Presence Of Sediments Research Articles

A microcosm experiment on sediment remediation: microbial community assessment in sediment in presence of granulated coal ash

A microcosm experiment on sediment remediation: microbial community assessment in sediment in presence of granulated coal ash

Incipient motion of sediment in presence of submerged flexible vegetation

The presence of submerged vegetation on river beds can change the water flow structure and alter the state of sediment motion. In this study, the incipient motion of sediment in the presence of submerged flexible vegetation in open channels was investigated in a laboratory experiment. The vegetation was simulated with flexible rubber cylinders arranged in parallel arrays. The effect of the vegetation density, water depth, and sediment grain size on the incipient motion was investigated. The experimental results indicate that the incipient motion velocity of sediment increases as the vegetation density decreases and the water depth and sediment grain size increase. With flexible plants, the incipient motion velocity of sediment is lower than it is without vegetation, and is larger than it is with rigid vegetation. A general incipient motion velocity equation was derived, which can be applied to both flexible and rigid vegetation conditions.

Molecular phylogenetic analysis of bacterial community and characterization of Cr(VI) reducers from the sediments of Tantloi hot spring, India.

BackgroundA geothermal ecosystem located at Tantloi, India has been found to be an interesting habitat for microbes of diverse nature. However, the microbial diversity of this habitat is poorly explored. In this study, a detailed phylogenetic study has been carried out to understand the bacterial diversity of this habitat and to identify prospective metal reducers using culture independent approach. The bacterial diversity of the sediments, which contain undetectable levels of Cr(VI), was analysed with respect to chromium reduction and the strains highly resistant to and efficiently reducing chromium under aerobic conditions were isolated and characterized.Results16S rRNA gene sequence analysis of Tantloi hot spring microbial community revealed a significant bacterial diversity represented by at least ten taxonomic divisions of Bacteria with clear predominance of Thermus. Similar sequence analysis of rRNA gene library clones derived from bacterial consortia enriched from sediments in presence of Cr(VI) revealed the abundance of the family Bacillaceae. Under aerobic conditions at 65°C, the consortia reduced 1 mM of Cr(VI) completely within 24 h and 5 mM in 6 days. A complete reduction of 1 mM Cr(VI) has been shown by five of our isolates within 36 h. 16S rRNA gene sequences of all the isolates showed high degree of similarity (97-99%) to Bacillaceae with ten of them being affiliated to Anoxybacillus. Crude extract as well as the soluble fraction from isolates TSB-1 and TSB-9 readily reduced Cr(VI); TSB-1 showed higher chromium reductase activity.ConclusionMost of the Tantloi Spring Bacterial (TSB) sequences analyzed in different taxonomic divisions could be related to representatives with known metabolic traits which indicated presence of organisms involved in redox processes of a variety of elements including iron, sulphur and chromium. Approximately 80% of the sequences obtained in this study represented novel phylotypes indicating the possibility of discovery of bacteria with biotechnologically important new biomolecules. Again, highly chromium-resistant and remarkably active Cr(VI)-reducing Anoxybacillus strains isolated in this study could serve as potential candidates for designing chromium bioremediation strategies at high temperatures and also at high chromium concentrations.

Grid stirred turbulence: applications to the initiation of sediment motion and lift-off studies

A laboratory experimental set - up for studying the behaviour of sediment in presence of a turbulent field with zero mean flow is presented. Particular interest is shown on the initiation of sediment motion and in the sediment lift - off. Some examples of the results obtained with this set-up are shown.A turbulent velocity u′ lower than that u estimated by the Shield diagram is required to start sediment motion. The minimum u′ required to start sediment lift - off, is a function of sediment size, cohesivity and resting time. The lutocline height depends on u′, and the vorticity at the lutocline seems constant for a fixed sediment size. Combining grid stirring and image analysis, sediment vertical fluxes and settling speeds could be measured.

Backscattered-electron imaging of the colloidal gold surface marker

A variety of markers have been used for surface labeling with the scanning electron microscope (1). They are all recognized in the secondary electron imaging (SEI) mode on the basis of their characteristic sizes and shapes. This makes it difficult, however, to recognize unambiguously markers of small size (smaller than 40 nm). Unfortunately, markers of such size are needed if one wishes to minimize steric hindrance phenomena (2) and therefore obtain high efficiency labeling. We have found that the atomic number contrast of the colloidal gold marker, expressed in the backscattered electron imaging (BEI) mode, alleviates this difficulty to a significant extent (3).Human peripheral blood leukocytes, separated by sedimentation in presence of Dextran, were attached to poly-1-lysine pretreated carbon coated grids. The cells were then fixed for 5 min with 0.25% solution of buffered glutaraldehyde, pH 7.2, extensively rinsed with 0.1% glycine in PBS, and incubated for 30 min, at room temperature with an IgM monoclonal antibody (D2) specifically recognizing, a surface antigen of mature granulocytes.

Infrared estimation of oil content in sediments in presence of biological matter

~~~~ The crude oil content of marine sediments was determined by ir spectrometry from the magnitude of 2925 cm-1 (-CHzstretching band) absorbance. Biological materials also absorb at 2925 cm-I and have a well-defined absorbance band at 1650 cm-1 (the -NH- band characteristic of proteins) whereas, crude oils do not exhibit an amide band. The relative contributions of oil and organic material of recent biological origin in marine sediments were determined from measurements of these two absorbance bands, and a correction applied which enables the calculation of the oil content in the presence of these biological materials. n a recent study of the effects of the winter 1969 oil blowI out at Platform A in the Santa Barbara Channel, analytical procedures for the rapid determination of the oil content of the channel bottom sediments using both transmission and internal reflectance ir spectrometry were reported (Mattson et al., 1970b; Kolpack et al., 1971; Yu et al., 1971). In these analyses, the oil content of the sediment wdS considered to be related to the magnitude of the 2925 cm-1 (-CHzstretching band) absorbance. Those analyses were made primarily on bottom sediments which were deposited following a major flood. The rate of sedimentation of this highly oxidized detrital flood material was very rapid and in most samples there were no significant amounts of organic material of recent biological origin present. However, some of the samples were obtained from the central part of the Santa Barbara Channel up to 18 months after the flood. The rate of detrital sedimentation in this area is much slower, and the surficial sediments often were mixed with organic debris of biological origin. The presence of biological material interfered with the determination of the oil content as the -CH*- groups of such biological matter also absorb at 2925 cm-l. This ir band is identical for any -CHz--containing compound, and the relative contributions of oil and biological matter to the observed absorbance cannot be determined by a simple measurement of the 2925 cm-l band. This paper reports a simple extension of the above ir procedure which permits estimation of the concentration of biological materials. This provides a method for correcting the 2925 cm-1 absorbance band to enable the estimation of the oil contribution alone.