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121.
We use reactive transport modeling to better understand the kinetics of chemical weathering in the Cretaceous Middendorf aquifer of South Carolina, USA, and the relationship of this process to subsurface microbial activity. We constructed a model accounting for the kinetics of mineral dissolution and precipitation, ion exchange, and the CO2 and bicarbonate produced by iron reducing and sulfate reducing bacteria in the aquifer. We then fit the model to observed trends in the chemical composition of groundwater along the aquifer by adjusting the rate constants for the kinetic reactions considered. The modeling portrays weathering in the Middendorf as a slow process by which groundwater gradually reacts toward equilibrium with minerals in the aquifer. The rate constants predicted are 6 to 7 orders of magnitude smaller than measured in laboratory experiments and 3 to 4 orders of magnitude less than those inferred from weathering rates in soils. The rate constants are smaller even than expected by projecting observed trends with the duration of weathering to the geologic age of the Middendorf. Weathering is driven largely by biological activity: about half the acid consumed is CO2 derived from the recharge area, and about half is supplied by iron reducing bacteria in the aquifer; only about 1% of the acid is of atmospheric origin, from CO2 dissolved in rainwater. 相似文献
122.
Alison Olcott Marshall Frank A. Corsetti Alex L. Sessions Craig P. Marshall 《Organic Geochemistry》2009,40(11):1115-1123
Extractable biomarkers can help elucidate the environment and biota of ancient glaciations, although the method must be applied with care, as glacial sediments have a potential for incorporation of older detrital carbon. In Phanerozoic glacial sediments, the distinct elemental, molecular and isotopic compositions of the terrestrial and marine biomass allow discrimination between primary marine and redeposited terrestrial organic matter. However, as the Proterozoic biosphere was largely microbial and marine, biomarker and isotopic analyses are insufficient for distinguishing primary organic matter from secondary reworked organic matter. Here, we report the combined application of Raman spectroscopy and biomarker analysis to Precambrian glacial sediments, which, together, allows discrimination between mixed pools of organic carbon and provides a promising new approach for rapidly screening Precambrian sediments for immature organic matter amenable to biomarker analysis. 相似文献
123.
Adam C. Landon Maarten H. Jacobs Craig A. Miller Jerry J. Vaske Brent D. Williams 《社会与自然资源》2020,33(5):574-593
AbstractIncreasing wolf populations are a concern for wildlife managers in the Midwestern U.S. Understanding the psychological mechanisms that contribute to public perceptions of risk will enable development of strategies that seek to mitigate these risks, and suggest where outreach efforts may facilitate acceptance of wolves. We examined the psychological factors that influence Illinois residents’ perceived risks from wolves. We hypothesized that individuals’ perceived risks from wolves were a function of their attitudes toward wolves, negative affect toward wolves, and basic beliefs about wildlife. Data were obtained from a survey of the Illinois public (n?=?784). Negative affect and attitudes toward wolves were direct predictors of perceived risks. Basic beliefs predicted attitudes and negative affect toward wolves. Negative affect predicted attitudes. Basic beliefs had direct and indirect effects on perceived risks. 相似文献
124.
Hamed Ketabchi Davood Mahmoodzadeh Behzad Ataie‐Ashtiani Adrian D. Werner Craig T. Simmons 《水文研究》2014,28(24):5938-5953
The fresh groundwater lenses (FGLs) of small islands can be highly vulnerable to climate change impacts, including sea‐level rise (SLR). Many real cases of atoll or sandy islands involve two‐layer hydrogeological conceptualizations. In this paper, the influential factors that affect FGLs in two‐layer small islands subject to SLR are investigated. An analytical solution describing FGLs in circular islands, composed of two geological layers, is developed for the simplified case of steady‐state and sharp‐interface conditions. An application of the developed model is demonstrated to estimate the FGL thickness of some real‐world islands by comparison with existing FGL thickness data. Furthermore, numerical modelling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases. Sensitivity analyses are used to assess the importance of land‐surface inundation caused by SLR, relative to other parameters (i.e. thickness of aquifer layers, hydraulic conductivity, recharge rate and land‐surface slope) that influence the FGL. Dimensionless parameters are used to generalize the findings. The results demonstrate that land‐surface inundation has a considerable impact on a FGL influenced by SLR, as expected, although the FGL volume is more sensitive to recharge, aquifer thickness and hydraulic conductivity than SLR impacts, considering typical parameter ranges. The methodology presented in this study provides water resource managers with a rapid‐assessment tool for evaluating the likely impacts of SLR and accompanying LSI on FGLs. 相似文献
125.
