Responding to Emerging Contaminant Impacts: Situational Management          下载免费PDF全文

Suthan S. Suthersan  John Horst  Ian Ross  Erica Kalve  Joseph Quinnan  Erika Houtz  Jeff Burdick 《Ground Water Monitoring & Remediation》2016,36(3):22-32

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Assessment of perfluorinated compounds (PFCs) in plasma of bottlenose dolphins from two southeast US estuarine areas: relationship with age, sex and geographic locations     

Fair PA  Houde M  Hulsey TC  Bossart GD  Adams J  Balthis L  Muir DC 《Marine pollution bulletin》2012,64(1):66-74

Plasma PFCs were measured in 157 bottlenose dolphins (Tursiops truncatus) sampled from two US southeast Atlantic sites (Charleston (CHS), SC and Indian River Lagoon (IRL), FL) during 2003-2005. ∑PFCs, perfluoroalkyl carboxylates (∑PFCAs), perfluoroalkyl sulfonates (∑PFSAs) and individual compounds were significantly higher in CHS dolphins for all age/sex categories compared to IRL dolphins. Highest ∑PFCs concentrations occurred in CHS juvenile dolphins (2340 ng/g w.w.); significantly higher than found in adults (1570 ng/g w.w. males; 1330 ng/g w.w. females). ∑PFCAs were much greater in CHS dolphins (≈ 21%) compared to IRL dolphins (≈ 7%); ∑PFSAs were 79% in CHS dolphins versus 93% in IRL dolphins. PFOS, the dominant compound, averaged 72% and 84%, respectively, in CHS and IRL dolphins. Decreasing PFC levels occurred with age on the bioaccumulation of PFCs in both sites. These observations suggest PFC accumulation in these two dolphin populations are influenced by site-specific exposures with significantly higher levels in CHS dolphins.  相似文献   

Heterogeneity in mycorrhizal inoculum potential of flood-deposited sediments     

Mary J. Harner  Jeff S. Piotrowski  Ylva Lekberg  Jack A. Stanford  Matthias C. Rillig 《Aquatic Sciences - Research Across Boundaries》2009,71(3):331-337

Riparian areas are diverse systems where flooding creates new sites for establishment of vegetation. Symbioses with soil microorganisms, such as mycorrhizal fungi, affect vascular plant growth and community composition. It is unknown, however, how mycorrhizal fungi are dispersed along rivers and what potential they have to inoculate roots of plants establishing on recently deposited sedimentary surfaces of flood plains. We measured AMF inocula in sediment deposited by an average spring flood along an expansive riverine flood plain in Montana, USA, to determine whether AMF inocula were present in sediments and what types of propagules (spores, hyphae, or colonized root fragments) contribute to AMF infectivity. Flood-deposited sediments contained sufficient inocula for AMF to colonize host plants (Sorghum sudanense) grown in a greenhouse, and both AMF hyphal lengths and spore densities were correlated with infectivity. Availability of mycorrhizal inocula, which is patchily distributed in this system, may lead to microsites that differ in ability to support establishment and growth of early-successional plants.  相似文献   

Evaluation of nearshore wave models in steep reef environments     

Mark Buckley  Ryan Lowe  Jeff Hansen 《Ocean Dynamics》2014,64(6):847-862

To provide coastal engineers and scientists with a quantitative evaluation of nearshore numerical wave models in reef environments, we review and compare three commonly used models with detailed laboratory observations. These models are the following: (1) SWASH (Simulating WAves till SHore) (Zijlema et al. 2011), a phase-resolving nonlinear shallow-water wave model with added nonhydrostatic terms; (2) SWAN (Simulating WAve Nearshore) (Booij et al. 1999), a phase-averaged spectral wave model; and (3) XBeach (Roelvink et al. 2009), a coupled phase-averaged spectral wave model (applied to modeling sea-swell waves) and a nonlinear shallow-water model (applied to modeling infragravity waves). A quantitative assessment was made of each model’s ability to predict sea-swell (SS) wave height, infragravity (IG) wave height, wave spectra, and wave setup ( \( \overline{\eta} \) ) at five locations across the laboratory fringing reef profile of Demirbilek et al. (2007). Simulations were performed with the “recommended” empirical coefficients as documented for each model, and then the key wave-breaking parameter for each model (α in SWASH and γ in both SWAN and XBeach) was optimized to most accurately reproduce the observations. SWASH, SWAN, and XBeach were found to be capable of predicting SS wave height variations across the steep fringing reef profile with reasonable accuracy using the default coefficients. Nevertheless, tuning of the key wave-breaking parameter improved the accuracy of each model’s predictions. SWASH and XBeach were also able to predict IG wave height and spectral transformation. Although SWAN was capable of modeling the SS wave height, in its current form, it was not capable of modeling the spectral transformation into lower frequencies, as evident in the underprediction of the low-frequency waves.  相似文献   

Two solution methods for dynamic game in reservoir operation     

Mehran Homayoun-far  Arman Ganji  Davar Khalili  Jeff Harris 《Advances in water resources》2010

