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41.
Evidence for sediment recirculation on an ebb-tidal delta of the East Frisian barrier-island system, southern North Sea 总被引：2，自引：2，他引：0
The Otzum ebb-tidal delta, located between Langeoog and Spiekeroog islands along the East Frisian barrier-island coast, southern
North Sea, was investigated with respect to its morphological evolution, sediment distribution patterns and internal sedimentary
structures. Bathymetric charts reveal that, over the last 50 years, the size of the Otzum ebb-tidal delta has slightly shrunk,
while sediment has accreted on the ebb-delta lobe to the east of the main inlet channel (west of Spiekeroog). Swash bars superimposed
on the eastern ebb-tidal shoal (Robben Plate) have migrated south or south-eastwards, i.e. towards the inlet throat. The main
ebb-delta body is composed of fine quartz sand, whereas the superimposed swash bars and the inlet channel bed consist of medium-grained
quartz sand containing high proportions of coarser bioclastic material. Internal sedimentary structures in short box-cores
(up to 30 cm long) are dominated by flood-oriented cross-beds. Longer vibro-cores (up to 1.5 m long) show that, at depth,
the sediment is dominated by storm-generated parallel (upper plane bed) laminations with intercalated shell layers and dune
cross-bedding. The cross-bedded sands in both box-cores and vibro-cores from the ebb-delta shoal predominantly dip towards
the south or southeast, indicating transport towards the inlet throat by the flood current. The observations demonstrate that,
contrary to previous contentions, the sediments of the highly mobile swash bars do not bypass the inlet but are instead being
continually recirculated by the combined action of tidal currents and waves. In this model, the cycle begins with both fine
and medium sands, including shell hash, being transported seawards in the main ebb channel until they reach the shallow ebb-delta
front. From here, the sediment is pushed onto the eastern ebb-delta shoal by the flood current assisted by waves, becoming
strongly size-sorted in the process. The medium sands together with the shell hash are formed into swash bars which migrate
along arcuate paths over a base of fine sand back to the main ebb channel located south of the ebb delta. By the same token,
the fine sand between the swash bars is transported south-eastwards by the flood current in the form of small dunes until
it cascades into the large flood channel located to the west of Spiekeroog. From here, the fine sand is fed back into the
main ebb channel, thus completing the cycle. No evidence was found on the ebb delta for alongshore sediment bypassing. 相似文献
42.
Bastien Girod Detlef P. van Vuuren Maria Grahn Alban Kitous Son H Kim Page Kyle 《Climatic change》2013,118(3-4):595-608
Transportation contributes to a significant and rising share of global energy use and GHG emissions. Therefore modeling future travel demand, its fuel use, and resulting CO2 emission is highly relevant for climate change mitigation. In this study we compare the baseline projections for global service demand (passenger-kilometers, ton-kilometers), fuel use, and CO2 emissions of five different global transport models using harmonized input assumptions on income and population. For four models we also evaluate the impact of a carbon tax. All models project a steep increase in service demand over the century. Technology change is important for limiting energy consumption and CO2 emissions, the study also shows that in order to stabilise or even decrease emissions radical changes would be required. While all models project liquid fossil fuels dominating up to 2050, they differ regarding the use of alternative fuels (natural gas, hydrogen, biofuels, and electricity), because of different fuel price projections. The carbon tax of 200 USD/tCO2 in 2050 stabilizes or reverses global emission growth in all models. Besides common findings many differences in the model assumptions and projections indicate room for further understanding long-term trends and uncertainty in future transport systems. 相似文献
43.
Sang Yong Chung Venkatramanan Senapathi Kye Hyun Park Joo Hyeong Son Selvam Sekar 《Arabian Journal of Geosciences》2018,11(24):769
Ulsan mine produced the iron ore minerals of magnetite, arsenopyrite, and scheelite in 1992, and serpentine was developed from 1977 to 2002. The soils of the mine were contaminated by heavy metals such as As, Zn, Ni, and Cd. Heavy metals of Ni and Zn came mostly from serpentinite, and As was derived mainly from arsenopyrite in the scan-type iron ore body. As, Zn, and Ni were major contaminants, but Cd was a minor contaminant on a basis of Korean standard. The heavy metals in the deep depth (>?5 m) came from the host rocks, and those in the shallow depth (<?5 m) were derived from the organic–mineral complexation soil. The remediation plan was a soil washing for highly contaminated soils and the containment of clay materials for less contaminated soils. Even though the remediation methods were successful, the continuous monitoring and the analysis of monitoring data are still necessary for the conservation of soil and groundwater around the study area. 相似文献
44.
