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111.
Laura Perdomo Ingo Ensminger Luisa fernanda Espinosa Carola Elster Mnica Wallner-kersanach Marie-Luise Schnetter 《Marine pollution bulletin》1999,37(8-12):393-403
Alteration of water flows and consequent hypersalinization caused the death of nearly 70% of mangroves at the Ciénaga Grande de Santa Marta, Colombia. Efforts to rehabilitate the ecosystem have been made through the construction of freshwater channels. Mangrove recovery was observed along a freshwater channel and at a small lagoon behind the beach ridge. Factors identified in this study influencing mangrove regeneration are: salinity of surface water, duration and height of flooding, leaching property of soils, dispersal of propagules and presence of fertile trees. Besides mangrove regeneration, a notable extension of freshwater plants was observed in the channel. Trace metal concentrations in sediments from the Magdalena River and its area of influence were investigated before the complete opening of the first channel. A relative comparison indicated that the highest concentrations of Cd, Cu, Ni and Zn were above international recommended limits. However, metal concentrations found in sediments at Clarín Channel did not affect the mangrove recovery. 相似文献
112.
Fco. Javier Pavón–Carrasco Maria Luisa Osete J. Miquel Torta Luis R. Gaya–Piqué 《Pure and Applied Geophysics》2008,165(6):1209-1225
The SCHA.DI.00 directional model for the geomagnetic field in Europe for the last 2000 years (Pavón–Carrasco
et al., 2008) has been updated by modelling the palaeointensity. This model, SCHA.DI.00, was developed from available Bayesian
European Palaeosecular Variation Curves using the regional Spherical Cap Harmonic Analysis technique. The comparison of the
palaeosecular variation curves, given by the regional model, with available archaeomagnetic data not used in its development
showed an improvement with respect to the fit obtained by global archaeomagnetic models. In this paper advantage is taken
of recently published palaeointensity databases to develop a complete (direction and intensity) regional archaeomagnetic model
for the last 2000 years valid for the European region: the SCHA.DI.00–F model. Not only does this complete model provide an
improvement for example for archaeomagnetic data studies, but it is also shown that this new regional model can be used to
study the recently proposed link between the centennial secular variation of the geomagnetic field and climate change. The
pattern of the archaeosecular variation of the field intensity obtained by SCHA.DI.00–F seems to verify the hypothesis presented
by Gallet et al. (2005) about a possible (causal) connection between changes in the geomagnetic field intensity and in climate parameters,
opening the door for more discussions on this challenging subject. 相似文献
113.
114.
Palynological studies undertaken in the mountainous regions of the northwest of the Iberian Peninsula are few in number and have been concerned largely with the second half of the Holocene. New pollen data from two Galician sierras, the Courel and Queixa Sierras, provide a 10000‐yr record of vegetation and climate change. In the Courel Sierra before 9750 yr BP, Laguna Lucenza (1420 m a.s.l.) reflects a period of open landscape covered by Poaceae and heliophilous plants, which may be correlated with the Younger Dryas. The onset of the Holocene is characterised by the expansion of oak woodland, prior to 9300 yr BP, following a short phase of birch along with the gradual decline of pine. The oak values reach a peak at 8350 ± 80 yr BP. Towards 8800 yr BP Corylus begins to expand, followed by Alnus (7500 yr BP) and Ulmus. During this period, the Fraga pollen assemblage (Queixa Sierra, 1360 m a.s.l.) indicates Betula woodland surrounding the site, masking the regional predominance of oak. After 5000 yr BP there is a gradual decrease in arboreal pollen values in both Sierras. Castanea appears in Laguna Lucenza (Courel Sierra) at 4075 ± 75 yr BP. There is widespread deforestation during the last 4000 yr. During this period the presence of large quantities of microcharcoal particles points to the occurrence of fire. The reduction in forest is associated with the arrival of cultivation at 4000 yr BP at low altitudes in the Queixa Sierra. At higher altitudes the first agricultural activity is dated at later than 2000 yr BP. This coincides with the first record of cereal cultivation at high altitude in the Courel Sierra. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
115.
