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  • 1
    In: Groundwater, March 2017, Vol.55(2), pp.149-149
    Description: Byline: Kamini Singha ***** No abstract is available for this article. *****
    Keywords: Geophysics;
    ISSN: 0017-467X
    E-ISSN: 1745-6584
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  • 2
    Language: English
    In: Journal of Hydrology, Sept 25, 2013, Vol.501, p.163(12)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhydrol.2013.08.007 Byline: Lance N. Larson, Michael Fitzgerald, Kamini Singha, Michael N. Gooseff, Jennifer L. Macalady, William Burgos Abstract: acents We imaged hyporheic exchange using electrical resistivity and a dilution tracer. acents We delineated subsurface regions of fast and slow rates of hyporheic exchange. acents Pore-water geochemical gradients were controlled by extent of hyporheic exchange. Article History: Received 5 January 2013; Revised 3 August 2013; Accepted 5 August 2013 Article Note: (miscellaneous) This manuscript was handled by Peter K. Kitanidis, Editor-in-Chief, with the assistance of Xunhong Chen, Associate Editor
    Keywords: Inland Water Pollution -- Electric Properties ; Acid Mine Drainage -- Electric Properties
    ISSN: 0022-1694
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Journal of Hydrology, May 2016, Vol.536, pp.327-338
    Description: The feedbacks among forest transpiration, soil moisture, and subsurface flowpaths are poorly understood. We investigate how soil moisture is affected by daily transpiration using time-lapse electrical resistivity imaging (ERI) on a highly instrumented ponderosa pine and the surrounding soil throughout the growing season. By comparing sap flow measurements to the ERI data, we find that periods of high sap flow within the diel cycle are aligned with decreases in ground electrical conductivity and soil moisture due to drying of the soil during moisture uptake. As sap flow decreases during the night, the ground conductivity increases as the soil moisture is replenished. The mean and variance of the ground conductivity decreases into the summer dry season, indicating drier soil and smaller diel fluctuations in soil moisture as the summer progresses. Sap flow did not significantly decrease through the summer suggesting use of a water source deeper than 60 cm to maintain transpiration during times of shallow soil moisture depletion. ERI captured spatiotemporal variability of soil moisture on daily and seasonal timescales. ERI data on the tree showed a diel cycle of conductivity, interpreted as changes in water content due to transpiration, but changes in sap flow throughout the season could not be interpreted from ERI inversions alone due to daily temperature changes.
    Keywords: Electrical Geophysics ; Transpiration ; Ponderosa Pine ; Soil Moisture ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 4
    Language: English
    In: Journal of Hydrology, Sept 19, 2014, Vol.517, p.362(16)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhydrol.2014.05.036 Byline: Adam S. Ward, Michael N. Gooseff, Michael Fitzgerald, Thomas J. Voltz, Kamini Singha Abstract: acents Distributed, field-based characterization of hyporheic transport processes. acents Hyporheic transport processes change during baseflow recession. acents Hydrogeophysical methods characterize heterogeneity in hyporheic transport. Article History: Received 3 June 2013; Revised 29 April 2014; Accepted 5 May 2014 Article Note: (miscellaneous) This manuscript was handled by Peter K. Kitanidis , Editor-in-Chief, with the assistance of Anthony Lee Endres, Associate Editor
    ISSN: 0022-1694
    Source: Cengage Learning, Inc.
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  • 5
    Language: English
    In: Journal of Hydrology, 25 September 2013, Vol.501, pp.163-174
    Description: Biological low-pH Fe(II)-oxidation creates terraced iron formations (TIFs) that remove Fe(III) from solution. TIFs can be used for remediation of acid mine drainage (AMD), however, as sediment depth increases, Fe(III)-reduction in anoxic subsurface areas may compromise treatment effectiveness. In this study we used near-surface electrical resistivity imaging (ERI) and pore-water samplers to spatially resolve bulk conductivity changes within a TIF formed in a stream emanating from a large abandoned deep clay mine in Cambria County, Pennsylvania, USA. Because of the high fluid electrical conductivity of the emergent AMD (1860 μS), fresh water (42 μS) was added as a dilution tracer to visualize the spatial and temporal extent of hyporheic exchange and to characterize subsurface flow paths. Distinct hydrogeochemical niches were identified in the shallow subsurface beneath the stream by overlaying relative groundwater velocities (derived from ERI) with pore-water chemistry profiles. Niches were classified based on relatively “fast” versus “slow” rates of hyporheic exchange and oxic versus anoxic conditions. Pore-water concentrations and speciation of iron, pH, and redox potential differed between subsurface flow regimes. The greatest extent of hyporheic exchange was beneath the center of the stream, where a shallower (〈10 cm) Fe(II)-oxidizing zone was observed. Meanwhile, less hyporheic exchange was observed near the channel banks, concurrent with a more pronounced, deeper (〉70 cm) Fe(II)-oxidizing zone. At these locations, relatively slower groundwater exchange may promote biotic Fe(II)-oxidation and improve the long-term stability of Fe sequestered in TIFs.
