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1.
The bacterial community in deep subseafloor sediments at a depth of 230 cm from the western Pacific "warm pool" is studied by construction of 16S rDNA clone library and PCR-RFLP (Restriction Fragment Length Polymorphism) analysis. The results indicate that the bacterial community in these sediments is mainly composed of five groups: α-Proteobacteria, β-Proteobacteria, CFB group (Cytophaga / Flexi-bacteria / Bacteroides), Acidobacteria and gram positive bacteria, with a few genera detected in each group. The most abundant bacteria group is α-Proteobacteria, and the next is β-Proteobacteria. The dominant species in α-and β-Proteobacteria are Sphingomonas paucimobilis and Pseudomonas alca-ligenes respectively. The CFB group is simply composed of members belonging to Flavobacterium. The gram positive bacteria are rich, and mainly consists of the genus Geobacillus. The analysis of bacterial community indicates that organic matter is still abundant in the subseafloor sediments at the depth of 230 cm in the western Pacific "warm pool" . These bacteria in this deep biosphere may play an impor-tant role in the nitrogen cycle of deep sea sediments at "warm pool" .  相似文献   

2.
To investigate vertical changes of bacterial communities from living plants to the associated sediments and bacterial biogeochemical roles in peatland ecosystem,samples of different part of individual Sphagnum palustre and the different layers of the underlying sediments were collected from Dajiuhu Peatland in central China.All samples were subject to 16S rRNA gene clone libraries and quantitative PCR analysis.Even though bacteria vary in abundance at the same order of magnitude in all samples,they show great profile difference in composition from the top part of S.palustre to the low layer of the sediments.Cyanobacteria and alpha-Proteobacteria dominate at the top part whereas Acidobacteria at the middle part of S.palustre.Alpha-Proteobacteria and Acidobacteria are the dominant phyla at the bottom part of S.palustre and in the surface peat sediment.In contrast,bacterial communities in the subsurface sediments are dominated by Acidobacteria.These profile distributions of different bacterial communities are closely related to their ecological functions in the peatland ecosystem.Specifically,most Cyanobacteria were observed at the top green part of S.palustre,a horizon where the active photosynthesis of the moss occurs,which infers their endosymbiosis.In contrast,Acidobacteria,dominant in the subsurface sediments,are able to decompose the specific compounds on the cell wall of Sphagnum moss and thus might play an important role in the formation of the peatland,including the acidic condition.Methane oxidizing process might have been underestimated in Sphagnum peatland due to the identification of Methylocystaceae in all parts of the moss investigated here.The vertical difference in bacterial composition and bacterial ecological functions presented here sheds light on the understanding of biogeochemical processes,in particular the CH4 flux,in peat ecosystems.  相似文献   

3.
《国际泥沙研究》2016,(4):341-350
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4.
Hyperconcentrated flows often occur in the middle and lower Yellow River(MLYR)and its tributaries,within which the main sediment source originates from the Loess Plateau of China due to serious water erosion.Little is known about the properties of river sediment that is transported by hyperconcentrated flows,particularly with respect to the mineral composition and size distribution.Samples of sediment and loess were collected in the northern,middle,and southern Loess Plateau and the mainstream and tributaries of the MLYR.A total of 18 loess samples and 24 river sediment samples were analyzed to determine their sediment size distribution and mineral composition.The bottom loess samples reflected the original sedimentary features of the Loess Plateau,and the median particle size reduced,and the clay content increased from the north to the south of the study region.The surface loess has been weathered under the action of wind and rainfall,and the clay particle content in the surface loess samples was higher than that in the undisturbed bottom loess.Erosion of the surface soil due to rainfall and surface runoff means that fine particles(mostly clay)have been washed away.The median diameter of surface loess particles was a little larger than that of the bottom loess particles where water erosion dominates.The particle size became coarser with increasing distance from the estuary in the MLYR,which reflects depositional sorting in the river channel.Significant logarithmic relations were found between the median diameter of the sediment particles and the i)non-clay mineral content and ii)clay mineral content.Thus,clay and non-clay mineral compositions can be conveniently estimated from the particle size distribution.  相似文献   

