Spatial interpolation methods for nonstationary plume data   总被引：1，自引：0，他引：1  

Reed PM  Ellsworth TR  Minsker BS 《Ground water》2004,42(2):190-202

Plume interpolation consists of estimating contaminant concentrations at unsampled locations using the available contaminant data surrounding those locations. The goal of ground water plume interpolation is to maximize the accuracy in estimating the spatial distribution of the contaminant plume given the data limitations associated with sparse monitoring networks with irregular geometries. Beyond data limitations, contaminant plume interpolation is a difficult task because contaminant concentration fields are highly heterogeneous, anisotropic, and nonstationary phenomena. This study provides a comprehensive performance analysis of six interpolation methods for scatter-point concentration data, ranging in complexity from intrinsic kriging based on intrinsic random function theory to a traditional implementation of inverse-distance weighting. High resolution simulation data of perchloroethylene (PCE) contamination in a highly heterogeneous alluvial aquifer were used to generate three test cases, which vary in the size and complexity of their contaminant plumes as well as the number of data available to support interpolation. Overall, the variability of PCE samples and preferential sampling controlled how well each of the interpolation schemes performed. Quantile kriging was the most robust of the interpolation methods, showing the least bias from both of these factors. This study provides guidance to practitioners balancing opposing theoretical perspectives, ease-of-implementation, and effectiveness when choosing a plume interpolation method.  相似文献   

Predation by the black-clawed mud crab,<Emphasis Type="Italic">Panopeus herbstii</Emphasis>, in Mid-Atlantic salt marshes: Further evidence for top-down control of marsh grass production     

Brian?Reed?SillimanEmail author  Craig?A.?Layman  Kane?Geyer  J.?C.?Zieman 《Estuaries and Coasts》2004,27(2):188-196

Although top-down control of plant growth has been shown in a variety of marine systems, it is widely thought to be unimportant in salt marshes. Recent caging experiments in Virginia and Georgia have challenged this notion and shown that the dominant marsh grazer (the periwinkle,Littoraria irrorata) not only suppresses plant growth, but can denude marsh substrate at high densities. In these same marshes, our field observations suggest that the black-clawed mud crab,Panopeus herbstii, is an abundant and potentially important top-down determinant of periwinkle density. No studies have quantitatively examinedPanopeus distribution or trophic interactions in marsh systems, and its potential impacts on community structure remained unexplored. We investigated distribution and feeding habits ofPanopeus in eight salt marshes along the Mid-Atlantic seashore (Delaware-North Carolina). We found that mud crabs were abundant in tall (4–82 ind m^?2), intermediate (0–15 ind m^?2), and short-form (0–5 ind m^?2)Spartina alterniflora zones in all marshes and that crab densities were negatively correlated with tidal height and positively correlated with bivalve density. Excavation of crab lairs r?utinely produced shells of plant-grazing snails (up to 36 lair^?1) and bivalves. Lab experiments confirmed that mud crabs readily consume these abundant marsh molluscs. To experimentally examine potential community effects of observed predation patterns, we manipulated crab and periwinkle densities in a 1-mo field experiment. Results showed thatPanopeus can suppress gastropod abundance and that predation rates increase with increasing snail density. In turn, crab suppression of snail density reduces grazing intensity on salt marsh cordgrass, suggesting presence of a trophic cascade. These results indicate that this previously under-appreciated consumer is an important and indirect determinant of community structure and contribute to a growing body of evidence challenging the long-standing notion that consumers play a minor role in regulating marsh plant growth.  相似文献   

The groundwater–land-surface–atmosphere connection: Soil moisture effects on the atmospheric boundary layer in fully-coupled simulations     

Reed M. Maxwell  Fotini Katopodes Chow  Stefan J. Kollet 《Advances in water resources》2007,30(12):2447-2466

