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131.
Microphytobenthic biomass and species composition in intertidal flats of the Nakdong River estuary, Korea 总被引:1,自引:0,他引:1
GuoYing Du Moonho Son Misun Yun Soonmo An Ik Kyo Chung 《Estuarine, Coastal and Shelf Science》2009,82(4):663-672
Intertidal microphytobenthos (MPB) were investigated monthly from August 2006 to March 2008 at four different sites in the sand flats of Nakdong River estuary, Korea. Samples of surface sediment (ca. 1 cm) were collected, and chlorophyll a was extracted as biomass estimation. Species identification and enumeration were carried out by light microscopy, assisted where necessary by scanning electronic microscopy. Biomass varied between 0.47 and 16.58 μg cm−3, abundance changed from 5.25 to 414.75 × 103 cells cm−3, while the Shannon diversity indexes ranged between 0.69 and 2.35 H′. Thirty-nine MPB taxa were identified, primarily composed of epipelic diatoms, among which Amphora and Navicula were the most abundant genera. Based on the biomass, abundance, species composition and their dynamics, MPB assemblages of sampling sites were grouped into three distinct communities corresponding to their sediment composition characteristics. Multivariate correlation analysis revealed that biomass was positively related to mud and very fine sand, negatively related to fine and medium sand, but not significantly related to environmental factors such as pore water nutrients, light intensity and salinity, which fluctuated rapidly during emersion period. Cluster analysis corroborated the division of MPB communities according to site types on seasonal scales, and also showed seasonality between sites by cluster of all summer groups. Principal component analysis identified that variability in species composition was significantly affected by mud, very fine sand, fine sand, light intensity, and sediment temperature. This study suggests that sediment composition plays an important role in the functioning of intertidal MPB communities in estuarine ecosystems. 相似文献
132.
Overburden soil beds situated above a fault are often deformed by propagation of bedrock thrusting from the fault during large earthquake. The deformed beds formed a triangular shear zone. This coseismic faulting often causes damage to underground tunnels located in the shear zone. The present research studies the deformation behavior of the overburden soil beds and the tunnel, the associated mechanism and the impact on the safety of tunnel linings induced by a large blind thrust slip. Based on sandbox experimental and numerical studies, it is found that results from numerical analysis are in agreement with the sandbox model tests with regard to growths of the shear zones within the soil beds, location of the tunnel in this shear zone and deformations of the tunnel. The potential major shear zone may be bent or bifurcated into two sub-shear zones owing to existence of a tunnel inside the shear zone. Furthermore, the occurrence of back-thrust faulting will threaten the safety of nearby structures. It was also identified that stiffness of the soil and the fault dip angles are among the major factors controlling the configuration of shear zones, the stresses within the soil, and the loads on tunnel linings. Based on the identified mechanisms, the strategies for hazard prevention are accordingly suggested and discussed. 相似文献
133.
Kyung-Ho Kim Kang-Kun Lee 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(6):785-794
A new methodology is proposed to optimize monitoring networks for identification of the extent of contaminant plumes. The
optimal locations for monitoring wells are determined as the points where maximal decreases are expected in the quantified
uncertainty about contaminant existence after well installation. In this study, hydraulic conductivity is considered to be
the factor that causes uncertainty. The successive random addition (SRA) method is used to generate random fields of hydraulic
conductivity. The expected value of information criterion for the existence of a contaminant plume is evaluated based on how
much the uncertainty of plume distribution reduces with increases in the size of the monitoring network. The minimum array
of monitoring wells that yields the maximum information is selected as the optimal monitoring network. In order to quantify
the uncertainty of the plume distribution, the probability map of contaminant existence is made for all generated contaminant
plume realizations on the domain field. The uncertainty is defined as the sum of the areas where the probability of contaminant
existence or nonexistence is uncertain. Results of numerical experiments for determination of optimal monitoring networks
in heterogeneous conductivity fields are presented. 相似文献
134.
A numerical program developed for field application is presented in this paper. We use the generalized Julien and Lan [8] rheological model to simulate debris flows. Due to the derivative discontinuous nature of the constitutive law, flow is
separated into plug region and bottom region (with stress greater than yield stress). The program solves the plug flow layer
solution first, and then corrects the solution with the bottom layer approximation. Numerical scheme with upwind method and
central difference in space and Adam–Bashforth third-order scheme in time is used for both layers. The scheme is tested against
analytical solutions and laboratory experiments with very good results. Application to a field case with more complicated
geometry also achieves good agreement, with error less than 5% compared to field measurements. The final example demonstrates
how this numerical program is used in a preliminary design. 相似文献
135.
