Vertical distribution and mobilization of arsenic in shallow alluvial aquifers of Chapai-Nawabganj district, Northwestern Bangladesh

Core sediments from two boreholes and groundwater from fifty four As-contaminated well waters were collected in the Chapai-Nawabganj area of northwestern Bangladesh for geochemical analysis. Groundwater arsenic concentrations in the uppermost aquifer (10 to 40 m of depth) range from 2.76?C315.15 mg/l (average 48.81 mg/l). Arsenic concentration in sediments ranges from 3.26?C10 mg/kg. Vertical distribution of arsenic in both groundwater and sediments shows that maximum As concentration (462 mg/l in groundwater and 10 mg/kg in sediments) occurs at a depth of 24 m. In January 2008, 2009 and 2010, maximum As concentration occurs at the same depth. Environmental scanning electron microscope (ESEM) with EDAX was used to investigate the presence of major and trace elements in the sediments. The dominant groundwater type is Ca-HCO₃ with high concentrations of As and Fe, but with low levels of NO₃ ^? and SO₃ ^?2. Statistical analysis clearly shows that As is closely associated with Fe (R² = 0.64) and Mn (R² = 0.91) in sediments while As is not correlated with Fe and Mn in groundwater samples. Comparatively low Fe and Mn concentrations in some groundwater, suggest that probably siderite and/or rhodochrosite precipitated as secondary mineral on the surface of the sediment particles. The correlations along with results of sequential leaching experiments suggest that reductive dissolution of FeOOH and MnOOH mediated by anaerobic bacteria represents mechanism for releasing arsenic into the groundwater.     

An investigation into the fault patterns in the Chadegan region, west Iran: Evidence for dextral brittle transpressional tectonics in the Sanandaj-Sirjan Zone

The NW-SE trending Sanandaj-Sirjan Zone (SSZ) is the internal part of the Zagros continental collision zone, which mainly consists of metamorphic rocks deformed in a dextral transpressional zone. This dextral transpression is attributed to brittle deformation related to late Cenozoic Arabia-Eurasia oblique continental collision. Major NW-trending faults, including the Dalan, Garmdareh, Yasechah, Sheida, and Ben faults, are reverse faults with a dextral strike-slip component. These faults were displaced by NW-trending synthetic and NE-trending antithetic faults. There are also E-trending thrusts and N-trending normal faults developing in directions that are, respectively, almost normal and parallel to the major shortening direction. The NW-trending Ben, Yasechah, and Sheida faults are NE-dipping faults, and the Dalan and Garmdareh faults are SW-dipping faults. These faults indicate the presence of a transpressive flower structure zone that probably led to the exhumation of Jurassic high-grade metamorphic rocks, such as eclogite, in the central part of the study area.     

Damage and management of cyclone Sidr-affected homestead tree plantations: a case study from Patuakhali, Bangladesh

Geographically, Bangladesh is considered to be one of the most cyclone-prone areas in the world. The super cyclone Sidr in 2007 was one of the most devastating disasters to have ever occurred in Bangladesh, having wind speeds of 223?km/h with a tidal surge of 6.1?C7.6?m high. In order to draw a pre- and post-Sidr damage and management scenario, a survey was conducted at Dumki upazila, Patuakhali district in Bangladesh with a pretested questionnaire. Primary data were collected through a questionnaire, while secondary data were collected from pertinent offices as well as academic journals. The major focus of this study was to assess the state of pre-Sidr tree plantations (woody and fruit trees), the devastation caused by Sidr on these tree plantations, and post-Sidr recovery and further sustainable management initiatives to counteract a possible future neo-Sidr. The post-Sidr study showed that about 16.84 million woody and fruit trees were uprooted by Sidr. A total of 3,120 rain tree (Samanea saman L.), 7,548 mahogany (Swietenia mahagoni L.), 1,444 royal siris (Albizzia richardiana L.), 702 white siris (Albizzia procera L.), 1,214 mango (Mangifera indica L.), 1,092 coconut (Cocos nucifera L.), 1,380 jackfruit (Artocarpus heterophyllus L.), and 7,640 betel nut (Areca catechu L.) trees were sampled among which 922, 1,662, 382, 210, 106, 38, 362, and 1,652 trees, respectively, were markedly damaged by Sidr. Sexually propagated woody trees with a damaged taproot were vulnerable to heavy wind during the cyclone. Fruit trees were more resistant to the cyclone than other types of trees, and the lack of proper tree training and pruning was one of the principal causes of the severe damage to woody trees. Hence, plantations of woody tree saplings with damaged taproots are strongly discouraged. However, proper training and pruning of homestead trees together with plantation of fruit trees rather than woody trees is suggested as a possible effective management strategy to protect the homestead ecosystem from devastation by future cyclones in Bangladesh.     