    Keywords: Iron Cycling ; Hyporheic Exchange ; Coal Mine Drainage ; In Situ Pore-Water ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 6
    Language: English
    In: Journal of Hydrology, 19 September 2014, Vol.517, pp.362-377
    Description: The transport of solutes along hyporheic flowpaths is recognized as central to numerous biogeochemical cycles, yet our understanding of how this transport changes with baseflow recession, particularly in a spatially distributed manner, is limited. We conducted four steady-state solute tracer injections and collected electrical resistivity data to characterize hyporheic transport during seasonal baseflow recession in the H.J. Andrews Experimental Forest (Oregon, USA). We used temporal moment analysis of pixels generated from inversion of electrical resistivity data to compress time-lapse data into descriptive statistics (mean arrival time, temporal variance, and temporal skewness) for each pixel. A spatial visualization of these temporal moments in the subsurface at each of five 2-D transects perpendicular to the stream was interpreted to inform transport processes. As baseflow recession progressed we found increasing first arrival times, persistence, mean arrival time, temporal variance, and coefficient of variation, and decreasing skewness. These trends suggest that changes in hydrologic forcing alter the relative influence of transport phenomena (e.g., advection vs. other transport processes such as dispersion) along flowpaths. Spatial coverage obtained from electrical resistivity images allowed for qualitative comparison of spatial patterns in temporal moments both at an individual cross-section as well as between cross sections. We found that geomorphologic controls (e.g., bedrock confinement vs. gravel wedge deposits) resulted in different distributions and metrics of hyporheic transport. Results of this study provide further evidence that hyporheic transport is highly variable both in space and through the baseflow recession period. Geophysical images differentiate advection-dominated flowpaths from those that are more affected by other transport processes (e.g., dispersion, mobile-immobile exchange).
    Keywords: Hyporheic ; Hydrogeophysics ; Solute Transport ; Baseflow Recession ; Electrical Resistivity Imaging ; Temporal Moment ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 7
    Language: English
    In: Ground Water, Jan-Feb, 2013, Vol.51, p.14(15)
    Description: To purchase or authenticate to the full-text of this article, please visit this link: http://onlinelibrary.wiley.com/doi/10.1111/j.1745-6584.2012.00911.x/abstract Byline: Adam S. Ward(1), Michael N. Gooseff(2), Kamini Singha(3) We investigated the role of increasingly well-constrained geologic structures in the subsurface (i.e., subsurface architecture) in predicting streambed flux and hyporheic residence time distribution (RTD) for a headwater stream. Five subsurface realizations with increasingly resolved lithological boundaries were simulated in which model geometries were based on increasing information about flow and transport using soil and geologic maps, surface observations, probing to depth to refusal, seismic refraction, electrical resistivity (ER) imaging of subsurface architecture, and time-lapse ER imaging during a solute tracer study. Particle tracking was used to generate RTDs for each model run. We demonstrate how improved characterization of complex lithological boundaries and calibration of porosity and hydraulic conductivity affect model prediction of hyporheic flow and transport. Models using hydraulic conductivity calibrated using transient ER data yield estimates of streambed flux that are three orders of magnitude larger than uncalibrated models using estimated values for hydraulic conductivity based on values published for nearby hillslopes (10.sub.-4 vs. 10.sub.-7 m.sub.2/s, respectively). Median residence times for uncalibrated and calibrated models are 10.sub.3 and 10.sub.0 h, respectively. Increasingly well-resolved subsurface architectures yield wider hyporheic RTDs, indicative of more complex hyporheic flowpath networks and potentially important to biogeochemical cycling. The use of ER imaging to monitor solute tracers informs subsurface structure not apparent from other techniques, and helps to define transport properties of the subsurface (i.e., hydraulic conductivity). Results of this study demonstrate the value of geophysical measurements to more realistically simulate flow and transport along hyporheic flowpaths. Author Affiliation: (1)Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802. (2)Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802; 814-867-0044; mgooseff@engr.psu.edu (3)Department of Geosciences, The Pennsylvania State University, University Park, PA 16802; 814-863-6649; ksingha@psu.edu Correspondence: (*) Department of Geoscience, The University of Iowa, 36 Trowbridge Hall, Iowa City, IA 52242; 319-353-2079; fax: 319-335-1821; adam-ward@uiowa.edu Received August 2011, accepted January 2012.
    Keywords: Hydrogeology -- Usage ; Architecture -- Usage ; Tracers (Biology) -- Usage ; Green Technology -- Usage ; Porosity -- Usage
    ISSN: 0017-467X
    Source: Cengage Learning, Inc.
