Phylogeny, diet, and habitat of an extinct ground sloth from Cuchillo Curá, Neuquén Province, southwest Argentina     

Michael Hofreiter  Julio L. Betancourt  Alicia Pelliza Sbriller  Vera Markgraf  H. Gregory McDonald 《Quaternary Research》2003,59(3):364-378

Advancements in ancient DNA analyses now permit comparative molecular and morphological studies of extinct animal dung commonly preserved in caves of semiarid regions. These new techniques are showcased using a unique dung deposit preserved in a late glacial vizcacha (Lagidium sp.) midden from a limestone cave in southwestern Argentina (38.5° S). Phylogenetic analyses of the mitochondrial DNA show that the dung originated from a small ground sloth species not yet represented by skeletal material in the region, and not closely related to any of the four previously sequenced extinct and extant sloth species. Analyses of pollen and plant cuticles, as well as analyses of the chloroplast DNA, show that the Cuchillo Curá ground sloth browsed on many of the same herb, grass, and shrub genera common at the site today, and that its habitat was treeless Patagonian scrub-steppe. We envision a day when molecular analyses are used routinely to supplement morphological identifications and possibly to provide a time-lapse view of molecular diversification.  相似文献   

On the Solar Origins of Intense Geomagnetic Storms Observed During 6–11 March 1993     

Srivastava  Nandita  Gonzalez  Walter D.  Gonzalez  Alicia L.C.  Masuda  Satoshi 《Solar physics》1998,183(2):419-434

Intense geomagnetic storms with DST index -100 nT were recorded on 9 March and 11 March 1993 associated with solar activity on 6 March and 9-10 March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6 March 1993 and in the other case, to two large filament disruptions on the disk during 9-10 March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here.  相似文献   

Comparison of four numerical models for simulating seepage from salt marsh sediments   总被引：1，自引：1，他引：1  

Leonard Robert Gardner  Alicia M. Wilson   《Estuarine, Coastal and Shelf Science》2006,69(3-4):427

A boundary integral equation method (BIEM) model and three differently formulated finite element method (FEM) models were implemented to explore the spatial and temporal patterns in marsh pore water seepage that each generated. The BIEM model is based on the Laplace equation coupled to a dynamic free-surface condition that assumes that, as the water-table changes, the aquifer instantaneously loses or gains an amount of water equal to the change in head times the specific yield. The FEM models all implement a simplified Richards equation that allows gradual desaturation or resaturation and thus flow in both the saturated and unsaturated zones of the aquifer. Two of the FEM models are based on the governing equation for the USGS model SUTRA and thus take into account fluid and aquifer compressibility. One of these was modified to take into account the effect of tidal loading on the total stress, which is assumed to be constant in the derivation of the original version of SUTRA. The third FEM model assumes that neither the fluid or aquifer matrix is compressible so that changes in storage are due solely to changes in saturation. The unmodified SUTRA model generated instantaneous boundary fluxes that were up to two orders of magnitude greater, and spatially more uniform, than those of the other models. The FEM model without compressibility generated spatial and temporal patterns of the boundary fluxes very similar to those produced by the BIEM model. The SUTRA model with the tidal stress modification gave fluxes similar in magnitude to the BIEM and no compressibility models but with distinctly different distributions in space and time. These results indicate that accurate simulation of seepage from marsh soils is highly sensitive to aquifer compressibility and to proper formulation of the effect of tidal loading on the total stress in the aquifer. They also suggest that accurate simulation may require total stress correction not only for tidal loading but for changes in the water table as well. Finally, to aid the development of methods for the measurement of compressibility, we present a schematic, pore-scale model to illustrate the factors that may govern the compressibility of marsh soils.  相似文献   

Characterizing the vadose zone and a perched aquifer near the Vosges ridge at the La Soutte experimental site,Obernai, France     

Pascal Sailhac  Maksim Bano  Mickael Behaegel  Jean-François Girard  Ester Falgàs Para  Juanjo Ledo  Guy Marquis  Pierre-Daniel Matthey  José Ortega-Ramírez 《Comptes Rendus Geoscience》2009,341(10-11):818-830