5.
Mercury（Hg） is well known as one of the most toxic elements to man.The coastal environments adjacent to industrial areas are reported to often be contaminated with mercury.Mercury becomes more toxic in the form of methylmercury（Me-Hg） which is converted from inorganic mercury in aqueous systems by microbial activity and can bio-magnify through the food chain.A simple method for the determination of total mercury and methylmercury in sediments was optimized by slightly modifying an old method using the direct mercury analyzer technique.Core sediment samples from Thane Creek,Mumbai,India were collected and analysed for total mercury and methylmercury.The Hg concentration in the creek varied between 0.54 to 16.03 μg g~（-1） while Me-Hg concentrations ranged between0.04 to 1.07 μg g~（-1）.In surface sediment,mercury concentrations ranged from 4.33 μg g~（-1） to 12.16μg g~（-1）.Total organic carbon content was found to be around 2 percent in different layers of the sediments.The enrichment factors,which indicate the extent of pollution in sediments,were estimated to range from 26 to 50 at different locations in the creek.Lithogenic and anthropogenic concentrations of mercury in the creek were also determined to compare the impact of anthropogenic and natural sources.Anthropogenic inventories were about 5-70 times more in concentration than the lithogenic in the different core sediments.  相似文献   

6.
Characteristics of shallow gas hydrate in Okhotsk Sea   总被引：1，自引：0，他引：1  
Multidisciplinary field investigations were carried out in Okhotsk Sea by R/V Akademik M.A. Lavrentyev (LV) of the Russian Academy of Sciences (RAS) in May 2006, supported by funding agencies from Ko- rea, Russia, Japan and China. Geophysical data including echo-sounder, bottom profile, side-scan- sonar, and gravity core sample were obtained aimed to understand the characteristics and formation mechanism of shallow gas hydrates. Based on the geophysical data, we found that the methane flare detected by echo-sounder was the evidence of free gas in the sediment, while the dome structure de- tected by side-scan sonar and bottom profile was the root of gas venting. Gas hydrate retrieved from core on top of the dome structure which was interbedded as thin lamination or lenses with thickness varying from a few millimeters to 3 cm. Gas hydrate content in hydrate-bearing intervals visually amounted to 5%―30% of the sediment volume. This paper argued that gases in the sediment core were not all from gas hydrate decomposition during the gravity core lifting process, free gases must existed in the gas hydrate stability zone, and tectonic structure like dome structure in this paper was free gas central, gas hydrate formed only when gases over-saturated in this gas central, away from these struc- tures, gas hydrate could not form due to low gas concentration.  相似文献   

7.
The input of organic substances(e.g.,rice straw)in rice field soils usually stimulates the production and emission of the greenhouse gas methane(CH4).However,the amount of CH4 derived from the applied rice straw,as well as the response of bacterial and archaeal communities during the methanogenic phase,are poorly understood for different rice field soils.In this study,samples of five different rice soils were amended with 13^C-labeled rice straw(RS)under methanogenic conditions.Immediately after RS addition,the RS-derived CH4 production rates were higher in soils(Uruguay,Fuyang)that possessed a stronger inherent CH4 production potential compared with other soils with lower inherent potentials(Changsha,the Philippines,Vercelli).However,soils with higher inherent potential did not necessarily produce higher amounts of CH4 from the RS applied,or vice versa.Quantitative PCR showed copy numbers of both bacteria and methanogens increased in straw-amended soils.High-throughput sequencing of 16 S rRNA genes showed distinct bacterial communities among the unamended soil samples,which also changed differently in response to RS addition.Nevertheless,RS addition generally resulted in all the rice field soils in a relative increase of primary fermenters belonging to Anaerolineaceae and Ruminococcaceae.Meanwhile,RS addition also generally resulted in a relative increase of Methanosarcinaceae and/or Methanocellaceae.Our results suggest that after RS addition the total amounts of RSderived CH4 are distinct in different rice field soils under methanogenic conditions.Meanwhile,there are potential core bacterial populations that are often involved in primary fermentation of RS under methanogenic conditions.  相似文献   