During the last decade, a number of models have been developed to consider the conflict in dynamic reservoir operation. Most of these models are discrete dynamic models which are developed based on game theory. In this study, a continuous model of dynamic game and its corresponding solutions are developed for reservoir operation. Two solution methods are used to solve the model of continuous dynamic game, namely the Ricatti equations and collocation methods. The Ricatti equations method is a closed form solution, requiring less computational efforts compared with discrete models. The collocation solution method applies Newton's method or a quasi-Newton method to find the problem solution. These approaches are able to generate operating policies for dynamic reservoir operation. The Zayandeh-Rud river basin in central Iran is used as a case study and the results are compared with alternative water allocation models. The results show that the proposed solution methods are quite capable of providing appropriate reservoir operating policies, while requiring rather short computational times due to continuous formulation of state and decision variables. Reliability indices are used to compare the overall performance of the proposed models. Based on the results from this study, the collocation method leads to improved values of the reliability indices for total reservoir system and utility satisfaction of water users, compared to the Ricatti equations method. This is attributed to the flexible structure of the collocation model. When compared to alternative water allocation models, lower values of reliability indices are achieved by the collocation method.  相似文献   

The effects of surface moisture on aeolian sediment transport threshold and mass flux on a beach   总被引：1，自引：0，他引：1  

Robin G. D. Davidson‐Arnott  Yanqi Yang  Jeff Ollerhead  Patrick A. Hesp  Ian J. Walker 《地球表面变化过程与地形》2008,33(1):55-74

This paper presents results from a study designed to explore the effects of beach surface moisture and fetch effects on the threshold of movement, intensity of sand transport by wind and mass flux. The experiment was carried out over a period of five weeks at Greenwich Dunes, Prince Edward Island, Canada in May and June 2002. Moisture content was measured with a Delta‐T moisture probe over a 50 m by 25 m grid established on the beach. Measurements of wind speed and direction were made with arrays of cup anemometers and a two‐dimensional sonic anemometer. Transport intensity was measured at a height of 2–4 cm above the bed using omnidirectional saltation probes which count the impact of saltating grains on a piezoelectric crystal. Anemometers and saltation probes were sampled at 1 Hz. Sand transport was measured with vertical integrating sand traps over periods of 10–20 minutes. Results show that where there is a considerable supply of dry sand the saltation system responds very rapidly (1–2 s) to fluctuations in wind speed, i.e. to wind gusts. Where sand supply from the surface is limited by moisture, mean transport rates are much lower and this reflects in both a reduction in the instantaneous transport rate and in a transport system that becomes increasingly intermittent. Threshold wind speed is significantly correlated with an increase in surface moisture content near the upwind end of the beach fetch, but the relationship is not significant at the downwind end where sediment transport is initiated primarily by saltation impact from upwind. Mass flux increases with increasing fetch length and the relationship is described best by a power function. Further work is necessary to develop a theoretical function to predict the increase in transport with fetch distance as well as the critical fetch distance. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Depositional history and evolution of the Paso del Indio site,Vega Baja,Puerto Rico     

Jeffrey J. Clark  Jeff Walker  Reniel Rodríguez Ramos 《Geoarchaeology》2003,18(6):625-648

Potshards discovered during excavation of bridge pilasters for a major expressway over the Rio Indio floodplain, a stream incised within the karsts of north‐central Puerto Rico, required large‐scale archaeological excavation. Five‐meter‐deep bridge pilaster excavations in the alluvial valley provide a 4500‐year history of deposition. Stratigraphic analysis of the exposed pilaster walls in combination with textural and organic carbon analyses of sediment cores obtained over a much broader area suggest a fluvial system dominated by overbank deposition. Six sequences of alternating light and dark layers of sediment were identified. The darker layers are largely composed of silts and clays, whereas the lighter layers are rich in sand‐sized sediment. Archaeological evidence indicates the organic‐rich dark layers, believed to be buried A horizons, coincide with pre‐historic occupation by Cedrosan Saladoid, Elenan Ostionoid, and Chican Ostionoid, extending from A.D. 450 to A.D. 1500. Lighter layers below the dark soil horizons are interpreted as overbank deposits from large magnitude flood events. The floodplain aggraded discontinuously with rapid deposition of sand followed by gradual accumulation of silt, clay, and organic material. An approximately 1‐m‐thick layer of coarse sand and gravel halfway up the stratigraphic column represents an episode of more frequent and severe floods. Based on radiocarbon ages, this layer aggraded between A.D. 1000 and A.D. 1100, which is well within the Elenan Ostionoid era (A.D. 900–1200). Rates of sedimentation during this period were approximately 8 mm per year, ten times greater than the estimates of sedimentation rates before and after this flood sequence. The cause for the change in deposition is unknown. Nonetheless the Elenan Ostionoid would have had to endure frequent loss of habitation structures and crops during these events. © 2003 Wiley Periodicals, Inc.  相似文献   

