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The Begnas Lake in the Pokhara Valley is one of the threatened habitats in Nepal. The major ion chemistry explains the status of most of the inorganic nutrients and their possible sources. However, the earlier studies mostly cover limnological investigations, and phytoplankton and zooplankton diversity. Thus, the present study has been conducted to investigate the geochemical processes and to examine the seasonal variation of chemical composition within Begnas Lake. The results showed that SO 4 2- , PO 4 3- , and NO 3 - increased compared with the previous values. The domination of Ca2+, Mg2+, and HCO 3 - explains the influence of carbonate weathering on the major ion concentration. In general, pH and dissolved oxygen decreased with the depth of water-column, while electric conductivity, total dissolved solids, HCO 3 - , Cl-, H4SiO4, K+, Mg2+, Ca2+, Mn2+, and Fe increased. Among the cations, the predominance of Ca2+ and Mg2+ as characterized by high (>0.6) (Ca2+ + Mg2+)/(Tz+) and (>0.8) (Ca2+ + Mg2+)/(Na+ + K+) equivalent ratios, also suggests prevalence of carbonate weathering. The low value of (Na+ + K+)/Tz+ ratio shows deficiency of Na+ and K+, suggesting low contribution of cations via aluminosilicate weathering. The C-ratio suggests a proton source derived both from oxidation of sulfide and dissolution and dissociation of atmospheric CO2 during different seasons. Though the major hydro-chemical parameters are within permissible limit, the increase in trophic state of the lake suggests that inherent biogeochemical processes make the limiting nutrients available, rendering eutrophic effect. Therefore, further comprehensive studies incorporating sediment–water interaction ought to be carried out to explain the ongoing phenomena and curb the eutrophication process in the lake. 相似文献
23.
Abdollah Shafieezadeh Karthik Ramanathan Jamie E. Padgett Reginald DesRoches 《地震工程与结构动力学》2012,41(3):391-409
Probabilistic seismic analysis of structures involves the construction of seismic demand models, often stated as probabilistic models of structural response conditioned on a seismic intensity measure. The uncertainty introduced by the model is often a result of the chosen intensity measure. This paper introduces the concept of using fractional order intensity measures (IMs) in probabilistic seismic demand analysis and uses a single frame integral concrete box‐girder bridge class and a seismically designed multispan continuous steel girder bridge class as case studies. The fractional order IMs considered include peak ground response and spectral accelerations at 0.2 and 1.0 s considering a single degree of freedom system with fractional damping, , as well as a linear single degree of freedom system with fractional response, . The study reveals the advantage of fractional order IMs relative to conventional IMs such as peak ground acceleration, peak ground velocity, or spectral acceleration at 0.2 and 1.0 s. Metrics such as efficiency, sufficiency, practicality, and proficiency are measured to assess the optimal nature of fractional order IMs. The results indicate that the proposed fractional order IMs produce significant improvements in efficiency and proficiency, whereas maintaining practicality and sufficiency, and thus providing superior demand models that can be used in probabilistic seismic demand analysis. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
24.
Rafi Yasmin Taj Sahaderan Renganathan Nagarajan Partha Gurunathan Baskar Manikom Velan 《洁净——土壤、空气、水》2009,37(10):787-792
In the present work, biosorption of Cr(VI) by Nymphaea rubra was investigated in batch studies. Batch experiments were conducted to study the effect of initial sorbent dosage, solution pH and initial Cr(VI) concentration. The results showed that the equilibrium uptake capacity was increased with decrease in biomass dosage. The Cr(VI) removal was influenced by the initial chromium compound concentration. Langmuir and Freundlich adsorption isotherm models were used to represent the equilibrium data. The Freundlich isotherm model was fitted very well with the equilibrium data when compared to Langmuir isotherm model. The sorption results were analyzed for pseudo‐first order and pseudo‐second order kinetic model. It was observed that the kinetic data fitted very well with the pseudo‐second order rate equation when compared to the pseudo‐first order rate equation. Fourier transform infrared spectrum showed the presence of different functional groups in the biomass. The surface morphology of the sorbent was exemplified by SEM analysis. Aquatic weeds seem to be a promising biosorbent for the removal of chromium ions from water environment. This paper reports the research findings of a laboratory‐based study on the removal of Cr(VI) from the synthetic solution using the dried stem of N. rubra as a biosorbent. 相似文献
25.
Climate change,the monsoon,and rice yield in India 总被引:4,自引:1,他引:3
Recent research indicates that monsoon rainfall became less frequent but more intense in India during the latter half of the
Twentieth Century, thus increasing the risk of drought and flood damage to the country’s wet-season (kharif) rice crop. Our statistical analysis of state-level Indian data confirms that drought and extreme rainfall negatively affected
rice yield (harvest per hectare) in predominantly rainfed areas during 1966–2002, with drought having a much greater impact
than extreme rainfall. Using Monte Carlo simulation, we find that yield would have been 1.7% higher on average if monsoon
characteristics, especially drought frequency, had not changed since 1960. Yield would have received an additional boost of
nearly 4% if two other meteorological changes (warmer nights and lower rainfall at the end of the growing season) had not
occurred. In combination, these changes would have increased cumulative harvest during 1966–2002 by an amount equivalent to
about a fifth of the increase caused by improvements in farming technology. Climate change has evidently already negatively
affected India’s hundreds of millions of rice producers and consumers. 相似文献
26.
