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排序方式: 共有196条查询结果,搜索用时 15 毫秒
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Francisco?Javier?Gómez-Puentes Marco?Antonio?Pérez-Flores Jaime?Alonso?Reyes-LópezEmail author Dina?L.?Lopez Fernando?Herrera-Barrientos Rafael?Onofre?García-Cueto Socorro?Romero-Hernández Fernando?Amílcar?Solís-Domínguez Miguel?Martín-Loeches Garrido 《Environmental Earth Sciences》2016,75(13):1062
In Mexico, open dumps that are maintained by the municipality but provide no covering of waste are not uncommon. Further, disposal at these sites is often performed by burning. The aim of this study was to determine the leachate plume from an open dump located in a depositional deltaic environment, with arid climate, low rainfall and where the water table is about 2 m below the surface. The methodology comprised analysis of groundwater monitoring wells and geophysical and geochemical prospecting techniques. The 3D geoelectric interpretation shows a typical area of these depositional environments with low resistive values (10–20 Ω-m) associated with the presence of sands and clays interbedded. However, there is a very low resistivity zone associated with the dump’s impact which reaches values below 5 Ω-m, and it is located where the disposal and burning of wastes occurred. Another zone with values above 16 Ω-m appears as a limit for the advance of the saline. This is interpreted as a sandy lenses area. These sandy lenses with higher porosity transport aquifer’s water. Thus the dump is in direct contact by this conduct with clean groundwater. Piper diagrams constructed with the chemical data analysis reveal that the groundwater in the area corresponds to the chlorinated and/or sulfated sodium type, showing the impact caused by the dump. The monitoring well (NP8, on-site) with the highest dissolved solids content behaves anomalously and belongs to the more conductive zone according to the geoelectric profiles. The subsoil geochemical behavior is influenced by the seasonal water table variations provoking the dissolution of burned and unburned wastes, but the effects of slow flows in the direction of the regional flow are not discarded. Although the most impacted area within the dump is characterized to a depth of 10 m, there is a slow flow in the direction of the regional flow that has been moving pollutants out of the dumpsite during its almost 20 years of operation. The results of this study provide valuable information for the authorities to carry out an appropriate restoration project. 相似文献
195.
Climatic and environmental controls on the occurrence and distributions of long chain alkenones in lakes of the interior United States 总被引:1,自引:0,他引:1
Jaime L. Toney Yongsong Huang Sherilyn C. Fritz Eric Grimm 《Geochimica et cosmochimica acta》2010,74(5):1563-7565
Long chain alkenones (LCA) are temperature-sensitive lipids with great potential for quantitative reconstruction of past continental climate. We conducted the first survey for alkenone biomarkers from 55 different lakes in the Northern Great Plains and Nebraska Sand Hills of the United States. Among those surveyed, we found 13 lakes that contain LCAs in the surface sediments. The highest concentrations of alkenones in sediments are found in cold (mean annual air temperature ∼11 °C versus 17 °C in our warmest sites), brackish to mesosaline (salinity = 8.5-9.7 g/L), and alkaline (pH = 8.4-9.0) lakes with high concentrations of sodium and sulfate. The dynamics of stratification and nutrient availability also appear to play a role in LCA abundance, as early spring mixing promotes a bloom of alkenone-producing haptophytes. Four of the alkenone-containing sites contain the C37:4 alkenone; however, we discovered an unprecedented lacustrine alkenone distribution in a cluster of lakes, with a total absence of C37:4 alkenone. We attribute this unusual composition to a different haptophyte species and show that the sulfate:carbonate ratio may control the occurrence of these two distinct populations. We created a new in-situ temperature calibration for lacustrine sites that contain C37:4 using a water-column calibration from Lake George, ND and show that is linearly correlated to lake water temperature (R2 = 0.74), but is not. A number of lakes contain an unidentified compound series that elutes close to the LCAs, highlighting the importance of routine GC-MS examination prior to using lacustrine LCAs for paleotemperature reconstructions. 相似文献
196.
Assessing the vulnerability of over-exploited volcanic aquifer systems using multi-parameter analysis,Toluca Basin,Mexico 总被引:1,自引:0,他引:1
The potential for contamination of groundwater in an over-exploited system led to this investigation on aspects of aquifer
vulnerability in the Toluca Basin, Mexico. This study involved the use of various hydrogeological, geochemical and isotopic
tools to better understand the susceptibility to contamination where heavy groundwater extraction along with industrial extensive
development is concentrated. Geochemical and isotopic analyses of groundwater from production wells along the mountain boundary
show little evidence of contamination at present time. Radiocarbon and tritium data collected in piezometers and wells penetrating
the Lower basalt aquifer indicate that the groundwater is of varying age and quality. These data, in addition to stable isotope
and chemical data also indicate evidence of contamination in the Lower aquifer; which could be associated with fast recharge
in the mountains or injection of waste water by illegal wells. Evidence found in this study of low downward gradients in the
valley fill sediments and the presence of low permeability aquitard deposits suggest that the aquifer system is currently
not highly threatened by surface sources of contamination. However, where urban and industrial development occurs, in the
centre of the valley and along the flanks of the Basin, the vulnerability of the aquifer system increases significantly. 相似文献