Assessment of Sentinel-1A data for rice crop classification using random forests and support vector machines 总被引：1，自引：0，他引：1
This study developed an approach to map rice-cropping systems in An Giang and Dong Thap provinces, South Vietnam using multi-temporal Sentinel-1A (S1A) data. The data were processed through four steps: (1) data pre-processing, (2) constructing smooth time series VH backscatter data, (3) rice crop classification using random forests (RF) and support vector machines (SVM) and (4) accuracy assessment. The results indicated that the smooth VH backscatter profiles reflected the temporal characteristics of rice-cropping patterns in the study region. The comparisons between the classification results and the ground reference data indicated that the overall accuracy and Kappa coefficient achieved from RF were 86.1% and 0.72, respectively, which were slightly more accurate than SVM (overall accuracy of 83.4% and Kappa coefficient of 0.67). These results were reaffirmed by the government’s rice area statistics with the relative error in area (REA) values of 0.2 and 2.2% for RF and SVM, respectively. 相似文献
45.
Application of electrical resistivity tomography (ERT) technique to detect underground cavities in a karst area of South Korea 总被引：1，自引：1，他引：0
Mi Kyung Park Samgyu Park Myeong-Jong Yi Changryol Kim Jung-Sul Son Jung-Ho Kim Adepelumi Adekunle Abraham 《Environmental Earth Sciences》2014,71(6):2797-2806
Recently, the electrical resistivity tomography (ERT) technique has been increasingly applied to underground cavity detection filled with groundwater and/or clay. In this study, an ERT survey was conducted to examine the spatial distribution and shape of underground cavities in a karst area in Korea. Numerical ERT modeling and inversion were carried out to select appropriate field survey parameters. Two geological structures, similar to those that exist in the field survey area, were modeled: a sinkhole model and a vein-type structure. Electrode configurations using pole–pole, pole–dipole, dipole–pole, and dipole–dipole arrays were tested with the two geologic models and compared. The numerical modeling showed that the resistivity distribution of the ERT tomogram using the pole–dipole array produced the best representation of the two models. The pole–dipole and pole–pole array configurations were applied in an ERT field survey using six boreholes. The field ERT results show that cavity areas filled with clay or groundwater appeared as low-resistivity anomalies in the limestone formation. This was particularly evident in the inclined vein-type structures attributed to fracture zones, where the field data were similar to the modeling results. Therefore, the ERT technique could be effectively used for detecting underground limestone cavities under similar geological conditions as those at our study area. 相似文献
46.
正Great Salt Lake(GSL),in northern Utah,is one of the largest lakes in the United States,with a total surface area of 4400 square kilometers.Arthropods constitute the most conspicuous and abundant animals inhabiting the waters 相似文献
47.
Flood forecasting in large rivers with data-driven models 总被引：1，自引：1，他引：0
Results from the application of adaptive neuro-fuzzy inference system (ANFIS) to forecast water levels at 3 stations along the mainstream of the Lower Mekong River are reported in this paper. The study investigated the effects of including water levels from upstream stations and tributaries, and rainfall as inputs to ANFIS models developed for the 3 stations. When upstream water levels in the mainstream were used as input, improvements to forecasts were realized only when the water levels from 1 or at most 2 upstream stations were included. This is because when there are significant contributions of flow from the tributaries, the correlation between the water levels in the upstream stations and stations of interest decreases, limiting the effectiveness of including water levels from upstream stations as inputs. In addition, only improvements at short lead times were achieved. Including the water level from the tributaries did not significantly improve forecast results. This is attributed mainly to the fact that the flow contributions represented by the tributaries may not be significant enough, given that there could be large volume of flow discharging directly from the catchments which are ungauged, into the mainstream. The largest improvement for 1-day forecasts was obtained for Kratie station where lateral flow contribution was 17 %, the highest for the 3 stations considered. The inclusion of rainfall as input resulted in significant improvements to long-term forecasts. For Thakhek, where rainfall is most significant, the persistence index and coefficient of efficiency for 5-lead-day forecasts improved from 0.17 to 0.44 and 0.89 to 0.93, respectively, whereas the root mean square error decreased from 0.83 to 0.69 m. 相似文献
48.