Baskar Balakrishnan Biraja Kumar Sahu Jayappriyan Kothilmozhian Ranishree Arockia Vasanthi Lourduraj Marimuthu Nithyanandam Nandakumar Packiriswamy Prabakaran Panchatcharam 《Environmental Earth Sciences》2017,76(1):58
Heavy metals are known to pose a potential threat to terrestrial and aquatic flora and fauna. Due to increasing human influence, heavy metal concentrations are rising in many mangrove ecosystems. Therefore, an assessment of heavy metal (Cd, Cr, Cu, Ni, Pb, Fe, Mn, and Zn) concentrations was conducted within the bulk soil and rhizosphere soil of Avicennia marina at the Pichavaram Mangrove Forest in India. The rhizosphere soil showed higher concentrations of metals than the bulk soil. Compared to the bulk soil, the metals Cd, Fe, Mn, and Zn were 6.0–16.7% higher, whereas Cr, Cu, Ni, and Pb were 1.7–2.8% higher concentration. Among the three selected sampling sites (dense mangrove forest, estuarine region, and sea region), the sea region had the highest concentration of all heavy metals except Zn. The trend of the mean metal concentration was Fe > Mn > Cr > Ni > Cu > Pb > Zn > Cd. Heavy metals concentrations elevated by the 2004 tsunami were persistent even after 4 years, due to sedimentary soil processes, the rhizosphere effect of mangroves, and anthropogenic deposition. Analysis of the heavy metal-resistant bacteria showed highest bacterial count for Cr-resistant bacteria and rhizosphere soil. The maximum level of heavy metal-resistant bacteria was observed at the site with the highest heavy metal contamination. The heavy metal-resistant bacteria can be used as indicator of heavy metal pollution and furthermore in bioremediation. 相似文献
27.
Geochemical assessment of groundwater quality in vicinity of Bhalswa landfill,Delhi, India,using graphical and multivariate statistical methods 总被引:1,自引:0,他引:1
A geochemical assessment of groundwater quality and possible contamination in the vicinity of the Bhalswa landfill site was
carried out by using a hydrochemical approach with graphical and multivariate statistical methods with the objective of identifying
the occurrence of various geochemical processes and understanding the impact of landfill leachates on groundwater quality.
Results indicate that nitrate, fluoride and heavy-metal pollution are in an alarming state with respect to the use of groundwater
for drinking purposes. Various graphical plots and statistical analyses have been applied to the chemical data based on the
ionic constituents, water types, and hydrochemical facies to infer the impact of the landfill on groundwater quality. The
statistical analysis and spatial and temporal variations indicate the leaching of contaminants from the landfill to the groundwater
aquifer system. The concentrations of heavy metals in the landfill leachates are as follows: Fe (22 mg/l), Mn (~20 mg/l),
Cu (~10 mg/l), Pb (~2 mg/l), Ni (0.25 mg/l), Zn (~10 mg/l), Cd (~0.2 mg/l), Cl− (~4,000 mg/l), SO42− (~3,320 mg/l), PO43− (~4 mg/l), NO3− (30 mg/l) and fluoride (~50 mg/l); all were much higher than the standards. The study reveals that the landfill is in a depleted
phase and is affecting groundwater quality in its vicinity and the surrounding area due to leaching of contaminants. 相似文献
28.
Sushmitha Baskar R. Baskar Natuschka Lee A. Kaushik P. K. Theophilus 《Environmental Geology》2008,56(2):237-243
The Borra caves, Vishakapatnam, India, can be described as a speleothem cave with significant amounts of unexplored microbial
mats in spring waters. Here, we present the first observations and hypotheses on the possible impact of the microorganisms
in these mats on the cave formation, focusing on their role on iron mineral precipitation. The spring waters (pH neutral 7.5–7.7)
contained dissolved metals like iron and the organic mat sludge (pH 7.0–7.3) had a TOC content of approximately 5.4 wt%. Geochemically,
the spring waters deep below the microbial mats contained Fe 369 ppb, Sr 198 ppb; and the organic mat sludge contained Mg
9 ppm, Fe 427 ppb, Zn 149 ppb, Sr 190 ppb. XRD observations displayed Fe minerals (dominantly hematite), minor amounts of
zinc gallium sulfide and nitrofuryl compounds. At least four groups of bacteria identified by direct microscopy and SEM-EDX
on the basis of morphology could be observed in all samples: Leptothrix-like organisms, entombed bacterial mineral sheaths, a few stalks of Gallionella-like organisms and some additional bacteria that could not be further identified. Leptothrix-like organisms contained 43.22–60.08 wt % Fe and the mineral precipitated near and around these bacteria (in the actual unaltered
samples on site) contained 30.76–45.22 wt% Fe as identified and quantified by SEM-EDX. This study indicates that the precipitation
of these iron-rich mats in the spring waters could be linked to the presence of abundant active communities of iron precipitating
bacteria at Borra caves, Vishakapatanam. 相似文献
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