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Nguyen Tai Tue Tran Dang Quy Hideki Hamaoka Mai Trong Nhuan Koji Omori 《Estuaries and Coasts》2012,35(4):1060-1068
The spatio-temporal variations in stable isotope signatures (??13C and ??15N) and C/N ratios of particulate organic matter (POM), and physicochemical parameters in a creek water column were examined in an estuarine mangrove ecosystem of Xuan Thuy National Park, Vietnam. The objective was to examine the factors influencing creek water properties, and the sources and exchange of POM in this important mangrove ecosystem. The diel and seasonal variations in water temperature, flow velocity, pH, dissolved oxygen, and salinity demonstrated that tidal level, season, and biological factors affected the creek water properties. Mangroves had relatively low ??15N and very low ??13C values, with respective average values of 1.5?±?0.9?? and ?28.1?±?1.4??. The low mangrove leaf ??15N indicated minor anthropogenic nitrogen loading to the mangrove forests. A significant positive correlation between POM?C??13C and salinity along the axis of Ba Lat Estuary, Red River, indicated that marine phytoplankton (??13C value, ?21.4?±?0.5??) was the predominant source of POM at the estuary mouth. Based on the co-variation of ??13C and C/N ratios, marine phytoplankton and mangrove detritus were predominant in POM of major creeks and small creeks, respectively. During the diurnal tidal cycle, the dynamics of POM were affected by sources of organic matter, tidal energy, and seasonal factors. The contribution of mangrove detritus to POM reached a maximum at the low tide and was enhanced during the rainy season, whereas marine phytoplankton contribution was highest at high tide. 相似文献
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Understanding the assemblage of basic grains is essential for predicting many soil properties. X-ray synchrotron microtomography with a high resolution was used for visualisation and quantification of the assemblage of silt grains with a clay phase containing 20% of clays. The 3D computed image was analysed after appropriate segmentation by using: (i) autocorrelation functions which enables anisotropy discussion of the assemblage; (ii) chord distribution which gives information on the size distribution of the void and solid phases; and (iii) the Hoshen-Kopelman algorithm (6-connectivity) in order to label each void with a unique number and thus enabling discussion of the connectivity. Our results show that X-ray synchrotron microtomography enables a more accurate analysis of the assemblage of silt grains with a clay phase than with conventional methods. Thus, it showed the isotropy of the silt-clay assemblage in the studied soil material. The void and solid phase volumes were smaller than 80 and 120 μm in all directions, respectively. The mean distance between two interfaces was 6.9 and 13.4 μm for the void and solid phase, respectively. X-ray synchrotron microtomography of the soil material studied also showed that the voids resulting from the assemblage of the silt grains with the clay phase can be considered as fully connected in the studied dried materials. 相似文献
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A. G. Vladimirov P. A. Balykin Phan Luu Anh N. N. Kruk Ngo Thi Phuong A. V. Travin Tran Trong Hoa I. Yu. Annikova M. L. Kuybida E. V. Borodina I. V. Karmysheva Bui An Nien 《Russian Journal of Pacific Geology》2012,6(5):395-411
New data obtained on the Khao Que-Tam Tao gabbro-granite pluton (Northern Vietnam) are discussed. It was established that this pluton was formed at the Permian-Triassic boundary (250.5 ± 3.2 Ma, 40Ar/39Ar isotopic age). Morphologically, it represents a hypabyssal fracture intrusion. The first stage was marked by the intrusion of the picrobasaltic melt, the differentiation of which resulted in the formation of the layered peridotite-gabbro series and the quartz-bearing monzodiorites and granophyres in its endocontact at the final stage. At the second stage, the Khao Que peridotite-gabbro massif was broken in its central part by a fault, along which the Tam Tao granodiorite-granite massif was localized. Numerical simulation using the COMAGMAT program for the basic system and geochemical estimates for the granite system allow the statement that the mafic and granitic melts evolved independently, and their final products were quartz-bearing monzodiorite and granophyre, on the one hand, and aplites and pegmatites, on the other hand. The compositional correlation of the Permian-Triassic magmatic associations in Northern Vietnam (the Nui Chua gabbro pluton and the Khao Que-Tam Tao gabbro-granite and Pia Bioc granite plutons) and in Southeast China (flood basalts) allows these complexes to be regarded as a part of a single large igneous province produced by the Emeishan plume activity. 相似文献
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Nguyen Tai Tue Hideki Hamaoka Atsushi Sogabe Tran Dang Quy Mai Trong Nhuan Koji Omori 《Environmental Earth Sciences》2011,64(5):1475-1486
In this study, two sediment cores (~70 cm) were collected from separate mangrove forests straddling the Ba Lat Estuary, Red
River of northern Vietnam, to examine the origins of sedimentary organic carbon (SOC) and reconstruct the paleoenvironment.
