Structure of soil bacterial communities in relation to environmental variables in a semi-arid region of Mongolia     

《Journal of Arid Environments》2013

Patterns in soil bacterial communities, and the factors that determine them, have been little explored in arid and semi-arid environments. It is unclear to what extent the diversity and community composition of arid-land soil bacterial communities follow vegetation habitats, or conversely other relatively independent soil variables. It is also unclear whether the factors (e.g. pH) that contribute to variation in bacterial communities in some moister environments also operate on a local scale in semi-arid environments. To identify the main factors in shaping bacterial community structure in semi-arid environments, we sampled a mosaic of habitats under different vegetation, landscape and edaphic conditions in central Mongolia, including steppe, forest-steppe, and abandoned wheat field. Soil DNA was extracted and pyrosequenced for 16S rRNA gene identification. NMDS results showed that bacterial community structures are slightly different from one habitat to another. However, the similarity between communities both within and between habitats is determined more strongly by soil texture than by vegetation type and drainage conditions. Moreover, the relative abundances of certain phyla are correlated with specific soil properties such as salinity and soil texture, in ways that have not previously been found in semi-arid environments. Actinobacteria, for example, show a negative correlation with salinity and Bacteroidetes display a positive relationship with percentage silt and clay. It also appears that the most important environmental variables (soil texture and salinity) affecting the bacterial community within this semi-arid environment are different from those found in moister environments, with no detectable effect of pH.  相似文献   

Soil organic matter transport along an sub-Arctic river–sea transect     

《Organic Geochemistry》2012

Bacteriohopanepolyols (BHPs) and glycerol dialkyl glycerol tetraethers (GDGTs) have potential as soil-tracing biomarkers for the extensive shelves of the Arctic Ocean. In this work these biomarkers were analysed in surface sediments along a well characterised sub-Arctic transect in the northernmost Baltic Sea from the Kalix River to the central Bothnian Bay to assess their environmental behaviour and potential for tracing the contribution of soil in this type of system. There was a high BHP diversity and enhanced total BHP concentration in the estuarine sediments, whereas a much less diverse pattern could be observed in the open bay with lower total BHP concentration. In addition, both soil marker BHPs (adenosylhopanes) and branched GDGTs were substantially more abundant in the estuarine than the open bay sediments.The $R_{\text{soil}}^{\prime }$ index, based on the R_soil index minus the contribution from the methylated soil marker BHPs, is suggested as a new approach for tracing soil derived organic matter (OM) in the (sub)-Arctic region. The index decreased along the transect in an off-river direction, correlating strongly with both the branched and isoprenoid tetraether (BIT) index and the stable carbon isotopic composition of the sedimentary organic carbon. These field results indicate that both the $R_{\text{soil}}^{\prime }$ and the BIT indices have potential for tracing soil derived OM in sub-Arctic to Arctic waters.  相似文献   

Discovery of a new hydrothermal vent based on an underwater,high-resolution geophysical survey     

《Deep Sea Research Part I: Oceanographic Research Papers》2013

A new hydrothermal vent site in the Southern Mariana Trough has been discovered using acoustic and magnetic surveys conducted by the Japan Agency for Marine-Earth Science and Technology's (JAMSTEC) autonomous underwater vehicle (AUV), Urashima. The high-resolution magnetic survey, part of a near-bottom geophysical mapping around a previously known hydrothermal vent site, the Pika site, during the YK09-08 cruise in June–July 2009, found that a clear magnetization low extends ∼500 m north from the Pika site. Acoustic signals, suggesting hydrothermal plumes, and 10 m-scale chimney-like topographic highs were detected within this low magnetization zone by a 120 kHz side-scan sonar and a 400 kHz multibeam echo sounder. In order to confirm the seafloor sources of the geophysical signals, seafloor observations were carried out using the deep-sea manned submersible Shinkai 6500 during the YK 10-10 cruise in August 2010. This discovered a new hydrothermal vent site (12°55.30′N, 143°38.89′E; at a depth of 2922 m), which we have named the Urashima site. This hydrothermal vent site covers an area of approximately 300 m×300 m and consists of black and clear smoker chimneys, brownish-colored shimmering chimneys, and inactive chimneys. All of the fluids sampled from the Urashima and Pika sites have chlorinity greater than local ambient seawater, suggesting subseafloor phase separation or leaching from rocks in the hydrothermal reaction zone. End-member compositions of the Urashima and Pika fluids suggest that fluids from two different sources feed the two sites, even though they are located on the same knoll and separated by only ∼500 m. We demonstrate that investigations on hydrothermal vent sites located in close proximity to one another can provide important insights into subseafloor hydrothermal fluid flow, and also that, while such hydrothermal sites are difficult to detect by conventional plume survey methods, high-resolution underwater geophysical surveys provide an effective means.  相似文献   

