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481.
The alluvial aquifer of the Alto Guadalquivir River is one of the most important shallow aquifers in Jaén, Spain. It is located
in the central-eastern part of the province, and its groundwater resources are used mainly for crop irrigation in an agriculture-dominated
area. Hydrochemical and water-quality data obtained through a 2-year sampling (2004–2006) and analysis program indicate that
nitrate pollution is a serious problem affecting groundwater due to the use of nitrogen (N)-fertilizers in agriculture. During
the study, 231 water samples were collected from wells and springs to determine water chemistry and the extent of nitrate
pollution. The concentration of nitrate in groundwater ranged from 1.25 to 320.88 mg/l. Considerable seasonal fluctuations
in groundwater quality were observed as a consequence of agricultural practices and other factors such as annual rainfall
distribution and the Guadalquivir River flow regime. The chemical composition of the water is not only influenced by agricultural
practices, but also by interaction with the alluvial sediments. The dissolution of evaporites accounts for part of the Na+, K+, Cl−, SO4
2−, Mg2+, and Ca2+, but other processes, such as calcite precipitation and dedolomitization, also contribute to groundwater chemistry. 相似文献
482.
Lucy J. Carpenter Stephen J. Andrews Richard T. Lidster Alfonso Saiz-Lopez Miguel Fernandez-Sanchez William J. Bloss Bin Ouyang Roderic L. Jones 《Journal of Atmospheric Chemistry》2017,74(2):145-156
Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH2I2) and chloro-iodomethane (CH2ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH2I2 and CH2ICl in air and of CH2I2 in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH2I2 was lower in amplitude than that of CH2ICl, despite its faster photolysis rate. We speculate that night-time loss of CH2I2 occurs due to reaction with NO3 radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k CH2I2+NO3 of ≤4 × 10?13 cm3 molecule?1 s?1; a previous kinetic study carried out at ≤100 Torr found k CH2I2+NO3 of 4 × 10?13 cm3 molecule?1 s?1. Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/? 0.8 nmol m?2 d?1 for CH2I2 and 3.7 +/? 0.8 nmol m?2 d?1 for CH2ICl), we show that the model overestimates night-time CH2I2 by >60 % but reaches good agreement with the measurements when the CH2I2 + NO3 reaction is included at 2–4 × 10?13 cm3 molecule?1 s?1. We conclude that the reaction has a significant effect on CH2I2 and helps reconcile observed and modeled concentrations. We recommend further direct measurements of this reaction under atmospheric conditions, including of product branching ratios. 相似文献
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José A. M. Demattê Julianne de Castro Oliveira Tiago Rodrigues Tavares Leonardo Ramirez Lopez Fabrício da Silva Terra Suzana Romeiro Araújo Caio Troula Fongaro Stoécio Malta Ferreira Maia Francisco Fujita de Castro Mello Rodnei Rizzo Simone Vicente Marco Antonio de Melo Bortolleto Pedro Henrique Ramos Cerqueira 《Environmental Earth Sciences》2016,75(18):1277
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Andreu Vinyoles Miguel Lpez‐Blanco Miguel Garcs Pau Arbus Luis Valero Elisabet Beamud Beln Oliva‐Urcia Patricia Cabello 《Basin Research》2021,33(1):447-477
The propagation of the deformation front in foreland systems is typically accompanied by the incorporation of parts of the basin into wedge‐top piggy‐back basins, this process is likely producing considerable changes to sedimentation rates (SR). Here we investigate the spatial‐temporal evolution of SR for the Tremp–Jaca Basin in the Southern Pyrenees during its evolution from a wedge‐top, foreredeep, forebulge configuration to a wedge‐top stage. SR were controlled by a series of tectonic structures that influenced subsidence distribution and modified the sediment dispersal patterns. We compare the decompacted SR calculated from 12 magnetostratigraphic sections located throughout the Tremp–Jaca Basin represent the full range of depositional environment and times. While the derived long‐term SR range between 9.0 and 84.5 cm/kyr, compiled data at the scale of magnetozones (0.1–2.5 Myr) yield SR that range from 3.0 to 170 cm/kyr. From this analysis, three main types of depocenter are recognized: a regional depocenter in the foredeep depozone; depocenters related to both regional subsidence and salt tectonics in the wedge‐top depozone; and a depocenter related to clastic shelf building showing transgressive and regressive trends with graded and non‐graded episodes. From the evolution of SR we distinguish two stages. The Lutetian Stage (from 49.1–41.2 Ma) portrays a compartmentalized basin characterized by variable SR in dominantly underfilled accommodation areas. The markedly different advance of the deformation front between the Central and Western Pyrenees resulted in a complex distribution of the foreland depozones during this stage. The Bartonian–Priabonian Stage (41.2–36.9 Ma) represents the integration of the whole basin into the wedge‐top, showing a generalized reduction of SR in a mostly overfilled relatively uniform basin. The stacking of basement units in the hinterland during the whole period produced unusually high SR in the wedge‐top depozone. 相似文献
489.
Antonio Gómez David Palacios Enrique Luengo Luis M. Tanarro Lothar Schulte Miguel Ramos 《Geografiska Annaler: Series A, Physical Geography》2003,85(2):165-182
The southernmost glacier in Europe formed during the Little Ice Age at the foot of the north wall of Picacho del Veleta (3 398 m) in Sierra Nevada, in the southeast region of the Iberian Peninsula (lat. 37δ03‘N, long. 3δ22‘W). The glacier gradually retreated during the last century, leaving a large talus slope at the base of the wall. The unconsolidated material covering the ice masses acted as a thermal insulator. Recent bottom temperature of snow (BTS) analyses and drillings indicate that the ice still exists within the talus. Evidence from field observations made during the period 1995–2001, revealed that large mass movements occurred during the driest summers (1998 and especially, 1999 and 2000) when the talus was snow free. These conditions suggest a direct relationship between talus stability and thermal insulation from the snow cover in areas where buried ice or decaying marginal permafrost exists. 相似文献
490.
A hindcast simulation of the Arctic and Antarctic sea ice variability during 1955-2001 has been performed with a global, coarse resolution ice-ocean model driven by the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis daily surface air temperatures and winds. Both the mean state and variability of the ice packs over the satellite observing period are reasonably well reproduced by the model. Over the 47-year period, the simulated ice area (defined as the total ice-covered oceanic area) in each hemisphere experiences large decadal variability together with a decreasing trend of Ø1% per decade. In the Southern Hemisphere, this trend is mostly caused by an abrupt retreat of the ice cover during the second half of the 1970s and the beginning of the 1980s. The modelled ice volume also exhibits pronounced decadal variability, especially in the Northern Hemisphere. Besides these fluctuations, we detected a downward trend in Arctic ice volume of 1.8% per decade and an upward trend in Antarctic ice volume of 1.5% per decade. However, caution must be exercised when interpreting these trends because of the shortness of the simulation and the strong decadal variations. Furthermore, sensitivity experiments have revealed that the trend in Antarctic ice volume is model-dependent. 相似文献