In addition, mangrove leaves and particulate organic matter were collected and measured for δ13C to trace the origins of SOC. The cores were analyzed by high-resolution sections for δ13C, TOC, C/N ratios, sediment grain size, water content, and porosity, with values of δ13C, TOC, and C/N ratios ranging from −28.19 to −22.5‰, 2.14–30.94 mg/g, and 10.29–18.32, respectively. The δ13C and TOC relationship indicated that there were some small residual effects of diagenetic processes on TOC and δ13C values in mangrove sediments. However, the shifts of δ13C and C/N ratios from the bottom to the surface sediment of the cores explained the change in organic matter sources, with
values of C/N > 12 and δ13C < −25‰, and C/N < 12 and δ13C > −25‰ indicated terrestrial (e.g., mangrove litter) and marine phytoplankton sources, respectively. The covarying δ13C, C/N ratios, and sediment grain sizes during the past 100 years in sediment cores showed that the paleoenvironment may be
reconstructed into three environments (subtidal, tidal flat, and intertidal mangrove). General trends in δ13C and C/N followed a gradual increase in the C/N ratio and a concomitant decrease in δ13C from the subtidal, through to tidal flat, and to the intertidal mangrove. δ13C and C/N ratios are therefore effective in measuring the continuum of environmental change in mangrove ecosystem. 相似文献
15.
Tracing carbon transfer and assimilation by invertebrates and fish across a tropical mangrove ecosystem using stable isotopes 
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下载免费PDF全文 Nguyen Tai Tue Tran Dang Quy Mai Trong Nhuan Luu Viet Dung Nguyen Dinh Thai 《Marine Ecology》2017,38(5)
Mangroves are highly productive ecosystems that exhibit a diverse range of habitats, including tidal creeks and flats, forest gaps and interior forest with varying understory light intensity, tidal dynamics, geomorphological settings, and overall biological production. Within mangrove ecosystems, invertebrates and fish feed on heterogeneous food sources, the occurrence of which is unevenly distributed across the system. This provides a basis for testing models of carbon transfer across mangrove ecosystems. We hypothesized that the carbon transfer and assimilation by fish and invertebrates will vary across the different mangrove habitats and that such variations can be predicted by their stable isotope compositions. We analysed δ13C and δ15N signatures of consumers and their potential organic carbon sources across a tropical mangrove ecosystem in Vietnam. The δ13C values of crabs and snails significantly decreased from the tidal flat to interior forest, indicating that variations in carbon transfer and assimilation occurred at small scales <30 m. Reduced variation in δ13C of suspension‐feeding bivalves suggested that tidal water was a vector for large‐scale transport of carbon across the mangrove ecosystem. An analysis of co‐variance using habitat as a fixed factor and feeding habit and movement capacity of consumers as co‐variates indicated that habitat and feeding types were major features that affected the δ13C values of invertebrates and fish. The findings demonstrate that carbon transfer and assimilation across mangrove ecosystems occur as a diverse combination of small (<30 m) and large (>30 m) scale processes. 相似文献
16.
