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981.
Falk Händel Gaisheng Liu Johann Fank Franz Friedl Rudolf Liedl Peter Dietrich 《Hydrogeology Journal》2016,24(8):2079-2091
An approach to establish the recharge component of managed aquifer recharge (MAR) has recently been proposed that uses small-diameter shallow wells installed using relatively inexpensive drilling methods such as direct push. As part of further development of that approach, a generalized procedure is presented for a technical and economic assessment of the approach’s potential in comparison to other systems. Following this procedure, the use of small-diameter wells was evaluated both experimentally and numerically for a site located in southern Styria, Austria. MAR is currently done at the site using a horizontal pipe infiltration system, and system expansion has been proposed with a target rate of 12 l/s using small-diameter wells as one possible option. A short-duration single-well field recharge experiment (recharge rate 1.3–3.5 l/s) was performed (recharge by gravity only). Numerical modeling of the injection test was used to estimate hydraulic conductivity (K). Quasi-steady-state, single-well recharge simulations for different locations, as well as a long-term transient simulation, were performed using the K value calibrated from the field injection test. Results indicate that a recharge capacity of 4.1 l/s was achievable with a maximum head rise of 0.2 m at the injection well. Finally, simulations were performed for three different well fields (4, 6 and 8 wells, respectively) designed to infiltrate a target rate of 12 l/s. The experimental and numerical assessments, supported by a cost analysis of the small-diameter wells, indicate that the small-diameter wells are a viable, cost-effective recharge approach at this and other similar sites. 相似文献
982.
Since the launch of the first satellite in 1972, ecologists have been equipped with new tools to address the degradation of
tropical forests, previously limited by field-based methods. This article is a review of the state of remote sensing technology
in characterizing the degradation of tropical forest. The factors responsible for the structural and functional degradation
of the tropical forest and its likely impacts are described in view of generating remote sensing based inputs. In order to
assess the degradation and utility of geo-informatics tools, 32 parameters are identified. The research developments at different
levels of information extraction from the historic to recent periods are elaborated, and future challenges are predicted.
The article concludes that an additional momentum of research is required to answer many unresolved questions of tropical
forest degradation. 相似文献
983.
Air–water gas exchange is an important process in aquatic systems, including tidal rivers and estuaries. While there are now
reliable and routine methods for determining gas exchange over a range of temporal and spatial scales in the ocean and these
measurements have resulted in widely used wind speed parameterizations to calculate air–sea gas exchange, the same has not
been true for coastal inland waterways. Some studies have suggested that this difference is methodological, while others point
to the existence of additional drivers for gas exchange besides wind in rivers and estuaries. Here, we present gas transfer
velocities measured in the tidal Hudson River with a method widely used in oceanic studies, the 3He/SF6 dual tracer technique. Airside and waterside forcings were determined with an anemometer and an acoustic Doppler current
profiler, respectively. The results confirm that wind is the dominant driver of gas exchange in the tidal Hudson River, with
negligible contribution from bottom-generated turbulence. Furthermore, a parameterization between wind speed and gas exchange
developed for the ocean is able to predict gas exchange in this environment with high accuracy. It is hoped that by transferring
methodology used in oceanic studies to rivers and estuaries, robust data can be obtained that will eventually allow development
of widely applicable relationships between easily measured environmental variables and gas exchange in tidal inland waters. 相似文献
984.
Numerous Fe–Cu deposits are hosted in the late Paleoproterozoic Dongchuan and Dahongshan Groups in the Kangdian region, SW
China. The Dongchuan Group is composed of siltstone, slate, and dolostone with minor volcanic rocks, whereas the Dahongshan
Group has undergone lower amphibolite facies metamorphism and consists of quartz mica-schist, albitite, quartzite, marble
and amphibolite with local migmatite. Deposits in the Dongchuan Group are commonly localized in the cores of anticlines, in
fault bends and intersections, and at lithological contacts. Orebodies are closely associated with breccias, which are locally
derived from the host rocks. Fe-oxides (magnetite and/or hematite) and Cu-sulfides (chalcopyrite, bornite) form disseminated,
vein-like and massive ores, and typically fill open spaces in the host rocks. The deposits have extensive albite alteration
and local K-feldspar alteration overprinted by quartz, carbonate, sericite and chlorite. Deposits in the Dahongshan Group
have orebodies sub-parellel to stratification and show crude stratal partitioning of metals. Fe-oxide ores occur as massive
and/or banded replacements within the breccia pipes, whereas Cu-sulfide ores occur predominantly as disseminations and veinlets
within mica schists and massive magnetite ores. Ore textures suggest that Cu-sulfides formed somewhat later than Fe-oxides,
but are possibly within the same mineralization event. Both ore minerals predated regional Neoproterozoic metamorphism. Both
orebodies and host rocks have undergone extensive alteration of albite, scapolite, amphibole, biotite, sericite and chlorite.