This study combines a variably-saturated groundwater flow model and a mesoscale atmospheric model to examine the effects of soil moisture heterogeneity on atmospheric boundary layer processes. This parallel, integrated model can simulate spatial variations in land-surface forcing driven by three-dimensional (3D) atmospheric and subsurface components. The development of atmospheric flow is studied in a series of idealized test cases with different initial soil moisture distributions generated by an offline spin-up procedure or interpolated from a coarse-resolution dataset. These test cases are performed with both the fully-coupled model (which includes 3D groundwater flow and surface water routing) and the uncoupled atmospheric model. The effects of the different soil moisture initializations and lateral subsurface and surface water flow are seen in the differences in atmospheric evolution over a 36-h period. The fully-coupled model maintains a realistic topographically-driven soil moisture distribution, while the uncoupled atmospheric model does not. Furthermore, the coupled model shows spatial and temporal correlations between surface and lower atmospheric variables and water table depth. These correlations are particularly strong during times when the land-surface temperatures trigger shifts in wind behavior, such as during early morning surface heating.  相似文献   

Burial and exhumation history of Pennsylvanian strata, central Appalachian basin: an integrated study     

Jason S. Reed  James A. Spotila  Kenneth A. Eriksson  Robert J. Bodnar 《Basin Research》2005,17(2):259-268

An inferred burial and exhumation history of Pennsylvanian strata in the central Appalachian foreland basin is constrained by integrating palaeothermometers, geochronometers and estimated palaeogeothermal gradients. Vitrinite reflectance data and fluid inclusion homogenization temperatures indicate that burial of Lower and Upper Pennsylvanian strata of the Appalachian Plateau in West Virginia exceeded ～4.4 km during the late Permian and occurred at a rate of ～100 m Myr^?1. Exhumation rates of ～10 m Myr^?1 from the late Permian to the early Cretaceous are constrained using maximum burial conditions and published apatite fission track (AFT) ages. AFT and radiogenic helium ages indicate exhumation rates of ～30–50 m Myr^?1 from the early to late Cretaceous. Radiogenic helium dates and present day sampling depths indicate that exhumation rates from the late Cretaceous to present were ～25 m Myr^?1. Exhumation rates for Upper and Lower Pennsylvanian strata within the Appalachian Plateau are remarkably similar. Early slow exhumation was possibly driven primarily by isostatic rebound associated with Triassic rifting. The later, more rapid exhumation can be attributed to thermal expansion followed by lithospheric flexure related to sediment loading along the passive margin.  相似文献   

THE GOSNELLS IRON — A FRAGMENT OF THE MOUNT DOOLING OCTAHEDRITE     

J.R. De Laeter  G.J.H. McCall  S.J.B. Reed 《Meteoritics & planetary science》1972,7(4):469-478

A 1.5 kg iron found in 1960 at Gosnells, near Perth, Western Australia, belongs to Wasson's chemical group I-An3 and is structurally unusual, being best described as a heat-altered granular coarse octahedrite. It is chemically and structurally very similar to the Mount Dooling iron, found in 1909 about 400 km away, and has a fracture surface which fits the Mount Dooling mass very closely. The Gosnells fragment was probably transported by human agency, though it is not known when or by whom.  相似文献   

Diagenetic evidence for an epigenetic origin of the Courtbrown Zn–Pb deposit, Ireland     

ChristopherP. Reed  MalcolmW. Wallace 《Mineralium Deposita》2001,36(5):428-441

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A nonlinear numerical model for sloped‐bottom tuned liquid dampers     

D. E. Olson  D. A. Reed 《地震工程与结构动力学》2001,30(5):731-743

Shaking‐table data for a tuned liquid damper with a sloped bottom of 30° with the horizontal are investigated using a non‐linear numerical model previously developed by Yu, Jin‐kyu, Nonlinear characteristics of tuned liquid dampers. Ph.D. Thesis, Department of Civil Engineering, University of Washington, Seattle, WA, 98195 (1997). Stiffness and damping parameters for this model are obtained and compared with those previously derived for box‐shaped tanks. The values for these parameters reflect the softening spring behaviour of the sloped‐bottom system in contrast to the hardening system evident for the box‐shaped TLD. Consequently, the sloped‐bottom tank should be tuned slightly higher than the fundamental structural frequency in order to obtain the most effective damping. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