Usually, one can explain the orthogonal distribution of first movement by the dislocation model of seismic sources, namely a uniform slip. However, other representations may be obtained if the normal component of the dislocation is present. When this component is less than 0.6 times the tangential one, we obtain conical distributions. Some models which simulate a volume phenomenon provide analogous results. We show that they could agree with some observations. 相似文献
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Trong C. D. Hoang N. Bach M. X. Luc N. M. Dung L. V. Trieu C. D. Syrbu N. S. Hai D. Th. Tuan Th. A. Toan N. Q. Thanh D. V. 《Geotectonics》2022,56(3):321-338
Geotectonics - This paper presents analysis of geomorphological indices for predicting the maximum observed earthquake (MOb?Max) in research region, conducted in three steps: (i)... 相似文献
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N. H. Tuyen Ph. V. Phach R. B. Shakirov C. D. Trong Ph. N. Hung L. D. Anh 《Geotectonics》2018,52(3):359-381
The goal of the paper is to reveal the hierarchical block structure in the Tuan Giao area (Northwest Vietnam) and, on that base, to identify areas prone to earthquakes with M ≥ 5. Four large geoblocks of the second rank have been delineated on the basis of the joint analysis of geological, geophysical, geomorphic, and remote sensing data. The second rank geoblocks have been divided into smaller sub-blocks of the third rank. The recent geodynamics of the geoblocks have been characterized using geomorphic, seismological, gravity, and GPS data.The system of the delineated geoblocks is viewed as the Geodynamic Blocks model. The areas prone to earthquakes with M ≥ 5 have been identified using the pattern recognition algorithm CORA-3. The objects of the recognition were defined as circular areas, where boundaries of the geoblocks intersect each other. The recognition results confirm high seismic potential of the study region and provide information on potential earthquake sources for seismic hazard assessment: a number of boundary intersections have been identified as areas prone to earthquakes with M ≥ 5, where events of such magnitude have not been recorded up to date. Mordern geothermal activity and anomalies of dissolved methane (up to 10000 nL/L), helium and hydrogen in the hot mineral water springs prove high permeability of the study area and its active seismo-tectonic state. 相似文献
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Origin of the Permian-Triassic komatiites,northwestern Vietnam 总被引：7，自引：0，他引：7
Eero?HanskiEmail author Richard?J.?Walker Hannu?Huhma Gleb?V.?Polyakov Pavel?A.?Balykin Tran Trong Hoa Ngo Thi Phuong 《Contributions to Mineralogy and Petrology》2004,147(4):453-469
Abstract Rare examples of Phanerozoic komatiites are found in the Song Da zone, NW Vietnam. These komatiites were erupted through continental crust and may belong to the SE extension of the Permo-Triassic Emeishan volcanic province located in SW China. They provide a good opportunity to study the source characteristics of starting plume magmas in a continental flood basalt province. Erupted on late-Permian carbonate rocks, the komatiitic rocks are interbedded with low-Ti olivine basalts. Basaltic komatiites display pyroxene spinifex textures, while more magnesian rocks (MgO up to 32 wt.%) are porphyritic, containing a single, cognate population of euhedral to elongated olivine phenocrysts with Fo up to 93.0%. This suggests a highly magnesian parental magma with 22–23 wt.% MgO. In terms of major and minor elements, the komatiites are similar to the ca. 89 Ma old Gorgona Island komatiites of Colombia. The Song Da komatiites are also strongly light-rare-earth-element- (LREE) depleted (CeN/YbN 0.30–0.62) and have unfractionated heavy rare earth element (HREE) patterns. The komatiites have high Os concentrations (up to 7.0 ppb), low but variable Re/Os ratios, and define an isochron with an age of 270±21 Ma, and an initial 188Os/187Os ratio of 0.12506± 0.00041 (Os=+0.02±0.40). The Os isotopic systematics of the komatiites show no effects of crustal contamination. In contrast, their initial Nd values range from +3 to +8, reflecting varying but generally small degrees of contamination with Proterozoic sialic basement material. Associated low-Ti basalts have low initial Nd values (–0.8 to –7.5), high initial Os values (15), flat or LREE-enriched REE patterns, and Nb-Ta depletion. These characteristics are also attributed to variable extents of crustal contamination.Editorial responsibility: T.L. Grove 相似文献