Variations and change in south American streamflow   总被引：4，自引：0，他引：4  

José A. Marengo 《Climatic change》1995,31(1):99-117

Long-term hydroclimatological records in tropical South America have been analyzed in order to determine whether or not there have been significant changes in the hydrological cycle. Streamflow data from several rivers in Peru, Brazil, Argentina and Venezuela, as well as rainfall in Northeast Brazil have been used here for the study of long-term and interannual variations on hydrological conditions in different regions of South America. The Mann-Kendall statistical test is applied to the historical streamflow annual series in order to detect trends or changes in the mean. The Studentt-test is also applied to study the relationship between interannual variability and the magnitude of change and length of data required to identify a statistically significant trend.It follows from the statistical analysis of the currently available historical river data set that there is no clear evidence of trend or change in the mean streamflow of South American rivers resulting from a climate change, even though significant trends towards drier conditions have been found for rivers in the Northwest coast of Peru and in eastern Brazil. Interannual variations characterized the hydrology of tropical South America, in association with the extreme phases of the Southern Oscillation. The change required to identify a statistically significant variation in the mean is directly proportional to the interannual variability. The effects of Amazon deforestation are not noticeable on the 1903-92 interannual variability of the Rio Negro series at Manaus nor in rainfall time series.  相似文献   

Health, Safety and Environmental Risks of Underground Co2 Storage – Overview of Mechanisms and Current Knowledge     

Kay Damen  André Faaij  Wim Turkenburg 《Climatic change》2006,74(1-3):289-318

CO₂ capture and storage (CCS) in geological reservoirs may be part of a strategy to reduce global anthropogenic CO₂ emissions. Insight in the risks associated with underground CO₂ storage is needed to ensure that it can be applied as safe and effective greenhouse mitigation option. This paper aims to give an overview of the current (gaps in) knowledge of risks associated with underground CO₂ storage and research areas that need to be addressed to increase our understanding in those risks. Risks caused by a failure in surface installations are understood and can be minimised by risk abatement technologies and safety measures. The risks caused by underground CO₂ storage (CO₂ and CH₄ leakage, seismicity, ground movement and brine displacement) are less well understood. Main R&D objective is to determine the processes controlling leakage through/along wells, faults and fractures to assess leakage rates and to assess the effects on (marine) ecosystems. Although R&D activities currently being undertaken are working on these issues, it is expected that further demonstration projects and experimental work is needed to provide data for more thorough risk assessment.  相似文献   

Tectonic framework and extensional pattern of the Malaguide Complex from Sierra Espuña (Internal Betic Zone) during Jurassic–Cretaceous: implications for the Westernmost Tethys geodynamic evolution     

Manuel Martín-Martín  Iván Martín-Rojas  Jesús E. Caracuel  Antonio Estévez-Rubio  Agustín Martín Algarra  José Sandoval 《International Journal of Earth Sciences》2006,95(5):815-826

Mapping, lithostratigraphic, biostratigraphic and structural detailed analyses in Sierra Espuña area (Internal Betic Zone, SE Spain) have allowed us to reconstruct the Jurassic–Cretaceous evolution of the Westernmost Mesomediterranean Microplate palaeomargin and, by correlation with other sectors (Northern Rift, central and western Internal Betic Zone), to propose a geodynamic evolution for the Westernmost Tethys. Extension began from Late Toarcian, when listric normal faults activated; these faults are arranged in three categories: large-scale faults, separating hectometric cortical blocks; main faults, dividing the former blocks into some kilometre-length blocks; and secondary faults, affecting the kilometric blocks. This fault ensemble, actually outcropping, in the Sierra Espuña area, broke the palaeomargin allowing the westerly Tethyan Oceanic aperture with an extension at about 17.2%. Extension was not homogeneous in time, being the Late Toarcian to the Dogger–Malm boundary the period when blocks underwent the greatest movement (rifting phase), leading to the drowning of the area (8.2% extension). During the Malm (drifting phase) extension followed (5.7%), while during the Cretaceous a change to pelagic facies is recorded with an extension of about 3.3% (post-drift stage). This evolution in the Westernmost Tethys seems to be related to areas out of the limit of significant crustal extension in the hanging wall block of the main cortical low-angle fault of the rifting.  相似文献   

Initial assessment of the infiltration and overland flow for different rainfall events in land constituted of sandstones of the Botucatu Formation (Guarani Aquifer), State of São Paulo, Brazil   总被引：1，自引：0，他引：1  