The Three Results of Sound Velocity Variance in Sediments During Controlled Stress-strain Testing from the South China Sea     

BO LU  Ganxian Li  Shaojian Huang  Shuzhuo Liu 《Marine Georesources & Geotechnology》2013,31(3):177-186

Sound velocity in each type of seafloor sediment from the South China Sea varies with the development of strain in the controlled stress-strain course. Experiments show that there may exist three cases for the maximum sound velocity: (1) it appears at the stress peak; (2) it appears in the phase of no load; and (3) it appears at the end of the strain course. These results are related to physical-mechanical properties and structure of sediments.  相似文献   

Microscale Response of Sediment Variables to Benthic Disturbance in the Central Indian Ocean Basin     

Shanta Nair  C. Mohandass  P. A. Loka Bharathi  G. Sheelu  Raghukumar Chandralata 《Marine Georesources & Geotechnology》2013,31(3):273-283

Abstract

The response of sediment bacteria and biochemical variables to benthic disturbance was investigated in the Central Indian Ocean Basin from cores at nine stations. Generally, bacterial density and biochemical variables declined vertically with depth in the upper layers of the cores. Mechanical disturbance caused by a hydraulic disturber brought about a substantial decrease in total bacterial numbers. However, the numbers of retrievable bacteria increased by two orders of magnitude. The biochemical parameters decreased in quantity with a shift in the linear relationship. The data suggest that abiotic artifacts will directly affect the biomass and biochemistry of the sediment.  相似文献   

Assessment of Impact on Seafloor Features in INDEX Area     

Rahul Sharma 《Marine Georesources & Geotechnology》2013,31(3):237-250

Abstract

Observations on seafloor features from subbottom profiling and seabed photography data show that the undisturbed and natural conditions before the benthic disturbance undergo a substantial change after operation of the disturber. The effects can be seen in the form of deep trenches and grooves, formed by the action of the sleds and the pumping of the sediment along its path, as well as sediment piles on either side of the track. Biological traces such as fecal coils, casts, tubes, burrows, and trails get obliterated in the areas of disturbance and resedimentation. The smooth, uniform nature of the seafloor observed in pre-disturbance phase shows microtopographic changes in and around the disturbed area as a result of sediment excavation and resettlement. Vertical mixing as well as lateral transport of sediment alter the geological, biological, physical, and chemical conditions on the seafloor, which need to be monitored over time to assess the process and the time taken for restoration of environmental conditions.  相似文献   

Geotechnical Properties of Surface Sediments in the INDEX Area     

N. H. Khadge 《Marine Georesources & Geotechnology》2013,31(3):251-258

Abstract

As a part of the environmental impact assessment studies, geotechnical properties of sediments were determined in the Central Indian Basin. The undrained shear strength and index properties of the siliceous sediments were determined on 20 box cores of uniform dimension collected from various locations in five preselected sites. The maximum core length encountered was 41 cm and most of the sediments were siliceous oozes consisting of radiolarian or diatomaceous tests. The shear strength measurements revealed that surface sediments deposited in recent times (0–10 cm) have a shear strength of 0–1 kPa; this value increases with depth, reaching 10 kPa at 40 cm deep. Older sediments have greater strength because of compaction. Water content varies in the wide range of 312–577% and decreases with depth. The clay minerals such as smectite and illite are dominant and show some control over water content. Wet density, specific gravity, and porosity do not indicate any notable variation with depth, thereby indicating a uniform, slow rate of sedimentation. The average porosity of sediments is 90.2%, specific gravity 2.18, and wet bulk density 1.12 g/cm³. Sediments exhibit medium to high plasticity characteristics, with the average plasticity index varying between 105% and 136%. Preliminary studies on postdisturbance samples showed an increase in natural water content and a decrease in undrained shear strength of sediments in the top 10- to 15-cm layer.  相似文献   

