Geologically based model of heterogeneous hydraulic conductivity in an alluvial setting   总被引：3，自引：2，他引：1  

Graham E. Fogg  Charles D. Noyes  Steven F. Carle 《Hydrogeology Journal》1998,6(1):131-143

  相似文献   

Numerical analysis of the hydrogeologic controls in a layered coastal aquifer system, Oahu, Hawaii, USA   总被引：3，自引：1，他引：2  

Delwyn S. Oki  William R. Souza  Edward L. Bolke  Glenn R. Bauer 《Hydrogeology Journal》1998,6(2):243-263

 The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units. Received, October 1996 Revised, August 1997 Accepted, September 1997  相似文献   

Chlorine-36 and the initial value problem     

Stanley N. Davis  DeWayne Cecil  Marek Zreda  Pankaj Sharma 《Hydrogeology Journal》1998,6(1):104-114

 Chlorine-36 is a radionuclide with a half-life of 3.01×10⁵a. Most ³⁶Cl in the hydrosphere originates from cosmic radiation interacting with atmospheric gases. Large amounts were also produced by testing thermonuclear devices during 1952–58. Because the monovalent anion, chloride, is the most common form of chlorine found in the hydrosphere and because it is extremely mobile in aqueous systems, analyses of both total Cl^– as well as ³⁶Cl have been important in numerous hydrologic studies. In almost all applications of ³⁶Cl, a knowledge of the initial, or pre-anthropogenic, levels of ³⁶Cl is useful, as well as essential in some cases. Standard approaches to the determination of initial values have been to: (a) calculate the theoretical cosmogenic production and fallout, which varies according to latitude; (b) measure ³⁶Cl in present-day precipitation and assume that anthropogenic components can be neglected; (c) assume that shallow groundwater retains a record of the initial concentration; (d) extract ³⁶Cl from vertical depth profiles in desert soils; (e) recover ³⁶Cl from cores of glacial ice; and (f) calculate subsurface production of ³⁶Cl for water that has been isolated from the atmosphere for more than one million years. The initial value from soil profiles and ice cores is taken as the value that occurs directly below the depth of the easily defined bomb peak. All six methods have serious weaknesses. Complicating factors include ³⁶Cl concentrations not related to cosmogenic sources, changes in cosmogenic production with time, mixed sources of chloride in groundwater, melting and refreezing of water in glaciers, and seasonal groundwater recharge that does not contain average year-long concentrations of ³⁶Cl. Received, December 1996 · Revised, August 1997 · Accepted, August 1997  相似文献   

The migration, dissolution, and fate of chlorinated solvents in the urbanized alluvial valleys of the southwestern USA     

R. E. Jackson 《Hydrogeology Journal》1998,6(1):144-155

 The migration, dissolution, and subsequent fate of spilled chlorinated solvents in the urban alluvial valleys of the southwestern U.S. appear to be governed by a unique set of hydrogeologic and geochemical processes occurring within terrigeneous clastic depositional systems. The alluvial and lacustrine fill of the basins, the trapping of solvents in fine-grained sediments beneath the urbanized valley centers, the oxic conditions typical of the deeper alluvium, and the contaminant-transport patterns produced by large-scale basin pumping combine to produce long aqueous-phase plumes derived from the dissolution of trapped chlorinated solvents. Although of limited aqueous solubility, these dense solvents are sufficiently mobile and soluble in the southwestern alluvial valleys to have produced aqueous plumes that have migrated several kilometers through the deeper alluvium and have contaminated valuable water-supply well fields in California, Arizona, and New Mexico. The typical length of these plumes and the presence of oxic groundwater indicate that it is unlikely that natural attenuation will be a practical remedial option in the southwestern alluvial valleys or in other alluvial systems in which similar hydrogeologic and geochemical conditions exist. Received, December 1996 · Revised, October 1997 · Accepted, November 1997  相似文献   

Mercury,Trace Elements and Organic Constituents in Atmospheric Fine Particulate Matter,Shenandoah National Park,Virginia, USA: A Combined Approach to Sampling and Analysis     

Allan Kolker  Mark A. Engle  William H. Orem  Joseph E. Bunnell  Harry E. Lerch  David P. Krabbenhoft  Mark L Olson  Jamey D. McCord 《Geostandards and Geoanalytical Research》2008,32(3):279-293

