Chloride loading in the South Fork of the Shenandoah River,Virginia, U.S.A.     

W. Cullen Sherwood 《Environmental Geology》1989,14(2):99-106

Loading trends and sources of CI^– in the South Fork of the Shenandoah River, Virginia were analyzed for the period 1929–1982. CI^– has increased from approximately 2 mg/L (2,776 tons/yr) to over 10 mg/L (14,256 tons/yr). Natural CI^– is estimated to be 1.01 mg/L (1,388 tons/yr) with precipitation providing 0.99 mg/L and rocks 0.02 mg/L. From 1929 to 1949 CI^– concentrations were relatively constant and independent of discharge, conforming to the Type II curve of Davis and Zobrist (1978), indicative of natural or relatively uncontaminated streams. Since 1952 CI^– concentrations increased exponentially as river discharge decreases conforming to the Type I curve of Davis and Zobrist for polluted streams. Since 1965 anthropogenic CI^– loading at 12,868 tons/yr has remained relatively constant. Four major sources contribute 92.2 percent (11,871 tons/yr) of the anthropogenic CI^–: (1) deicing salts—4,149 tons/yr, (2) domestic sewage—3,015 tons/yr, (3) livestock and poultry wastes—2,458 tons/yr, and (4) commercial fertilizers—2,249 tons/yr.  相似文献   

Future trends in transport and fate of diffuse contaminants in catchments,with special emphasis on stable isotope applications     

Jeffrey Turner  Hans‐Jrgen Albrechtsen  Mike Bonell  Jean‐Pierre Duguet  Bob Harris  Rainer Meckenstock  Kevin McGuire  Roger Moussa  Norman Peters  Hans H. Richnow  Barbara Sherwood‐Lollar  Stefan Uhlenbrook  Henny van Lanen 《水文研究》2006,20(1):205-213

A summary is provided of the first of a series of proposed Integrated Science Initiative workshops supported by the UNESCO International Hydrological Programme. The workshop brought together hydrologists, environmental chemists, microbiologists, stable isotope specialists and natural resource managers with the purpose of communicating new ideas on ways to assess microbial degradation processes and reactive transport at catchment scales. The focus was on diffuse contamination at catchment scales and the application of compound‐specific isotope analysis (CSIA) in the assessment of biological degradation processes of agrochemicals. Major outcomes were identifying the linkage between water residence time distribution and rates of contaminant degradation, identifying the need for better information on compound specific microbial degradation isotope fractionation factors and the potential of CSIA in identifying key degradative processes. In the natural resource management context, a framework was developed where CSIA techniques were identified as practically unique in their capacity to serve as distributed integrating indicators of process across a range of scales (micro to diffuse) of relevance to the problem of diffuse pollution assessment. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Anthropogenic CO₂ in the oceans estimated using transit time distributions     

D. W. WAUGH  T. M. HALL  B. I. McNEIL  R. KEY  R. J. MATEAR 《Tellus. Series B, Chemical and physical meteorology》2006,58(5):376-389

  相似文献   

Extreme precipitation in WRF during the Newcastle East Coast Low of 2007     

James B. Gilmore  Jason P. Evans  Steven C. Sherwood  Marie Ekström  Fei Ji 《Theoretical and Applied Climatology》2016,125(3-4):809-827

In the context of regional downscaling, we study the representation of extreme precipitation in the Weather Research and Forecasting (WRF) model, focusing on a major event that occurred on the 8^th of June 2007 along the coast of eastern Australia (abbreviated “Newy”). This was one of the strongest extra-tropical low-pressure systems off eastern Australia in the last 30 years and was one of several storms comprising a test bed for the WRF ensemble that underpins the regional climate change projections for eastern Australia (New South Wales/Australian Capital Territory Regional Climate Modelling Project, NARCliM). Newy provides an informative case study for examining precipitation extremes as simulated by WRF set up for regional downscaling. Here, simulations from the NARCliM physics ensemble of Newy available at ～10 km grid spacing are used. Extremes and spatio-temporal characteristics are examined using land-based daily and hourly precipitation totals, with a particular focus on hourly accumulations. Of the different physics schemes assessed, the cumulus and the boundary layer schemes cause the largest differences. Although the Betts-Miller-Janjic cumulus scheme produces better rainfall totals over the entire storm, the Kain-Fritsch cumulus scheme promotes higher and more realistic hourly extreme precipitation totals. Analysis indicates the Kain-Fritsch runs are correlated with larger resolved grid-scale vertical moisture fluxes, which are produced through the influence of parameterized convection on the larger-scale circulation and the subsequent convergence and ascent of moisture. Results show that WRF qualitatively reproduces spatial precipitation patterns during the storm, albeit with some errors in timing. This case study indicates that whilst regional climate simulations of an extreme event such as Newy in WRF may be well represented at daily scales irrespective of the physics scheme used, the representation at hourly scales is likely to be physics scheme dependent.  相似文献   

