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51.
Temporal evolution of DNAPL source and contaminant flux distribution: impacts of source mass depletion 总被引:1,自引:1,他引:0
Basu NB Rao PS Falta RW Annable MD Jawitz JW Hatfield K 《Journal of contaminant hydrology》2008,95(3-4):93-109
We investigated, using model simulations, the changes occurring in the distribution of dense non-aqueous phase liquid (DNAPL) mass (Sn) within the source zone during depletion through dissolution, and the resulting changes in the contaminant flux distribution (J) at the source control plane (CP). Two numerical codes (ISCO3D and T2VOC) were used to simulate selected scenarios of DNAPL dissolution and transport in three-dimensional, heterogeneous, spatially correlated, random permeability fields with emplaced sources. Data from the model simulations were interpreted based on population statistics (mean, standard deviation, coefficient of variation) and spatial statistics (centroid, second moments, variograms). The mean and standard deviation of the Sn and J distributions decreased with source mass depletion by dissolution. The decrease in mean and standard deviation was proportional for the J distribution resulting in a constant coefficient of variation (CV), while for the Sn distribution, the mean decreased faster than the standard deviation. The spatial distributions exhibited similar behavior as the population distribution, i.e., the CP flux distribution was more stable (defined by temporally constant second moments and range of variograms) than the Sn distribution. These observations appeared to be independent of the heterogeneity of the permeability (k) field (variance of the log permeability field=1 and 2.45), correlation structure (positive vs. negative correlation between the k and Sn domains) and the DNAPL dissolution model (equilibrium vs. rate-limited), for the cases studied. Analysis of data from a flux monitoring field study (Hill Air Force Base, Utah) at a DNAPL source CP before and after source remediation also revealed temporal invariance of the contaminant flux distribution. These modeling and field observations suggest that the temporal evolution of the contaminant flux distribution can be estimated if the initial distribution is known. However, the findings are preliminary and broader implications to sampling strategies for remediation performance assessment need to be evaluated in additional modeling and experimental studies. 相似文献
52.
Zhang C Yoon H Werth CJ Valocchi AJ Basu NB Jawitz JW 《Journal of contaminant hydrology》2008,102(1-2):49-60
Nonaqueous phase liquid (NAPL) dissolution was studied in three-dimensional (3D) heterogeneous experimental aquifers (25.5 cm x 9 cm x 8.5 cm) with two different longitudinal correlation lengths (2.1 cm and 1.1 cm) and initial spill volumes (22.5 ml and 10.5 ml). Spatial and temporal distributions of NAPL during dissolution were measured using magnetic resonance imaging (MRI). At high NAPL spill volume, average effluent concentrations initially increased during dissolution, as NAPL pools transitioned to NAPL ganglia, and then decreased as the total NAPL-water interfacial area decreased over time. Experimental results were used to test six dissolution models: (i and ii) a one-dimensional (1D) model using either specific NAPL-water interfacial area values estimated from MR images at each time step (i.e., 1D quasi-steady state model), or an empirical mass transfer (Sh') correlation (i.e., 1D transient model), (iii and iv) a multiple analytical source superposition technique (MASST) using either the NAPL distribution determined from MR images at each time step (i.e., MASST steady state model), or the NAPL distribution determined from mass balance calculations (i.e., MASST transient model), (v) an equilibrium streamtube model, and (vi) a 3D grid-scale pool dissolution model (PDM) with a dispersive mass flux term. The 1D quasi-steady state model and 3D PDM captured effluent concentration values most closely, including some concentration fluctuations due to changes in the extent of flow reduction. The 1D transient, MASST steady state and transient, and streamtube models all showed a monotonic decrease in effluent concentration values over time, and the streamtube model was the most computationally efficient. Changes during dissolution of the effective NAPL-water interfacial area estimated from imaging data are similar to changes in effluent concentration values. The 1D steady state model incorporates estimates of the effective NAPL-water interfacial area directly at each time point; the 3D PDM does so indirectly through mass balance and a relative permeability function, which causes reduced water flow through high saturation NAPL regions. Hence, when model accuracy is required, the results indicate that a surrogate of this effective interfacial area is required. Approaches to include this surrogate in the MASST and streamtube models are recommended. 相似文献
53.
Jennifer Rutkiewicz Doug Crump Niladri Basu 《Environmental pollution (Barking, Essex : 1987)》2010,158(8):2733-2737
Herring gulls (Larus argentatus) bioaccumulate mercury (Hg) but it is unknown whether they are exposed at levels of neurological concern. Here we studied brain tissues from gulls at five Great Lakes colonies and one non-Great Lakes colony during spring of 2001 and 2003. Total brain Hg concentrations ranged from 0.14 to 2.0 μg/g (dry weight) with a mean of 0.54 μg/g. Gulls from Scotch Bonnet Island, on the easternmost edge of the Great Lakes, had significantly higher brain Hg than other colonies. No association was found between brain Hg concentration and [3H]-ligand binding to neurochemical receptors (N-methyl-d-aspartate, muscarinic cholinergic, nicotinic cholinergic) or nicotinic receptor α-7 relative mRNA expression as previously documented in other wildlife. In conclusion, spatial trends in Hg contamination exist in herring gulls across the Great Lakes basin, and herring gulls accumulate brain Hg but not at levels associated with sub-clinical neurochemical alterations. 相似文献
54.
Soorangkattan Saravanan Nalluchamy Kamala Dhasan Arumugam Sudha Sivagnanam Chandrasekaran Thulasinathan Boobalan Ramu Satheesh Murugan Alagarsamy Arun Muthuramalingam Jothi Basu 《Environmental science and pollution research international》2021,28(26):33957-33957
Environmental Science and Pollution Research - A Correction to this paper has been published: https://doi.org10.1007/s11356-021-14573-3 相似文献
55.
