Arsenic incorporation into authigenic pyrite, Bengal Basin sediment, Bangladesh     

Heather A. Lowers  George N. Breit  John Whitney  Md. Nehal Uddin 《Geochimica et cosmochimica acta》2007,71(11):2699-2717

Sediment from two deep boreholes (∼400 m) approximately 90 km apart in southern Bangladesh was analyzed by X-ray absorption spectroscopy (XAS), total chemical analyses, chemical extractions, and electron probe microanalysis to establish the importance of authigenic pyrite as a sink for arsenic in the Bengal Basin. Authigenic framboidal and massive pyrite (median values 1500 and 3200 ppm As, respectively), is the principal arsenic residence in sediment from both boreholes. Although pyrite is dominant, ferric oxyhydroxides and secondary iron phases contain a large fraction of the sediment-bound arsenic between approximately 20 and 100 m, which is the depth range of wells containing the greatest amount of dissolved arsenic. The lack of pyrite in this interval is attributed to rapid sediment deposition and a low sulfur flux from riverine and atmospheric sources. The ability of deeper aquifers (>150 m) to produce ground water with low dissolved arsenic in southern Bangladesh reflects adequate sulfur supplies and sufficient time to redistribute the arsenic into pyrite during diagenesis.  相似文献   

Water quality parameters along rivers     

Md. J. B. Alam  M. R. Islam  Z. Muyen  M. Mamun  S. Islam 《International Journal of Environmental Science and Technology》2007,4(1):159-167

Water samples have been collected from a part of Surma River along different points and analyzed for various water quality parameters during dry and monsoon periods. Effects of industrial wastes, municipal sewage, and agricultural runoff on river water quality have been investigated. The study was conducted within the Chattak to Sunamganj portion of Surma River, which is significant due to the presence of two major industries-a paper mill and a cement factory. The other significant feature is the conveyors that travel from India to Chattak. This study involves determination of physical, biological and chemical parameters of surface water at different points. The river was found to be highly turbid in the monsoon season. But BOD and fecal coliform concentration was found higher in the dry season. The water was found slightly acidic. The mean values of parameters were Conductivity 84–805μs; DO: dry- 5.52 mg/L, monsoon-5.72 mg/L; BOD: dry-1 mg/L, monsoon-0.878 mg/L; Total Solid: dry-149.4 mg/L, monsoon- 145.7 mg/L. A model study was also conducted and values of different model parameters were estimated.  相似文献   

Long-term patterns in the diets of Japanese temperate bassLateolabrax japonicus larvae and juveniles in Chikugo estuarine nursery ground in Ariake Bay, Japan     

Shahidul Islam Md.  Manabu Hibino  Taro Ohta  Kouji Nakayama  Masaru Tanaka 《Estuaries and Coasts》2006,29(3):519-529

Larval and juvenile Japanese temperate bass (Lateolabrax japonicus) samples were collected from a wide range of spatial gradients (covering a distance of approximately 30 km) in Chikugo estuary, Ariake Bay, Japan over a period of 8 yr (1997–2004) in order to observe changes in diet. Gut contents were studied by separating, identifying, counting, and estimating the dry weight of prey organisms. Copepod samples were collected during each cruise to observe the numerical composition, abundance, and biomass in the estuary. Considerable spatial and temporal variations were observed in copepod distributions in ambient water and the diets of the fish. Two distinctly different copepod assemblages were identified in the estuary: One in the upper estuarine turbidity maximum (ETM), dominated by a single speciesSinocalanus sinensis and the other in the lower estuary consisting of a multispecies assemblage, dominated byOithona davisae, Acartia omorii, Paracalanus parvus, andCalanus sinicus. The gut content composition of the fish in the upper estuary was dominated byS. sinensis, while in the lower estuary, it consisted ofP. parvus, O. davisae, andA. omorii. Within the size group analyzed (13.0–27.0 mm SL), the smaller individuals were found to feed on a mixed diet composed of smaller prey. The diets gradually shifted to bigger prey composed predominantly ofS. sinensis for larger size groups. Greater proportions of empty guts were recorded in the smaller individuals and dropped with increasing fish size. Higher dry biomass of copepods in the environment, as well as higher dry weights of gut contents, were recorded in the upper estuary, indicating that the upper estuarine ETM areas are important nursery grounds for the early life stages of the Japanese temperate bass. The early life stages of the Japanese temperate bass are adapted to use the upstream nursery grounds and ascending to the nursery areas to useS. sinensis is one of the key survival strategies of the Japanese temperate bass in the Chikugo estuary.  相似文献   