Silica and carbonate alterations are also widespread. Ore-hosting strata have a LA-ICP-MS zircon U–Pb age of 1681 ± 13 Ma,
and a dolerite dyke cutting the Fe-oxide orebodies has an age of 1659 ± 16 Ma. Thus, the mineralization age of the Dahongshan
deposit is constrained at between the two. All ores from the two groups have high Fe and low Ti, with variable Cu contents.
Locally they are rich in Mo, Co, V, and REE, but all are poor in Pb and Zn. Sulfides from the Fe–Cu deposits have δ34S values mostly in the range of +2 to +6 per mil, suggesting a mix of several sources due to large-scale leaching of the strata
with the involvement of evaporites. Isotopic dating and field relationships suggest that these deposits formed in the late
Paleoproterozoic. Ore textures, mineralogy and alteration characteristics are typical of IOCG-type deposits and thus define
a major IOCG metallogenic province with significant implications for future exploration. 相似文献
985.
Assessment of groundwater vulnerability to pollution in Dire Dawa,Ethiopia using DRASTIC 总被引:1,自引:0,他引:1
Assessment of groundwater vulnerability to pollution is an effective tool for the delineation of groundwater protection zones.
DRASTIC approach was used to determine vulnerability zones in Dire Dawa groundwater basin, a semiarid region of Ethiopia.
Maps of the seven DRASTIC parameters were prepared. GIS-ArcView was used for mapping and performing weighted-overlay analysis.
The result of the analysis indicated that eastern part of the study area, in which Dire Dawa town is located, is highly vulnerable.
A low aquifer vulnerability class was determined for the western portion of the study area as a result of greater groundwater
depths, higher relative soil-clay content, and relatively low recharge rates for this area. The area between the two zones
is of medium vulnerability. Observed nitrate concentrations in boreholes are in accordance with the vulnerability map. Some
of the boreholes in the Sabian well field (Dire Dawa area) already deliver groundwater with nitrate levels significantly exceeding
health standards set by the World Health Organization, while boreholes in the western part (low vulnerability zone) contain
almost no nitrate. The result of this study is useful for risk assessments and for the development of effective groundwater
management strategies for this region and others like it. 相似文献
986.
This paper presents the results of a comparative analysis of the socioeconomic impacts of the construction and operation of two nuclear generating stations. Although the construction of nuclear power plants is typically a multiyear process utilizing large numbers of workers and requiring large expenditures for equipment and materials, the socioeconomic changes in the areas in which the plants are located were small and temporary. The extent and size of the changes were found to be related to the size of the work force residing in the local area, the magnitude of local utility and contractor purchases, the amount of tax payments resulting from the plant, and the level of involvement of area groups over plant-related issues. 相似文献
987.
Yongjun Gao Jochen Hoefs Eric Hellebrand Anette von der Handt Jonathan E. Snow 《Contributions to Mineralogy and Petrology》2007,153(4):429-442
Major and trace element profiles of clinopyroxene grains in oceanic gabbros from ODP Hole 735B have been investigated by a
combined in situ analytical study with ion probe, and electron microprobe. In contrast to the homogeneous major element compositions,
trace elements (REE, Y, Cr, Sr, and Zr) show continuous core to rim zoning profiles. The observed trace element systematics
in clinopyroxene cannot be explained by a simple diffusive exchange between melts and gabbros along grain boundaries. A simultaneous
modification of the melt composition is required to generate the zoning, although Rayleigh fractional crystallization modelling
could mimic the general shape of the profiles. Simultaneous metasomatism between the cumulate crystal and the porous melt
during crystal accumulation is the most likely process to explain the zoning. Deformation during solidification of the crystal
mush could have caused squeezing out of the incompatible element enriched residual melts (interstitial liquid). Migration
of the melt along grain boundaries might carry these melt out of the system. This process named as synkinematic differentiation
or differentiation by deformation (Natland and Dick in J Volcanol Geotherm Res 110(3–4):191–233, 2001) may act as an important magma evolution mechanism in the oceanic crust, at least at slow-spreading ridges. 相似文献
988.