Geology and jungle fieldwork in eastern Indonesia     

SIMON BAKER  ROBERT HALL  EMILY FORDE 《Geology Today》1994,10(1):18-23

Collecting geological information from the jungles and islands of eastern Indonesia depends largely on traditional fieldwork methods involving much footwork and messing about in boats. Coupled with modern laboratory and computing techniques, information gained on the ground is being used to interpret the tectonic development of east Indonesia, the Philippine Sea and the western Pacific.  相似文献   

Colloidally separated samples from Allende residues: Noble gases,carbon and an ESCA-study     

Ulrich Ott  Johann Kronenbitter  Jose Flores  Sherwood Chang 《Geochimica et cosmochimica acta》1984,48(2):267-280

A non-colloidal fraction separated by physical means from an $\text{HF}\text{HCl}$-resistant residue of the Allende carbonaceous meteorite exhibits a ratio of isotopically “normal” (Q-type) xenon to “anomalous” xenon (X-type) that is ~4 times larger than usually observed. Coincidentally this fraction contains carbon that is isotopically heavier by ~10%. than bulk Allende residue samples. ESCA analyses of companion colloidal separates show that the major portion of the S contained in our $\text{HF}\text{HCl}$-residues is elemental rather than a sulfide. They also confirm earlier observations that no elementally distinct surface coating is present, in accord with the absence of a surface-sited sulfur-bearing gas carrier, and that the oxygen content is increased after etching with nitric acid. For these separates noble gas data coupled with the ESCA data for nitrogen and the isotopic data for carbon point to the existence of heterogeneities among the noble gas-, carbon- and nitrogen-bearing phases and, thus, preservation of discrete components from the variety of source regions (or production mechanisms, or both) sampled by the Allende parent body. In sharp contrast to the success of physical and chemical methods in yielding samples in which one of the major noble gas components predominates to an extraordinary degree over the other, carbon isotopic compositions that have been inferred for the respective carrier phases in these same samples are strongly contradictory. Mass and isotope balance considerations lead us to conclude that a major fraction of the carbonaceous matter in Allende is noble-gas-poor, a result that could be confirmed by direct isolation of a sample, the carbon in which is dominated by this variety; and for that reason no simple relationship is discernable yet between observed isotopic compositions and either major noble gas component. Similar ambiguities may exist for nitrogen. The possible relationship between carbon-rich phases in ureilites and carbonaceous chondrites is considered.  相似文献   

World-wide increase in tropospheric methane, 1978–1983     

Donald R. Blake  F. Sherwood Rowland 《Journal of Atmospheric Chemistry》1986,4(1):43-62

Tropospheric concentrations of methane in remote locations have averaged a yearly world-wide increase of 0.018±0.002 parts per million by volume (ppmv) during the period from January 1978 to December 1983. The concentrations in the north temperate zone are always greater than those in the south temperate zone by 7±1% because the major methane sources are all predominantly located in the northern hemisphere. The average world-wide tropospheric concentration of methane in dry air was 1.625 ppmv at the end of 1983, measured against an NBS standard certified as 0.97 ppmv (but with an accuracy of only ±1%). The world-wide concentration increases are described by a linear equation with a standard deviation of 0.003 ppmv for ten different collection periods during 1978–1983. The precision of measurement of the methane concentration in the atmospheric samples and in the standard was measured to be ±0.4% for each. Repetitive measurements of an air sample collected in November 1977 have shown the same concentration for six years with a standard deviation for these data of ±0.003 ppmv.The causes for the steady increase in methane concentration in the troposphere cannot be fixed with certainty from present data. Contributing causes can include increases in the source strengths from cattle and rice fields. The atmospheric concentrations of CO, CH₄ and HO are all closely coupled with one another, and increased concentrations of CO and/or CH₄ should cause reduced concentrations of HO, which in turn should lengthen the atmospheric lifetimes of CO and CH₄.Among other physical and chemical effects, a increase of 0.18 ppmv per decade should contribute a greenhouse warming of about 0.04°C per decade. Other secondary contributions to the greenhouse effect from increases in CH₄ may arise from methane-induced increases in stratospheric H₂O, in tropospheric O₃, and in numerous other trace species whose concentration is controlled by reaction with HO radicals.An increased CH₄ source strength may result from the effect of increasing atmospheric temperatures on the known aqueous biological CH₄ sources, such as swamps, and may be an added consequence of the greenhouse effect.  相似文献   