The 150 m thick late Miocene Graveyard Point sill (GPS) is situated at the Idaho-Oregon border near the southwestern edge
of the western Snake River Plain. It records from bottom to top continuous fractional crystallization of a tholeiitic parent
magma (lower chilled border, FeO/(FeO+MgO) = 0.59, Ni = 90 ppm) towards granophyres (late pods and dikes, FeO/(FeO+MgO) = 0.98,
78 wt% SiO2 3.5 wt% K2O, <4 ppm Ni) showing a typical trend of Fe and P enrichment. Fractionating minerals are olivine (Fo79-Fo2), augite (X
Fe = 0.18−0.95), feldspars (An80Or1-An1Or62), Fe-Ti oxides (Ti-rich magnetite and ilmenite), apatite and in two samples super-calcic pigeonite (Wo18–28 Fs41–54). The granophyres may bear some quartz. Compositionally zoned minerals record a large interval of the fractionation process
in every single sample, but this interval changes with stratigraphic height. In super-calcic pigeonite-bearing samples, olivine
is scarce or lacking and because super-calcic pigeonite occurs as characteristic overgrowths on augite, its formation is interpreted
to be related to the schematic reaction: augite + olivine (component in melt) + SiO2 (in melt) = pigeonite, that defines the cotectic between augite and pigeonite in olivine-saturated basaltic systems. Line
measurements with the electron microprobe reveal that the transition from augite to super-calcic pigeonite is continuous.
However, some crystals show an abrupt “reversal” towards augite after super-calcic pigeonite growth. Two processes compete
with each other in the GPS: fractional crystallization of the bulk liquid (the bulk melt separates from solids and interstitial
liquids in the solidification front) and fractional crystallization of interstitial melt in the solidification front itself.
Interplay between those two processes is proposed to account for the observed variations in mineral chemistry and mineral
textures.
Received: 25 November 1998 / Accepted: 14 June 1999 相似文献
126.
127.
A simple and fast treatment of hydrogeologic features with irregularly shaped boundaries in two‐dimensional analytic element groundwater flow models is presented. The star domain shapes of the features are restricted to closed shapes represented as smooth and continuous single‐valued functions of distance from a focus point, . The element can be used to treat a variety of boundary and continuity conditions, including those of irregularly shaped lakes or heterogeneities in hydraulic conductivity. The new element is demonstrated via some simple illustrative test cases and shown to be efficient, accurate, and much simpler to implement than existing solutions for irregular shapes. 相似文献
128.
Grain Size Analysis and Permeametry for Estimating Hydraulic Conductivity in Engineered Porous Media
Grain size analysis and permeametry are common methods for estimating the hydraulic conductivity (K) of porous media. It is well known that these methods have limited accuracy when they are used to characterize natural sediments. However, hydrogeological research has increasingly introduced technologies dependent on engineered porous media that may be less problematic because complex geologic structures are eliminated in the lab and field-scale packings. The recently introduced Horizontal Reactive Media Treatment Wells (HRX® Wells), for in situ, passive remediation of groundwater is one such example. The HRX Well passively collects groundwater and directs it through a horizontal pipe packed with an engineered porous medium. In this project, grain size analysis was conducted for sand and sand-iron mixtures to estimate K using the 16 algorithms provided in the HydrogeoSieveXL2.3.2 software. The results were compared to K determined by permeametry and a field-scale column, 30 cm long and 25 cm in diameter, representing an HRX Well. The best comparability of K estimates from grain size analysis and permeametry were obtained using the USBR, Slichter, and Shepherd K estimation methods. These also showed good agreement between lab-scale and field-scale K estimations, with reproducibility within the range ±20%. This study shows that laboratory K estimations can be representative across various relevant scales, including the field-scale, for engineered porous media. This finding extends to filter packs, and other engineered porous media design methods by emphasizing and demonstrating one case of accuracy in lab-scale permeability estimation for field-scale implementations. 相似文献
129.
