Organic carbon mobilization in a Bangladesh aquifer explained by seasonal monsoon-driven storativity changes

Currently, the most widely accepted hypothesis to explain high As concentrations in Bangladesh groundwaters is that dissolved organic C (DOC) reduces solid Fe (hydr)oxides and mobilizes sorbed arsenate. The nature of the DOC and its release mechanism are still controversial. Based on weekly to biweekly sampling over the course of one monsoon cycle at six monitoring wells of different depths, it is proposed that storativity changes drive natural DOC release from clay–peat layers to the adjacent aquifers. With a decrease in hydraulic heads during the dry season, total mineralization and DOC concentrations increased. With the onset of the rainy season and an increase in hydraulic heads, release of clay–peat derived components stopped and vertical water displacement due to groundwater recharge from rainwater occurred, causing aquifer flushing and a decrease in total mineralization and DOC concentrations. Total As and DOC concentrations correlated over depth. However, at the depth of maximum concentrations, the As peak was observed during the rainy season. At present, the reason for this inverse seasonal trend between As and DOC is unclear. Higher mineralization or DOC concentrations could lead to increased As sorption or the increased arsenite release is a time-lag abiotic or microbial response to the DOC peak. The vulnerability of the Pleistocene aquifer towards increased As concentrations was found to be much higher than previously assumed. Though sorption capacities were determined to be higher than in the Holocene aquifer, probably due to intact Fe (hydr)oxides, long-term continuous As input from overlying clay and peat layers by the proposed seasonal storativity changes has led to increased aqueous As concentrations of 85 μg/L, considerably higher than drinking water standards. Until now, aquifer and especially aquitard and aquiclude hydraulics have not been considered sufficiently when attempting to explain As mobilization in Bangladesh.     

Precious-metal distribution and fluid-inclusion petrography of the Elatsite porphyry copper deposit,Bulgaria

The Elatsite porphyry copper deposit occurs in an island-arc setting hosted by Late Cretaceous monzonitic-monzodioritic porphyry stocks which were emplaced into Precambrian-Cambrian phyllites. Trace element data of the Late Cretaceous intrusive rocks suggest that they are I-type volcanic arc granitoids. Two main ore mineral assemblages are distinguished: (1) magnetite-bornite-chalcopyrite, and (2) chalcopyrite-pyrite. The first one is linked to potassic-propylitic, and the second to phyllic-argillic alteration. Minor ore minerals are hematite, molybdenite, sphalerite, pyrrhotite, marcasite, hessite, and solid solutions of linnaeite-siegenite-carrollite, tetrahedrite-tennantite, clausthalite-galena, gold-electrum and merenskyite-moncheite. Precious-metal contents are relatively high throughout the deposit but Au, Pd and Pt are concentrated more strongly in the magnetite-bornite-chalcopyrite assemblage. Average grades of Au, Ag, Pd and Pt calculated for the 0.33% Cu ore body are 0.96, 0.19, 0.007 and 0.002 g/t respectively. Analyses of flotation concentrates revealed 25.6% Cu, and Ag, Au, Pd and Pt contents of 33.0, 13.6, 0.72 and 0.15 g/t respectively. The copper mineralisation at Elatsite took place at pressures of 120 to 300 bar, corresponding to depths of formation of 1 to 3 km under hydrostatic conditions. The precious metals were probably transported jointly as chloride complexes in highly saline magmatic-hydrothermal solutions. The fluids had temperatures of 340 to >700 °C and salinities of 28 to 64% NaCl, and mixed with meteoric water.     

Entropy in Markov analysis of late paleozoic cyclical coal measures of East Bokaro basin, Bihar, India

Randomness in the occurrence of lithologies in a cyclical succession is evaluated in terms of entropies which can be calculated from a Markov chain matrix. Two types of entropies are linked with every lithologic state; one is the entropy before deposition E ^(pre) and the other is that after deposition E ^(post),which together form an entropy set. The entropy sets for pebbly sandstone, sandstone, shale, and coal for the Karharbari coal measures, and sandstone, shale, carbonaceous shale, and coal for the Barakar coal measures were plotted separately and compared with Hattori's idealized plots. These coal measures probably were essentially of symmetrical cyclical pattern (Type-B)of Hattori. The entropy of the whole sedimentation unit readily fits under the broad framework of fluvial cycles.     

