Field Measurement of Dissolved Oxygen: A Comparison of Methods     

Richard T. Wilkin  Mary S. McNeil  Cherri. J. Adair.  John T. Wilson 《Ground Water Monitoring & Remediation》2001,21(4):124-132

The ability to confidently measure the concentration of dissolved oxygen (D.O.) in ground water is a key aspect of remedy selection and assessment. Presented here is a comparison of the commonly practiced methods for determining D.O. concentrations in ground water, including colorimetric, membrane-covered electrode, and modified Winkler techniques. The Winkler titration (azide and permanganate modifications) is the most accurate and precise technique for determining D.O. and is appropriate for applications with stringent data quality objectives. In addition, excellent correlation over a wide range of D.O. concentrations was found between Winkler titrations and colorimetric tests using the rhodazine D (below 1 part per million [ppm]) and indigo carmine reagents (above 1 ppm). Electrode measurements represent the simplest method for determining D.O. concentrations on a continuous basis and electrode determinations positively correlate with Winkler results above 1 ppm. Below 1 ppm, electrodes provide only a qualitative measure of low D.O. level, apparently due to slow electrode response.  相似文献   

A close-interval sampler for collection of sediment pore waters for nutrient analyses     

John R. Montgomery  Mary T. Price  John Holt  Carl Zimmermann 《Estuaries and Coasts》1981,4(1):75-77

An in situ sediment pore water sampler is described. It can simultaneously and continuously sample at four discrete 1 cm levels at one location without disturbing the sediment or the sample. The sampler can maintain an anaerobic environment, and can be used over extended periods of time. Laboratory tests indicate 98 to 100 percent recoveries for ammonium, silicate, reactive phosphate, nitrate and nitrite. Vertical profiles for ammonium, reactive phosphate and silicate are shown from field studies.  相似文献   

Metal ion complex formation constants of some sedimentary humic acids with Zn(II), Cu(II) and Cd(II)     

Mary L Sohn  Michael C Hughes 《Geochimica et cosmochimica acta》1981,45(12):2393-2399

Metal ion complex formation constants were determined for several sedimentary humic acids (SHA) derived from a fresh water lake and several coastal marine environments, using a method based on size exclusion chromatography. Only one type of binding site was observed in all cases, and conditional log K_f values of between 5 and 7 (at pH 8, I = 0.01 M) were found. Elemental composition of the SHA was similar to soil HA, except that nitrogen content was significantly higher in the SHA. Other chemical properties of the SHA were consistent with those reported by other workers. While spectroscopic measurements indicated that the SHA may have contained significant amounts of polysaccharide compounds which were not removed by conventional separation and purification procedures, analysis indicated only very low levels of polysaccharides were present in the SHA.  相似文献   

The Use of Ground-Water Flow Models for Estimating Lake Seepage Rates     

James A. Munter  Mary P. Anderson 《Ground water》1981,19(6):608-616

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Geomagnetic field variations in southeastern Europe between 6500 and 100 years B.C.     

Mary Kovacheva  Dushan Veljovich 《Earth and Planetary Science Letters》1977,37(1):131-138

Results from joint work between the Geophysical Institute (Sofia, Bulgaria), and the Geomagnetic Institute (Grocka, Yugoslavia) on the geomagnetic field variation in the prehistoric past are presented. Preliminary curves of variation of the three geomagnetic elements: declination, inclination and intensity are presented. The movement of the virtual pole position for the 6500 years time period B.C. is derived. The curves and the virtual pole positions provide a dating tool for archaeological purposes and determination of the periodicities in the geomagnetic secular variations in southeastern Europe.  相似文献   

Nonlinear Plasma Phenomena in the Ionosphere: A.V. Gurevich. Springer-Verlag,New York-Heidelberg-Berlin, 1978 370 pp., US $ 49.00, ISBN 3-540-08605-6     

Mary K. Hudson 《Physics of the Earth and Planetary Interiors》1980,23(1):79

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Apparent propagation velocity of body waves     

Michael J. O'Rourke  Mary C. Bloom  Ricardo Dobry 《地震工程与结构动力学》1982,10(2):283-294

The apparent horizontal propagation velocity, that is the propagation velocity of seismic waves with respect to the ground surface, is discussed in this paper. This parameter is needed to determine the effects of earthquakes on long structures such as bridges and buried pipelines as well as the torsional rotation of foundations of multi-storey buildings. A time window intensity tensor introduced by Penzien and Kubo is used herein to determine the predominant directions of ground motion during an earthquake. Considering the reflection of waves at a free surface, an approximate relationship between the predominant direction and the angle of incidence of body waves with respect to the ground surface is presented. Knowing the material properties of the top layer and the angle of incidence, the desired propagation velocity with respect to the ground surface is readily calculated. The median value of the apparent propagation velocity of shear waves for near field sites which recorded the 1971 San Fernando earthquake was determined to be about 2-1 km/s using the above method. A similar value for the 1979 Imperial Valley earthquake is 3·7 km/s. These values are consistent with the range of values for the apparent propagation velocity determined by other researchers.  相似文献   

