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51.
Md. Abu Sayeed Mostafa Ali Reza Hossain Md. Abdul Wahab Md. Tawheed Hasan Kumar Das Simon Sabuj Kanti Mazumder 《中国海洋湖沼学报》2015,33(4):895-904
A study was conducted to investigate the status of the water and sediment quality in the Chalan Beel——a major fresh water fish reservoir of the country for a period of one year from July 2007 to June 2008. The mean values of water quality parameters(depth: 214.73±152.22 cm, temperature 27.68±4.26℃, transparency 123±82 cm, p H 9.7±0.47, total alkalinity 137±42 mg/L, conductivity 307±147 μs/cm, total dissolved solids 183±89 mg/L, ammonia-N 0.27±0.39 mg/L, nitrate-N 0.09±0.07 mg/L, phosphate-P 2.01±2.53 mg/L) and sediment quality parameters(p H 7.21±0.35, organic matter 2.59±0.52%, total nitrogen 0.09±0.04%, available phosphorus 5.4±3.6 Meq./100 g and exchangeable potassium 0.43±0.14 Meq./100 g) were within the range recommended for most of the inland fishes of Bangladesh. Although the water and sediment quality parameters except ammonia and phosphate are in the suitable range, the overall results suggest that better management techniques should be practiced in order to overcome the declining trend of associated aquatic life(fauna and flora) of this important fresh water body of Bangladesh. 相似文献
52.
A total of 103 surface sediment samples collected from the water depth range of 15—3300 m along Vijaydurg-Karwar stretch of central west coast of India were analyzed for foraminiferal content. Relict benthic foraminiferal assemblage was noted within 50—135 m water depth.The relict benthic foraminiferal assemblage that includes Amphistegina,Operculum and Alveolinetta in sediment samples within the water depth of 85—135 m indicates presence of coral reef at this depth during Early Holocene. The presence of barnacle fouling on Relict foraminifera at 60—90 m confirms the paleo-shoreline. The shallow depth zone is characterized by presence of agglutinated relict foraminifera.The agglutinated forms indicate freshwater influx,which eventually increased the sea level and subsequently deteriorated the paleo-coral reef. 相似文献
53.
K. Sreelash Rajat Kumar Sharma J. A. Gayathri B. Upendra K. Maya D. Padmalal 《Journal of the Geological Society of India》2018,92(5):548-554
The Western Ghats plays a pivotal role in determining the hydrological and hydroclimatic regime of Peninsular India. The mountainous catchments of the Ghats are the primary contributors of flow in the rivers that sustains the life and agricultural productivity in the area. Although many studies have been conducted in the past decades to understand long term trends in the meteorological and hydrological variables of major river basins, not much attention have been made to unfold the relationship existing among rainfall and river hydrology of natural drainages on either side of the Western Ghats which host one of the unique biodiversity hotspots across the world. Therefore, an attempt has been made in this paper to examine the short term (last three decades) changes in the rainfall pattern and its influence on the hydrological characteristics of some of the important rivers draining the southern Western Ghats as a case study. The short term, annual and seasonal trends in the rainfall, and its variability and discharge were analyzed using Mann-Kendall test and Sen’s estimator of slope. The study showed a decreasing trend in rainfall in the southwest monsoon while a reverse trend is noticed in northeast monsoon. Correspondingly, the discharge of the west and east flowing rivers also showed a declining trend in the southwest monsoon season. The runoff coefficient also followed the trends in the discharge. The runoff coefficient of the Periyar river showed a decreasing trend, whereas the Cauvery river exhibited an increasing trend. A high-resolution analysis of rainfall data revealed that the number of moderate rainfall events showed a decreasing trend throughout the southern Western Ghats, whereas the high intensity rainfall events showed an opposite trend. The decline in groundwater level in the areas which recorded an increase in high intensity rainfall events and decrease in moderate rainfall events showed that the groundwater recharge process is significantly affected by changes in the rainfall pattern of the area. 相似文献
54.
The grain-size fractions in the bedload transported over the five heterogeneous sediment beds of different values of bed roughness were computed from the flume experiments. The existence of an entrapment factor associated with the sorting observed from the bed to active layer was modeled based on the modified critical shear stress to estimate the grain-size fractions in the transport layer under given hydraulic conditions. The efficiency of these models was tested with the observed data. Subsequently, the patterns of observed grain-size distributions in the transport layer were tested to identify the distributions developed in the active layer due to sorting using three probability density functions (pdf), such as, log-normal, log-hyperbolic and log-skew-Laplace. Tests indicated that a log-skew-Laplace distribution fitted best for 49%, a log-hyperbolic for 31%, and a log-normal for 20% out of forty-five bedload samples collected under unidirectional flow with changes in flow discharge and bed roughness. The results of this study would be useful to specify the grain-size distributions in the bedload formed under different hydrodynamic conditions in various sedimentary environments. 相似文献
55.
