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11.
María Fernanda Hernández‐López Isabelle Braud Jorge Gironás Francisco Suárez José Francisco Muñoz 《水文研究》2016,30(25):4704-4719
The need to understand and simulate hydrological phenomena and their interactions, and the impact of anthropogenic and climate changes on natural environments have promoted the study of evaporation from bare soils in arid climates. In closed Altiplano basins, such as those encountered in arid and hyper arid basins in northern Chile, evaporation from shallow groundwater is the main source of aquifer depletion, and thus, its study is crucial for water resources management. The objective of this work is to understand the mechanisms of evaporation in saline soils with shallow water tables, in order to better quantify evaporation fluxes and improve our understanding of the water balance in these regions. To achieve this objective, a model that couples fluid flow with heat transfer was developed and calibrated using column experiments with saline soils from the Huasco salt flat basin, Chile. The model enables determination of both liquid and water vapour fluxes, as well as the location of the evaporation front. Experimental results showed that salt transport inside the soil profile modified the water retention curve, highlighting the importance of including salt transport when modelling the evaporation processes in these soils. Indeed, model simulations only agreed with the experimental data when the effect of salt transport on water retention curves was taken into account. Model results also showed that the evaporation front is closer to the soil surface as the water table depth reduces. Therefore, the model allows determining the groundwater level depth that results in disconnection of liquid fluxes in the vadose zone. A sensitivity analysis allowed understanding the effect of water‐flux enhancements mechanisms on soil evaporation. The results presented in this study are important as they allow quantifying the evaporation that occurs in bare soils from Altiplano basins, which is typically the main water discharge in these closed basins. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
12.
In the central part of the Bolivian Altiplano, the shallow groundwater presents electrical conductivities ranging from 0·1 to 20 mS/cm. In order to study the origin of this salinity pattern, a good knowledge is required of the geometry of the aquifer at depth. In this study, geophysics has been used to complement the sparse data available from drill holes. One hundred time‐domain electromagnetic (TDEM) soundings were carried out over an area of 1750 km2. About 20 geological logs were available close to some of the TDEM soundings. Three intermediate results were obtained from the combined data: (i) the relationship between the electrical conductivity of the groundwater and the formation resistivity, (ii) geoelectrical cross‐sections and (iii) geoelectrical maps at various depths. The limited data set shows a relationship between resistivity and the nature of the rock. From the cross‐sections, a conductive substratum with a resistivity of less than 1 Ω·m was identified at most of the sites at depths ranging from 50 to 350 m. This substratum could be a clay‐rich formation containing brines. Using derived relationships, maps of the nature of the formation (sandy, intermediate and clayey sediments) were established at depths of 10 and 50 m. Discrimination between sand and clays was impossible where groundwater conductivity is high (>3 mS/cm). In the central part of the area, where the groundwater conductivity is low, sandy sediments are likely to be present from the surface to a depth of more than 200 m. Clayey sediments are more likely to be present in the south‐east and probably constitute a hydraulic barrier to groundwater flow. In conclusion, the study demonstrates the efficiency of the TDEM sounding method to map conductive zones. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
13.
Santiago Giralt Ana Moreno Roberto Bao Alberto Sáez Ricardo Prego Blas L. Valero-Garcés Juan José Pueyo Penélope González-Sampériz Conxita Taberner 《Journal of Paleolimnology》2008,40(1):195-215
A high resolution multiproxy study (magnetic susceptibility, X-ray diffraction, XRF scanner, gray-colour values, Total Organic
Carbon, Total Inorganic Carbon, Total Carbon and Total Biogenic Silica) of the sedimentary infill of Lago Chungará (northern
Chilean Altiplano) was undertaken to unravel the environmental forcings controlling its evolution using a number of different
multivariate statistical techniques. Redundancy analyses enabled us to identify the main provenance of the studied proxies
whereas stratigraphically unconstrained cluster analyses allowed us to distinguish the “outsiders” as result of anomalous
XRF scanner acquisitions. Principal Component Analysis (PCA) was employed to identify and isolate the main underlying environmental
gradients that characterize the sedimentary infill of Lago Chungará. The first eigenvector of the PCA could be interpreted
as an indicator of changes in the input of volcaniclastic material, whereas the second one would indicate changes in water
availability. The chronological model of this sedimentary sequence was constructed using 17 AMS 14C and 1 238U/230Th dates in order to characterize the volcaniclastic input and the changes in water availability in the last 12,300 cal years
BP.
