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941.
Ahmed Murad 《中国地球化学学报》2010,29(2):152-156
The stable isotopes of oxygen and hydrogen have been implemented to assess the recharge mechanisms in an area in the UAE bounded to the northwestern part of the Gulf of Oman and the southeastern part of the Arabian Gulf. The conversion of stable isotopes to deuterium excess was utilized as a supportive tool to understand the process of groundwater recharge. The concluding results of this study showed that the origin of moisture is the Mediterranean Sea. The precipitation is the main source of recharge, in which the precipitation having undergone evaporation before recharge occurs. The comparison between regression line for data collected in 1996 and regression line for samples collected in 2006 suggests that the precipitation water which recharged the groundwater, was diluted with groundwater and this dilution is observed from decreasing of the deuterium excess of collected groundwater samples with increasing isotopes of oxygen. The dilution of groundwater with the recharge water suggests modern-day recharge as it is seen from high deuterium excess that exceeded the deuterium excess of LMWL and was close to MMWL. 相似文献
942.
Sushmitha Baskar R. Baskar Natuschka Lee P. K. Theophilus 《Environmental Geology》2009,57(5):1169-1186
The Mawsmai cave and Krem Phyllut caves, East Khasi hills, Meghalaya, India has so far not yet attracted the attention of
geomicrobiologists. Observations and hypotheses on the possible influence of identified microorganisms for speleothem formations
in Meghalaya are reported for the first time. XRD studies identified calcite in speleothems and gypsum in cave wall deposits
as the dominant minerals. SEM-EDAX showed interesting microfabric features showing strong resemblance with fossilised bacteria,
calcified filaments, needle calcite and numerous nano scale calcite crystals, highly weathered and disintegrated crystals
of calcite, that point towards a significant microbial influence in its genesis. Thin section petrography showed laminated
stromatolitic features. The microorganisms identified by conventional isolation and further evaluation of isolates by molecular
techniques include Bacillus cereus, Bacillus mycoides, Bacillus licheniformis, Micrococcus luteus, and Actinomycetes. Microscopic observations also showed unidentifiable cocci and four unidentifiable strains of CaSO4 (gypsum) precipitating bacteria. Experimental studies confirmed that these bacteria are able to precipitate calcium minerals
(calcite, gypsum, minor amounts of dolomite) in the laboratory. These results allow us to postulate that species like these
may contribute to active biogenic influence in the cave formations at Meghalaya. 相似文献
943.
The Jönköping Anorthositic Suite (JAS) in S. Sweden has characteristics typical for (Proterozoic) massif-type anorthosites. The interstitial liquid of these plagioclase-porphyritic rocks solidified at 1,455 ± 6 Ma, as determined by U–Pb isotope analysis of baddeleyite. The JAS developed during a regional 1.47–1.44 event in Fennoscandia that generated widespread mafic magmatism (basalts, and diabase dykes and sills) in the north and emplacement of felsic plutons in the south. The event of 1.47–1.44 Ga magmatism in Fennoscandia largely coincides in age with dynamic high-grade metamorphism in SW Sweden and was probably related to convergent active-margin processes during the Danopolonian orogeny. 相似文献
944.
945.
Elena Dunca Harry Mutvei Peter Göransson Carl-Magnus Mörth Bernd R. Schöne Martin J. Whitehouse Mikael Elfman Susanne P. Baden 《International Journal of Earth Sciences》2009,98(1):3-17
Shells of Arctica islandica collected between 1884 and 2004 from Öresund, Kattegat and Skagerrak (Swedish West Coast) were used to monitor local climate variations and the influence of human activities on the local environment. For this purpose, we analysed the growth, structure and chemical composition of these shells and compared them with shells collected from Kiel Bay, Norway and Iceland. The growth rate of the studied shells registers an NAO periodicity of ca 8 years. However, the observed signal is weak because of other environmental interferences that are either of natural or anthropogenic origin. For example, the oxygen isotope ratios show temperature fluctuation, but also the influx of low salinity water. Higher contents of S, N, Cu, Zn, As, Cd and P in shell portions formed during the last century are related to human activities such as mining and industrial development. Our study indicates that in order to use Arctica shells as archives of climate change it is necessary to study the full range of environmental data that is recorded in the shells by using a multi element and isotope approach in combination with different analytical techniques including investigation of growth rates and shell structure. 相似文献
946.
