Factors affecting arsenic concentration in groundwaters from Northwestern Chaco-Pampean Plain,Argentina     

María Gabriela García  Ondra Sracek  Diego Sebastián Fernández  Margarita del Valle Hidalgo 《Environmental Geology》2007,52(7):1261-1275

The concentration of arsenic measured in groundwater from three aquifers in the study area located in the Eastern Tucuman province, Argentina, mostly depends on the lithology, but the spatial and temporal variations of concentrations seem to be also controlled by pH changes, climatic factors, and human perturbations. The highest concentrations of As (more than 1,000 μg L⁻¹) were found in the shallow aquifer, made of As-rich loess, while the lowest concentrations were measured in the deep confined aquifer, consisting of alternating layers of alluvial sands/gravels and clays. Intermediate values were measured in the semiconfined aquifer made of the fluvial sediments deposited in the Salí River valley, that alternate in the upper part of the sedimentary sequence with layers of loess. Because most of As in the loess is considered to be adsorbed onto Fe-oxyhydroxide coatings, the increase of pH in the flow direction (west-east) leads to increasing arsenic concentrations towards the eastern border of the study area. The decomposition of organic wastes poured into the Salí River or associated with local and diffuse sources of contamination in the eastern part of the study area depletes dissolved oxygen, which leads to the reductive dissolution of Fe and Mn oxyhydroxides, and to the subsequent release of the adsorbed and co-precipitated As. This process mainly affects shallow groundwater and the upper part of the semiconfined aquifer. Geochemical and hydrological data also suggest that rising water table levels at the end of the wet season may also lead to reductive dissolution of As-rich Fe oxyhydroxides in the shallow aquifer.  相似文献   

Analyzing ice dynamics using Sentinel-1 data at the Solheimajoküll Glacier,Iceland     

Diego Gómez  Pablo Salvador  Julia Sanz  Mikhail Urbazaev  José Luis Casanova 《地理信息系统科学与遥感》2020,57(6):813-829

ABSTRACT

The climate in southern Iceland has warmed over the last 70 years, resulting in accelerated glacier dynamics at the Solheimajoküll glacier. In this study, we compare glacier terminus locations from 1973 to 2018, to changes in climate across the study area, and we derive ice-surface velocities (2015–2018) from satellite remote-sensing imagery (Sentinel-1) using the offset-tracking method. There have been two regional temperature trends in the study period: cooling (1973–1979) and warming (1980–2018). Our results indicate a time lag of about 20 years between the onset of glacier retreat (?53 m/year since 2000) and the inception of the warming period. Seasonally, the velocity time series suggest acceleration during the summer melt season since 2016, whereas glacier velocities during accumulation months were constant. The highest velocities were observed at high elevations where the ice-surface slope is the steepest. We tested several scenarios to assess the hydrological time response to glacier accelerations, with the highest correlations being found between one and 30 days after the velocity estimates. Monthly correlation analyses indicated inter-annual and intra-annual variability in the glacier dynamics. Additionally, we investigate the linkage between glacier velocities and meltwater outflow parameters as they provide useful information about internal processes in the glacier. Velocity estimates positively correlate with water level and negatively correlate with water conductivity between April and August. There is also a disruption in the correlation trend between water conductivity and ice velocity in June, potentially due to a seasonal release of geothermal water.  相似文献   

On a four-body problem     

Armando Majorana 《Celestial Mechanics and Dynamical Astronomy》1981,25(3):267-270

In this paper we study a particular four-body problem: three bodies revolve around their center of mass in circular orbits under the influence of their mutual gravitational attraction, while a fourth body moves in the plane defined by the three bodies but non influencing their motion. The linear stability of the eight equilibrium points is studied, and it is found that it depends on the values of the masses.  相似文献   

Consequences of a freshwater canal discharge on the benthic community and its habitat on an exposed sandy beach     

Lercari D  Defeo O  Celentano E 《Marine pollution bulletin》2002,44(12):1397-1404

This paper analyses the spatial and temporal effects of a freshwater discharge (Canal Andreoni) on the macroinfauna community and its habitat in a sandy beach of Uruguay. Bimonthly, we examined 17 environmental variables plus macroinfauna abundance, biomass, richness, evenness and diversity of three sites: Andreoni, at the canal mouth, Coronilla, at 1 km, and Barra, at 13 km from the mouth. Both univariate and multivariate techniques showed an increasing degree of perturbation towards the canal. This was reflected by abiotic and biotic differences between sites and by a consistent two-dimensional ordination of the samples. A clear seasonal pattern was found, specially accentuated at Coronilla, where the effects of the canal were stronger in winter and weaker in summer. Multivariate linking between macroinfauna and its habitat highlighted the role of salinity as explanatory variable of the observed trends.  相似文献   

SECIS: The Solar Eclipse Coronal Eclipse Imaging System     

Phillips  K.J.H.  Read  P.D.  Gallagher  P.T.  Keenan  F.P.  Rudawy  P.  Rompolt  B.  Berlicki  A.  Buczylko  A.  Diego  F.  Barnsley  R.  Smartt  R.N.  Pasachoff  J.M.  Babcock  B.A. 《Solar physics》2000,193(1-2):259-271

The Solar Eclipse Coronal Imaging System (SECIS) is an instrument designed to search for short-period modulations in the solar corona seen either during a total eclipse or with a coronagraph. The CCD cameras used in SECIS have the capability of imaging the corona at a rate of up to 70 frames a second, with the intensities in each pixel digitised in 12-bit levels. The data are captured and stored on a modified PC. With suitable optics it is thus possible to search for fast changes or short-period wave motions in the corona that will have important implications for the coronal heating mechanism. The equipment has been successfully tested using the Evans Solar Facility coronagraph at National Solar Observatory/Sacramento Peak and during the 11 August 1999 eclipse at a site in north-eastern Bulgaria. The instrument is described and preliminary results are outlined.  相似文献   