Three types of periglacial deposits (breccias, stratified breccias and grèzes litées are described from Córdoba Province in southern Spain. Their physico-chemical properties, in particular clay mineralogy in relation to terra rossas in the area, indicate two different ages for these deposits. Younger terra rossas and younger periglacial deposits contain illite and kaolinite whereas older terra rossas and older periglacial deposits contain vermiculite and kaolinite. Geomorphological evidence (altitude and relationships to the surfaces described by earlier authors in southern Spain) indicate approximate ages for the deposits. Secondary carbonate from one of the younger breccias gave a uranium series date of 80 000 yr BP, suggesting that some of the younger breccias were deposited in a periglacial climate before 80 000 BP. © 1997 John Wiley & Sons, Ltd. 相似文献
116.
Enrique Villa Juan L. Cano Beatriz Aja J. Vicente Terán Luisa de la Fuente Ángel Mediavilla Eduardo Artal 《Experimental Astronomy》2018,45(1):127-146
This paper describes the analysis, design and characterization of a polarimetric receiver developed for covering the 35 to 47 GHz frequency band in the new instrument aimed at completing the ground-based Q-U-I Joint Tenerife Experiment. This experiment is designed to measure polarization in the Cosmic Microwave Background. The described high frequency instrument is a HEMT-based array composed of 29 pixels. A thorough analysis of the behaviour of the proposed receiver, based on electronic phase switching, is presented for a noise-like linearly polarized input signal, obtaining simultaneously I, Q and U Stokes parameters of the input signal. Wideband subsystems are designed, assembled and characterized for the polarimeter. Their performances are described showing appropriate results within the 35-to-47 GHz frequency band. Functionality tests are performed at room and cryogenic temperatures with adequate results for both temperature conditions, which validate the receiver concept and performance. 相似文献
117.
Daniele Penna Giulia Zuecco Stefano Crema Sebastiano Trevisani Marco Cavalli Luisa Pianezzola Lorenzo Marchi Marco Borga 《水文研究》2017,31(4):768-782
In this study, we investigate the surface flow time of rise in response to rainfall and snowmelt events at different spatial scales and the main sources originating channel runoff and spring water in a steep nested headwater catchment (Rio Vauz, Italian Dolomites), characterized by a marked elevation gradient. We monitored precipitation at different elevations and measured water stage/streamflow at the outlet of two rocky subcatchments of the same size, representative of the upper part of the catchment dominated by outcropping bedrock, at the outlet of a soil‐mantled and vegetated subcatchment of similar size but different morphology, and at the outlet of the main catchment. Hydrometric data are coupled with stable isotopes and electrical conductivity sampled from different water sources during five years, and used as tracers in end‐member mixing analysis, application of two component mixing models and analysis of the slope of the dual‐isotope regression line. Results reveal that times of rise are slightly shorter for the two rocky subcatchments, particularly for snowmelt and mixed rainfall/snowmelt events, compared to the soil‐mantled catchment and the entire Rio Vauz Catchment. The highly‐variable tracer signature of the different water sources reflects the geomorphological and geological complexity of the study area. The principal end‐members for channel runoff and spring water are identified in rainfall and snowmelt, which are the dominant water sources in the rocky upper part of the study catchment, and soil water and shallow groundwater, which play a relevant role in originating baseflow and spring water in the soil‐mantled and vegetated lower part of the catchment. Particularly, snowmelt contributes up to 64 ± 8% to spring water in the concave upper parts of the catchment and up to 62 ± 11% to channel runoff in the lower part of the catchment. These results offer new experimental evidences on how Dolomitic catchments capture and store rain water and meltwater, releasing it through a complex network of surface and subsurface flow pathways, and allow for the construction of a preliminary conceptual model on water transmission in snowmelt‐dominated catchments featuring marked elevation gradients. 相似文献
118.