A diatom-conductivity transfer function for Spanish salt lakes   总被引：3，自引：0，他引：3  

J.M. Reed 《Journal of Paleolimnology》1998,19(4):399-416

Diatom-salinity transfer functions for interpretation of palaeosalinity and palaeoclimate change have been developed successfully for parts of North America and North and East Africa, but there is a need for data-sets in other saline lake regions of the world. A data-set of 74 modern diatom samples and associated water chemistry data is described from Spain. The influence of conductivity and other environmental variables on diatom distribution is explored using canonical correspondence analysis (CCA) and partial CCAs. A transfer function is derived for conductivity (70 samples) whose apparent predictive ability is high (apparent r² = 0.91). Performance under jackknifing is poor due to the heterogeneous nature of the data-set and poor coverage of the freshwater end of the salinity gradient. There is a lack of suitable low-salinity sites in Spain, and the accuracy of estimated salinity optima and tolerance ranges may be improved by merging this data-set with those of other regions. The Spanish transfer function has strong affinities with the African data-set and contributes important ecological data for diatom taxa which are absent or poorly represented in the modern flora of African lakes, and for which, in fossil material, there were previously no good modern analogues.  相似文献   

Wave-adjusted boundary condition for longshore current in finite-volume circulation models     

Christopher W. Reed  Adele Militello 《Ocean Engineering》2005,32(17-18):2121-2134

Numerical modeling of coastal circulation encompassing the nearshore requires forcing by tide, surface gravity waves, and possibly other factors. In the nearshore, the wave-induced longshore current and setup are dominant hydrodynamic processes, and lateral boundary conditions representing tide and oceanic forcing typically do not include surface-wave contributions. Without proper boundary conditions, significant gradients in current and water level can occur that contaminate the solution in the internal domain. A standard strategy is to place the boundaries far from the site of interest, but this strategy greatly increases computational demands, and it may not be appropriate for long-term simulations. This paper describes a wave-adjusted boundary condition that accounts for wave-induced water level and current acting in combination with tidal forcing. The wave-adjusted boundary condition is demonstrated for an idealized case of a parallel-contour beach and for an engineering application at Ocean City, MD.  相似文献   

An investigation of methods commonly used for the selective removal and characterization of trace metals in sediments     

Reed Van Valin 《Marine Chemistry》1982,11(6):535-564

The characterization of solid phase-associated transition metals is important in understanding solid—seawater interactions. This has proven to be a difficult problem because of the complex nature of most sediments and suspended particulate matter. Many chemical techniques have been proposed to describe sedimentary metal phases. Most rely on characterizing equivalent chemical reactivities from the various metal phases rather than the characterization of the actual physical phases with which the metals are associated. In this study, several of the most widely used trace metal extraction techniques are compared for many of the most commonly measured transition metals using a variety of naturally occurring major marine sediment types. All solid concentrations are normalized to total metal values as obtained by neutron activation and X-ray fluorescence analyses.One weak, four intermediate strength, and two strong metal extraction methods were studied individually. The weak method had the lowest degree of extraction efficiency, but dissolved all solid carbonate phases. Its probable inability to retain released metals quantitatively in solution is a major problem. Three of the four intermediate methods are similar. The other and simplest of the four methods (0.5 N HCl), released much lower amounts of most metals studied when compared to these other three. It cannot be classified as a weak method, however, as it does attack some moderately resistant solid phases. Only one of the other three intermediate methods (a reducing acetic acid solution), was relatively free from analytical difficulties and it is preferred for this reason. The two strong extraction methods are quite similar, with neither yielding total metal concentrations.A five-step sequential extraction scheme was also evaluated. The results were generally quite good, both with regard to metal phase fractionation and overall total extraction of available metals. Based on the results of this study, a sequential extraction scheme is a useful method for characterizing solid phase-associated transition metals.  相似文献