Changes in the frequency of tropical cyclones over the North Indian Ocean   总被引：3，自引：0，他引：3  

O. P. Singh  T. M. Ali Khan  Md. S. Rahman 《Meteorology and Atmospheric Physics》2000,75(1-2):11-20

Summary  Changes in the frequency of tropical cyclones developing over the Arabian Sea and the Bay of Bengal have been studied utilizing 122 year (1877–1998) data of tropical cyclone frequency. There have been significant increasing trends in the cyclone frequency over the Bay of Bengal during November and May which are main cyclone months. During transitional monsoon months; June and September however, the frequency has decreased. The results have been presented for five months, i.e., May-November which are relevant as far as tropical cyclone frequency over the Arabian Sea and the Bay of Bengal are concerned. The tropical cyclone frequency in the Arabian Sea has not shown any significant trend, probably due to small normal frequency. The frequency time series has been subjected to the spectral analysis to obtain the significant periods. The cyclone frequency over the Bay of Bengal during May has shown a 29 year cycle. A significant 44 year cycle has been found during November. Over the Arabian Sea significant cycles of 13 and 10 years have been observed during May-June and November, respectively. The tropical cyclone frequency in the North Indian Ocean has a prominent El Ni?o-Southern Oscillation (ENSO) scale cycle (2–5 years) during all above five months. The annual cyclone frequency exhibits 29 year and ENSO scale (2–4 years) oscillations. There is a reduction in tropical cyclone activity over the Bay of Bengal in severe cyclone months May and November during warm phases of ENSO. Examination of the frequencies of severe cyclones with maximum sustained winds ≥ 48 knots has revealed that these cyclones have become more frequent in the North Indian Ocean during intense cyclone period of the year. The rate of intensification of tropical disturbances to severe cyclone stage has registered an upward trend. Received June 7, 1999/Revised March 20, 2000  相似文献   

Entropy,consistency in rainfall distribution and potential water resource availability in Australia     

Md Masud Hasan  Peter K Dunn 《水文研究》2011,25(16):2613-2622

Understanding the variability in monthly rainfall amounts is important for the management of water resources. We use entropy, a measure of variability, to quantify the rainfall variability in Australia. We define the entropy of stable rainfall (ESR) to measure the long‐term average rainfall variability across the months of the year. The stations in northern Australia observe substantially more variability in rainfall distributions and stations in southern Australia observe less variability in rainfall distribution across the months of the year. We also define the consistency index (CI) to compare the distribution of the monthly rainfall for a given year with the long‐term average monthly rainfall distribution. Higher value of the CI indicates the rainfall in the year is consistent with the overall long‐term average rainfall distribution. Areas close to the coastline in northern, southern and eastern Australia observe more consistent rainfall distribution in individual years with the long‐term average rainfall distribution. For the studied stations, we categorize the years into different potential water resource availability on the basis of annual rainfall amount and CI. For almost all Australian rainfall stations, El Niño years have a greater risk of having below median and relatively inconsistent rainfall distribution than La Niña years. The results may be helpful for developing area‐specific water usage strategies. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Estimation of catchment yield and associated uncertainties due to climate change in a mountainous catchment in Australia          下载免费PDF全文

Md Mahmudul Haque  Ataur Rahman  Dharma Hagare  Golam Kibria  Fazlul Karim 《水文研究》2015,29(19):4339-4349

This paper examines the impacts of climate change on future water yield with associated uncertainties in a mountainous catchment in Australia using a multi‐model approach based on four global climate models (GCMs), 200 realisations (50 realisations from each GCM) of downscaled rainfalls, 2 hydrological models and 6 sets of model parameters. The ensemble projections by the GCMs showed that the mean annual rainfall is likely to reduce in the future decades by 2–5% in comparison with the current climate (1987–2012). The results of ensemble runoff projections indicated that the mean annual runoff would reduce in future decades by 35%. However, considerable uncertainty in the runoff estimates was found as the ensemble results project changes of the 5^th (dry scenario) and 95^th (wet scenario) percentiles by ?73% to +27%, ?73% to +12%, ?77% to +21% and ?80% to +24% in the decades of 2021–2030, 2031–2040, 2061–2070 and 2071–2080, respectively. Results of uncertainty estimation demonstrated that the choice of GCMs dominates overall uncertainty. Realisation uncertainty (arising from repetitive simulations for a given time step during downscaling of the GCM data to catchment scale) of the downscaled rainfall data was also found to be remarkably high. Uncertainty linked to the choice of hydrological models was found to be quite small in comparison with the GCM and realisation uncertainty. The hydrological model parameter uncertainty was found to be lowest among the sources of uncertainties considered in this study. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Parameter uncertainty of the AWBM model when applied to an ungauged catchment          下载免费PDF全文