8.
Effect of streambed sediment on benthic ecology   总被引：5，自引：2，他引：3  
Benthic macroinvertebrates have been commonly used as indicator species for assessment of aquatic ecology. Streambed sediment, or substrate, plays an important role in habitat conditions for macroinvertebrate communities. Field investigations were done to study the benthic diversity and macroinvertebrate compositions in various stream substrata. Sampling sites with different bed sediment, latitude, and climate were selected along the Yangtze River, the Yellow River, the East River, and the Juma River, in China. The results show that benthic community structures found in different substrata clearly differ, while those found in substrata of similar composition and flow conditions but in different macroclimates are similar. The study, thus, demonstrates that the benthic macroinvertebrate community is mainly affected by substrate composition and flow conditions, but is generally unaffected by latitudinal position and macroclimate. Taxa richness of the maeroinvertebrate community was found to be the highest on hydrophyte-covered cobbles, high on moss-covered bedrock, and low on clay beds and cobble beds devoid of plant biomass. Sandy beds are compact and unstable, thus, no benthic macroinvertebrates were found colonizing such substrata. Aquatic insects account for most of the macroinvertebrates collected in these rivers. Different insects dominate in different types of substrata： mainly EPT species （Ephemeroptera, Ptecoptera, Tfichoptera） in cobble, gravel, and moss-covered bedrock; and Chironomidae larvae in clay beds. The relation between the number of species in the samples and the size of the sampling area fits a power function of the species area. One square meter （lm） is suggested as the minimum sampling area. A substrate suitability index is proposed by integrating the suitability of sediment, periphyton, and benthic organic materials for macroinvertebrates. The biodiversity of macroinvertebrates increases linearly with the substrate suitability index. Benthic taxa richness increases linearly with the suitability index.  相似文献   

9.
The fluvial process of the Yalu Tsangpo River occurs concurrently with the uplift of the Qinghai-Tibet Plateau.Therefore,the river exhibits unique features in morphology and sediment deposition.Field investigations were performed from 2009–2011and the depth of the interface between the sediment deposits and bed rock was detected with an electromagnetic imaging system(EH4)at 29 cross sections.Sediment deposits were sampled along the Yalu Tsangpo valley from Xietongmen to the Yalu Tsangpo Canyon.The results show that a huge amount of sediment has been deposited in four wide valley sections because the uplift rate in these sections was lower than that in the downstream gorge sections over the past million years.About 518 billion m3of gravel and sand have been stored in the high mountain river valleys,which has changed the V-shaped mountain river valley into a U-shaped wide river valley in the four sections.In the sections with high uplift rates the river bed is incised and has formed gorges and the Yalu Tsangpo Canyon.  相似文献   

10.
Sediment load plays a major role in the morphological evolution of rivers.Therefore,the analysis of the sediment load interaction with hydraulic structures is of main importance in order to enhance the preservation of fish habitats and river morphological characteristics.The present study analyzes the scour mechanisms downstream of a block ramp in live bed conditions,when the sediment supplied by the approaching flow is balanced by the sediment transported out of the scour hole.Experiments were performed in a model flume and the effect of the approaching sediment concentration on the scour geometry was analyzed.It was observed that the scour features depend deeply on the approaching sediment concentration and four main profile configurations were distinguished.The experimental data were analyzed and empirical relationships were developed in order to evaluate the depth and length of a scour hole,the dune height and the distance of the transversal section of maximum dune height from the ramp toe for different hydraulic and geometric conditions.It was also proved that the dynamic equilibrium shape of a scour hole does not depend on the sediment load time history.  相似文献   

