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排序方式: 共有173条查询结果,搜索用时 31 毫秒
91.
J. Marques Monteiro F. Santos R. Graça R. Castro L. Aires-Barros L. Mendes Victor 《Hydrogeology Journal》2001,9(6):584-596
The Vilarelho da Raia-Chaves region, located in northern Portugal adjacent to the Spanish border, is characterized by both
hot and cold CO2-rich mineral waters issuing from springs and drilled wells. The present paper updates the conceptual circulation model of
the Vilarelho da Raia cold CO2-rich mineral waters. Vilarelho da Raia mineral waters, dominated by Na and HCO3 ions, have formed mainly by interaction with CO2 of deep-seated mantle origin. The δ
18O, δ
2H and 3H values indicate that these waters are the result of meteoric waters infiltrating into Larouco Mountain, NW of Vilarelho
da Raia, circulating at shallow depths in granitic rocks and moving into Vilarelho da Raia area. The conceptual geochemical
and geophysical circulation model indicates that the hot and cold CO2-rich mineral waters of Chaves (76 °C) and Vilarelho da Raia (17 °C) should be considered manifestations of similar but not
the same geohydrological systems.
Electronic Publication 相似文献
92.
93.
冈底斯弧前区域地层沉积记录,对新特提斯洋消亡和印度-亚洲碰撞过程的研究具有十分重要的意义。位于西藏南部札达地区的达机翁组,北邻冈底斯岩浆弧,南靠雅鲁藏布江缝合带。岩石组成主要包括砾岩、岩屑砂岩、泥页岩和灰岩等。沉积环境分析认为达机翁组形成于扇三角洲相环境。火山灰锆石U-Pb定年、碎屑锆石最年轻年龄以及底栖有孔虫化石组合共同约束达机翁组的形成时代为晚白垩世-始新世早期(即ca.73~49Ma)。物源区分析结果表明达机翁组物源类似于区域上分布的日喀则弧前盆地沉积,直接以北侧冈底斯岩浆弧为主要物质源区。通过与区域弧前沉积对比,为冈底斯弧前盆地海相地层时代提供制约,结果显示新特提斯洋在亚洲大陆南缘的弧前海退存在东西方向上的穿时性,即海水自东向西逐渐退出,并最终在~49Ma退出冈底斯-拉达克弧前区域。 相似文献
94.
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96.
Runoff and sediment lost due to water erosion were recorded for 36 (1 m2) plots with varying types of vegetative cover located on sloping gypsiferous fields in the South of Madrid. 75% of the events had maximum 30‐minute intensity (I30) less than 10 mm h?1 in the period studied (1994–2005). As for the vegetative cover, maximum correlation between runoff and soil loss was found in the least protected plots (0–40% cover) during the most intense rainfall events; however, a significant positive correlation was also observed in plots with greater coverage (40–60%). If coverage exceeded 60%, rainfall erosivity declined. The average amount of sediment produced in high‐intensity events was significantly greater (approximately 7 g m?2 per I30 event >10 mm h?1) than that produced in the rest of the moderate‐intensity events (approximately 3 g m?2 per I30 event <10 mm h?1), but due to the high rate of occurrence of the latter throughout the year sediment loss during the period studied totaled 128 g m?2. By comparison, only 40 g m?2 was produced by the I30 events greater than 10 mm h?1. Even though the amount of soil lost is relatively insignificant from a quantitative standpoint, the organic matter content lost in the sediment (six times more than in the soil) is a permanent loss that threatens the development of the surface of the soil in this area when the vegetative cover is less than 40%. The soil here experiences a chronic loss of 0·02 mm annually as a consequence of frequent, moderate events, in addition to any loss produced by extraordinary events, which, though less frequent, are much more erosive. If moderate events are ignored, an important part of soil loss will be lost in the long run. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
97.
Richarde Marques da Silva Celso Augusto Guimares Santos José Yure Gomes dos Santos 《国际泥沙研究》2018,33(2):117-125
This paper quantifies the runoff and sediment yield for four different land covers in a semiarid region of Brazil. The WESP model, a distributed, event-oriented runoff-erosion model, was applied and its physical parameters, Ns and KR, were adjusted based on observed runoff and sediment yield data using simulated rainfall with an average intensity of 53 mm h-1. The sediment yield obtained was 53.02 kg ha-1 (caatinga vegetation), 231.96 kg ha-1 (bare soil), 309.75 kg ha-1 (beans), and 847.38 kg ha-1(corn). The results showed that caatinga cover yields the lowest erosion and runoff when compared to the other treatments. The results also show that the sediment yield and runoff values simulated with Ns, KI, and KR parameters were well calibrated, within acceptable deviations. The caatinga vegetation was more effective in protecting the soil, when compared to the other types of coverage. The beans and corn covers had the highest values of runoff and sediment yield, even higher than those observed for bare soil. 相似文献
98.