Compliance with U.S. air quality regulatory standards for atmospheric fine particulate matter (PM_2.5) is based on meeting average 24 hour (35 μ m^?3) and yearly (15 μg m^?3) mass‐per‐unit‐volume limits, regardless of PM_2.5 composition. Whereas this presents a workable regulatory framework, information on particle composition is needed to assess the fate and transport of PM_2.5 and determine potential environmental/human health impacts. To address these important non‐regulatory issues an integrated approach is generally used that includes (1) field sampling of atmospheric particulate matter on filter media, using a size‐limiting cyclone, or with no particle‐size limitation; and (2) chemical extraction of exposed filters and analysis of separate particulate‐bound fractions for total mercury, trace elements and organic constituents, utilising different USGS laboratories optimised for quantitative analysis of these substances. This combination of sampling and analysis allowed for a more detailed interpretation of PM_2.5 sources and potential effects, compared to measurements of PM_2.5 abundance alone. Results obtained using this combined approach are presented for a 2006 air sampling campaign in Shenandoah National Park (Virginia, USA) to assess sources of atmospheric contaminants and their potential impact on air quality in the Park. PM_2.5 was collected at two sampling sites (Big Meadows and Pinnacles) separated by 13.6 km. At both sites, element concentrations in PM₂₅ were low, consistent with remote or rural locations. However, element/Zr crustal abundance enrichment factors greater than 10, indicating anthropogenic input, were found for Hg, Se, S, Sb, Cd, Pb, Mo, Zn and Cu, listed in decreasing order of enrichment. Principal component analysis showed that four element associations accounted for 84% of the PM_2.5 trace element variation; these associations are interpreted to represent: (1) crustal sources (Al, REE); (2) coal combustion (Se, Sb), (3) metal production and/or mobile sources (Mo, Cd, Pb, Cu, Zn) and (4) a transient marine source (Sr, Mg). Concentrations of Hg in PM_2.5 at background levels in the single pg m^?3 were shown by collection and analysis of PM_2.5 on filters and by an automated speciation analyser set up at the Big Meadows air quality site. The speciation unit revealed periodic elevation of reactive gaseous mercury (RGM) that co‐occurred with peaks in SO₂, indicating an anthropogenic source. GC/MS total ion current chromatograms for the two sites were quite similar indicating that organic signatures were regional in extent and/or that the same compounds were present locally at each site. Calculated carbon preference index values for n‐alkanes indicated that plant waxes rather than anthropogenic sources, were the dominant alkane source. Polycyclic aromatic hydrocarbons (PAHs) were detected, with a predominance of non‐alkylated, and higher molecular weight PAHs in this fraction, suggestive of a combustion source (fossil fuel or forest fires).  相似文献   

Reactions and reaction rates in the regional aquifer beneath the Pajarito Plateau,north-central New Mexico,USA     

Anne G. Hereford  Elizabeth H. Keating  George D. GuthrieJr  Chen Zhu 《Environmental Geology》2007,52(5):965-977

Reactions and reaction rates within aquifers are fundamental components of critical hydrological processes. However, reactions simulated in laboratory experiments typically demonstrate rates that are much faster than those observed in the field. Therefore, it is necessary to conduct more reaction rate analyses in natural settings. This study of geochemical reactions in the regional aquifer in the Pajarito Plateau near Los Alamos, New Mexico combines modeling with petrographic assessment to further knowledge and understanding of complex natural hydrologic systems. Groundwater geochemistry shows marked evolution along assumed flow paths. The flow path chosen for this study was evaluated using inverse mass balance modeling to calculate the mass transfer. X-ray diffraction and field emission gun scanning electron microscopy were used to identify possible reactants and products. Considering the mineralogy of the aquifer and saturation indices for the regional water refined initial interpretations. Calculations yielded dissolution rates for plagioclase on the order of 10⁻¹⁵ mol s⁻¹ m⁻² and for K-feldspar on the order of 10⁻¹⁷ mol s⁻¹ m⁻², orders of magnitude slower than laboratory rates. While these rates agree with other aquifer studies, they must be considered in the light of the uncertainty associated with geometric surface area estimates, ¹⁴C ages, and aquifer properties.  相似文献   

Impact of urbanization on storm response of White Rock Creek,Dallas, TX   总被引：1，自引：0，他引：1  

Julie?Vicars-Groening  Harry?F.?L.?WilliamsEmail author 《Environmental Geology》2007,51(7):1263-1269

This study documents hydrological changes resulting from urbanization of the upper sub-basin of White Rock Creek watershed in Collin and Dallas counties, Texas. The 172-km² watershed was transformed from 87% rural in 1961 to 95% urban in 2002, following construction of the Dallas suburbs of Richardson, Addison, Plano and Frisco. The objective of the study was to investigate changes in the storm response of White Rock Creek in terms of peak storm flow, storm flow volume and lag time. The approach employed to compare pre- and post-urbanization hydrology was to develop average unit hydrographs for each time period and use them to generate the creek’s storm flow response to a set of six hypothetical precipitation events. The results suggest that substantial hydrological changes have occurred. The average infiltration capacity of the watershed was reduced by about 60% so that storm flow was generated at lower precipitation intensities in the post-urbanization period. Storm flow peak discharge and volume were more than doubled for a hypothetical 10-year precipitation event. Average lag time was about 49 min shorter in the post-urbanization period. Urbanization has significantly impacted the storm response of the creek and increased the potential for flooding. It is anticipated that similar hydrological changes will occur in other rapidly urbanizing watersheds in the Dallas-Fort Worth Metropolitan region. Watershed managers should take likely changes in storm response into account when planning future storm water management needs.  相似文献   