The Power Spectral Density technique applied to micropulsation analysis     

W. F. Stuart  Vicki Sherwood  Sheena M. Macintosh 《Pure and Applied Geophysics》1971,92(1):150-164

Summary An empirical investigation has been conducted on the practical methods of obtaining the spectra of micropulsation activity, and the interpretational limits which can be applied to the detailed use of spectra computed by the Power Spectral Density (PSD) method. Results indicate that sufficiently high resolution may be obtained reliably from the PSD method for it to be regarded as a useful improvement over handscaling methods. The limitation is shown to remain in the selection of events rather than in computational or instrumental properties.  相似文献   

High-Pressure and -Temperature Subophiolitic Kyanite--Garnet Amphibolites Generated during Initiation of Mid-Tertiary Subduction, Palawan, Philippines   总被引：1，自引：0，他引：1  

ENCARNACIoN  J. P.; ESSENE  E. J.; MUKASA  S. B.; HALL  C. H. 《Journal of Petrology》1995,36(6):1481-1503

Metamorphic rocks exposed near the base of a pre-middle Eoceneophiolite in central Palawan, Philippines, preserve a recordof the P-T-t conditions under which the ophiolite was detachedand emplaced onto the rifted southeast margin of China. Garnetamphibolites in contact with mantle harzburgite preserve peakmetamorphic temperatures of 700–760°C and minimumpressures of 9 kbar, consistent with the presence of kyanite.Garnet grains which preserve strong prograde zoning (Pyp₁₁ incores to Pyp₄₃ in rims) contain inclusion assemblages that constrainpressures above 5–6 kbar at 4O0–500°C. Thisrepresents an early prograde clockwise path consistent withunderthrusting. Two amphibolite samples yield hornblende ³⁹Ar/⁴⁰Ar–³⁶Ar/Ar⁴⁰Arisochron ages of 34•0±0•6 Ma (2) (early Oligocene),which are indistinguishable from a 34•3±0•2Ma isochron age of muscovite from a kyanitechlorite-muscoviteschist that is interlayered with the amphibolites. The highpressures (equivalent to a depth of >30 km in oceanic lithosphere)and temperatures, and the age difference between ophiolite crystallizationand metamorphism of the sole, are incompatible with the rockshaving formed in a mature subduction zone or oceanic spreadingcenter. Instead, the timing, P-T conditions, and regional geologysuggest metamorphism in a nascent subduction zone. Rapid coolingand exhumation of the metamorphic rocks followed peak metamorphicconditions in the earliest Oligocene, perhaps by the rapid thickeningof the accretionary complex that is preserved beneath the ophiolite.The amphibolites formed during the inception of southward subductionwithin proto-South China Sea oceanic lithosphere south of theEurasian margin. This led to the formation of an arc-trenchsystem that accommodated extension along southeast China andthe opening of the South China Sea. KEY WORDS: ophiolite; thermobarometry; garnet amphibolite; subduction  相似文献   

Field measurements of fairweather bottom boundary layer processes and sediment suspension on the Louisiana inner continental shelf   总被引：1，自引：0，他引：1  

L. D. Wright  C. R. Sherwood  R. W. Sternberg 《Marine Geology》1997,140(3-4):329-345

Field measurements of bottom boundary layer and sediment-transport processes were made on the Louisiana inner continental shelf in spring 1992 at a depth of 15.5 m, and in spring and summer 1993 at a depth of 20.5 m. Two different wave–current boundary layer/sediment-transport models were applied to the measured near-bed flows. In addition, the log-profile method was applied to estimate hydraulic roughness and bed stress. Consistent with the results of others, our measurements show that near-bed flows were very weak under non-storm conditions. Bed stresses were typically too low to resuspend bed sediments. However, the advection of high-turbidity layers or plumes past the instrumentation apparently caused a sustained period of high suspended sediment concentration throughout the log layer in spring 1993. In the absence of wave activity or high suspended sediment concentrations, boundary layer profiles showed the bed to have been hydraulically very smooth with cm. However, wave agitation, combined with increased suspended sediment concentration caused hydraulically rough conditions with cm.  相似文献