Ana Lígia Primo Ulisses Miranda AzeiteiroSónia Cotrim Marques Filipe MartinhoMiguel Ângelo Pardal 《Estuarine, Coastal and Shelf Science》2009
The influence of climate variability on the diversity and distribution patterns of zooplankton communities was investigated in the Mondego estuary (Portugal) during four consecutive years characterized by highly variable precipitation and, consequently, river flow regime. Monthly samples were collected along the estuarine gradient at five sampling stations. Seasonal, inter-annual and spatial distributions were evaluated by multivariate analyses and three diversity indices were applied (Species number, Shannon Diversity and Average Taxonomic Distinctness). A two-year drought period presented significant differences in salinity values, especially in 2005 (extreme drought event). During the study period, copepoda was the main dominant group and Acartia tonsa the most abundant species, with the exception of autumn 2006, where high abundances of the cladoceran Penilia avirostris were noticed. Multivariate analysis indicated that zooplankton communities changed from a pre- to a post-drought period indicating the influence of hydrological parameters in communities' structure. The dry period was associated with an increase in zooplankton density, a reduction in seasonality and higher abundance and prevalence of marine species throughout the year. Seasonally, winter/spring communities were distinct from those in summer/autumn. Spatially, salinity-associated differences between upstream and downstream communities were reduced during the drought years, but during the post-drought year, these differences were detected again. 相似文献
99.
Erwan Garel Susana Nunes João Magalhães Neto Rodrigo Fernandes Ramiro Neves João Carlos Marques Óscar Ferreira 《Geo-Marine Letters》2009,29(5):331-341
This technical paper describes an autonomous recording system with remote data access for the continuous, long-term in situ
monitoring of water quality and discharge, as well as current velocity. The Simpatico system has been recently deployed in three estuaries in Portugal (Mondego and Tagus in July 2007; Guadiana in March 2008),
highly suitable to illustrate its multifaceted potential applications: surveillance of the effects of mitigation measures
to combat eutrophication (lower Mondego Estuary); real-time implementation of boundary conditions for a water modelling system
(upper Tagus Estuary); study of dam-induced impacts in terms of water quality, water discharge and sediment budgets (mouth
of the Guadiana Estuary). An extract of recorded data serves as an example to discuss data reliability, as well as field maintenance
of the system, with implications for labour and operational costs. The use of a new generation of copper-based anti-biofouling
kits significantly reduced the need for field maintenance operations. Other examples of possible application of the system
include the assessment of gas accumulation in coastal waters. 相似文献
100.
Long term macrobenthos data together with physical habitat parameters were analysed to investigate spatial and temporal changes at an estuary under different anthropogenic pressures, mainly increasing shellfish farming. The aim was to assess the possible impacts of these pressures on the macrobenthic communities by comparing a period before and after changes in these pressures. Benthic samples were seasonally collected in 1990 (before major anthropogenic changes), 2000 and 2005 at the same sampling stations located on three different habitats in the Eo estuary (Northern Spanish coast). Multivariate and univariate methods were used to assess spatial variability of benthic assemblages and to compare community changes over time. Data from 1990 was assumed as the reference situation to appraise the subsequent impacts. We observed a significant spatial variability of the benthic assemblages in the system as a function of habitat heterogeneity in relation to sediment composition, presence/absence and density of seagrasses, and hydrodynamic regime. Changes were detected in the community composition at all sites during this 15 year period. The extent of changes was related to initial community conditions, rather than the intensity of the pressure. The results suggest that the responses of the benthic communities to human induced perturbations occurring in the system are largely dependent on its intrinsic buffer capacity, and that these communities have been able to cope with an increasing environmental stress (organic enrichment). In conclusion, to keep shellfish farming at a sustainable level without undesirable impacts, the disturbance intensity must be kept below the system carrying capacity. This will allow natural communities to cope with pressures and thus avoid further deterioration in ecological quality. 相似文献