Interpretation of metal concentrations in estuarine sediments of Florida using aluminum as a reference element   总被引：2，自引：0，他引：2  

Steven J. Schropp  F. Graham Lewis  Herbert L. Windom  Joe D. Ryan  Fred D. Calder  Louis C. Burney 《Estuaries and Coasts》1990,13(3):227-235

Metal contamination of estuarine sediments is an increasing problem in Florida and elsewhere as urbanization extends into previously undeveloped areas. Effective estuarine management practices require scientifically valid tools to assess the extent of estuarine contamination. Interpretation of anthropogenic metal contributions has been hampered by the fact that natural metal concentrations in sediments vary by orders of magnitude in different sediments. Normalization of metal concentrations to a reference element, aluminum, appears to be a promising method for comparing estuarine sediment metal concentrations on a regional basis. In this paper we describe an interpretive method based on the relationship between sediment metals and aluminum derived from statewide data on natural estuarine sediments in Florida. We show how the method can be used to interpret metal concentrations with an example using data from the Miami River and Biscayne Bay.  相似文献   

A Field Evaluation of In-Situ Biodegradation of Chlorinated Ethenes: Part I, Methodology and Field Site Characterization     

Paul V. Roberts  Gary D. Hopkins  Douglas M. Mackay  Lewis Semprini 《Ground water》1990,28(4):591-604

  相似文献   

The geology of the Eastern part of the Peak district     

W.G. Fearnsides  W.S. Bisat  Wilfrid Edwards  H.P. Lewis  W.H. Wilcockson 《Proceedings of the Geologists' Association. Geologists' Association》1932,43(2):152-IN3

  相似文献   

Summer field meeting, 1944: August 24th–September 2nd     

A. Hubert Cox  H.P. Lewis 《Proceedings of the Geologists' Association. Geologists' Association》1945,56(2):59-IN2

  相似文献   

Instrumental waveform distortion on ocean bottom seismometers     

Brian T. R. Lewis  Jonathan D. Tuthill 《Marine Geophysical Researches》1981,5(1):79-85

Data from the 1978 Lopez Island OBS Intercomparison Experiment and deep sea data from University of Washington OBSs show that there is a considerable amount of waveform distortion resulting from the conversion of horizontal motion into vertical motion, here called cross-coupling distortion. This distortion, which substancially reduces the significance of waveform matching with synthetic seismograms, appears to result from rotation imparted to the OBS package by near-vertically traveling shear energy. The degree of this rotation seems to depend on the instrument surface area above the seafloor and the geometry and surface area of the feet connecting the package to the seafloor. The sensitivity and response of the seismometers within the package to this rotation depends on the precise location of the seismometers with respect to the axis of rotation. The results suggest how to modify OBS designs to minimize these effects.University of Washington Contribution No. 1225.  相似文献   

The principal factors contributing to the flux of salt in a narrow, partially stratified estuary     

R. E. Lewis  J. O. Lewis 《Estuarine, Coastal and Shelf Science》1983,16(6)

Observations of the velocity and salinity structure of the Tees estuary were made at eight stations along the estuary axis between Victoria Bridge and the sea during the summer of 1975. The measurements were made on ten separate tidal periods covering neap and spring tides.The data were collected over a period of relatively low freshwater flows and the residual current was found to have a strong dependence on the Stokes drift. At the upstream stations, the residuals were more than an order of magnitude greater than the currents anticipated from the freshwater discharge. Although the mean stratification decreased as the tidal range increased, the vertical circulation was stronger on spring tides than on neaps. Vertical variations in the amplitude and phase of the tidal current results in a current which strengthens the vertical circulation. However, this effect only made a relatively small contribution to the observed vertical circulation.The relative contribution of the individual salt flux terms to the net upstream transport of salt varies along the estuary. As the estuary narrows, the contribution by the oscillatory terms dominates that from the shear in the steady state flow. Of these oscillatory terms, the correlation of velocity and salinity fluctuations plays a key rôle in the salt transport. The depth mean values make a greater contribution than deviations from the depth mean and the flux due to phase variations over depth is smaller than either of these. Since the Stokes drift is compensated by a down-stream steady state flow, it does not contribute to the tidal mean transport of salt.At the seaward end of the estuary, the salt fluxes due to the steady state vertical shear and the convariance of the tidal fluctuations act in a complementary way to counter the seaward transport of salt by the freshwater flow. With the possible exceptions of the wide or narrow reaches of the Tees, the longitudinal fluxes of salt due to transverse variations in velocity, salinity and depth and turbulent fluctuations are of secondary importance as contributors to the estuary salt budget.On both neap and spring tides, the computed total salt transports at the Newport and Victoria bridges did not match the values required for a salt balance with the corresponding freshwater flows. These fluxes were probably the cause of the observed downstream displacement of the tidal mean salinity distribution between neap and spring tides.  相似文献   