Alfonso Encinas Victor Maksaev Luisa Pinto Jacobus P. Le Roux Francisco Munizaga Marcos Zentilli 《Journal of South American Earth Sciences》2006,20(4):369-381
Lahar deposits occur within a shallow marine sedimentary succession of the Pliocene La Cueva Formation in the Coastal Cordillera of central Chile (33°40′–34°15′S). Provenance studies of the abundant volcanic material in the lahar deposits suggest that they derive from denudation by mass wasting of Oligocene–Miocene volcanic rocks on the western slopes of the Main Andean Cordillera at the same latitude. Pliocene rock debris deposits preserved in the region of El Teniente (34°S) and scattered along the westernmost part of the Andes of central Chile indicate catastrophic erosive events related to the rapid uplift of the cordilleran block. This rock debris was deposited by avalanches and transformed further downslope into lahars by dilution with stream water. Lahars were channeled along the ancient drainage system that reached a shallow Pliocene sea at the site of the present Coastal Cordillera. The exceedingly rapid exhumation of active porphyry systems during the Early Pliocene in this part of the Andes may have played a role in affecting hydrothermal processes, brecciation, and diatreme formation at the porphyry systems of El Teniente and Río Blanco–Los Bronces. 相似文献
119.
DI VINCENZO GIANFRANCO; TONARINI SONIA; LOMBARDO BRUNO; CASTELLI DANIELE; OTTOLINI LUISA 《Journal of Petrology》2006,47(7):1439-1465
Different lithologies (impure marble, eclogite and graniticorthogneiss) sampled from a restricted area of the coesite-bearingBrossascoIsasca Unit (Dora Maira Massif) have been investigatedto examine the behaviour of 40Ar39Ar and RbSrsystems in phengites developed under ultrahigh-pressure (UHP)metamorphism. Mineralogical and petrological data indicate thatzoned phengites record distinct segments of the PT path:prograde, peak to early retrograde in the marble, peak to earlyretrograde in the eclogite, and late retrograde in the orthogneiss.Besides major element zoning, ion microprobe analysis of phengitein the marble also reveals a pronounced zoning of trace elements(including Rb and Sr). 40Ar39Ar apparent ages (3562Ma, marble; 89170 Ma, eclogite; 3552 Ma, orthogneiss),determined through Ar laserprobe data on phengites (step-heatingand in situ techniques), show wide intra-sample and inter-samplevariations closely linked to within-sample microchemical variations:apparent ages decrease with decreasing celadonite contents.These data confirm previous reports on excess Ar and, more significantly,highlight that phengite acted as a closed system in the differentlithologies and that chemical exchange, not volume diffusion,was the main factor controlling the rate of Ar transport. Conversely,a RbSr internal isochron from the same eclogite yieldsan age of 36 Ma, overlapping with the time of the UHP metamorphicpeak determined through UPb data and thereby corroboratingthe previous conclusion that UHP metamorphism and early retrogressionoccurred in close succession. Different phengite fractions ofthe marble yield calcitephengite isochron ages of 36to 60 Ma. Although this time interval matches Ar ages from thesame sample, RbSr data from phengite are not entirelyconsistent with the whole dataset. According to trace elementvariations in phengite, only RbSr data from two wet-groundphengite separates, yielding ages of 36 and 41 Ma, are internallyconsistent. The oldest age obtained from a millimetre-sizedgrain fraction enriched in progradepeak phengites mayrepresent a minimum age estimate for the prograde phengite relics.Results highlight the potential of the in situ 40Ar39Arlaser technique in resolving discrete PT stages experiencedby eclogite-facies rocks (provided that excess Ar is demonstrablya negligible factor), and confirm the potential of RbSrinternal mineral isochrons in providing precise crystallizationages for eclogite-facies mineral assemblages. KEY WORDS: 40Ar39Ar dating; RbSr dating; phengite; SIMS; UHP metamorphism 相似文献
120.
The interaction of multiple inflows entering a reservoir (Thomson Reservoir, Australia) is investigated with a field experiment and three-dimensional numerical model simulations. The focus of the study is the mixing and transport patterns within the reservoir of the inflowing water. Data from the field experiment showed the existence of multiple inflows intruding horizontally into the reservoir immediately below the thermocline and selectively propagating into the reservoir at a depth determined by the individual density of each inflow. The results serve to show that inflows slot into a stratified reservoir in an orderly fashion, their depth dependent on the separation of inflow densities and reservoir bed, with minimal mixing between intrusions. Inflows thus do not take their nutrient load into the reservoir as a whole, but rather slot their load into an intrusion layer at an appropriate depth. Nutrients brought in via inflows become accessible only when vertical mixing, either directly at the base of the surface layer, or indirectly via the benthic boundary layer flux, transports the intrusion waters into the surface layer. 相似文献