Comparison of the reconstructed volcaniclastic input of Lago Chungará with the dust particle record from the Nevado Sajama
ice core suggested that the Parinacota volcano eruptions were the main source of dust during the mid and Late Holocene rather
than the dry out lakes as has previously been pointed out. The comparison of the water availability reconstruction of Lago
Chungará with three of the most detailed paleoenvironmental records of the region (Paco Cocha, Lake Titicaca and Salar Uyuni)
showed an heterogeneous (and sometimes contradictory) temporal and spatial pattern distribution of moisture. Although the
four reconstructions showed a good correlation, each lacustrine ecosystem responded differently to the moisture oscillations
that affected this region. The variations in the paleoenvironmental records could be attributed to the dating uncertainities,
lake size, lake morphology, catchment size and lacustrine ecosystem responses to the abrupt arid events. 相似文献
14.
Isoleg theory predicts that coexistence between two competing species can occur when the subordinate, generalist species uses alternative patches of resources as the density of the dominant specialist species increases. These models provide a framework to determine if a native species is subordinate to an introduced one, thus requires conservation considerations. We investigated habitat interactions between a wild neotropical camelid and domestic exotic ungulates in the Andean Puna semi-desert of South America. The Puna or Altiplano is an arid environment located in high altitudes, with cold and dry weather, and two main types of habitats, steppes and swamp areas. There was a high overlap of diets between species. Vicuñas were generalists in the use of habitat, but invested foraging effort in swamp habitats, while livestock were taken to swamp habitats by local people. Vicuñas and livestock were spatially segregated. Vicuñas used the preferred habitat less than expected from their foraging preference. We concluded that vicuñas and livestock coexist because vicuñas occupy sub-optimal habitats whilst livestock concentrate in the richest ones. Vicuñas can deal with poor habitats because they have several adaptations to live in deserts. 相似文献
15.
Along the Central Andes a pattern of vertical axis rotations has been paleomagnetically identified. Such rotations are counterclockwise north of Arica Deflection (∼19° S) and clockwise to the south. Different hypothesis and models have been proposed to explain the Central Andean Rotation Pattern (CARP). However, the origin of the CARP is a subject of ongoing debate. Recently, different authors have proposed the possible existence of a close correlation between the time–space distribution of deformation and the amount of registered vertical axis rotations in the Southern Central Andes. In order to further investigate such relationship, new paleomagnetic studies were carried out in Upper Oligocene–Lower Miocene rocks of the Northern Argentine Puna and the Southern Bolivian Altiplano. Our results indicate that while one of the sampled localities did not undergo significant vertical axis rotations, the other two recorded clockwise vertical axis rotations larger than 30°. These results suggest the occurrence of small-block rotations in the Southern Bolivian Altiplano–Northern Argentine Puna prior to 15 Ma, which would correspond to the local accommodation of the regional deformation field. 相似文献
16.
Stratigraphic relationships, radiocarbon dating, sediment and peat characteristics, and rates of peat and carbon accumulation from a soligenous peatland, or “bofedal,” in the Chilean Altiplano shows the peatland to be unusually young, dynamic, and sensitive to environmental changes. The site lies in the National Park Nevado de Tres Cruces in the puna desert grassland at an elevation of 4300 m a.s.l. Eight peat cores were extracted from a 1.75-km transect yielding a maximum of 3.6 m of organic sediment. Organic matter began to accumulate 1700-1100 cal yr B.P. under a progressively arid local climate, after a period when regional climate is believed to have been more humid than at present. Areas of greater relief and better drainage in the valley bottom eventually fostered the growth of a riparian cushion plant community after water flowing down the valley began to diminish. This led to rapid lateral expansion of the riparian peatland communities over open water in topographic depressions at a rate heretofore unprecedented in the peatland literature. It appears that development of the peatland has been encouraged by autoregulation of internal hydrology. The drainage impediment created by organic mass accumulation in lower-relief areas probably reduced the amount of water arriving at the lower reaches of the peatland. These areas have become progressively drier and have since died and oxidized. Through endogenous peat accumulation and a concomitant drainage impediment, the ecosystem has been migrating upstream over the past 50 years. 相似文献
17.