A late Wisconsin and Holocene vegetation history from the central brooks range: Implications for Alaskan palaeoecology     

Linda B. Brubaker  Harriet L. Garfinkee  Mary E. Edwards 《Quaternary Research》1983,20(2):194-214

Five pollen diagrams reveal late Wisconsin and Holocene vegetation changes in the Walker Lake/Alatna Valley region of the central Brooks Range, approximately 100 km west of the area studied by D. A. Livingstone (1955, Ecology36, 587–600). New insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate Picea glauca and P. mariana pollen. Three major pollen zones are identified: (1) a basal herb zone, characterized by high percentages of Cyperaceae, Gramineae, Salix, and Artemisia, and low total pollen influx; (2) a shrub Betula zone with increased total pollen influx and very high percentages of Betula pollen, predominantly in the size range of B. nana and B. glandulosa; and (3) and Alnus zone dominated by Alnus pollen. Lakes currently within the boreal forest or near tree line show relatively high percentages of Picea pollen in the Alnus zone. Several striking vegetation changes occurred between ca. 10,000 and 7000 yr B.P. Between ca. 11,000 and 10,000 yr B.P., Populus balsamifera pollen percentages as great as 30% indicate that this species was present at low-elevation sites near Walker Lake. These populations declined abruptly ca. 10,000 yr ago and have never regained prominence. About 8500 yr B.P., Picea glauca pollen reached 10–15%, indicating the arrival of P. glauca in or near the study area. P. glauca populations evidently decreased ca. 8000 yr ago, when Picea pollen percentages and influx fell to low values. About 7000 yr B.P., Alnus pollen percentages and influx rose sharply as alder shrubs became established widely. Picea once more expanded ca. 5000 yr ago, but these populations were dominated by P. mariana rather than P. glauca, which increased slowly at this time and may still be advancing northward. Some vegetation changes have been remarkably synchronous over wide areas of interior Alaska, and probably reflect responses of in situ vegetation to environmental changes, but others may reflect the lagged responses of species migrating into new areas.  相似文献   

Subtidal variability of transverse flow off a cape     

Arnoldo?Valle–LevinsonEmail author  Mary Catherine?Brown 《Ocean Dynamics》2003,53(3):166-175

Time series of velocity profiles at two Chesapeake Bay entrance sites were used to characterize the subtidal variability of transverse flows off a cape. A shallow sampling site was located near Cape Henry over 6 m of water and separated from a deep site, 20 m deep, by a distance of 4 km. The velocity profiles showed that wind-induced subtidal variations in general masked curvature effects (centrifugal accelerations) that may produce secondary circulation associated with tidal flow around a cape. Such secondary circulation, consisting of flow away from the cape at surface and toward the cape at depth, was observed only during periods of weak winds. Most of the time, transverse flows were unidirectional throughout the water column and moved in opposite directions at the two sites examined. This caused convergence of transverse flow between the two sites under the influence of northerly winds and divergence of transverse flow with southwesterly winds. In addition to unidirectional and curvature-induced secondary flows, other modes of subtidal variability consisted of (1) two-layered responses with surface flow toward the cape, and (2) three-layered responses. These two- and three-layered structures were observed more frequently at the deep site, where greater stratification is expected, than at the shallow site.Responsible Editor: Iris Grabemann  相似文献   

Determining extreme parameter correlation in ground water models   总被引：4，自引：0，他引：4  

Hill MC  Osterby O 《Ground water》2003,41(4):420-430

In ground water flow system models with hydraulic-head observations but without significant imposed or observed flows, extreme parameter correlation generally exists. As a result, hydraulic conductivity and recharge parameters cannot be uniquely estimated. In complicated problems, such correlation can go undetected even by experienced modelers. Extreme parameter correlation can be detected using parameter correlation coefficients, but their utility depends on the presence of sufficient, but not excessive, numerical imprecision of the sensitivities, such as round-off error. This work investigates the information that can be obtained from parameter correlation coefficients in the presence of different levels of numerical imprecision, and compares it to the information provided by an alternative method called the singular value decomposition (SVD). Results suggest that (1) calculated correlation coefficients with absolute values that round to 1.00 were good indicators of extreme parameter correlation, but smaller values were not necessarily good indicators of lack of correlation and resulting unique parameter estimates; (2) the SVD may be more difficult to interpret than parameter correlation coefficients, but it required sensitivities that were one to two significant digits less accurate than those that required using parameter correlation coefficients; and (3) both the SVD and parameter correlation coefficients identified extremely correlated parameters better when the parameters were more equally sensitive. When the statistical measures fail, parameter correlation can be identified only by the tedious process of executing regression using different sets of starting values, or, in some circumstances, through graphs of the objective function.  相似文献