Distribution of heavy metals in the Severn Estuary     

J ButterworthP Lester  G Nickless 《Marine pollution bulletin》1972

There has been considerable agitation in recent months about heavy metal pollution in the Bristol Channel and Severn Estuary and on land around Bristol. Concentrations of zinc, cadmium and lead in water, sediments, seaweeds and shore animals are recorded from a number of sites on the southern shore of the estuary. Contamination is detectable ninety miles downstream of Avonmouth where the highest concentrations of these heavy metals are found.  相似文献   

A recent history of metal accumulation in the sediments of the Thames Estuary, United Kingdom   总被引：4，自引：0，他引：4  

S. B. O’Reilly Wiese  C. L. MacLeod  J. N. Lester 《Estuaries and Coasts》1997,20(3):483-493

Sediment cores were collected from the Tilbury Tidal Basin in the Thames Estuary to determine the depositional history of metals in the estuary. Profiles of metals in sediments deposited in the lower Thames Estuary show a 30–50% decrease in concentration for Ag, Cd, Cu, Pb, and Zn, and a 70% decrease for Hg in recent decades. Historic depth soundings data showed the decreases in metal concentrations occurred between 1944 and 1966. The decline in sediment metal concentrations has been attributed to reduced inputs to the estuary, following updating of the major sewage treatment works in 1959 and 1963. This is indicated by the through-core distribution of Mn which implies that prior to 1960 the sediments were deposited in anoxic conditions, which subsequently improved. An increase in Mn concentrations observed in one of the cores has been attributed to increases in the dissolved oxygen of the estuarine waters resulting from the increased efficiency of the sewage treatment works.  相似文献   

A statistical study of ion frictional heating observed by EISCAT   总被引：1，自引：0，他引：1  

J. A. Davies  M. Lester  I. W. McCrea 《Annales Geophysicae》1997,15(11):1399-1411

Results of a statistical survey of F-region ion frictional heating are presented, a survey which is based on over 4000 h of common programme observations taken by the European incoherent scatter (EISCAT) UHF radar facility. The criterion adopted in this study for the identification of ion frictional heating was that defined by McCrea et al., requiring an enhancement in the F-region field-parallel ion temperature exceeding 100 K over two consecutive integration periods, which was itself based on a selection criterion for frictional heating derived for the study of high-latitude F-region ion temperature observations from the Atmospheric Explorer-C satellite. In the present study, the diurnal distribution of ion frictional heating observed by EISCAT is established and, furthermore, its dependence on geomagnetic activity and the orientation of the interplanetary magnetic field (IMF) is investigated; results are interpreted with reference to corresponding distributions of enhanced ion velocity, again derived from the extended set of EISCAT UHF common programme observations. The radar, due to its location relative to the large-scale convection pattern, observes ion frictional heating principally during the night, although preferentially during the post-midnight hours where there is reduced coupling between the ion and neutral populations. There is an increased preponderance of frictional heating during intervals of high geomagnetic activity and for a southward z component of the IMF and, moreover, evidence of asymmetries introduced by the y component of the IMF.  相似文献   

A crop-based rainfall chronology for pre-instrumental record southern California     

Lester B. Rowntree 《Climatic change》1985,7(3):327-341

Although measured climatic records begin in California about 1850, agricultural records from the earlier Spanish period (1769–1834) can be used to develop information about annual precipitation. This historical material should be used, however, only with a full understanding of the numerous cultural variables that influenced agricultural production. A study by Lynch in 1931, which is widely cited in the literature of Pacific Coast climate reconstruction, contains serious shortcomings because of incorrect assumptions about the Spanish agricultural system, and, more specifically, the amount of climatic information expressed in yearly harvest data. In this article, mission data are analyzed more rigorously to produce a revised annual rainfall index for southern California that encompasses most of the pre-instrumental record period.  相似文献   

Calculation of equilibrium distributions of chemical species in aqueous solutions by means of monotone sequences     

Thomas J. Wolery  Lester J. Walters Jr. 《Mathematical Geology》1975,7(2):99-115

A numerical method for the calculation of equilibrium distributions of chemical species in aqueous solutions of electrolytes is presented. This method is constructed by transforming the problem of determining the set of unknown concentrations satisfying the mass balance and mass action equations into the equivalent problem of finding the limits of certain well-behaved mathematical sequences in a multivariable direct iteration scheme. The total (analytical) concentrations are taken as the starting estimates, and the recursive equations are constructed from the starting equations. It is shown that the sequences so constructed are both monotonic and bounded, hence convergent in an orderly fashion by a mathematical axiom. Each unknown free ion concentration (that is, each limit) is approached simultaneously from above and from below, being effectively sandwiched in an ever tightening manner. Strict error bounds therefore are easily constructed. The method has been found to be exceedingly efficient in practice, with the error bound (maximum fractional error in taking the upper estimate as the final answer) decreasing in an approximately exponential fashion with respect to iteration number, commonly 0.5–1.5 orders of magnitude per iteration. Correction for nonideality is presented, and the possibility of this giving rise to more than one solution is discussed in connection with three examples of natural waters of low-, medium-, and high-ionic strengths.  相似文献   

