Other Types of Contamination     

Evan K. Nyer  Eric P. Carman  Raymond M. Flynn 《Ground Water Monitoring & Remediation》1999,19(2):61-64

"Hazardous levels of methane in the subsurface occur at numerous locations across the United States."  相似文献   

Identification and mapping of riverbed sediment facies in the Columbia River through integration of field observations and numerical simulations     

Zhangshuan Hou  Timothy D. Scheibe  Christopher J. Murray  William A. Perkins  Evan V. Arntzen  Huiying Ren  Robert D. Mackley  Marshall C. Richmond 《水文研究》2019,33(8):1245-1259

In the Hanford Reach of the Columbia River, a thin layer of recent alluvium overlies the sedimentary formations that comprise the unconfined groundwater aquifer. Experimental and modelling studies have demonstrated that this alluvial layer exerts significant control on the exchange of groundwater and surface water (hydrologic exchange flux), and is associated with elevated levels of biogeochemical activity. This layer is also observed to be strongly heterogeneous, and quantifying the spatial distribution of properties over the range of scales of interest is challenging. Facies are elements of a sediment classification scheme that groups complex geologic materials into a set of discrete classes according to distinguishing features. Facies classifications have been used as a framework for assigning heterogeneous material properties to grid cells of numerical models of flow and reactive transport in subsurface media. The usefulness of such an approach hinges on being able to relate facies to quantitative properties needed for flow and reactive transport modelling, and on being able to map facies over the domain of interest using readily available information. Although aquifer facies have been used in various modelling contexts, application of this concept to riverbed sediments is relatively new. Here, we describe an approach for categorizing and mapping recent alluvial (riverbed) sediments based on the integration of diverse observations with numerical simulations of river hydrodynamics. The facies have distinct distributions of sediment texture that correspond to variations in hydraulic properties, and therefore provide a useful framework for assigning heterogeneous properties in numerical simulations of hydrologic exchange flows and biogeochemical processes.  相似文献   

Petroi Metabasalt: Alkaline within‐plate mafic rocks from the Nambucca Slate Belt,northeastern New South Wales     

Deepanker Asthana  Evan C. Leitch 《Australian Journal of Earth Sciences》2013,60(3):261-277

The Petroi Metabasalt comprises approximately 2000 m of massive and pillowed metabasalt flows, breccias, and metadolerite sills that overlie and are intercalated with Early Permian epiclastic rocks of the Nambucca Slate Belt. Both the basaltic rocks and associated sedimentary material were multiply deformed and metamorphosed to pumpellyite‐actinolite facies grade at about 255 Ma. Metamorphism and earlier sea‐floor alteration of these mafic rocks have led to hydration, carbonation and oxidation and considerable redistribution of the major elements and the more labile traces, notably Rb, Ba and Sr. However, abundances of TiO₂, the high field strength trace elements, Ni, Cr and V, the light rare earths and yttrium are interpretable as being the largely unmodified magmatic abundances of mildly alkaline within‐plate basalts. This interpretation is supported by the composition of relic Ca‐rich pyroxenes in the metadolerites which fall in the fields of mildly alkaline basalts. The field relationships, age and composition of these rocks suggest either eruption on oceanic crust covered by a thick sequence of epiclastic rocks and subsequent incorporation into an accretionary subduction complex, or generation during rifting of the eastern part of the New England Fold Belt and accumulation, together with the associated sedimentary rocks, in a graben. The chemical and mineral characteristics of the igneous rocks indicate that the volcanism was not related to magmatic arc activity, and their presence demonstrates the rocks of the Nambucca Slate Belt are neither fore‐arc basin nor slope‐basin deposits.  相似文献   

Kernel distributed residual function in a revised multiple order autoregressive model and its applications in hydrology     

Nesa Ilich  Amr Gharib  Evan G. R. Davies 《水文科学杂志》2013,58(12):1745-1758

ABSTRACT

This paper describes a new approach to fill missing data in hydrologic series. Based on a multiple-order autoregressive model, our algorithm represents the random term with an empirical distribution function that includes different parameters for the low, medium and high ranges of the modelled hydrologic variable. The algorithm involves a corrective mechanism that preserves the original statistical distribution of the series that are filled, while also eliminating the possibility of obtaining negative values for low flows. The algorithm requires multiple correlated hydrologic time series with sufficient data to permit accurate calculation of their statistical properties. It ensures that both the original statistical dependence among the data series and the statistical distribution functions will be preserved after the missing data had been filled. The model has been tested using 15 streamflow series in the Upper Bow River watershed in Alberta, Canada.  相似文献   

Legacy sediment stored in sinkholes: a case study of three urban watersheds in Tennessee,United States of America     

Evan A. Hart 《自然地理学》2014,35(6):514-531

As closed topographic depressions, sinkholes effectively divide karst regions into a series of subwatersheds, where swallets within each sinkhole define the downstream end of each subwatershed. Water and sediment are temporarily stored in sinkholes before continuing to underground streams. While pathways and travel times of water in karst terrain are commonly found using tracing techniques, such techniques do not provide information about the movement and travel time of sediment through these systems. This paper reviews the literature regarding sediment storage within sinkholes and presents a case study, the objective of which is to estimate the magnitude and timing of sediment deposition within three sinkholes in an urbanized area in Tennessee, United States of America. Sedimentation rates in sinkholes were estimated based on age determination of cultural artifacts (buried trash and coal fragments) and by ¹⁴C dating. For the three study sinkholes, minimum deposition rates (maximum residence times) were 15?cm?yr ^?1(6 yrs), 1.5?cm?yr ^?1(81?yrs), and 0.2?cm?yr^?1(640 yrs). The analysis revealed that sinkholes undergo fill and flush cycles at different timescales caused by changes in upland sediment supply and morphologic changes at swallet openings. Sinkholes that lack swallet openings, or with swallets that have become blocked by debris, are effectively disconnected from master streams with regard to sediment. Sediment stored in sinkholes may be released downstream when swallet conditions change.  相似文献   