Hydrologic variation during the last 170,000 years in the southern hemisphere tropics of South America 总被引：1，自引：0，他引：1
Sherilyn C Fritz Paul A Baker Tim K Lowenstein Catherine A Rigsby Pedro M Tapia Teh-Lung Ku 《Quaternary Research》2004,61(1):95-104
Despite the hypothesized importance of the tropics in the global climate system, few tropical paleoclimatic records extend to periods earlier than the last glacial maximum (LGM), about 20,000 years before present. We present a well-dated 170,000-year time series of hydrologic variation from the southern hemisphere tropics of South America that extends from modern times through most of the penultimate glacial period. Alternating mud and salt units in a core from Salar de Uyuni, Bolivia reflect alternations between wet and dry periods. The most striking feature of the sequence is that the duration of paleolakes increased in the late Quaternary. This change may reflect increased precipitation, geomorphic or tectonic processes that affected basin hydrology, or some combination of both. The dominance of salt between 170,000 and 140,000 yr ago indicates that much of the penultimate glacial period was dry, in contrast to wet conditions in the LGM. Our analyses also suggest that the relative influence of insolation forcing on regional moisture budgets may have been stronger during the past 50,000 years than in earlier times. 相似文献
18.
Marcela Mrquez-García Irma Vila Luis Felipe Hinojosa Marco A. Mndez Jos Luis Carvajal María Catalina Sabando 《Limnologica》2009,39(4):314-318
We compared the distribution and seasonal fluctuations in the aquatic biota in relation to chemical and physical water variables in the Altiplano watersheds of the Ascotán, Carcote and Huasco salars; Chungará and Cotacotani lakes; Isluga and Lauca Rivers and the Parinacota wetland. We sampled during the austral autumn–winter of 2006 and in the spring–summer of 2006–2007, using three sampling stations for each system. We used canonical correspondence analysis to establish relations between frequency of taxa and environmental variables.We demonstrate that the structure and composition of the aquatic biota in humid areas of the Altiplano is determined by physical and chemical variables of the water. The most relevant one is total nitrogen, which is also the limiting nutrient for phytoplankton production in tropical systems.Benthos and zooplankton showed significant associations with the set of environmental variables (Monte Carlo test, p<0.05); however, the association was not significant for phytoplankton. Lake Chungará showed the greatest variation in composition and abundance of zooplankton between autumn-winter and spring-summer, while in the Huasco salar the physical and chemical characteristics were related to the composition and abundance of the benthonic fauna. Thus, changes in the water volume of these systems would have repercussions in chemical and physical variables, altering the species assemblage and possibly the efficiency and stability of ecosystem functions. 相似文献
19.
机场建设工程选址勘察为机场建设工程的决策者和工作者提供科学依据.通过实践,总结了机场建设工程选址勘察的目的、内容、过程及方法. 相似文献
20.
On June 23, 2001, an M8.4 earthquake that originated in southern Peru triggered the partial collapse of the Chislluma bofedal (water meadows) in the Altiplano (high-altitude plateau) of northern Chile. The seismic waves evidently produced the liquefaction of the bofedal and caused its partial collapse generating a flow. The flow deposit was mainly made of long-fiber grass and water, with minor amounts of clastic material. It traveled more than 14 km downstream at a peak velocity of 50 km/h. It destroyed the water meadows and killed more than 20 llamas. Slurry flows caused by meadow liquefaction are a previously unrecognized seismic-induced geological hazard for high-altitude plateau areas such as the Altiplano. 相似文献