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57.
William C. Anderson Sukanta Basu Chris W. Letchford 《Environmental Fluid Mechanics》2007,7(3):195-215
Several non-dynamic, scale-invariant, and scale-dependent dynamic subgrid-scale (SGS) models are utilized in large-eddy simulations
of shear-driven neutral atmospheric boundary layer (ABL) flows. The popular Smagorinsky closure and an alternative closure
based on Kolmogorov’s scaling hypothesis are used as SGS base models. Our results show that, in the context of neutral ABL
regime, the dynamic modeling approach is extremely useful, and reproduces several establised results (e.g., the surface layer
similarity theory) with fidelity. The scale-dependence framework, in general, improves the near-surface statistics from the
Smagorinsky model-based simulations. We also note that the local averaging-based dynamic SGS models perform significantly
better than their planar averaging-based counterparts. Lastly, we find more or less consistent superiority of the Smagorinsky-based
SGS models (over the corresponding Kolmogorov’s scaling hypothesis-based SGS models) for predicting the inertial range scaling
of spectra. 相似文献
58.
D. K. Basu J. Saxena F. W. Stoss J. Santodonato M. W. Neal F. C. Kopfler 《Chemosphere》1987,16(10-12)
The primary objectives of this study were to examine the changes in concentration of six polycyclic aromatic hydrocarbons (PAH) and the possibility of changes in mutagenic potential of treated waters as a result of their passage through commonly used distribution pipes. With the exception of the finished water taken at one treatment plant in which the total concentration of the six PAH was 138.5 parts per trillion (ppt), the total initial concentration in all other treated water ranged from 0 to 13.4 ppt. The corresponding total PAH concentration in water after passage through the distribution pipes varied from 0 to 61.6 ppt. This demonstrated that PAH concentration in water can increase as a result of their passage through coated distribution pipes. Mutagenic activity was also detected in many of the treated water samples, however, the levels of this activity did not correlate with either the transit of water through the distribution system or the levels of PAH in the water. There was some evidence to indicate that the water treatment process itself may have contributed to the mutagenicity observed in the finished water. 相似文献
59.
Ping Gong Niladri Basu Anton M. Scheuhammer Edward J. Perkins 《Environmental science and pollution research international》2010,17(1):181-186
Background, aim, and scope
Hexanitrohexaazaisowurtzitane (CL-20) is a relatively new energetic compound sharing some degree of structural similarity with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a known neurotoxic compound. Previously, we demonstrated using a noninvasive electrophysiological technique that CL-20 was a more potent neurotoxicant than RDX to the earthworm Eisenia fetida. In the present study, we investigated the effect of CL-20 exposure and subsequent recovery on muscarinic acetylcholine receptors (mAChRs) to further define the mechanism of reversible neurotoxicity of CL-20 in E. fetida.Materials and methods
We used a noninvasive electrophysiological technique to evaluate neurotoxicity in CL-20-treated worms, and then measured how such exposures altered levels of whole-body mAChR in the same animals.Results and discussion
A good correlation exists between these two types of endpoints. Effect on mAChR levels was most prominent at day 6 of exposure. After 7 days of recovery, both conduction velocity and mAChR were significantly restored. Our results show that sublethal concentrations of CL-20 significantly reduced mAChR levels in a concentration- and duration-dependent manner, which was accompanied with significant decreases in the conduction velocity of the medial and lateral giant nerve fibers. After 7-day post exposure recovery, worms restored both neurochemical (mAChR) and neurophysiological (conduction velocity) endpoints that were reduced during 6-day exposures to CL-20 concentrations from 0.02 to 0.22 µg/cm2.Conclusions and perspectives
Our findings support the idea that CL-20 induced neurotoxic effects are reversible, and suggest that CL-20 neurotoxicity may be mediated through the cholinergic system. Future studies will investigate other neurotransmission systems such as GABA, glutamate, and monoamine. Ion channels in the nerve membrane should be examined to further define the precise mechanisms underlying CL-20 neurotoxicity. 相似文献60.
In countries like India where multiple risks interact with socio-economic differences to create and sustain vulnerability, assessing the vulnerability of people, places, and systems to climate change is a critical tool to prioritise adaptation. In India, several vulnerability assessment tools have been designed spanning multiple disciplines, by multiple actors, and at multiple scales. However, their conceptual, methodological, and disciplinary underpinnings, and resulting implications on who is identified as vulnerable, have not been interrogated. Addressing this gap, we systematically review peer-reviewed publications (n = 78) and grey literature (n = 42) to characterise how vulnerability to climate change is assessed in India. We frame our enquiry against four questions: (1) How is vulnerability conceptualised (vulnerability of whom/what, vulnerability to what), (2) who assesses vulnerability, (3) how is vulnerability assessed (methodology, scale), and (4) what are the implications of methodology on outcomes of the assessment. Our findings emphasise that methods to assess vulnerability to climate change are embedded in the disciplinary traditions, methodological approaches, and often-unstated motivations of those designing the assessment. Further, while most assessments acknowledge the importance of scalar and temporal aspects of vulnerability, we find few examples of it being integrated in methodology. Such methodological myopia potentially overlooks how social differentiation, ecological shifts, and institutional dynamics construct and perpetuate vulnerability. Finally, we synthesise the strengths and weaknesses of current vulnerability assessment methods in India and identify a predominance of research in rural landscapes with a relatively lower coverage in urban and peri-urban settlements, which are key interfaces of transitions. 相似文献