Md Mahmudul Haque  Ataur Rahman  Dharma Hagare  Golam Kibria 《水文研究》2015,29(6):1493-1504

In this study, a quantitative assessment of uncertainty was made in connection with the calibration of Australian Water Balance Model (AWBM) for both gauged and ungauged catchment cases. For the gauged catchment, five different rainfall data sets, 23 different calibration data lengths and eight different optimization techniques were adopted. For the ungauged catchment case, the optimum parameter sets obtained from the nearest gauged catchment were transposed to the ungauged catchments, and two regional prediction equations were used to estimate runoff. Uncertainties were ascertained by comparing the observed and modelled runoffs by the AWBM on the basis of different combinations of methods, model parameters and input data. The main finding from this study was that the uncertainties in the AWBM modelling outputs could vary from ?1.3% to 70% owing to different input rainfall data, ?5.7% to 11% owing to different calibration data lengths and ?6% to 0.2% owing to different optimization techniques adopted in the calibration of the AWBM. The performance of the AWBM model was found to be dominated mainly by the selection of appropriate rainfall data followed by the selection of an appropriate calibration data length and optimization algorithm. Use of relatively short data length (e.g. 3 to 6 years) in the calibration was found to generate relatively poor results. Effects of different optimization techniques on the calibration were found to be minimal. The uncertainties reported here in relation to the calibration and runoff estimation by the AWBM model are relevant to the selected study catchments, which are likely to differ for other catchments. The methodology presented in this paper can be applied to other catchments in Australia and other countries using AWBM and similar rainfall–runoff models. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Stability analysis of multi-directional anchored rock slope subjected to surcharge and seismic loads     

Sanjay Kumar Shukla  Md. Monir Hossain 《Soil Dynamics and Earthquake Engineering》2011,31(5-6):841-844

More than one set of anchors with different orientations can be an economical solution to completely stabilize the rock slope. In this note, a general analytical expression for the factor of safety of a multi-directional anchored rock slope (MDARS) against plane failure is derived, incorporating most of the practically occurring destabilizing forces under surcharge and seismic loading conditions. Several special cases of this expression are found to be similar to those reported in the literature. A graphical presentation shows that for any specific inclination of one set of anchors to the normal at failure plane, the variation in the inclination of the second set of anchors to the normal at failure plane, when greater than approximately 60°, does not cause a significant change in the factor of safety of the MDARS.  相似文献   

Stable isotope dynamics of groundwater interactions with Ganges river     

Prerona Das  Abhijit Mukherjee  Syed Aaquib Hussain  Md. Shahid Jamal  Kousik Das  Ashok Shaw  Mrinal K. Layek  Probal Sengupta 《水文研究》2021,35(1):e14002

Groundwater depletion has been an emerging crisis in recent years, especially in highly urbanized areas as a result of unregulated exploitation, thus leaving behind an insufficient volume of usable freshwater. Presently Ganges river basin, the sixth largest prolific fluvial system and sustaining a huge population in South Asia, is witnessed to face (i) aquifer vulnerability through surface waterborne pollutant and (ii) groundwater stress due to summer drying of river as a result of indiscriminate groundwater abstraction. The present study focuses on a detailed sub-hourly to seasonally varying interaction study and flux quantification between river Ganges and groundwater in the Indian subcontinent which is one of the first documentations done on a drying perennial river system that feeds an enormous population. Contributing parameters to the total discharge of a river at its middle course on both temporal and spatial scale is estimated through three-component hydrograph separation and end-member mixing analysis using high-resolution water isotope (δ¹⁸O and δ²H) and electrical conductivity data. Results from this model report groundwater discharge in river to be the highest in pre-monsoon, that is, 30%, whereas, during post-monsoon the contribution lowers to 25%; on the contrary, during peak monsoon, the flow direction reverses thus recharging the groundwater which is also justified using annual piezometric hydrographs of both river water and groundwater. River water-groundwater interaction also shows quantitative variability depending on river morphometry. The current study also provides insight on aquifer vulnerability as a result of pollutant mixing through interaction and plausible attempts towards groundwater management. The present study is one of the first in South Asian countries that provides temporally and spatially variable detailed quantification of baseflow and estimates contributing parameters to the river for a drying mega fluvial system.  相似文献   

Local perceptions of and adaptation to climate variability and change: the case of shrimp farming communities in the coastal region of Bangladesh     

Masud Iqbal Md Shameem  Salim Momtaz  Anthony S. Kiem 《Climatic change》2015,133(2):253-266

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