Detecting critical periods in larval flatfish populations     

R. Christopher Chambers  David A. Witting  Stephen J. Lewis 《Journal of Sea Research》2001,45(3-4)

We evaluate the time-course of deaths and evidence of periods of increased mortality (i.e., critical periods) in laboratory populations of larval flatfish. First, we make the distinction between age-at-death and abundance-at-time data for fish larvae, the latter being typical in studies of natural populations. Next, we describe an experimental investigation of age- and temperature-dependent mortality in larval winter flounder, Pseudopleuronectes americanus. The survivorship curves of these populations differed significantly in both the magnitude and time-course of mortality among the four water temperatures evaluated (7, 10, 13, and 16°C). Mortality was highest in the cooler temperatures and concentrated in the third quarter of larval life, largely concurrent with settlement of surviving members of the cohort. Among the statistical methods for analysing survival data, the proportional-hazards model with time-varying covariates proved best at capturing the patterns of age-specific mortalities. We conclude that fair appraisals of recruitment hypotheses which are predicated on periods of high, age-specific mortality that vary with environmental conditions (e.g., Hjort's critical period hypothesis) will require: (1) data that are based on age, not time; (2) data that are of higher temporal resolution than commonly available at present and (3) analytical methods that are sensitive to irregularities in survivorship curves. We suggest four research approaches for evaluating critical periods in nature.  相似文献   

THE ADJUSTMENT OF SOME HYDRAULIC VARIABLES AT DISCHARGES LESS THAN ONE CFS*     

Laurence A. Lewis 《The Professional geographer》1966,18(4):230-234

  相似文献   

Dietary Shifts in the Queen Triggerfish, Balistes vetula, in the Absence of its Primary Food Item, Diadema antillarum     

Peter N.  Reinthal  Brian  Kensley Sara M.  Lewis 《Marine Ecology》1984,5(2):191-195

Abstract. The long-spined sea urchin Diadema antillarum has been reported to be the major food item of the queen triggerfish, Balistes vetula in the Caribbean. This sea urchin has undergone a massive mortality on reefs throughout the Caribbean during 1983. The dietary habits of twenty-three queen triggerfish from patch reef habitats in Belize were examined. It was found that crabs and chitons now form the major dietary items when D. antillarum is not available. It is suggested that this predator, which was previously specialized on a single food item, is able to shift resource utilization in the absence of its primary food source, and that the queen triggerfish can capture diverse prey from a wide variety of habitats.  相似文献   

Parametric sensitivity analysis of coupled mechanical consolidation and contaminant transport through clay barriers     

T.W. Lewis  P. Pivonka  S.G. Fityus  D.W. Smith 《Computers and Geotechnics》2009,36(1-2):31-40

In this paper, an extensive parametric sensitivity analysis of coupled consolidation and solute transport in composite landfill liner systems has been undertaken. The analysis incorporates results of more than 3000 simulations for various combinations of barrier thickness, waste loading rate, initial void ratio, compression index, hydraulic conductivity and dispersion coefficient. However, it is noted that to limit the extent of the study a constant coefficient of consolidation is assumed in the analysis presented here, though this assumption is easily relaxed. Results of the parametric sensitivity analysis are succinctly presented using dimensionless plots, which allow the comparison of results for a large number of parameter values, and so the clear identification of the most important determinants on contaminant transport through the liner system. The dimensionless plots demonstrate a pessimum (for which the ‘breakthrough time’ is minimised). Numerical results reveal that in cases of extreme liner compressibility an order of magnitude reduction in contaminant transit time may arise due to coupling between solute transport and consolidation, while for barriers of low compressibility and porosity (such as well-engineered composite compacted clay landfill liners), it is found that the contaminant transit time may still be reduced by more than 30%. The numerical results suggest that the use of coupled consolidation–contaminant transport models are sometimes required for informed and conservative landfill liner design.  相似文献