Regional and global projections of twenty-first century glacier mass changes in response to climate scenarios from global climate models   总被引：1，自引：0，他引：1  

Valentina Radić  Andrew Bliss  A. Cody Beedlow  Regine Hock  Evan Miles  J. Graham Cogley 《Climate Dynamics》2014,42(1-2):37-58

A large component of present-day sea-level rise is due to the melt of glaciers other than the ice sheets. Recent projections of their contribution to global sea-level rise for the twenty-first century range between 70 and 180 mm, but bear significant uncertainty due to poor glacier inventory and lack of hypsometric data. Here, we aim to update the projections and improve quantification of their uncertainties by using a recently released global inventory containing outlines of almost every glacier in the world. We model volume change for each glacier in response to transient spatially-differentiated temperature and precipitation projections from 14 global climate models with two emission scenarios (RCP4.5 and RCP8.5) prepared for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. The multi-model mean suggests sea-level rise of 155 ± 41 mm (RCP4.5) and 216 ± 44 mm (RCP8.5) over the period 2006–2100, reducing the current global glacier volume by 29 or 41 %. The largest contributors to projected global volume loss are the glaciers in the Canadian and Russian Arctic, Alaska, and glaciers peripheral to the Antarctic and Greenland ice sheets. Although small contributors to global volume loss, glaciers in Central Europe, low-latitude South America, Caucasus, North Asia, and Western Canada and US are projected to lose more than 80 % of their volume by 2100. However, large uncertainties in the projections remain due to the choice of global climate model and emission scenario. With a series of sensitivity tests we quantify additional uncertainties due to the calibration of our model with sparsely observed glacier mass changes. This gives an upper bound for the uncertainty range of ±84 mm sea-level rise by 2100 for each projection.  相似文献   

Regional and seasonal intercomparison of CMIP3 and CMIP5 climate model ensembles for temperature and precipitation   总被引：2，自引：1，他引：1  

Devashish Kumar  Evan Kodra  Auroop R. Ganguly 《Climate Dynamics》2014,43(9-10):2491-2518

Regional and seasonal temperature and precipitation over land are compared across two generations of global climate model ensembles, specifically, CMIP5 and CMIP3, through historical twentieth century skills and multi-model agreement, and twenty first century projections. A suite of diagnostic and performance metrics, ranging from spatial bias or model-consensus maps and aggregate time series plots, to measures of equivalence between probability density functions and Taylor diagrams, are used for the intercomparisons. Pairwise and multi-model ensemble comparisons were performed for 11 models, which were selected based on data availability and resolutions. Results suggest little change in the central tendency or variability or uncertainty of historical skills or consensus across the two generations of models. However, there are regions and seasons, at different levels of aggregation, where significant changes, performance improvements, and even degradation in skills, are suggested. The insights may provide directions for further improvements in next generations of climate models, and in the meantime, help inform adaptation and policy.  相似文献   

U–Pb geochronology and petrology of the late Paleozoic Gil Marquez pluton: magmatism in the Variscan suture zone,southern Iberia,during continental collision and the amalgamation of Pangea     

Evan R. Gladney  James A. Braid  J. Brendan Murphy  Cecilio Quesada  Christopher R. M. McFarlane 《International Journal of Earth Sciences》2014,103(5):1433-1451

The origin of plutonic complexes that stitch suture zones developed during collision is not well understood. In southern Iberia, the Pulo du Lobo suture zone (PDLZ) is intruded by the syn- to postcollisional Gil Marquez pluton (GMP), thought to be part of the Sierra Norte Batholith. U–Pb (LA-ICPMS, zircon) data on various phases of the GMP yield from oldest to youngest: (1) a 354.4 ± 7.6 Ma unfoliated gabbro; (2) a 345.6 ± 2.5 Ma foliated intermediate phase; (3) a 346.5 ± 5.4 Ma unfoliated porphyritic granite; (4) a 335.1 ± 2.8 Ma unfoliated biotite granite. This sequence is consistent with cross-cutting relationships observed in the field. The range in ages is consistent with interpretations that the GMP is part of the composite (ca. 350–308 Ma) SNB. Inherited ages preserved in the GMP intermediate and felsic phases indicate that its magmas traversed through South Portuguese Zone and PDLZ crust during emplacement. The ca. 345 Ma emplacement of the late kinematic foliated intermediate phase constrains the age of late-stage strike slip deformation within the PDLZ, and the lack of a foliation in the older gabbro indicates that is was not proximal to a shear zone neither at the time of emplacement, nor during its subsequent history. The unfoliated porphyritic granite and unfoliated biotite granite cut the foliation of the intermediate phase indicating emplacement during the waning stages of collision, while the ca. 335 Ma biotite granite intrudes the Santa Ira Flysch, thereby providing a tight constraint for the latest stage of deformation in the PDLZ.  相似文献   

Changing the Environment vs. Molecule-to-Molecule Reaction     

Evan K. Nyer 《Ground Water Monitoring & Remediation》2002,22(2):38-42

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Temperature correlations in a finite universe     

Evan Scannapieco  Janna Levin  Joseph Silk 《Monthly notices of the Royal Astronomical Society》1999,303(4):797-800

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