We consider a series of hydrogeophysical techniques that provide a multiscale investigation of the water content in the vadose zone and of the perched aquifer at the experimental site of “La Soutte” in the Vosges Mountains (France). It is located in a catchment area where several springs and streams occur along fractured volcanic and weathered plutonic rocks. The site is the object of a long-term study that uses both continuous and repeated measurements to monitor hydrogeological processes. The main results from AMT and DC resistivity techniques allow the determination of a high-resolution 3D resistivity model over a large range of depths (from 10⁰ to 10³ m). We discuss their use and propose a hydrogeological model (porosity, water conductivity and water content). We also use MRS and GPR for a detailed investigation of the shallow part of the catchment that consists of soil and weathered rocks of highly varying thickness (0 to 15 m). MRS is used to map the thickness and total water volume content by unit surface of the saturated weathered zone. It also yields estimates of the vadose zone thickness through the depth to the top of the saturated zone. Moreover, we show results from GPR CMP measurements that yield estimates of the water content and porosity in the shallowest layer (0–30 cm) by simple interpretation of the ground direct wave.  相似文献   

3D magnetotelluric characterization of the geothermal anomaly in the Llucmajor aquifer system (Majorca, Spain)     

C. Arango  A. Marcuello  J. Ledo  P. Queralt 《Journal of Applied Geophysics》2009,68(4):479-488

In the Llucmajor aquifer system (Majorca Island, Spain) some geothermal evidences have appeared. This phenomenon is not isolated to Majorca and it is present in other areas, where it can be associated with structural conditions, especially to the extensional event suffered by the island after the Alpine Orogeny. However, the origin of this anomaly in Llucmajor is not well known, and there is no surface geological evidence of these structural conditions. With the aim of delineating the geoelectrical structure of the zone and identifying the geological structure that allows the presence of this anomaly, an audiomagnetotelluric (AMT) survey was carried out. The AMT data was processed using a Wavelet Transform-based scheme. Dimensionality analysis indicates that the geoelectrical structure is mainly 3D. The 3D model was obtained by trial and error forward modeling, taking accounting of the responses from the determinant of the impedance tensor. The model shows a vertical resistivity distribution with three horizons associated with different units: on the top, a shallow high resistive media related to an unconfined shallow aquifer; in the middle, a conductive layer related to the aquitard, and below it, another resistive media related to the confined deeper aquifer. The intermediate horizon shows a sudden thinning beneath the thermal anomalous zone that can be identified as a weakness zone (fault or fracture) connecting both aquifers. An exploratory well was drilled after the AMT survey and reached almost 700 m in depth. This allowed correlating the resistivity distribution of the 3D model with data logging and lithology obtained from the well, showing a proper agreement between them.  相似文献   

3-D Magnetotelluric Exploration of Tenerife Geothermal System (Canary Islands,Spain)     

P. Piña-Varas  J. Ledo  P. Queralt  A. Marcuello  F. Bellmunt  R. Hidalgo  M. Messeiller 《Surveys in Geophysics》2014,35(4):1045-1064

The resistivity structure of the Tenerife geothermal system has been determined by the 3-D inversion of data from different magnetotelluric surveys. In this paper, the ocean and topography effects on the magnetotelluric data were investigated by constructing a 3-D conceptual geoelectrical model of the island. The study showed that these effects should be taken into account in order to obtain a reliable subsurface model of the island. Data from 148 sites were used during three-dimensional inversion. The most interesting feature in the final geoelectrical model of the geothermal system is a low resistivity structure (<10 Ωm) above the resistive core of the system. The low resistivity structure has been interpreted as a hydrothermal clay alteration cap typically generated in the conventional geothermal systems. The resistivity model has been correlated with a recent seismic velocity model, showing that a low resistivity structure surrounds an area with high P wave velocity and medium–high resistivity. This medium–high resistivity area can be associated with a slowly solidified magma and, therefore, with a hotter part of the geothermal system.  相似文献   

Comparison of marine and river water humic substances in a Patagonian environment (Argentina)     

María del Carmen Scapini  Víctor Hugo Conzonno  Vilma Teresa Balzaretti  Alicia Fernández Cirelli 《Aquatic Sciences - Research Across Boundaries》2010,72(1):1-12

Structural aspects of humic substances (HSs) in marine waters of Engaño Bay (Atlantic Ocean) and water from the Chubut River (Patagonia, Argentina) were compared. The HSs were isolated, purified, and analyzed using a multiple-method approach for structural characterization: elemental analysis, nuclear magnetic resonance (¹³C and ¹H NMR), infrared spectroscopy (FTIR), UV-visible absorption and fluorescence. Similarities between the marine and freshwater components were evaluated on the basis of N and O contents, H/C and C/N atomic ratios, infrared bands from nitrogen-containing and carboxylic groups, percentage of functional groups obtained from NMR spectra, spectral slope coefficient of absorption spectra, absorbance ratios at 250 and 365 nm (E ₂/E ₃), aromaticity, excitation–emission matrices and fluorescence quantum yield. Both the Engaño Bay and Chubut River waters have HSs that are mainly composed of fulvic acids (FAs); although they are very similar, they may be distinguished from one another. Similarities include the predominance of aliphatic carbon content (low aromatic content); however, the water bodies differed in their content of proteins and carboxylic acids. The Engaño Bay FAs have mainly an aquatic origin; although the Chubut River FAs suggest a similar aquagenic origin, there is also evidence of contributions from pedogenic FAs.  相似文献   

