Analysis of a vertical dipole tracer test in highly fractured rock   总被引：1，自引：0，他引：1  

Sanford WE  Cook PG  Dighton JC 《Ground water》2002,40(5):535-542

The results of a vertical dipole tracer experiment performed in highly fractured rocks of the Clare Valley, South Australia, are presented. The injection and withdrawal piezometers were both screened over 3 m and were separated by 6 m (midpoint to midpoint). Due to the long screen length, several fracture sets were intersected, some of which do not connect the two piezometers. Dissolved helium and bromide were injected into the dipole flow field for 75 minutes, followed by an additional 510 minutes of flushing. The breakthrough of helium was retarded relative to bromide, as was expected due to the greater aqueous diffusion coefficient of helium. Also, only -25% of the total mass injected of both tracers was recovered. Modeling of the tracer transport was accomplished using an analytical one-dimensional flow and transport model for flow through a fracture with diffusion into the matrix. The assumptions made include: streamlines connecting the injection and withdrawal point can be modeled as a dipole of equal strength, flow along each streamline is one dimensional, and there is a constant Peclet number for each streamline. In contrast to many other field tracer studies performed in fractured rock, the actual travel length between piezometers was not known. Modeling was accomplished by fitting the characteristics of the tracer breakthrough curves (BTCs), such as arrival times of the peak concentration and the center of mass. The important steps were to determine the fracture aperture (240 microm) based on the parameters that influence the rate of matrix diffusion (this controls the arrival time of the peak concentration); estimating the travel distance (11 m) by fitting the time of arrival of the centers of mass of the tracers; and estimating fracture dispersivity (0.5 m) by fitting the times that the inflection points occurred on the front and back limbs of the BTCs. This method works even though there was dilution in the withdrawal well, the amount of which can be estimated by determining the value that the modeled concentrations need to be reduced to fit the data (approximately 50%). The use of two tracers with different diffusion coefficients was not necessary, but it provides important checks in the modeling process because the apparent retardation between the two tracers is evidence of matrix diffusion and the BTCs of both tracers need to be accurately modeled by the best fit parameters.  相似文献   

"Relationship Between Pumping-Test and Slug-Test Parameters: Scale Effect or Artifact?" by J.J. Butler Jr. and J.M. Healey     

Charles W. Rovey II  William L. Niemann 《Ground water》1998,36(6):866-867

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Use of Multiple Isotope Tracers to Evaluate Denitrification in Ground Water: Study of Nitrate from a Large-Flux Septic System Plume   总被引：15，自引：0，他引：15  

Ramon Aravena  William D. Robertson 《Ground water》1998,36(6):975-982

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Dissolution Enthalpies of Magnesian Calcites     

William D. Bischoff 《Aquatic Geochemistry》1998,4(3-4):321-336

A series of synthetic and biogenicmagnesian calcites was dissolved in weak acetic acidsolutions to measure the enthalpies of dissolution at25°C. For the synthetic phases, heat releasedwas 33.5 kJ/mol for calcite, decreasing to 33 kJ/molfor a phase of 2 mol % MgCO3, and increasing to35 kJ/mol for a phase of 15 mol %. Values of excessenthalpies, ΔHxs, calculated using calciteand magnesite end-members, average about -1 kJ/mol forthe synthetic phases. Total entropies of solidsolution formation, ΔSSS, also werecalculated using available data on Gibbs free energiesof formation and these excess enthalpies. Values ofΔSSS range from -2 J/(mol-K) at 2 mol % to-5 J/(mol-K) at 15 mol % MgCO3. These negativevalues of ΔHxs and ΔSSSsuggest that some form of ordering (cation?) isobtained in the synthetic phases, and that vibrationalentropies of the solid solution are diminished incomparison to the end-members. In contrast, biogenic samples generally have positivevalues of ΔHxs, increasing from +1 kJ/molat 5 mol % to +3 kJ/mol at 20 mol % MgCO3. Mostvalues of ΔSSS are equal (within errors)to values expected from configurational enthalpyalone. Thus, in most biogenic materials cationordering probably is not obtained, and most phases aremore typical of equivalent-site solid solutions.  相似文献   

Abundance and size of larval fishes outside the entrance to Beaufort Inlet, North Carolina     

William F. Hettler  Jonathan A. Hare 《Estuaries and Coasts》1998,21(3):476-499

Synoptic ichthyoplankton sampling was conducted on two transects, one on either side of Beaufort Inlet, North Carolina, during the winter immigration season of seven ocean-spawned, estuarine-dependent fishes;Brevoortia tyrannus (Atlantic menhaden),Leiostomus xanthurus (spot),Micropogonias undulatus (Atlantic croaker),Lagodon rhomboides (pinfish),Paralichthys albigutta (Gulf flounder),P. dentatus (summer flounder), andP. lethostigma (southern flounder). Densities and lengths of larvae were significantly different among sampling dates, with distance offshore, and between sides of the inlet. Flood-tide stage had minimal effect on larval densities and lengths except forP. albigutta andP. lethostigma. Changes in larval densities with distance offshore were not coherent among species; densities ofB. tyrammus increased offshore whereas densities of the other species decreased offshore. Average larval densities on a sampling date were coherent among species. Patterns in larval lengths were also coherent among the four non-flounder species. Larval densities outside of Beaufort Inlet were correlated with larval densities inside of Beaufort Inlet. Larval densities outside of Beaufort Inlet were also correlated with the north component of the wind, nearshore water temperature, and distance to the mid-shelf front. Differences in larval density across the inlet were significantly correlated with the east component of the wind. The patterns in larval densities outside of Beaufort Inlet were complex and apparently influenced by both the physical processes that supply larvae to the nearshore region and nearshore physical dynamics.  相似文献   