11.
The bacterial community in deep subseafloor sediments at a depth of 230 cm from the western Pacific “warm pool” is studied by construction of 16S rDNA clone library and PCR-RFLP (Restriction Fragment Length Polymorphism) analysis. The results indicate that the bacterial community in these sediments is mainly composed of five groups: α-Proteobacteria, β-Proteobacteria, CFB group (Cytophaga / Flexibacteria / Bacteroides), Acidobacteria and gram positive bacteria, with a few genera detected in each group. The most abundant bacteria group is α-Proteobacteria, and the next is β-Proteobacteria. The dominant species in α-and β-Proteobacteria are Sphingomonas paucimobilis and Pseudomonas alcaligenes respectively. The CFB group is simply composed of members belonging to Flavobacterium. The gram positive bacteria are rich, and mainly consists of the genus Geobacillus. The analysis of bacterial community indicates that organic matter is still abundant in the subseafloor sediments at the depth of 230 cm in the western Pacific “warm pool”. These bacteria in this deep biosphere may play an important role in the nitrogen cycle of deep sea sediments at “warm pool”. Supported by the National Key Basic Research Support Foundation of China (Grant No. G2000078500) and China Ocean Mineral Resources R&D Association Project (Grant No. DY105-4-2-4)  相似文献   

12.
In this paper, climatic and environmental changes were reconstructed since 1129A.D. based on the Malan ice core from Hol Xil, the northern Tibetan Plateau. The record of δ 18O in the Malan ice core indicated that the warm-season air temperature variations displayed a general increase trend, the 20th-century warming was within the range of natural climate variability, and the warmest century was the 17th century while the warmest decade was the 1610s, over the entire study period. The “Medieval Warm Epoch” and “Little Ice Age” were also reflected by the ice core record. The dust ratio in the Malan ice core is a good proxy for dust event frequency. The 870-year record of the dust ratio showed that dust events occurred much frequently in the 19th century. Comparing the variations of δ 18O and the dust ratio, it is found that there was a strong negative correlation between them on the time scales of 101―102 years. By analyses of all the climatic records of ice cores and tree rings from the northern Tibetan Plateau, it was revealed that dust events were more frequent in the cold and dry periods than in the warm and wet periods.  相似文献   

13.
A serics of low-latitude marginal seas, ranging from the southern South China Sea in the north to the Arafura Sea in the south, are located within the Western Pacific Warm Pool. As shown by rnicropaleontological, isotopical and organic geochemical analyses, the sea surface temperatures in the marginal seas at the last glacial maximum were much cooler than those in the open Western Pacific Ocean. The emergence of extensive shelves of the marginal seas at the glacial low sea-level stand and the decrease of surface temperatures in their deeper water parts resulted in a remarkable reduction of the ability of vapor and heat transport to the atmosphere, causing variabilities to the Warm Pool in the glacial cycles. The intensification of winter monsoon at the glacial stages not only led to a decrease of the surface water temperature and hence to an enhanced seasonality, but also carried moisture from the sea to the tropical islands, giving rise to the downward shift of snowline and mountainous vegetation zones there. It may offer a new alternative in solution of the “Tropical Ocean Paleo-temperature Enigma”. Project supported by the National Natural Science Foundation of China (Grant No. 49576286).  相似文献   

14.
In 2007/08, a study was undertaken on the sediment dynamics in shallow Lake Markermeer (the Netherlands). Firstly, sediment characteristics were determined at 49 sites in the lake. Parameters such as median grain size and loss on ignition showed a spatial as well as water depth related pattern, indicating wind-induced sediment transport. Highly significant correlations were found between all sediment parameters. Lake Markermeer sediment dynamics were investigated in a sediment trap field survey at two permanent stations in the lake. Sediment yields, virtually all coming from sediment resuspension, were significantly correlated with average wind speeds, though periods of extreme winds also played a role. Sediment resuspension rates for Lake Markermeer were high, viz. on average ca. 1,000 g m−2 day−1. The highly dynamic nature of Lake Markermeer sediments must be due to the overall shallowness of the lake, together with its large surface area (dynamic ratio = [√(area)]/[average depth] = 7.5); wind-induced waves and currents will impact most of the lake’s sediment bed. Indeed, near-bed currents can easily reach values >10 cm/s. Measurements of the thickness of the settled “mud” layer, as well as 137Cs dating, showed that long-term deposition only takes place in the deeper SE area of the lake. Finally, lake sediment dynamics were investigated in preliminary laboratory experiments in a small “micro-flume”, applying increasing water currents onto five Lake Markermeer sediments. Sediment resuspension started off at 0.5–0.7 cm/s and showed a strongly exponential behaviour with respect to these currents.  相似文献   