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  • 8
    In: Geophysical Journal International, October 2011, Vol.187(1), pp.214-224
    Description: Difference geophysical tomography (e.g. radar, resistivity and seismic) is used increasingly for imaging fluid flow and mass transport associated with natural and engineered hydrologic phenomena, including tracer experiments, remediation and aquifer storage and recovery. Tomographic data are collected over time, inverted and differenced against a background image to produce ‘snapshots’ revealing changes to the system; these snapshots readily provide qualitative information on the location and morphology of plumes of injected tracer, remedial amendment or stored water. In principle, geometric moments (i.e. total mass, centres of mass, spread, etc.) calculated from difference tomograms can provide further quantitative insight into the rates of advection, dispersion and mass transfer; however, recent work has shown that moments calculated from tomograms are commonly biased, as they are strongly affected by the subjective choice of regularization criteria. Conventional approaches to regularization (Tikhonov) and parametrization (image pixels) result in tomograms which are subject to artefacts such as smearing or pixel estimates taking on the sign opposite to that expected for the plume under study. Here, we demonstrate a novel parametrization for imaging plumes associated with hydrologic phenomena. Capitalizing on the mathematical analogy between moment‐based descriptors of plumes and the moment‐based parameters of probability distributions, we design an inverse problem that (1) is overdetermined and computationally efficient because the image is described by only a few parameters, (2) produces tomograms consistent with expected plume behaviour (e.g. changes of one sign relative to the background image), (3) yields parameter estimates that are readily interpreted for plume morphology and offer direct insight into hydrologic processes and (4) requires comparatively few data to achieve reasonable model estimates. We demonstrate the approach in a series of numerical examples based on straight‐ray difference‐attenuation radar monitoring of the transport of an ionic tracer, and show that the methodology outlined here is particularly effective when limited data are available.
    Keywords: Image Processing ; Inverse Theory ; Ground Penetrating Radar ; Hydrogeophysics
    ISSN: 0956-540X
    E-ISSN: 1365-246X
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  • 9
    Language: English
    In: Journal of Contaminant Hydrology, December 2015, Vol.183, pp.29-39
    Description: Time-lapse electrical resistivity (ER) was used to capture the dilution of a seasonal pulse of acid mine drainage (AMD) contamination in the subsurface of a wetland downgradient of the abandoned Pennsylvania mine workings in central Colorado. Data were collected monthly from mid-July to late October of 2013, with an additional dataset collected in June of 2014. Inversion of the ER data shows the development through time of multiple resistive anomalies in the subsurface, which corroborating data suggest are driven by changes in total dissolved solids (TDS) localized in preferential flow pathways. Sensitivity analyses on a synthetic model of the site suggest that the anomalies would need to be at least several meters in diameter to be adequately resolved by the inversions. The existence of preferential flow paths would have a critical impact on the extent of attenuation mechanisms at the site, and their further characterization could be used to parameterize reactive transport models in developing quantitative predictions of remediation strategies.
    Keywords: Acid Mine Drainage ; Electrical Resistivity ; Wetland ; Engineering ; Environmental Sciences ; Geography
    ISSN: 0169-7722
    E-ISSN: 1873-6009
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  • 10
    Language: English
    In: Journal of Applied Geophysics, 2010, Vol.72(1), pp.10-19
    Description: Multiple types of physical heterogeneity have been suggested to explain anomalous solute transport behavior, yet determining exactly what controls transport at a given site is difficult from concentration histories alone. Differences in timing between co-located fluid and bulk apparent electrical conductivity data have previously been used to estimate solute mass transfer rates between mobile and less-mobile domains; here, we consider if this behavior can arise from other types of heterogeneity. Numerical models are used to investigate the electrical signatures associated with large-scale hydraulic conductivity heterogeneity and small-scale dual-domain mass transfer, and address issues regarding the scale of the geophysical measurement. We examine the transport behavior of solutes with and without dual-domain mass transfer, in: 1) a homogeneous medium, 2) a discretely fractured medium, and 3) a hydraulic conductivity field generated with sequential Gaussian simulation. We use the finite-element code COMSOL Multiphysics to construct two-dimensional cross-sectional models and solve the coupled flow, transport, and electrical conduction equations. Our results show that both large-scale heterogeneity and subscale heterogeneity described by dual-domain mass transfer produce a measurable hysteresis between fluid and bulk apparent electrical conductivity, indicating a lag between electrical conductivity changes in the mobile and less-mobile domains of an aquifer, or mass transfer processes, at some scale. The shape and magnitude of the observed hysteresis is controlled by the spatial distribution of hydraulic heterogeneity, mass transfer rate between domains, and the ratio of mobile to immobile porosity. Because the rate of mass transfer is related to the inverse square of a diffusion length scale, our results suggest that the shape of the hysteresis curve is indicative of the length scale over which mass transfer is occurring. We also demonstrate that the difference in sampling scale between fluid conductivity and geophysical measurements is not responsible for the observed hysteresis. We suggest that there is a continuum of hysteresis behavior between fluid and bulk electrical conductivity caused by mass transfer over a range of scales from small-scale heterogeneity to macroscopic heterogeneity. ►Hysteresis between fluid and bulk apparent electrical conductivity can be caused by both large-scale heterogeneity and subscale heterogeneity described by dual-domain mass transfer. ►The shape and magnitude of the observed hysteresis is controlled by the spatial distribution of hydraulic heterogeneity, mass transfer rate between domains, and ratio of mobile to immobile porosity. ►The shape of the hysteresis curve is indicative of the length scale over which mass transfer is occurring.
    Keywords: Solute Transport ; Dual-Domain Mass Transfer ; Electrical Resistivity ; Comsol ; Engineering
    ISSN: 0926-9851
    E-ISSN: 1879-1859
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