Opening pupils' eyes to the skies     

Francisco Diego 《Astronomy& Geophysics》2006,47(5):5.18-5.20

Francisco Diego describes a successful outreach scheme that takes schoolchildren into an observatory and shows them what astronomy is all about.  相似文献   

Sumatra tsunami: lessons from modeling   总被引：1，自引：0，他引：1  

Diego Arcas  Vasily Titov 《Surveys in Geophysics》2006,27(6):679-705

The need for the combination of seismic data with real-time wave height information for an effective prediction of tsunami impact is emphasized in the paper. A preliminary, but comprehensive study of arrival times, wave heights and run-up values at a number of locations and tide gage stations throughout the Indian Ocean seaboard is presented. Open ocean wave height data from satellite observations are analyzed and used in the reconstruction of a tsunami source mechanism for the December 26, 2004 event. The reconstructed source is then used to numerically estimate tsunami impact along the Indian Ocean seaboard, including wave height, and arrival times at 12 tide gage stations, and inundation at 3 locations on the coast of India. The December 2004, as well as the March 28, 2005 tsunamis are investigated and their differences in terms of tsunami generation are analyzed and presented as a clear example of the need for both, seismic and real-time tsunami data for a reliable tsunami warning system in the Indian Ocean.  相似文献   

The Effect of Vegetation Productivity on Millet Prices in the Informal Markets of Mali, Burkina Faso and Niger     

Molly E. Brown  Jorge E. Pinzon  Stephen D. Prince 《Climatic change》2006,78(1):181-202

Systematic evaluation of food security throughout the Sahel has been attempted for nearly two decades. Food security analyses have used both food prices to determine the ability of the population to access food, and satellite-derived vegetation indices that measure vegetation production to establish how much food is available each year. The relationship between these two food security indicators is explored here using correspondence analysis and through the use of Markov chain models. Two sources of quantitative data were used: 8 km normalized difference vegetation index (NDVI) data from the Advanced Very High Resolution Radiometers (AVHRR) carried on the NOAA series of satellites, and monthly millet prices from 445 markets in Mali, Niger and Burkina Faso. The results show that the growing season vegetation production is related to the price of millet at the annual and the seasonal time scales. If the growing season was characterized by erratic, sparse rainfall, it resulted in higher prices, and well-distributed, abundant rainfall resulted in lower prices. The correspondence between vegetation production and millet prices is used to produce maps of millet prices for West Africa.  相似文献   

Discussion of: Ortega-Flores et al. (2018) Provenance analysis of Oligocene sandstone from the Cerro Pelón area,southern Gulf of Mexico.https://doi.org/10.1080/00206814.2018.1476922     

Roberto Stanley Molina–Garza  Jim Pindell  Diego Villagómez 《International Geology Review》2020,62(4):415-420

ABSTRACT

We discuss the 2018 publication that reports petrographic, heavy mineral data, mineral chemistry, and zircon geochronology for Oligocene sandstones in the Cerro Pelón area in southern Mexico Sureste basin. As the title of their paper says, the goal of their study is to establish the source (s) of the voluminous Cenozoic section in this region, reaching several kilometres in thickness and important as a petroleum system. These authors conclude that Oligocene sandstones of La Laja Formation were mostly sourced from eclogite- to greenschist-facies metasedimentary, metaigneous, and ultramafic rocks of the Guatemala suture complex. Minor contributions from the Chiapas Massif Complex, exposed directly to the south ~60 km of the Cerro Pelón area, were also suggested by the authors. They thus conclude that the Palaeogene stratigraphic record in southeastern Mexico was mostly controlled by the development of the Caribbean–North America plate boundary rather than by orogenic processes at the Pacific margin of North America. Presently, we do not agree with the conclusions of Ortega Flores and colleagues who studied the Cerro Pelón section, thus some discussion is required. Serpentinite bearing Nanchital Conglomerate is well exposed in the Cerro Pelón area, and high- to low-grade metamorphic rocks experienced an uplift in the vicinity of the Cerro Pelón area at the time of deposition of the La Laja Formation. We believe the data are better explained by multiple local sources in southern and eastern Oaxaca as well as sources to the south and southwest, which include the Cenozoic coastal batholith, the Grenvillean/Guichicovi basement complexes, the Chiapas Massif, the Mazatlán schist and other units in the Cuicateco Belt, as well as the Mesozoic cover of these areas (Todos Santos Formation, Cretaceous carbonate rocks, and Paleogene strata such as the Soyaló and Bosque Formations).  相似文献   

Changes in interstitial water salinity of a Mississippi tidal marsh     

Courtney T. Hackney  Armando A. de la Cruz 《Estuaries and Coasts》1978,1(3):185-188

The salinity of interstitial water (i.e., the salinity of the free soil water) was examined at 11 equidistant stations along a transect on a Mississippi tidal marsh dominated byJuncus roemerianus andSpartina cynosuroides. Changes in the nearby surface water (e.g., bay water) were reflected in the changes in interstitial water salinity. The salinity of interstitial water was usually higher, varying between 2.5 and 15.8‰ from February 1975 through January 1976, than the salinity of the nearby surface water which ranged from 0.0 to 11.5‰. Following a long period of high salinity in the bay and sound (exceeding 14‰), the salinity of the interstitial water increased to a maximum of 16.8‰ in October. The salinity increased as the distance of the sampling station from the source of the flood water increased. Mean interstitial wate salinity across the marsh studied was within 10‰ which did not seem to influence the marsh plant zonation occurring on the marsh.  相似文献