Mapping vertical profile of discontinuous permafrost with ground penetrating radar at Nalaikh depression,Mongolia 总被引:3,自引:0,他引:3
Tonghua Wu Qinxue Wang Masataka Watanabe Ji Chen Dorjgotov Battogtokh 《Environmental Geology》2009,56(8):1577-1583
Ground-penetrating radar (GPR) has become an important geophysical tool which can provide a wealth of interpretive information
about the vertical profile of discontinuous permafrost. A GPR investigation was conducted in October 2006 at the Nalaikh site
at the southern boundary of the Siberian discontinuous permafrost region in Mongolia. GPR data were collected along four 100-m-long
profiles to identify the location of the permafrost body, which included an in situ drilling borehole and analysis of temperature
observations and soil water content measurements from boreholes. The GPR interpretation results indicated that the thickness
of discontinuous permafrost at the study site was only 1.9–3.0 m and the permafrost is vulnerable to climate change. The soil
temperature and soil water content data demonstrate the precision of GPR image interpretation. This case demonstrated that
GPR is well suited for mapping the internal structure of discontinuous permafrost with relatively low soil water content. 相似文献
947.
948.
Eutrophication-induced changes to benthic faunal activities are problems of significant ecological impact, affecting global
nutrient budgets as well as local trophic connections. We address the question of how nitrogen loads to estuarine embayments
alter the bioturbation activities of benthic fauna. Specifically, we related local benthic activities to calculated local
nitrogen concentrations for 22 northeastern US estuaries. These local nitrogen concentrations were derived from the calculated
nitrogen loading for the embayment together with the spatial distribution of the local flushing time. Our results showed a
maximum bioturbation rate at intermediate nitrogen concentrations or a “hump-shaped” pattern of response. This behavior was
evident in all embayments that had a range of concentrations including low, intermediate, and high values. Embayments where
sampling did not include this full range did not show this behavior. This work provides methods and guidance to help managers
make decisions concerning the effects of nitrogen loading on the activities and well-being of benthic fauna in coastal embayments.
The novelty of this approach lies in identifying the response of bioturbation to nitrogen loading in many systems, without
costly and time-consuming speciation of benthic fauna, and also in rapidly identifying embayments and aquatic areas with vulnerable
fauna. These results are ecologically significant in supporting the hypothesis that benthic organism abundance and activity
will peak at mid-levels of nitrogen due to the interplay of food availability and oxygen levels, noting that the critical
levels of these factors differ among water bodies. 相似文献
949.
Large landslides and deep-seated gravitational slope deformations (DSGSD) represent an important geo-hazard in relation to the deformation of large structures and infrastructures and to the associated secondary landslides. DSGSD movements, although slow (from a few millimetres to several centimetres per year), can continue for very long periods, producing large cumulative displacements and undergoing partial or complete reactivation. Therefore, it is important to map the activity of such phenomena at a regional scale. Ground surface displacements at DSGSD typically range close to the detection limit of monitoring equipment but are suitable for synthetic aperture radar (SAR) interferometry. In this paper, permanent scatterers (PSInSAR?) and SqueeSAR? techniques are used to analyse the activity of 133 DSGSD, in the Central Italian Alps. Statistical indicators for assigning a degree of activity to slope movements from displacement rates are discussed together with methods for analysing the movement and activity distribution within each landslide. In order to assess if a landslide is active or not, with a certain degree of reliability, three indicators are considered as optimal: the mean displacement rate, the activity index (ratio of active PS, displacement rate larger than standard deviation, overall PS) and the nearest neighbor ratio, which allows to describe the degree of clustering of the PS data. According to these criteria, 66% of the phenomena are classified as active in the monitored period 1992–2009. Finally, a new methodology for the use of SAR interferometry data to attain a classification of landslide kinematic behaviour is presented. This methodology is based on the interpretation of longitudinal ground surface displacement rate profiles in the light of numerical simulations of simplified failure geometries. The most common kinematic behaviour is rotational, amounting to 41 DSGSDs, corresponding to the 62.1% of the active phenomena. 相似文献
950.
A compositional multivariate approach was used to analyse regional-scale soil geochemical data obtained as part of the Tellus Project generated by the Geological Survey of Northern Ireland. The multi-element total concentration data presented comprise X-ray fluorescence (XRF) analyses of 6862 rural soil samples collected at 20-cm depth on a non-aligned grid at one site per \(2\,\hbox {km}^{2}\). Censored data were imputed using published detection limits. Each soil sample site was assigned to the regional geology map, resulting in spatial data for one categorical variable and 35 continuous variables comprised of individual and amalgamated elements. This paper examines the extent to which soil geochemistry reflects the underlying geology or superficial deposits. Since the soil geochemistry is compositional, log-ratios were computed to adequately evaluate the data using multivariate statistical methods. Principal component analysis (PCA) and minimum/maximum autocorrelation factors (MAF) were used to carry out linear discriminant analysis (LDA) as a means to discover and validate processes related to the geologic assemblages coded as age bracket. Peat cover was introduced as an additional category to measure the ability to predict and monitor fragile ecosystems. Overall prediction accuracies for the age bracket categories were 68.4 % using PCA and 74.7 % using MAF. With inclusion of peat, the accuracy for LDA classification decreased to 65.0 and 69.9 %, respectively. The increase in misclassification due to the presence of peat may reflect degradation of peat-covered areas since the creation of superficial deposit classification. 相似文献