Dong-Soo Kim Choong-Ki Chung Chang-Guk Sun Eun-Seok Bang 《Soil Dynamics and Earthquake Engineering》2002,22(5):358
The earthquake hazard has been evaluated for 10 km×10 km area around Kyeongju. The ground motion potentials were determined based on equivalent linear analysis by using the data obtained from in situ and laboratory tests. In situ tests include 16 boring investigations, 4 crosshole, 12 downhole, 26 spectral analysis of surface waves tests, and in the laboratory, resonant column tests were performed. The peak ground accelerations range between 0.141g and 0.299g on collapse level earthquake and between 0.050g and 0.120g on operation level earthquake, respectively, showing the high potential of amplification in the deep alluvial layer in Kyeongju area. Distribution maps of site amplification for the peak acceleration, amplification factors (Fa and Fv) and dominant site period of Kyeongju are constructed using geographic information system tools. The amplification factor based on the Korean seismic design guide underestimated the motion in short range and overestimated the motion in mid-period range in Kyeongju. The importance of site-specific analysis and the need for the improved site characterization method are introduced. 相似文献
136.
How much does dry‐season fog matter? Quantifying fog contributions to water balance in a coastal California watershed 下载免费PDF全文
The seasonally‐dry climate of Northern California imposes significant water stress on ecosystems and water resources during the dry summer months. Frequently during summer, the only water inputs occur as non‐rainfall water, in the form of fog and dew. However, due to spatially heterogeneous fog interaction within a watershed, estimating fog water fluxes to understand watershed‐scale hydrologic effects remains challenging. In this study, we characterized the role of coastal fog, a dominant feature of Northern Californian coastal ecosystems, in a San Francisco Peninsula watershed. To monitor fog occurrence, intensity, and spatial extent, we focused on the mechanisms through which fog can affect the water balance: throughfall following canopy interception of fog, soil moisture, streamflow, and meteorological variables. A stratified sampling design was used to capture the watershed's spatial heterogeneities in relation to fog events. We developed a novel spatial averaging scheme to upscale local observations of throughfall inputs and evapotranspiration suppression and make watershed‐scale estimates of fog water fluxes. Inputs from fog water throughfall (10–30 mm/year) and fog suppression of evapotranspiration (125 mm/year) reduced dry‐season water deficits by 25% at watershed scales. Evapotranspiration suppression was much more important for this reduction in water deficit than were direct inputs of fog water. The new upscaling scheme was analyzed to explore the sensitivity of its results to the methodology (data type and interpolation method) employed. This evaluation suggests that our combination of sensors and remote sensing allows an improved incorporation of spatially‐averaged fog fluxes into the water balance than traditional interpolation approaches. 相似文献
137.
Real‐time river bed scour monitoring and synchronous maximum depth data collected during Typhoon Soulik in 2013 下载免费PDF全文
A critical concern regarding river bed stabilization and river engineering is the short‐term general scour that occurs in a field setting far from a river‐crossing structure or embankment during a typhoon‐induced flood. This study investigated the improvement of existing techniques that have been used to measure river bed scour. One of these techniques is the numbered‐brick column or scour chains method, in which only the maximum general scour depth of river bed is observed. A wireless tracer for monitoring real‐time scour was set‐up with a numbered‐brick column and was employed to collect synchronous data. The proposed method was successfully used to observe both real‐time scour and the maximum depth at flood peak. This observation was conducted at a steep gravel‐bed reach of the Shuideliaw Embankment on the intermittent Choshui River in Central Taiwan during Typhoon Soulik, which occurred in 2013. Future studies must be conducted to complete the development of an automatic real‐time scour and flood monitoring system for use in severe weather and flow conditions; this would facilitate the identification of river bed scour during conditions of unstable flow and the improvement of flood prevention engineering, bridge closure detection and emergency evacuation procedures. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
138.