Young Baek Son Wilford D. Gardner Mary Jo Richardson Joji Ishizaka Joo-Hyung Ryu Sang-Hyun Kim Sang H. Lee 《Journal of Oceanography》2012,68(5):743-760
To trace offshore surface low-salinity water (LSW) in the northeastern Gulf of Mexico, a proxy was developed using the surface water beam attenuation coefficient (c p), and salinity matched with synchronous Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite data from three annual summer cruises (July 1998–August 2000) using a two-step empirical approach. First, a relationship between in-situ salinity and c p was obtained. Second, in-situ c p was matched with SeaWiFS radiance ratios of all available blue-to-green wavelengths. Finally, satellite-derived surface salinity was determined directly by combining the two empirical relationships, providing a robust estimate over a range of salinities (26–36). This significantly improves the limited spatial and temporal resolution of surface salinity distribution obtained by shipboard sampling. The resulting correlation is best explained as mixing between low-salinity plume waters and normal salinity Gulf waters. The empirical relationships were used to map satellite-derived salinity using the average of SeaWiFS images during each summer cruise. As expected for summer, spatial patterns of LSW plumes with high c p, particulate matter (PM), particulate organic carbon (POC), and chlorophyll-a (Chl-a) were connected to the mouth of the Mississippi River Delta and extended to the east-southeast. Normal salinity Gulf water with lower c p, PM, POC, and Chl-a was confined to the shelf and upper slope in the eastern part of the study area, outside the plumes. This proxy approach can be applied throughout the region of shipboard sampling for more detailed coverage and analysis. 相似文献
49.
50.
The Cretaceous Kusandong Tuff, Korea, is a thin (1–5 m thick) but laterally extensive (~ 200 km) silicic ignimbrite emplaced in a fluviolacustrine basin adjacent to a continental volcanic arc. The tuff has been used as an excellent key bed because of its great lateral continuity and unique lithology, characterized by the virtual absence of juvenile clasts and an abundance of quartz and feldspar crystals (up to 55–73 vol.%). The tuff is mostly massive and ungraded and locally shows crude internal layering, basal inverse grading and near-top normal grading of crystals, either erosional or non-erosional lower surfaces, and flat-lying to imbricated grain fabrics. Fragile intraformational clasts of mudstone and tuff are also included. These features provide only ambiguous information on the properties of the responsible pyroclastic density currents: i.e. whether they were dense and laminar or dilute and turbulent. The overall lateral continuity and sheet-like geometry of the tuff suggests, however, that the transport system of the currents was highly expanded, dilute, and turbulent. A plug-flow or slab-flow model cannot explain the origin of crude internal layering, imbricated grain fabrics, and the high crystal content, which is most likely the result of vigorous sorting processes within a dilute and turbulent current. Features indicative of deposition from a dense and laminar transporting medium are locally present, suggesting that a dense and laminar depositional system could develop locally at the base of the dilute and turbulent transport system. The virtual absence of juvenile clasts in the tuff is interpreted to be due to rapid ascent, sudden decompression, and full fragmentation of silicic magma into fine glass shards and crystals. Scarcity of basement-derived accidental components together with the absence of pumiceous fallout deposits beneath the tuff is interpreted to be due to shallow-level fragmentation of magma followed by immediate generation of pyroclastic density currents from shallow-level blasts at the onset of eruption. The eruption occurred through multiple vent sites in a short period of time, producing a seemingly single but actually composite ignimbrite unit. Such an eruption was probably possible because of a regional tectonic event within the basin or in its vicinity. It is proposed that a composite ignimbrite with the characteristics of the Kusandong Tuff can be an exemplary product of syntectonic volcanism that can provide an insight into the interpretation of structural and stratigraphic evolution of a sedimentary basin. 相似文献