Lázaro Valentin Zuquette  Janaina Barrios Palma  Osni José Pejon 《Environmental Geology》2006,50(3):371-387

This study was carried out in the Córrego do Vaçununga basin constituted of eolic sandstones of Botucatu Formation and residual unconsolidated materials (>90%), considered the most important unconfined aquifer in Brazil, in the city of Luiz Antonio, State of São Paulo, Brazil. Laboratory and in situ tests were performed to characterize the unconsolidated materials in terms of basic physical properties, potential infiltration rate, suction and hydraulic conductivity. The results for infiltration and overland flow depths were obtained according to Morel-Seytoux and Khanji (Water Resour Res 10(4):795–800, 1976) and Chu (Water Resour Res 14(3):461–466, 1978) adaptation of the Green and Ampt [J Agr Sci 4(Part 1):1–24, 1911] model for steady and transient rainfalls, respectively. Rainfall data were collected from January of 2000 to December of 2002, and 12 scenarios were defined considering the intensity and durations. Rather than high homogeneity in terms of the texture of unconsolidated materials, the infiltration and overland flow ratio depends on the type of land use and associated management practices. The results showed that rainfall with high intensity and short duration do not produce high overland flow ratio as we have observed for transient scenarios with long duration and low intensities.  相似文献   

From granitoid to kyanite-bearing micaschist during fluid-assisted shearing (Ile d’Yeu, France)     

Caroline Sassier  Philippe Boulvais  Denis Gapais  Ramon Capdevila  Hervé Diot 《International Journal of Earth Sciences》2006,95(1):2-18

We describe amphibolite-facies shear zones affecting an orthogneiss from the Armorican Hercynian belt (Ile d’Yeu, western France). The deformation pattern is consistent with top-to-the-South thrusting followed by E–W extension, as documented elsewhere in the region. Shearing was accompanied by channelled fluid flow that transformed the orthogneiss into a peraluminous micaschist. Structural and mineralogical data indicate rather early strain localization. Then, temperature increase associated with crustal thickening favoured more distributed deformations marked by shear zone stretching and the development of a HT regional foliation. Chemical analyses made across five shear zones show mass transfers that mainly implied losses in Ca and Na, and gains in H₂O, Mg, and K. Most results indicate constant volume transformation, but some suggest records of either gains or losses of volume (between +20% and −30%). This might reflect variable records of fluid-rock interactions according to the timing of initiation and subsequent evolution of individual shear zones, early thrusting stages being marked by up-temperature flow, and late thrusting stages by down-temperature flow. δ¹⁸O analyses suggest that fluids experienced significant isotopic exchange with orthogneisses.  相似文献   

Human Impact Since Medieval Times and Recent Ecological Restorationin a Mediterranean Lake: The Laguna Zoñar, Southern Spain     

Blas L. Valero-Garcés  Penélope González-Sampériz  Ana Navas  Javier Machín  Pilar Mata  Antonio Delgado-Huertas  Roberto Bao  Ana Moreno  José S. Carrión  Antje Schwalb  Antonio González-Barrios 《Journal of Paleolimnology》2006,35(3):441-465

The multidisciplinary study of sediment cores from Laguna Zoñar (37°29′00′′ N, 4°41′22′′ W, 300 m a.s.l., Andalucía, Spain) provides a detailed record of environmental, climatic and anthropogenic changes in a Mediterranean watershed since Medieval times, and an opportunity to evaluate the lake restoration policies during the last decades. The paleohydrological reconstructions show fluctuating lake levels since the end of the Medieval Warm Period (ca. AD 1300) till the late 19th century and a more acute dry period during the late 19th century – early 20th century, after the end of the Little Ice Age. Human activities have played a significant role in Laguna Zoñar hydrological changes since the late 19th century, when the outlet was drained, and particularly in the mid-20th century (till 1982) when the spring waters feeding the lake were diverted for human use. Two main periods of increased human activities in the watershed are recorded in the sediments. The first started with the Christian conquest and colonization of the Guadalquivir River Valley (13th century) particularly after the fall of the Granada Kingdom (15th century). The second one corresponds to the late 19th century when more land was dedicated to olive cultivation. Intensification of soil erosion occurred in the mid-20th century, after the introduction of farm machinery. The lake was declared a protected area in the early 1980s, when some agricultural practices were restricted, and conservation measures implemented. As a consequence, the lake level increased, and some littoral zones were submerged. Pollen indicators reflect this limnological change during the last few decades. Geochemical indicators show a relative decrease in soil erosion, but not changes in the amount of chemical fertilizers reaching the lake. This study provides an opportunity to evaluate the relative significance of human vs. climatic factors in lake hydrology and watershed changes during historical times. Paleolimnological reconstructions should be taken into account by natural resources agencies to better define lake management policies, and to assess the results of restoration policies.  相似文献   