Hyein Park Chul E. Chung Annica M. L. Ekman Jung-Ok Choi 《Asia-Pacific Journal of Atmospheric Sciences》2014,50(3):377-390
This study examines and evaluates simulated aerosol optical depth (AOD) and fine-mode AOD (fAOD) from the ACCMIP and CMIP5 global model archives. Satellite data nudged to AERONET data are used to construct reliable global observations of AOD and fAOD for validating the simulations. The difference in simulated global average AOD among models is of the order of a factor of 2, and the difference is even larger (~factor of 3) for fAOD. Compared to the observations, the models tend to underestimate AOD and fAOD significantly over eastern China. Another important discrepancy is that the models show larger fAOD over the Indus-Ganga Plain in summer than in winter, whereas the observations display an opposite feature. The models also overestimate the fAOD over the biomass burning regions of central Africa in DJF and underestimate the fAOD over the biomass burning regions of southern Africa in JJA. To evaluate the effect of the discrepancy between modeled and observed fAOD on aerosol direct radiative forcing, an offline radiation model is utilized. Comparing the model-fAODderived fine-mode forcing with the fine-mode forcing derived from the fAOD observation, the models tend to give too large (negative) value. This result implies that the calculated anthropogenic aerosol forcing in ACCMIP and CMIP5 models has a negative bias. 相似文献
139.
Choon-Ki?Lee Shin-Chan?HanEmail author Dieter?Bilitza Jong-Kyun?Chung 《Journal of Geodesy》2011,85(12):921-929
The in situ measurements of electron contents from GRACE K-band (dual-frequency) ranging system and CHAMP planar Langmuir
probe were used to validate the international reference ionosphere (IRI) models. The comparison using measurements from year
2003 to 2007 shows a general agreement between data and the model outputs. The improvement in the newer IRI model (IRI-2007)
is evident with the measurements from the GRACE satellites orbiting at the higher altitude. We present the comparison between
the models and data comprehensively for various cases in solar activity, local time, season, and latitude. The IRI models
do not well predict the electron density in the years 2006 and later, when the solar activity is extremely low. The IRI models
generally overestimate the electron density during local winter while they underestimate during local summer. In the equatorial
region, the large difference at local sunrise lasts for all years and all seasons. The IRI models do not perform well in predicting
the anomaly in the polar region such as the Weddell Sea Anomaly. These discrepancies are likely due to smoothed (12-month
averaged) solar activity indices used in the IRI models and due to insufficient spherical harmonic representation not able
to capture small spatial scales. In near future, further improvement on the IRI models is expected by assimilating those in
situ satellite data by implementing higher resolution (spatial and temporal) parameterizations. 相似文献
140.
Di-Cheng Zhu Zhi-Dan Zhao Yaoling Niu Xuan-Xue Mo Sun-Lin Chung Zeng-Qian Hou Li-Quan Wang Fu-Yuan Wu 《Earth and Planetary Science Letters》2011,301(1-2):241-255
The Lhasa Terrane in southern Tibet has long been accepted as the last geological block accreted to Eurasia before its collision with the northward drifting Indian continent in the Cenozoic, but its lithospheric architecture, drift and growth histories and the nature of its northern suture with Eurasia via the Qiangtang Terrane remain enigmatic. Using zircon in situ U–Pb and Lu–Hf isotopic and bulk-rock geochemical data of Mesozoic–Early Tertiary magmatic rocks sampled along four north–south traverses across the Lhasa Terrane, we show that the Lhasa Terrane has ancient basement rocks of Proterozoic and Archean ages (up to 2870 Ma) in its centre with younger and juvenile crust (Phanerozoic) accreted towards its both northern and southern edges. This finding proves that the central Lhasa subterrane was once a microcontinent. This continent has survived from its long journey across the Paleo-Tethyan Ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the Qiangtang Terrane to the north and with the Indian continent to the south. Zircon Hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks (e.g., ~ 50–90%, 0–70%, and 30–100% to the Mesozoic magmatism in the southern, central, and northern Lhasa subterranes, respectively). We suggest that much of the Mesozoic magmatism in the Lhasa Terrane may be associated with the southward Bangong–Nujiang Tethyan seafloor subduction beneath the Lhasa Terrane, which likely began in the Middle Permian (or earlier) and ceased in the late Early Cretaceous, and that the significant changes of zircon εHf(t) at ~ 113 and ~ 52 Ma record tectonomagmatic activities as a result of slab break-off and related mantle melting events following the Qiangtang–Lhasa amalgamation and India–Lhasa amalgamation, respectively. These results manifest the efficacy of zircons as a chronometer (U–Pb dating) and a geochemical tracer (Hf isotopes) in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics. 相似文献