Blossom N. Nzeribe Wen Li Michelle Crimi Guangming Yao Craig E. Divine Jeff McDonough Jack Wang 《Ground Water Monitoring & Remediation》2020,40(3):30-41
This study is focused on a passive treatment system known as the horizontal reactive treatment well (HRX Well®) installed parallel to groundwater flow, which operates on the principle of flow focusing that results from the hydraulic conductivity (K) ratio of the well and aquifer media. Passive flow and capture in the HRX Well are described by simplified equations adapted from Darcy's Law. A field pilot-scale study (PSS) and numerical simulations using a finite element method (FEM) were conducted to verify the HRX Well concept and test the validity of the HRX Well-simplified equations. The hydraulic performance results from both studies were observed to be within a close agreement to the simplified equations and their hydraulic capture width approximately five times greater than the well diameter (0.20 m). Key parameters affecting capture included the aquifer thickness, well diameter, and permeability ratio of the HRX Well treatment media and aquifer material. During pilot testing, the HRX Well captured 39% of flow while representing 0.5% of the test pit cross-sectional volume, indicating that the well captures a substantial amount of surrounding groundwater. While uncertainty in the aquifer and well properties (porosity, K, well losses), including the effects of boundary conditions, may have caused minor differences in the results, data from this study indicate that the simplified equations are valid for the conceptual design of a field study. A full-scale HRX Well was installed at Site SS003 at Vanderberg Air Force Base, California, in July/August 2018 based on outcomes from this study. 相似文献
130.
Craig E. Divine Jesse Wright Michelle Crimi J.F. Devlin Michael Lubrecht Jack Wang Jeff McDonough Michael Kladias Jesse Hinkle Allison Cormican Trevor Osorno Blossom N. Nzeribe Fiona Laramay Daniel Ombalski Kathleen Gerber Hunter Anderson 《Ground Water Monitoring & Remediation》2020,40(3):42-54
The horizontal reactive media treatment well (HRX Well®) uses directionally drilled horizontal wells filled with a treatment media to induce flow-focusing behavior created by the well-to-aquifer permeability contrast to passively capture proportionally large volumes of groundwater. Groundwater is treated in situ as it flows through the HRX Well and downgradient portions of the aquifer are cleaned via elution as these zones are flushed with clean water discharging from the HRX Well. The HRX Well concept is particularly well suited for sites where long-term mass discharge control is a primary performance objective. This concept is appropriate for recalcitrant and difficult-to-treat constituents, including chlorinated solvents, per- and polyfluoroalkyl substances (PFAS), 1,4-dioxane, and metals. A full-scale HRX Well was installed and operated to treat trichloroethene (TCE) with zero valent iron (ZVI). The model-predicted enhanced flow through the HRX Well (compared to the flow in and equivalent cross-sectional area orthogonal to flow in the natural formation before HRX Well installation) and treatment zone width was consistent with flows and widths estimated independently by point velocity probe (PVP) testing, HRX Well tracer testing, and observed treatment in downgradient monitoring wells. The actual average capture zone width was estimated to be between 45 and 69 feet. Total TCE mass discharge reduction was maintained through the duration of the performance monitoring period and exceeded 99.99% (%). Decreases in TCE concentrations were observed at all four downgradient monitoring wells within the treatment zone (ranging from 50 to 74% at day 436), and the first arrival of treated water was consistent with model predictions. The field demonstration confirmed the HRX Well technology is best suited for long-term mass discharge control, can be installed under active infrastructure, requires limited ongoing operation and maintenance, and has low life cycle energy and water requirements. 相似文献