Jan Šafanda Philipp Heidinger Helmut Wilhelm Vladimír Čermák 《Hydrogeology Journal》2007,15(2):423-428
As part of the International Continental Scientific Drilling Program (ICDP), the 1.5-km-deep borehole Yaxcopoil-1, located in the Chixculub meteor impact structure in Mexico, has undergone further study after drilling operations ceased. Temperature logs were repeated ten times at intervals 0.3–0.8, 15, 24 and 34 months after borehole shut-in. The logs bear a distinct signature of transient heat transfer by groundwater flow manifested by a gradual distortion of the linear temperature profile when a cold wave of 0.8–1.6°C amplitude was detected propagating downward from 145 to 312 m at a rate of 4–6 m/month. To understand the nature of this moving anomaly, a 20-day monitoring of the cold wave was carried out at a depth of 307 m that showed further cooling of 0.6°C during the first 16 days of the passage followed by temperature stabilisation. As an explanation of this unusual phenomenon, a theory is proposed, whereby the drilling mud has accumulated within the overlying and cooler highly porous and permeable karstic rocks during the drilling and migrates downward. The observed migration rate suggests a permeability higher than 10?11 m2. This indicates a high vulnerability to contamination of the only freshwater aquifer in the Yucatan region. 相似文献
989.
Habib Belayouni Angelida Di Staso Francesco Guerrera Manuel Martín Martín Crina Miclǎuş Francisco Serrano Mario Tramontana 《International Journal of Earth Sciences》2009,98(1):157-176
An integrated stratigraphic analysis has been made of the Tarcău Nappe (Moldavidian Domain, Eastern Romanian Carpathians),
coupled with a geochemical study of organic-rich beds. Two Main Sequence Boundaries (Early Oligocene and near to the Oligocene–Aquitanian
boundary, respectively) divide the sedimentary record into three depositional sequences. The sedimentation occurred in the
central area of a basin supplied by different and opposite sources. The high amount of siliciclastics at the beginning of
the Miocene marks the activation of the “foredeep stage”. The successions studied are younger than previously thought and
they more accurately date the deformation of the different Miocene phases affecting the Moldavidian Basin. The intervals with
black shales identified are related to two main separate anoxic episodes with an age not older than Late Rupelian and not
before Late Chattian. The most important organic-rich beds correspond to the Lower Menilites, Bituminous Marls and Lower Dysodilic
Shales Members (Interval 2). These constitute a good potential source rock for petroleum, with homogeneous Type II oil-prone organic matter, highly lipidic and thermally immature. The deposition of black shales has been interpreted as occurring
within a deep, periodically isolated and tectonically controlled basin. 相似文献
990.
Thomas M. Soniat Eileen E. Hofmann John M. Klinck Eric N. Powell 《International Journal of Earth Sciences》2009,98(1):99-114
The eastern oyster (Crassostrea virginica) is affected by two protozoan parasites, Perkinsus marinus which causes Dermo disease and Haplosporidium nelsoni which causes MSX (Multinucleated Sphere Unknown) disease. Both diseases are largely controlled by water temperature and salinity and thus are potentially sensitive to climate variations resulting from the El Niño-Southern Oscillation (ENSO), which influences climate along the Gulf of Mexico coast, and the North Atlantic Oscillation (NAO), which influences climate along the Atlantic coast of the United States. In this study, a 10-year time series of temperature and salinity and P. marinus infection intensity for a site in Louisiana on the Gulf of Mexico coast and a 52-year time series of air temperature and freshwater inflow and oyster mortality from Delaware Bay on the Atlantic coast of the United States were analyzed to determine patterns in disease and disease-induced mortality in C. virginica populations that resulted from ENSO and NAO climate variations. Wavelet analysis was used to decompose the environmental, disease infection intensity and oyster mortality time series into a time–frequency space to determine the dominant modes of variability and the time variability of the modes. For the Louisiana site, salinity and Dermo disease infection intensity are correlated at a periodicity of 4 years, which corresponds to ENSO. The influence of ENSO on Dermo disease along the Gulf of Mexico is through its effect on salinity, with high salinity, which occurs during the La Niña phase of ENSO at this location, favoring parasite proliferation. For the Delaware Bay site, the primary correlation was between temperature and oyster mortality, with a periodicity of 8 years, which corresponds to the NAO. Warmer temperatures, which occur during the positive phase of the NAO, favor the parasites causing increased oyster mortality. Thus, disease prevalence and intensity in C. virginica populations along the Gulf of Mexico coast is primarily regulated by salinity, whereas temperature regulates the disease process along the United States east coast. These results show that the response of an organism to climate variability in a region is not indicative of the response that will occur over the entire range of a particular species. This has important implications for management of marine resources, especially those that are commercially harvested. 相似文献