Geochemistry of stratabound scheelite mineralisation and associated calc-silicate rocks from Chitral,NE Hindu Kush,Pakistan

Tungsten mineralisation in the NE Hindu Kush terrain occurs 8 km NW of the Tirich Boundary Zone suture between Karakoram and Eastern Hindu Kush. Scheelite occurs mainly in calc-silicate rocks and subordinately in tourmalinites associated with metasediments at Miniki Gol, Chitral. The investigated area underwent two phases of deformation and was metamorphosed up to sillimanite grade, followed by the emplacement of leucogranite and hydrothermal activity. The mineral assemblages of the calc-silicate rocks, comprising clinozoisite, quartz, calcic-amphibole, plagioclase, chlorite, biotite, calcite, sphene, garnet and scheelite, clearly express a skarn type environment. The coexistence of the scheelite grains with clinozoisite and the occurrence of anomalous values of ZrO₂ and Ta₂O₅ in the scheelite grains imply a genetic link between the scheelite mineralisation and post-magmatic hydrothermal fluids. The enrichment of Zr, Hf, Be, Sn, W, Th, U, Ga, Nb, F and Y along with total REE in the scheelite-bearing calc-silicate rocks compared with the associated metasediments assigns that the rocks at Miniki Gol have undergone a pronounced hydrothermal activity. Strong positive correlations between Zr, Hf, Nb, Y, Ta, F and REE, and the mobility of REE are consistent with this consideration. Aqueous fluid inclusions in the scheelite-bearing calc-silicate rocks display very low salinity, suggesting a mixing of magmatic fluids with meteoric water. The formation of intergrown scheelite and clinozoisite indicates a high pH and CO₂-deficient fluid. The tungsten mineralization may be related to the Miniki Gol leucogranite which occurs at a distance of only 400 m.     

Traffic ‐and Industry‐Related Air Pollution Exposure Assessment in an Asian Megacity

Like other Asian countries, Pakistan is facing the issue of air pollution due to rapid urbanization, enormous transportation increases, and other related human activities. Moreover, continuously increasing emission sources have not only raised pollutant concentrations but also their types, thus damaging both human health and the environment. Faisalabad is the third largest megacity of Pakistan and its state of air quality is getting worse due to factors such as industrialization, high traffic volumes, and extensive fossil‐fuel‐burning activities. This review article aims to highlight the present status of air pollution in this city with special reference to particulate matter, elemental profiles, gaseous pollutants, organic–inorganic particulate contents as well as their sources. The concentration levels of these entities were also compared with other national and international cities, and related environmental standards. It is found that current levels of these pollutants are beyond safety limits as specified by various environment protection agencies and organizations. Several weak aspects and gaps are also identified along with suggestions for improvements of the present situation and directions for future research.     

Hydrogeochemical evaluation and statistical analysis of groundwater of Sylhet,north-eastern Bangladesh

To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and analyzed for temperature, pH, Eh, EC,DO, DOC, Na^+, K^+, Ca²⁺, Mg²⁺, Cl^-, SO_4^2-, NO_3^-,HCO_3^-, SiO_2^-, Fe, Mn and As. Besides, 12 surface water samples from Surma and Kushiyara Rivers were also collected and analyzed to understand the influence into aquifers. Results revealed that, most of the groundwater samples are acidic in nature, and Na–HCO_3 is the dominant groundwater type. The mean value of temperature, EC,Na^+, K^+, Ca²⁺, Mg²⁺, Cl^-, NO_3^- and SO_4^2- were found within the range of permissible limits, while most of the samples exceeds the allowable limits of Fe, Mn and As concentrations. However, relatively higher concentration of Fe and Mn were found in deep water samples and reverse trend was found in case of As. The mean concentrations of As in shallow, intermediate and deep wells were 39.3, 25.3and 21.4 lg/L respectively, which varied from 0.03 to148 lg/L. From spatial distribution, it was found that Fe,Mn and As concentrations are high but patchy in northern,north-western, and south-western part of Sylhet region. The most influential geochemical process in study area were identified as silicate weathering, characterized by active cation exchange process and carbonate weathering, which thereby can enhance the elemental concentrations in groundwater. Pearson's correlation matrix, principal component analysis and cluster analysis were also employed to evaluate the controlling factors, and it was found that, both natural and anthropogenic sources were influencing the groundwater chemistry of the aquifers. However, surface water has no significant role to contaminate the aquifers,rather geogenic factors affecting the trace elemental contamination. Thus it is expected that, outcomes of this study will provide useful insights for future groundwater monitoring and management of the study area.     

基于Ecopath模型的孟加拉国孟加拉湾海域营养结构和能量流动分析

依据现有研究提供的信息,在孟加拉国孟加拉湾（BoB）新划定的超过90 000 km²的海域基于Ecopath方法利用2016年7月至2017年6月的数据构建了该生态系统的营养通道模型。对食物网中营养级从1（主要生产者和碎屑）到3.45（鲨鱼）的各功能群之间的营养相互作用进行评估,所研究的共19个功能群被认为代表了其中所有的营养级。大多数消费者的生态营养转换效率（EE）超过0.80;表明这是一个被高度利用的生态系统,并且从低营养级到高营养级有较高的能量转换效率。此外,整个生态系统的净效率（0.0018）和能量转换效率（11.12%）标志着当前这一"正在发展中的生态系统"已趋向成熟。生态系统的冗余度（64.6）和聚合度（35.4）也表明了这一生态系统的稳定性。因此,本研究认为这一海域具有显著的后备力量面对压力情况并有能力快速恢复到初始状态。