15.
Global Seismic Hazard Assessment Program maps are erroneous   总被引：6，自引：0，他引：6  
The March 11, 2011 megathrust on the Pacific coast of the Tohoku Region, Japan, and its consequences once again confirmed the presence of evident problems in the conventional methodology of risk and earthquake loss evaluation. A systematic analysis shows that the results of the Global Seismic Hazard Assessment Program (GSHAP, 1992–1999) contradict the actual occurrence of strong earthquakes. In particular, since the publication of the GSHAP final results in 1999, all 60 earthquakes with magnitudes of 7.5 or higher were “surprises” for the GSHAP maps. Moreover, in half of the cases they were “big surprises,” when instead of the expected “light” or “moderate,” “significant” or even “total” destruction took place. All twelve of the deadliest earthquakes happened in 2000–2011 (total number of deaths exceeded 700000 people) prove that the GSHAP results, as well as underlying methodologies, are deeply flawed and, evidently, unacceptable for any critical risk assessments entitled to prevent disasters caused by earthquakes.  相似文献   

16.
This research was carried out with the aim to explore the heterotrophic microbial population of two sediments in different oxic conditions of the Lake of Lugano (Lago di Lugano). The values of the viable bacterial counts found in our sediment samples were typical for an eutrophic lake.The increase in the proportion of anaerobic to aerobic bacteria at 30 °C observed in the sediment samples of Agno may reflect the depletion of oxygen concentrations in the water column.The generaAeromonas, Pseudomonas, Bacillus andClostridium, as well as strains belonging to the Coryneform-group, represented the major taxonomic groups of heterotrophic bacterial communities in the water-sediment interface.  相似文献   

17.
We characterize the Kamchatka seismicity for the period 2005–2007. Regional catalogs of Kamchatka earthquakes were used to develop 2D distributions of parameters of background seismicity. The characteristics we consider include the activity A 10, the slope of the recurrence curve γ, the parameters involved in the methods RTL, ΔS, and the “Z-function”, as well as the control of earthquake clustering. We have detected the space-time agreement between the anomalies exhibited by several parameters.  相似文献   

18.
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19.
Variation of snow water resources in northwestern China, 1951–1997   总被引：19，自引：0，他引：19  
Two models are used to simulate the high-altitude permafrost distribution on the Qinghai-Xizang Plateau. The two models are the “altitude model”, a Gaussian distribution function used to describe the latitudinal zonation of permafrost based on the three-dimensional rules of high-altitude permafrost, and the “frost number model”, a dimensionless ratio defined by manipulation of freezing and thawing degree-day sums. The results show that the “altitude model” can simulate the high-altitude permafrost distribution under present climate conditions accurately. Given the essential hypotheses and using the GCM scenarios from HADCM2, the “altitude model” is used for predicting the permafrost distribution change on the Qinghai-Xizang Plateau. The results show that the permafrost on the plateau will not change significantly during 20–50 a, the percentage of the total disappeared area will not be over 19%. However, by the year 2099, if the air temperature increases by an average of 2.91°C on the plateau, the decrease in the area of permafrost will exceed 58%—almost all the permafrost in the southern plateau and in the eastern plateau will disappear. Project “Fundamental Research of Cryosphere” supported by the Chinese Academy of Sciences.  相似文献   

20.
IntroductionIn the book Future CataS~ologr published in 1992, we proposed a viewpoiflt on using the"criterion of activity in quiescence" to predict big eathquake (MsZ7) (GUO, et al, 1992), and predicted in the book that in futore several years or in ten years a big earthquake (Ms27) will be possible to occur in the Zhongdian and nearby in Yunnan Province. In the 1994 nation-wide earthquake tendency consultation meeting we pointed out, once more, in the Zhongdian region of Yunnan Province…  相似文献   

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