种成因模式可用来解释巴西的大多数大型滑石矿床,同时也适用于其他地区,如中国辽宁和乌拉尔南部的滑石成矿。  相似文献   

Geochemical and stable isotopic evolution of the Guarani Aquifer System in the state of São Paulo, Brazil     

Ondra Sracek  Ricardo Hirata 《Hydrogeology Journal》2002,10(6):643-655

The purpose of this report is to explain geochemical and stable isotopes trends in the Brazilian unit of the Guarani Aquifer System (Botucatu and Piramboia aquifers) in S?o Paulo State, Brazil. Trends of dissolved species concentrations and geochemical modeling indicated a significant role of cation exchange and dissolution of carbonates in downgradient evolution of groundwater chemistry. Loss of calcium by the exchange for sodium drives dissolution of carbonates and results in Na–HCO₃ type of groundwater. The cation-exchange front moves downgradient at probably much slower rate compared to the velocity of groundwater flow and at present is located near to the cities of Sert?ozinho and águas de Santa Barbara (wells PZ-34 and PZ-148, respectively) in a shallow confined area, 50–70 km from the recharge zone. Part of the sodium probably enters the Guarani Aquifer System. together with chloride and sulfate from the underlying Piramboia Formation by diffusion related to the dissolution of evaporates like halite and gypsum. High concentrations of fluorine (up to 13.3 mg/L) can be explained by dissolution of mineral fluoride also driven by cation exchange. However, it is unclear if the dissolution takes place directly in the Guarani Aquifer System or in the overlying basaltic Serra Geral Formation. There is depletion in δ ²H and δ ¹⁸O values in groundwater downgradient. Values of δ ¹³C(DIC) are enriched downgradient, indicating dissolution of calcite under closed system conditions. Values of δ ¹³C(DIC) in deep geothermal wells are very high (>–6.0‰) and probably indicate isotopic exchange with carbonates with δ ¹³C about –3.0‰. Future work should be based on evaluation of vertical fluxes and potential for penetration of contamination to the Guarani Aquifer System. Electronic Publication  相似文献