Rana W. El-Sabaawi Akash R. Sastri John F. Dower Asit Mazumder 《Estuaries and Coasts》2010,33(3):738-752
Characterizing trophic flows is central to our understanding of energy transfer in marine ecosystems. The food webs of coastal
systems are difficult to study because the proportion of autochthonous to allochthonous sources often varies seasonally and
is often overlaid on a seasonal cycle of zooplankton composition. Here, we use a combination of fatty acids and stable isotopes
to disentangle the trophic pathways in a productive coastal system (the Strait of Georgia (SoG), Canada). Over the span of
a year, Metridia pacifica, a ubiquitous omnivorous copepod, can utilize a wide range of dietary items including diatoms, flagellates, bacteria, detritus,
and microzooplankton. M. pacifica can switch from herbivory to carnivory in response to declining chlorophyll concentrations after the spring bloom and can
occasionally utilize detrital sources. These findings are discussed in the context of previous knowledge of the SoG ecosystem,
the current state of ecosystem modeling in the region, and the use of stable isotopes and fatty acids to assess trophic dynamics. 相似文献
56.
C. S. Jahan Q. H. Mazumder A. T. M. M. Islam M. I. Adham 《Journal of the Geological Society of India》2010,76(2):134-142
The Barind Integrated Area Development Project (BIADP), NW Bangladesh launched in late eighties of last century boosted cropping
intensity from 117% in pre-BIADP to about 200% at present. Increasing trend of rainfall for the period 1980–2006 in the southern
portion had a positive impact on BIADP, but in the northeastern part, reverse trend is indicated. The groundwater outflow
from the central part following the surface gradient is indicative of effluent drainage characteristics. Although rainfall
has increased in the southern part, there has been progressive decline in groundwater level due to increase in irrigation
demand. In the northern part there has been decline in groundwater level due to less resource potential. The PET, ETcrops and net irrigation requirement generally has decreased from pre- to post-Project implementation stages and rainwater has
been the supplementary irrigation resource and thus dependency on groundwater has been reduced with exception in northwestern
part. While the southern part is marching towards humid condition, north is creeping towards semi-aridity. Proper groundwater
resource management with ecological balance is warranted for the sustainability of BIADP. 相似文献
57.
58.
Asit Mazumder D. J. McQueen W. D. Taylor D. R. S. Lean 《Aquatic Sciences - Research Across Boundaries》1990,52(2):144-155
Large lakes enclosures were used to examine the influence of nutrient (P, N) enrichment and planktivorous fish (1 + yellow perch) predation on hypolimnetic oxygen depletion. Results were compared to similar data for lakes with high (Lake St. George) and low (Haynes Lake) abundances of planktivorous fish. In both the unfertilized and fertilized enclosures, fish predation on large cladocerans increased the biomasses of pico- and nanoplankton (0.2–20 µm), phytoplankton (chlorophyll a) and total phosphorus (TP), reduced sedimentation, water clarity, and hypolimnetic oxygen concentrations (AHO). Fertilized enclosures without fish had highest TP and sedimentation rates, but the AHO were low. The high planktivore lake had higher pico- and nanoplankton, higher chlorophyll a, reduced water clarity, and lower AHO than the low planktivore lake. Areal hypolimnetic oxygen depletion (AHOD) rates were strongly related with Secchi depth and plankton size-distribution (r
2 = 0.77, and 0.79, respectively), but not as strongly with TP, chlorophyll a, and sedimentation rates (r
2 = 0.25, 0.53, and 0.02, respectively). Such observations are useful in forming a generalized hypothesis that lakes with low planktivory and high water clarity have lower oxygen depletion because 1) plankton that are settling are larger and spend less time in the hypolimnetic water column before reaching the sediment, and therefore undergo less decomposition, and 2) the euphotic depth extends into the hypolimnion and production of oxygen can take place. 相似文献
59.
Hydrochemistry and origin of salinity in groundwater in parts of Lower Tista Floodplain,northwest Bangladesh 总被引：1，自引：0，他引：1
Rumy Afroza Quamrul H. Mazumder Chowdhury S. Jahan M. A. I. Kazi M. A. Ahsan M. A. Al-Mansur 《Journal of the Geological Society of India》2009,74(2):223-232
Hydrochemistry in parts of the Lower Tista Floodplain in northwest Bangladesh is dominated by alkalies and weakly acid, having highest concentration of sodium cations and bicarbonate anions respectively. Groundwater is characterized by sodium-calcium and sodium-potassium cation and bicarbonate-chloride-sulphate anion facies, and genetically ‘normal chloride’, ‘normal sulphate’, and ‘normal carbonated’ type, and soft to saline. Based on electrical conductivity values, the area is divided into northern fresh and southern saline groundwater zone, and values like salinity, Na%, SAR, and RSC and a good correlation between Na+ and Cl?, and Cl? and salinity reveals increasing salinity with depth indicating a mixing of fresh and saline bodies due to marine transgression (?) during Holocene period in the Bengal delta. The rock weathering is likely to affect the groundwater quality by dolomite dissolution and calcium precipitation, representing reverse softening process and is brine seawater. Water extracted from shallow zone (from 20 to 30 m) has suitability for drinking purpose, livestock consumption and irrigation purposes, and partially suitable for industrial use, but that from deeper zone (from 30 to 50 m) is generally poor and unsuitable especially for irrigation purposes with low alkali and moderate to high salinity hazard. So groundwater can be used for irrigation in the area of fine textured soil with proper management practices. 相似文献
60.
Astronomy Reports - We observe a coronal jet around 22 : 08 UT on March 23, 2017, in a quiet region towards the north-east of the solar disk. A minifilament eruption leads to this jet. We analyze... 相似文献