Enhancing environmental quality in the United States by linking biomass energy consumption and load capacity factor     

《地学前缘(英文版)》2023,14(3):101531

This study analyzes the impact of biomass energy, financial development, and economic growth on environmental quality using the novel Fourier autoregressive distributed lag (ARDL) approach on annual data for the period 1965–2018 in the United States (USA). The study analyzes the impact of related variables on the load capacity factor (LCF) as well as on indicators of environmental degradation such as carbon dioxide emissions and ecological footprint. The LCF is one of the most comprehensive environmental indicators to date, encompassing both biocapacity and ecological footprint. In this regard, this study contributes to the environmental economics literature by examining, for the first time, the impact of biomass energy on the LCF. The results of the cointegration test show that there is only a long-run relationship between the LCF and the independent variables. According to the Fourier ARDL results, biomass energy improves the environmental quality, while financial development has no effect on the LCF. Moreover, the increase in per capita income reduces the LCF. Furthermore, since the income elasticity is larger in the long run than in the short-run, the environmental Kuznets curve is validated. Therefore, the United States government should encourage the use of biomass and investment in this form of energy.  相似文献   

Relative importance of multiple environmental variables in structuring benthic macroinfaunal assemblages in chronically metal-polluted salt marshes   总被引：1，自引：0，他引：1  

Daisuke Goto  William G. Wallace 《Marine pollution bulletin》2010,60(3):363-375

In this study, we assessed importance of sediment-associated trace metals in structuring benthic macroinfaunal assemblages along multiple environmental gradients in chronically polluted salt marshes of the Arthur Kill - AK (New York, USA). More than 90% of benthic macroinfaunal communities at the northern AK sites consisted of a considerably large number of only a few polychaete and oligochaete species. Approximately 70% of among-site variances in abundance and biomass of benthic macroinfaunal communities was strongly associated with a few environmental variables; only sediment-associated mercury consistently contributed to a significant proportion of the explained variances in species composition along natural environmental gradients (e.g., salinity). Although sediment-associated copper, lead, and zinc were substantially elevated at some of the AK sites, their ecological impacts on benthic macroinfaunal communities appeared to be negligible. These findings suggest that cumulative metal-specific impacts may have played an important role in structuring benthic macroinfaunal communities in chronically polluted AK ecosystems.  相似文献   

Sediment transport on the Palos Verdes shelf,California     

Bénédicte Ferré  Christopher R. Sherwood  Patricia L. Wiberg 《Continental Shelf Research》2010

Sediment transport and the potential for erosion or deposition have been investigated on the Palos Verdes (PV) and San Pedro shelves in southern California to help assess the fate of an effluent-affected deposit contaminated with DDT and PCBs. Bottom boundary layer measurements at two 60-m sites in spring 2004 were used to set model parameters and evaluate a one-dimensional (vertical) model of local, steady-state resuspension, and suspended-sediment transport. The model demonstrated skill (Brier scores up to 0.75) reproducing the magnitudes of bottom shear stress, current speeds, and suspended-sediment concentrations measured during an April transport event, but the model tended to underpredict observed rotation in the bottom-boundary layer, possibly because the model did not account for the effects of temperature–salinity stratification. The model was run with wave input estimated from a nearby buoy and current input from four to six years of measurements at thirteen sites on the 35- and 65-m isobaths on the PV and San Pedro shelves. Sediment characteristics and erodibility were based on gentle wet-sieve analysis and erosion-chamber measurements. Modeled flow and sediment transport were mostly alongshelf toward the northwest on the PV shelf with a significant offshore component. The 95th percentile of bottom shear stresses ranged from 0.09 to 0.16 Pa at the 65-m sites, and the lowest values were in the middle of the PV shelf, near the Whites Point sewage outfalls where the effluent-affected layer is thickest. Long-term mean transport rates varied from 0.9 to 4.8 metric tons m⁻¹ yr⁻¹ along the 65-m isobaths on the PV shelf, and were much higher at the 35-m sites. Gradients in modeled alongshore transport rates suggest that, in the absence of a supply of sediment from the outfalls or PV coast, erosion at rates of ∼0.2 mm yr⁻¹ might occur in the region southeast of the outfalls. These rates are small compared to some estimates of background natural sedimentation rates (∼5 mm yr⁻¹), but do not preclude higher localized rates near abrupt transitions in sediment characteristics. However, low particle settling velocities and strong currents result in transport length-scales that are long relative to the narrow width of the PV shelf, which combined with the significant offshore component in transport, means that transport of resuspended sediment towards deep water is as likely as transport along the axis of the effluent-affected deposit.  相似文献