Assessment of heavy metal contamination in the surficial sediments from the lower Meghna River estuary,Noakhali coast,Bangladesh

Sediment samples were collected from ten selected sites of the lower Meghna River estuary,and six heavy metals were analyzed with Atomic Absorption Spectrophotometry(AAS)to assess the contamination level and the metals’association with sediment grain size.The current results revealed that the mean concentrations of the studied metals were ranked in descending order of iron(Fe)(1.29×103 mg/kg)>zinc(Zn)(42.41 mg/kg)>lead(Pb)(12.48 mg/kg)>chromium(Cr)(10.59 mg/kg)>copper(Cu)(6.22 mg/kg)>cadmium(Cd)(0.28 mg/kg).The geo-accumulation,contamination,and pollution load indexes suggested that the lower Meghna river estuary was not contaminated by Fe,Zn,Pb,Cr,and Cu.The mean size of the sediment ranged from 28.92 to 126.2 mm,and the Pearson correlation coefficient showed a significant association between Fe and Pb(coefficient of determination,r2=0.836;p<0.05),and no significant correlation was found between individual metals and grain size,indicating no or low influence on the metals distribution.     

Nexus between natural and technical disaster shocks,resource depletion and growth-specific factors: evidence from quantile regression

Natural Hazards - Debris flows are a hazardous natural calamity in mountainous regions of Nepal. Torrential rainfall within a very short period of the year is the main triggering factor for...     

Analytical method for analysis of slope stability

An analytical method is presented for analysis of slope stability involving cohesive and non-cohesive soils. Earthquake effects are considered in an approximate manner in terms of seismic coefficient-dependent forces. Two kinds of failure surfaces are considered in this study: a planar failure surface, and a circular failure surface. The proposed method can be viewed as an extension of the method of slices, but it provides a more accurate treatment of the forces because they are represented in an integral form. The factor of safety is obtained by using the minimization technique rather than by a trial and error approach used commonly. The factors of safety obtained by the analytical method are found to be in good agreement with those determined by the local minimum factor-of-safety, Bishop's, and the method of slices. The proposed method is straightforward, easy to use, and less time-consuming in locating the most critical slip surface and calculating the minimum factor of safety for a given slope. Copyright © 1999 John Wiley & Sons, Ltd.     

Dynamic response of a thick plate on viscoelastic foundation to moving loads

A finite element algorithm is presented to evaluate the dynamic response of pavements including aircraft-guideway-foundation interaction. The pavement-foundation system is modeled by a series of thick plate elements supported by discrete springs and dashpots at the nodal points representing the viscoelastic foundation. The moving aircraft loads are represented by masses each supported by a spring and dashpot suspension system and having a specified horizontal velocity and acceleration. The accuracy of the algorithm is verified by comparing the finite element solution with available analytical results. A parametric study is conducted to determine the effects of various parameters on the dynamic response of pavements to moving loads.     

Propagation of monochromatic water wave trains

A nonlinear numerical model has been formulated to study the propagation of a monochromatic surface wave. The model is formulated through the vertical integration of the continuity equation and the equations of motion. This model is investigated for wave propagation, velocity distribution, energy propagation and varying Courant, Friedrichs and Lewy's (CFL) condition. The applicability of this model for both shallow- and deep-water wave is also examined. The results and analyses are shown in details. The results obtained from the model are compared with the Stokes third-order wave theory and with the relevant experimental data.     

Varietals differences in agronomic performance of six wheat varieties grown under saline field environment

Six wheat varieties (SARC-1, SARC-2, SARC-3, SARC-4, LU26S and Punjab-85) were planted in the field to evaluate their comparative performance under saline conditions. LU26S appeared the most salt-tolerant variety and gave the highest grain weight due to its low Na⁺ uptake, high K⁺/Na⁺ ratio, higher dry weight of shoots and spikes and better grain development. Better exclusion of Na⁺ and other ions from the leaves of salt-tolerant variety LU2 6S could also be a reason for its ability to maintain a higher grain weight in the saline soil. Punjab-85 appeared the most saltsensitive variety as its dry weight of main shoots and spikes were also found to be the lowest. High Na⁺ uptake, lower K⁺/Na⁺ ratio, lower dry weight of main shoots and spikes and lower 100 grain weight were the main reasons for saltsensitivity in Punjab-85. Dry weight of shoots, spikes and grain weight of SARC-3 under saline soil conditions was almost similar to the salt-sensitive variety Punjab-85 and could be classified as salt-sensitive. Flag leaf area decreased drastically due to salt stress in all the varieties and this could be a major cause for low yield. There was however, a very low linear correlation between the flag leaf area and the grain weight in pooled data for all the six wheat varieties.     

FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh: provenance and petrogenetic implications

The present research deals with the FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh. Major heavy minerals in the sediments consist of garnet (8.5–21.3%), kyanite (5.35–11.9%), monazite (2.3–5.3%), sillimanite (1.8–4.7%), zircon (3.6–9.1%), and a considerable amount of opaques mainly Fe-Ti oxide minerals (23.1–35.4%). The detrital Fe-Ti oxide minerals carry significant clues to the parent rocks or sources. In these contexts, detrital opaques (Fe-Ti oxides) have been analyzed with an electron probe microanalyzer (EPMA). These opaques (Fe-Ti oxide) display six types of textural patterns, dominantly seriate with granular, emulsion, and acicular sandwich structures and trellis type of textural patterns. These textural patterns belong to five intergrowths of Fe-Ti oxide minerals such as (1) ilmenite-hematite, (2) magnetite-ilmenite, (3) hematite-rutile, (4) ilmenite-hematite-rutile, and (5) ilmenite-rutile, where ilmenite-hematite intergrowth is common. Alteration is seen in both exsolved and unexsolved ilmenites. Textural patterns and mineral chemistry of the studied ilmenite minerals provide lines of evidence of low-temperature magmatic inheritance, later modified by diffusional processes. The estimated temperature and oxygen fugacity from the magnetite-ilmenite exsolution range from 547.6 to 558.2 °C and from 10^?21.4 to 10^?21.7, respectively. The data are also consistent with hematite-ilmenite temperature (between 537 and 540 °C) and oxygen fugacity (10^?21.7 to 10^?21.9) measurements in Cox’s Bazar beach placers. These temperatures and oxygen fugacities specify Fe-Ti oxide assemblages equilibrated in a T-fO₂ field very near to the FMQ buffer curve suggesting a crustal source (magmatic and/or metamorphic), which is modified significantly by metamorphic processes.