Biostratigraphic Analysis of the Top Layer of Sediment Cores from the Reference and Test Sites of the INDEX Area     

Shyam M. Gupta 《Marine Georesources & Geotechnology》2013,31(3):259-262

Abstract

Radiolarian fossil study in the sediment cores collected during the pre- and postdisturbance cruises of the Environmental Impact Assessment (EIA) Indian Ocean Experiment (INDEX) program of deep sea mining in the Central Indian Ocean Basin suggests a pronounced directional deposition of fossil radiolarians exhumed during the deep sea benthic disturbance experiment. The relative occurrences of the Stylatractus universus species that became extinct ～0.425 million years before present were mostly confined to the older and deeper strata of the sediment of the disturbance tract in the southwestern direction. This pattern is remarkable and suggests that the disturbance plume has been preferentially redeposited in the southwestern direction. This observation is in concurrence with the prevailing southwestern abyssal current during the disturbance experiment in the Central Indian Basin.  相似文献   

Changes in metal contamination levels in estuarine sediments around India – An assessment     

《Marine pollution bulletin》2014,78(1-2):15-25

This review is the first attempt to comprehend the changes in metal contamination levels in surface estuarine sediments with changing time around India. Contamination factor, geoaccumulation index, pollution load index, effects range low and effects range median analysis were used to evaluate the quality of the estuarine sediments (by using the available literature data). This study suggests that estuarine sediments from the east coast of India were comparatively less contaminated by metals than the west coast. Sediments from those estuaries were found to be more contaminated by metals on which major cities are located. An improvement in estuarine sediment quality (in terms of metal contamination) over time around India was noticed. This study provides managers and decision-makers of environmental protection agency with a better scientific understanding for decision-making in controlling metal pollution in estuarine sediments around India.  相似文献   

Glass and Mineral Chemistry of Northern Central Indian Ridge Basalts:Compositional Diversity and Petrogenetic Significance     

Dwijesh RAY  Ranadip BANERJEE  Sridhar D IYER  Basavaraju BASAVALINGU  Subir MUKHOPADHYAY 《《地质学报》英文版》2009,83(6):1122-1135

Abstract: The glass and mineral chemistry of basalts examined from the northern central Indian ridge (NCIR) provides an insight into magma genesis around the vicinity of two transform faults: Vityaz (VT) and Vema (VM). The studied mid-ocean ridge basalts (MORBs) from the outer ridge flank (VT area) and a near-ridge seamount (VM area) reveal that they are moderately phyric plagioclase basalts composed of plagioclase (phenocryst [An60–90] and groundmass [An35–79]), olivine (Fo81–88), diopside (Wo45–51, En25–37, Fs14–24), and titanomagnetite (FeOt ~63.75 wt% and TiO2 ~22.69 wt%). The whole-rock composition of these basalts has similar Mg# [mole Mg/mole(Mg+Fe2+)] (VT basalt: ~0.56–0.58; VM basalt: ~0.57), but differ in their total alkali content (VT basalt: ~2.65; VM basalt: ~3.24). The bulk composition of the magma was gradually depleted in MgO and enriched in FeOt, TiO2, P2O5, and Na2O with progressive fractionation, the basalts were gradually enriched in Y and Zr and depleted in Ni and Cr. In addition, the SREE of magma also increased with fractionation, without any change in the (La/Yb)N value. Glass from the VM seamount shows more fractionated characters (Mg#: 0.56–0.57) compared to the outer ridge flank lava of the VT area (Mg#: 0.63–0.65). This study concludes that present basalts experienced low-pressure crystallization at a relatively shallow depth. The geochemical changes in the NCIR magmas resulted from fractional crystallization at a shallow depth. As a consequence, spinel was the first mineral to crystallize at a pressure >10 kbar, followed by Fe-rich olivine at <10 kbar pressure.  相似文献