Set-up of a decision support system to support sustainable development of the Laguna de Bay,Philippines   总被引：2，自引：0，他引：2  

Nauta TA  Bongco AE  Santos-Borja AC 《Marine pollution bulletin》2003,47(1-6):211-218

Over recent decades, population expansion, deforestation, land conversion, urbanisation, intense fisheries and industrialisation have produced massive changes in the Laguna de Bay catchment, Philippines. The resulting problems include rapid siltation of the lake, eutrophication, inputs of toxics, flooding problems and loss of biodiversity. Rational and systematic resolution of conflicting water use and water allocation interests is now urgently needed in order to ensure sustainable use of the water resources. With respect to the competing and conflicting pressures on the water resources, the Laguna Lake Development Authority (LLDA) needs to achieve comprehensive management and development of the area. In view of these problems and needs, the Government of the Netherlands was funding a two-year project entitled 'Sustainable Development of the Laguna de Bay Environment'.A comprehensive tool has been developed to support decision-making at catchment level. This consists of an ArcView GIS-database linked to a state-of-the-art modelling suite, including hydrological and waste load models for the catchment area and a three-dimensional hydrodynamic and water quality model (Delft3D) linked to a habitat evaluation module for the lake. In addition, MS Office based tools to support a stakeholder analysis and financial and economic assessments have been developed. The project also focused on technical studies relating to dredging, drinking water supply and infrastructure works. These aimed to produce technically and economically feasible solutions to water quantity and quality problems. The paper also presents the findings of a study on the development of polder islands in the Laguna de Bay, addressing the water quantity and quality problems and focusing on the application of the decision support system.  相似文献   

An evaluation of glass prisms in boat docks to reduce shading of submerged aquatic vegetation in the lower St. Johns River,Florida     

Alicia?M.?SteinmetzEmail author  Michelle?M.?Jeansonne  Emily?S.?Gordon  John?W.?Burns 《Estuaries and Coasts》2004,27(6):938-944

The effectiveness of glass prisms in boat docks was assessed to determine if shading impacts to submerged aquatic vegetation (SAV), primarilyVallisneria americana, were reduced. Six experimental docks, three with prisms and three without prisms, were constructed in the lower St. Johns River, Florida. SAV percent cover and photosynthetically active radiation (PAR) were monitored under each dock and in an adjacent control area with no experimental docks. Subsurface PAR during the growing season of the first year of the study was not significantly greater beneath docks having prisms than beneath docks without prisms. Postconstruction SAV monitoring (February 2000 to May 2002) revealed no significant differences in SAV percent cover between dock treatments, although coverage declined in both dock treatments and the control area. Declining water quality conditions at the study site clearly impacted the health of the SAV habitat as indicated by the decline in SAV coverage in the control area initially in the study. Given the subsequent resurgence of SAV in the control area, the additional light transmitted through the prisms did not appear to be biologically significant or adequate to counteract effects from larger-scale environmental stressors.  相似文献   

Weathering profiles in granites, Sierra Norte (Córdoba, Argentina)     

Alicia Kirschbaum  Estela Martínez  Gisela Pettinari  Silvana Herrero 《Journal of South American Earth Sciences》2005,19(4):479-493

Two weathering profiles evolved on peneplain-related granites in Sierra Norte, Córdoba province, were examined. Several weathering levels, of no more than 2 m thickness, were studied in these profiles. They had developed from similar parent rock, which had been exposed to hydrothermal processes of varying intensity. Fracturing is the most notable feature produced by weathering; iron oxides and silica subsequently filled these fractures, conferring a breccia-like character to the rock. The clay minerals are predominantly illitic, reflecting the mineral composition of the protolith. Smaller amounts of interstratified I/S RO type are also present, as well as scarce caolinite+chlorite that originated from the weathering of feldspar and biotite, respectively. The geochemical parameters define the weathering as incipient, in contrast to the geomorphological characteristics of Sierra Norte, which point to a long weathering history. This apparent incompatibility could be due to the probable erosion of the more weathered levels of the ancient peneplains, of which only a few relicts remain. Similar processes have been described at different sites in the Sierras Pampeanas. Reconstruction and dating of the paleosurfaces will make it possible to set time boundaries on the weathering processes studied and adjust the paleographic and paleoclimatic interpretations of this great South American region.  相似文献