Bounds on the complex conductivity of geophysical mixtures     

Alan C. Tripp  Elena Cherkaeva  Jeff Hulen 《Geophysical Prospecting》1998,46(6):589-601

Following previous work on bounds for complex dielectrics, bounds on the complex conductivity of a mixture of two isotropic components can be developed which are independent of any special assumption concerning the geometry of the mixture. If certain broad restrictions are assumed, such as isotropy of the mixture, then the bounds can be made more restrictive. These bounds reveal the range of the induced polarization response which can be caused by a mixture of two materials of known complex conductivity. The bounds can also be generalized for spectral responses. The bounds are conservative lithologically in the sense that many of the special models corresponding to boundary responses have lithological counterparts. The chief use for the given bounds is to gain insight into the nature of the induced polarization response. It is also possible to use the bounds to estimate the volume fractions of the components. We illustrate how this is done for the case of a general anisotropic medium.  相似文献   

Minimum work, fault activity and the growth of critical wedges in fold and thrust belts   总被引：3，自引：0，他引：3  

Stuart Hardy  Chris Duncan  Jeff Masek  & Dennis Brown 《Basin Research》1998,10(3):365-373

Many studies of critical wedges treat the interior of the wedge as continuous and do not address the manner in which it grows from the undeformed state to a typical imbricate wedge. In this paper we present a 2D kinematic–mechanical model which attempts to explain the development of a critical wedge in a fold and thrust belt in terms of both gravitational and frictional work. In the undeformed model a series of thrust faults are defined which have the potential to take up an external displacement. The active fault at a given time is that which minimizes gravitational and frictional work as a result of displacement. Displacement on the active fault causes a change in topography and deformation of other faults which may favour an alternative fault at the next time step. The model is a mixed Lagrangian–Eulerian scheme in which the upper surface, in addition to being deformed, is also subject to erosion, transport and sedimentation. The model predicts propagation of thrust fault activity towards the foreland through time as a result of increasing topographic (gravitational) loads and frictional work on deformed hinterland faults. As the zone of fault activity progresses through the developing critical wedge several faults are active over time-scales of ≈1 Myr. However, a simple chronology or sequence of fault activity cannot be assumed as out-of-sequence thrusting occurs during this overall foreland propagation. The detailed spatial and temporal activity of faults is complex and reflects the interaction between the development of topography, the contrast between basal (décollement) and internal coefficients of friction and the effects of erosion and sedimentation. In particular, rates of erosion and sedimentation are found to be important controls on fault activity both spatially and temporally. Erosion, by locally removing topography above a fault, reduces gravitational and frictional work enabling continued fault activity or reactivation. Sedimentation, conversely, acts to increase gravitational and frictional work on a fault, and therefore has the potential to blanket faults and render them inactive. Model results illustrate the complex feedbacks that can exist between tectonic and surficial mass transport processes.  相似文献   

Silicon control of strontium and cesium partitioning in hydroxide-weathered sediments     

Jon Chorover  Sunkyung Choi  R. Jeff Serne  Caleb Strepka  Karl T. Mueller 《Geochimica et cosmochimica acta》2008,72(8):2024-2047

Cation partitioning and speciation in an aqueous soil suspension may depend on the coupling of reaction time, sorbate amount and mineral weathering reactions. These factors were varied in sediment suspension experiments to identify geochemical processes that affect migration of Sr²⁺ and Cs⁺ introduced to the subsurface by caustic high level radioactive waste (HLRW). Three glacio-fluvial and lacustrine sediments from the Hanford Site (WA, USA) were subjected to hyperalkaline (pH > 13), Na-Al-NO₃-OH solution conditions within a gradient field of (i) sorptive concentration (10⁻⁵-10⁻³ m) and (ii) reaction time (0-365 d). Strontium uptake (q_Sr) exceeded that of cesium at nearly all reaction times. Sorbent affinity for both Cs⁺ and Sr²⁺ increased with clay plus silt content at early times, but a prolonged slow uptake process was observed over the course of sediment weathering that erased the texture effect for Sr²⁺; all sediments showed similar mass normalized uptake after several months of reaction time. Strontium became progressively recalcitrant to desorption after 92 d, with accumulation and aging of neoformed aluminosilicates. Formation of Cs⁺ and Sr²⁺-containing cancrinite and sodalite was observed after 183 d by SEM and synchrotron μ-XRF and μ-XRD. EXAFS data for q_Sr ≈ 40 mmol kg⁻¹ showed incorporation of Sr²⁺ into both feldspathoid and SrCO₃(s) coordination environments after one year. Adsorption was predominant at early times and low sorbate amount, whereas precipitation, controlled largely by sediment Si release, became increasingly important at longer times and higher sorbate amount. Kinetics of contaminant desorption at pH 8 from one year-weathered sediments showed significant dependence on background cation (Ca²⁺ versus K⁺) composition. Results of this study indicate that co-precipitation and ion exchange in neoformed aluminosilicates may be an important mechanism controlling Sr²⁺ and Cs⁺ mobility in siliceous sediments impacted by hyperalkaline HLRW.  相似文献