The effect of open-marsh water management on summer bird populations on Topsail Island, North Carolina     

Gilbert S. Grant  William W. Kirby-Smith 《Estuaries and Coasts》1998,21(2):361-363

Open-marsh water management (OMWM) manipulates selected areas of an estuarine marsh by constructing narrow, deep ditches that harbor resident populations of predators of mosquito larvae. It does not, however, alter the surrounding vegetation by deposition of spoil mounds. We censused the summer (breeding and nonbreeding) bird populations in two adjacent salt marsh sites on Topsail Island, North Carolina, for two summers before OMWM ditching occurred and for four seasons postditching. A total of 53 nonbreeding species and five breeding species of birds were encountered on the study sites. None of the interannual changes in bird populations can be attributed to OMWM.  相似文献   

On the nature of the radial velocity variability of Aldebaran: a search for spectral line bisector variations     

Artie P. Hatzes  & William D. Cochran 《Monthly notices of the Royal Astronomical Society》1998,293(4):469-478

The shape of the Ti  i 6303.8-Å spectral line of Aldebaran as measured by the line bisector was investigated using high signal-to-noise ratio, high-resolution data. The goal of this study was to understand the nature of the 643-d period in the radial velocity for this star reported by Hatzes & Cochran. Variations in the line bisector with the radial velocity period would provide strong evidence in support of rotational modulation or stellar pulsations as the cause of the 643-d period. A lack of any bisector variability at this period would support the planet hypothesis.
Variations in the line asymmetries are found with a period of 49.93 d. These variations are uncorrelated with the 643-d period found previously in the radial velocity measurements. It is demonstrated that this 50-d period is consistent with an m =4 non-radial sectoral g-mode oscillation. The lack of spectral variability with the radial velocity period of 643 d may provide strong evidence in support of the hypothesis that this variability stems from the reflex motion of the central star due to a planetary companion having a mass of 11 Jupiter masses. However, this long-period variability may still be the result of a low-order ( m =2) pulsation mode as these would cause bisector variations of less than the error measurement.  相似文献   

Paleohydrologic implications of 18O enriched Lake Agassiz water     

William M. Buhay  Robert N. Betcher 《Journal of Paleolimnology》1998,19(3):285-296

Lake Agassiz water oxygen isotopic compositions inferred from sediment core organics and pore waters provide some additional insight into the paleohydrology of the Great Lakes and their drainage into the North Atlantic during the late glacial and early Holocene. Isotopically enriched Lake Agassiz water supports the hypothesis that high Huron Basin lake (Mattawa) phases, during the early Holocene (9600–9300 and 9100–8100 years BP) resulted from an influx of Lake Agassiz water and suggests that low lake (Stanley) phases (9800–9600, 9300–9100, 8100–7400 years BP) were influenced more by regional influxes of isotopically depleted glacial melt water. Eastward drainage of enriched early Lake Agassiz water supports an active Port Huron outlet between 11000 and 10500 years BP and also helps to explain the absence of an ¹⁸O depleted interval in North Atlantic foram records. This may be the result of a balance between the opposing isotopic effects of depleted Lake Agassiz water and lower sea surface temperatures on carbonate precipitation between 11000 and 10000 years BP.  相似文献   

Paleolimnology of Lake Winnipeg     

Brian J. Todd  C. F. Michael Lewis  L. Harvey Thorleifson  Erik Nielsen  William M. Last 《Journal of Paleolimnology》1998,19(3):211-213

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Seasonal trends in the uranium-series istopic signatures of lake waters and sediments: Hawes Water, north-west England     

William H. Blake  Andrew J. Plater  John F. Boyle 《Journal of Paleolimnology》1998,20(1):1-14

Potential seasonal variation in the U-series radioisotopic signatures of lake and input waters was investigated in Hawes Water, north-west England, and the sedimentary record was examined to establish whether any observed seasonality is preserved in the sediment U and Th radioisotopic activity ratios. U-series disequilibrium in the waters is indicative of both surface and shallow sub-surface origins for the dissolved U, and that this supply is influenced by changes in the prevailing hydrological regime. However, the lake is buffered from this seasonality in that the ²³⁴U/²³⁸U activity ratio remains constant during the year, and the U content undergoes only a marginal decrease during summer. The change in the mechanism of lake sedimentation from allochthonous organic input during winter to autochthonous carbonate formation during summer has a more significant influence on the U-series radioisotopic characteristics of sedimentary record in that the proportion of organic and carbonate material both exhibit a strong control on the²³⁴U/²³⁸U activity ratio and U content. In addition, significant proportions of sediment U and Th are associated with ferromanganese oxyhydroxides. Given this seasonality, it is of some significance that the ²³⁴U/²³⁸U activity ratios of the bottom sediments preserve a reasonable record of lake U-series disequilibrium and are, therefore, potential indicators of long-term changes in catchment hydrology.  相似文献