Distribution of diatoms, chironomids and cladocera in surface sediments of thirty mountain lakes in south-eastern Switzerland   总被引：6，自引：0，他引：6  

Christian Bigler  Oliver Heiri  Renata Krskova  André F. Lotter  Michael Sturm 《Aquatic Sciences - Research Across Boundaries》2006,68(2):154-171

  相似文献   

Arsenic in the groundwater of Ouro Preto (Brazil): its temporal behavior as influenced by the hydric regime and hydrogeology     

José Augusto Costa Gonçalves  Jorge Carvalho de Lena  José Fernando Paiva  Hermínio Arias Nalini Jr  Janice Cardoso Pereira 《Environmental Geology》2007,53(4):785-793

In the city of Ouro Preto (MG), water catchment for public supply originates from superficial drainage, springs, old abandoned mines and some driven wells. In the rocks of the region, As is originally found in gold-enriched sulphide-bearing mineral deposits. The weathering process introduces As into the hydrological system by dissolution of this element into the leachate. Measurement of the As content in the groundwater of some catchments was carried out during 1 year and these measurements demonstrated high As content—up to 224 μg L⁻¹ of As(V)—during the rainy season (the maximum concentration limit according to World Health Organization is 10 μg L⁻¹). Lower values were observed during the dry season and in some sampling stations, As was not even detected. The As concentration variability during 1 year shows a strict and direct relationship to seasonal and hydrological conditions. For city authorities, responsible for public water supply, it is necessary to perform a complete inventory of the water sources used and constantly monitor the As content in the water.  相似文献   

Dynamics and contribution of karst groundwater to surface flow during Mediterranean flood     

Hervé Jourde  Axel Roesch  Vincent Guinot  Vincent Bailly-Comte 《Environmental Geology》2007,51(5):725-730

This paper describes the role of groundwater contribution to surface flow at the Causse d’Aumelas, a karst system near Montpellier (France), which is traversed by an intermittent river, the Coulazou. A first hydrologic model integrating a digital terrain model shows the inability of a standard rainfall-runoff model to replicate recorded flood hydrographs. While the flood peaks are routed through the karstic system along the Coulazou without a phase lag, the peak magnitude is somewhat modified. These results indicate an initial karst system recharge followed by a significant contribution to surface flow. A hydrodynamic analysis of ground-water flow confirms these results: the karst system first absorbs part of the rainfall, which induces a general water table rise within the aquifer, and then contributes to surface flow in the Coulazou.  相似文献   

Precursory Subsurface 222Rn and 220Rn Degassing Signatures of the 2004 Seismic Crisis at Tenerife, Canary Islands     

Nemesio M. Pérez  Pedro A. Hernández  Eleazar Padrón  Gladys Melián  Rayco Marrero  Germán Padilla  José Barrancos  Dácil Nolasco 《Pure and Applied Geophysics》2007,164(12):2431-2448

Precursory geochemical signatures of radon degassing in the subsurface of the Tenerife Island were observed several months prior to the recent 2004 seismic-volcanic crisis. These premonitory signatures were detected by means of a continuous monitoring of ²²²Rn and ²²⁰Rn activity from a bubbling CO₂-rich gas spot located at 2.850 m depth inside a horizontal gallery for groundwater exploitation at Tenerife. Multivariate Regression Analysis (MRA) on time series of the radon activity was applied to eliminate the radon activity fluctuation due to external variables such as barometric pressure, temperature and relative humidity as well as power supply. Material Failure Forecast Method (FFM) was successfully applied to forecast the anomalous seismicity registered in Tenerife Island in 2004. The changes in the ²²²Rn/²²⁰Rn ratio observed after the period of anomalous seismicity might suggest a higher gas flow rate and/or changes in the vertical permeability induced by seismic activity.  相似文献