Whistler duct structure and formation     

M. Lester  A.J. Smith 《Planetary and Space Science》1980,28(6):645-654

Whistler components received by the VLF goniometer at Halley, Antarctica, have been scaled for nose frequency and direction of arrival. The data were taken from two separate one hour periods on either side of local midnight (0023–0133 UT and 0340–0450 UT, 5 June 1975). Because of the high whistler occurrence rate at this time and the rapid processing facilitated by the Sheffield semi-automated whistler analyser, it has been possible to scale 1850 whistler components and hence obtain high resolution mapping of the whistler duct structure. The number of observable ducts increased from 4 at 0030 UT to about 15 at 0130 UT and had reached about 31 by 0400 UT. This increasing number of ducts together with an observed clustering of ducts in the second one hour period, provides evidence for duct formation. The observations have been compared with the various duct generation mechanisms which have been proposed. The duct formation process may have been associated with a negative change in Dst which occurred at the same time, and this possibility is discussed.  相似文献   

Sources of bias in weighted average inferences of environmental conditions     

Lester L.?YuanEmail author 《Journal of Paleolimnology》2005,34(2):245-255

Weighted averaging is widely used for inferring environmental conditions from an observed species assemblage. However, weighted average inferences are known to be systematically biased, and linear corrections (i.e., deshrinking functions) are commonly applied to adjust for this bias. In this analysis, the magnitude of the biases in weighted average inferences (and therefore the values of the deshrinking coefficients) are shown to depend upon the range of conditions sampled in the calibration data set and the true optima and niche breadths of the species observed in the calibration data set. Since the range of conditions and the observed species can differ between the calibration data set and the new data set for which environmental conditions are inferred, the coefficients for the deshrinking function derived using the calibration data may not be applicable to inferences computed using a new data set. Thus, environmental inferences may still exhibit systematic errors even after application of the linear correction. The findings from the theoretical analysis are demonstrated using stream temperature and macroinvertebrate data collected from wadeable streams in the western United States.  相似文献   

Dayside convection and auroral morphology during an interval of northward interplanetary magnetic field   总被引：1，自引：0，他引：1  

S. E. Milan  M. Lester  S. W. H. Cowley  M. Brittnacher 《Annales Geophysicae》2000,18(4):436-444

We investigate the dayside auroral dynamics and ionospheric convection during an interval when the interplanetary magnetic field (IMF) had predominantly a positive B_z component (northward IMF) but varying B_y. Polar UVI observations of the Northern Hemisphere auroral emission indicate the existence of a region of luminosity near local noon at latitudes poleward of the dayside auroral oval, which we interpret as the ionospheric footprint of a high-latitude reconnection site. The large field-of-view afforded by the satellite-borne imager allows an unprecedented determination of the dynamics of this region, which has not previously been possible with ground-based observations. The location of the emission in latitude and magnetic local time varies in response to changes in the orientation of the IMF; the cusp MLT and the IMF B_y component are especially well correlated, the emission being located in the pre- or post-noon sectors for B_y < 0 nT or B_y > 0 nT, respectively. Simultaneous ground-based observations of the ionospheric plasma drift are provided by the CUTLASS Finland HF coherent radar. For an interval of IMF B_y 0 nT, these convection flow measurements suggest the presence of a clockwise-rotating lobe cell contained within the pre-noon dayside polar cap, with a flow reversal closely co-located with the high-latitude luminosity region. This pattern is largely consistent with recent theoretical predictions of the convection flow during northward IMF. We believe that this represents the first direct measurement of the convection flow at the imaged location of the footprint of the high-latitude reconnection site.  相似文献   

Analyzing Slug Tests in Wells Screened Across the Watertable: A Field Assessment     

Stanford  Kristen L.  McElwee  Carl D. 《Natural Resources Research》2000,9(2):111-124

The slug test is the most widely used technique for the in situ estimation of hydraulic conductivityin confined and unconfined formations. Currently, there are no generally accepted methods in thegroundwater literature for the analysis of response data from slug tests performed in wells screenedacross the watertable. A field study was undertaken in an attempt to develop a set of practicalguidelines for tests conducted in such wells. Three wells, screened within unconsolidated materialexhibiting a range of hydraulic conductivities (.05–30.0 m/day), were installed to depths of up to9 m (30 ft) in Kansas River alluvium that ranges in thickness from 15 m to 21 m (50 ft to 70 ft)near Lawrence, Kansas. Intensive well-development efforts removed any drilling debris that couldinterfere with well-formation hydraulics. Once the wells were developed properly, a series of slugtests was performed at each well. The tests were designed to assess the role of the unsaturatedzone and the appropriateness of assuming a fixed hydraulic head upper boundary. The results ofthis investigation can be summarized as follows: (1) the sufficiency of well development shouldbe based on repeat slug tests and not the clarity of pumped water; (2) the effective screen radiusfor best model analysis should be based on a mass balance and not nominal screen dimensions;(3) the watertable can be represented as a constant head boundary and flow in the unsaturatedzone can be ignored in most situations; (4) conventional techniques for the analysis of slug-testdata seem to be reasonable for slug tests conducted in wells screened across the watertable, whenused with the appropriate effective screen radius and normalized head range; and (5) fluctuationsin the watertable elevation through time can be exploited to obtain some insight into the natureof vertical variation in hydraulic conductivity at a well. The results of this investigation indicatethat multiple slug tests should be performed at wells screened across the watertable in order toreliably assess the sufficiency of well development and the appropriateness of conventional theory.  相似文献   

Groundwater cooling of a supercomputer in Perth,Western Australia: hydrogeological simulations and thermal sustainability     

Heather A. Sheldon  Peter M. Schaubs  Praveen K. Rachakonda  Michael G. Trefry  Lynn B. Reid  Daniel R. Lester  Guy Metcalfe  Thomas Poulet  Klaus Regenauer-Lieb 《Hydrogeology Journal》2015,23(8):1831-1849

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