Evaluation of soil collapse potential in regional scale

Collapsible soils have considerable strength and stiffness in their dry natural state but settle dramatically when they become wet. This paper documents a low-cost, qualitative evaluation scheme using fuzzy set analysis to determine site collapsibility based on subjective knowledge of the geological, geotechnical, and environmental conditions and their uncertainty. For each category, factors or subcategories were defined in a decision tree based on relevant literature. Each category and subcategory was then weighted or rated using linguistic terms developed from expert assessment. The linguistic data or information obtained from the assessments was represented and processed using fuzzy sets. To calibrate the criteria, 87 collapse potential tests were performed on undisturbed soil samples gathered from 27 different locations throughout Iran, leading to the definition of a standard collapse potential fuzzy set. Finally, on the basis of the established criteria, a collapse potential map was prepared for a suburban area in the western part of the city of Kerman, Iran.     

Robust attenuation relations for peak time-domain parameters of strong ground motions

This study presents new attenuation models for the estimation of peak ground acceleration (PGA), peak ground velocity (PGV), and peak ground displacement (PGD) using a hybrid method coupling genetic programming and simulated annealing, called GP/SA. The PGA, PGV, and PGD were formulated in terms of earthquake magnitude, earthquake source to site distance, average shear-wave velocity, and faulting mechanisms. A worldwide database of strong ground motions released by Pacific Earthquake Engineering Research Center (PEER) was employed to establish the models. A traditional genetic programming analysis was performed to benchmark the proposed models. For more validity verification, the GP/SA models were employed to predict the ground-motion parameters of the Iranian plateau earthquakes. Sensitivity and parametric analyses were carried out and discussed. The results show that the GP/SA attenuation models can offer precise and efficient solutions for the prediction of estimates of the peak time-domain characteristics of strong ground motions. The performance of the proposed models is better than or comparable with the attenuation relationships found in the literature.     

Durability assessment of the Ala?at? tuff (Izmir) in western Turkey

Ala?at? tuff has been used extensively as a source of building stone for outdoor and indoor decorations since the historical times in and around the tourist town of Ala?at? (western Turkey). The use of the Alacati tuff in buildings has been made compulsory by the Ala?at? municipality, for preserving the historical appearance of the buildings, after 2005 in Ala?at?. It has been noticed that, evident deteriorations developed in tuff surfaces of the stone buildings and garden walls within 5?C6?years of their emplacement. Durability properties of the Ala?at? tuff are evaluated by determining the mineralogical, chemical, and physico-mechanical properties of the fresh tuff samples obtained from the only operative quarry in the area. Ageing tests such as Na₂SO₄ and MgSO₄ salt crystallization, freezing?Cthawing, and wetting?Cdrying were conducted on the fresh tuff samples to assess their durability. Additionally, the durability of the tuff is also evaluated by determining its average pore diameter, saturation coefficient, wet-to-dry strength ratio, static rock and slake-durability indices. Fresh Ala?at? tuff has high porosity and low unit weight and strengths and are classified to be very poor to moderately durable stone based on the test results of different durability assessment methods. Mineralogical and geochemical analyses have also been carried out on the deteriorated tuff samples collected from the surfaces of the stone buildings to determine the effect of weathering on tuff and the test results have been compared with those of the fresh tuff samples. There is no major difference observed between the mineralogy and chemistry of the fresh and weathered tuff samples thus, it has been concluded that physical weathering has been dominant in the area in deterioration of tuff.     

The mineralogy and petrology of the Pahnavar Fe skarn, In the Eastern Azarbaijan, NW Iran

The Pahnavar calcic Fe-bearing skarn zone is located in the Eastern Azarbaijan (NW Iran). This skarn zone occurs along the contact between Upper Cretaceous impure carbonates and an Oligocene granodioritic batholith. The skarnification process can be categorized into two discrete stages: prograde and retrograde. The prograde stage began immediately after the initial emplacement of the granodioritic magma into the enclosing impure carbonate rocks. The effect of heat flow from the batholith caused the enclosing rocks to become isochemically marmorized in the pure limestone layers and bimetasomatized (skarnoids) in the impure clay-rich carbonates. Segregation and evolution of an aqueous phase from the magma that infiltrated to the marbles and skarnoids through fractures and micro-fractures took place during the emplacement of magma. The influx of Fe, Si and Mg from the granodiorite to the skarnoids and marbles led to the crystallization of anhydrous calc-silicates (garnet and pyroxene). The retrograde stage can be divided, in turn, into two distinct sub-stages. During earliest sub-stage, the previously formed skarn assemblages were affected by intense hydro-fracturing; in addition, Cu, Pb, Zn, along with H₂S and CO₂ were added. Consequently, hydrous calc-silicates (epidote and tremolite-actinolite), sulfides (pyrite, chalcopyrite, galena and sphalerite), oxides (magnetite and hematite) and carbonates (calcite) deposited the anhydrous calc-silicates. The late-retrograde sub-stage was due the incursion of colder oxidizing fluids into the skarn system, causing the alteration of the previously formed calc-silicate assemblages and the development of fine-grained aggregates of chlorite, illite, kaolinite, hematite and calcite. The lack of wollastonite in the mineral assemblage, along with the garnet-clinopyroxene paragenesis, suggests that the prograde stage formed under temperature and fO₂ conditions of 430?C550°C and 10^?26?C10^?23, respectively.