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771.
Removal of atmospheric particles by leaves and twigs of urban trees: Some preliminary observations and assessment of research needs 总被引:3,自引:0,他引:3
This paper reviews the various lines of evidence that support the hypothesis that above-ground plant parts remove particulates from the atmosphere. Some scanning electron microscope observations of the particulate burden on leaves of London planetree are discussed. The authors present an outline of the kinds of research required to support or reject the hypothesis that urban woody plants are important air filters. 相似文献
772.
ABSTRACT. The need for accurate, independent records of flow on the Columbia River at The Dalles, Oregon, has been met by the installation of an acoustic streamflow-measuring system. This device provides an index of the velocity of flow by measuring the difference in traveltimes of acoustic pulses transmitted through the water in each direction along a diagonal path across the river. The flow of water along the path increases the speed of one signal and retards the speed of the other. The difference in time of travel is related linearly to the water velocity along the path. Installation of the system, which is the first application of an acoustic flowmeter in a large natural channel, was completed in April 1969. It has been in continuous operation since that date. The velocity index and water-surface elevation are used as a two-variable index in the computation of flow. These variables, correlated against current-meter measurements made by use of specialized boat equipment, provide a reliable basis for computations of instantaneous and daily mean discharges. 相似文献
773.
Harman Smith 《Journal of the American Water Resources Association》1976,12(6):iii-iv
774.
Abdel-Aziz I. Kashef J. C. Smith 《Journal of the American Water Resources Association》1975,11(6):1107-1120
ABSTRACT: In coastal confined aquifers, the extent of the salt-water wedge due to natural ground-water flow can be determined by available methods. If water is pumped by a discharge well, the quality of the water depends upon the rate and duration of pumping as well as the location of the well. A study has been made to find the extent of the progress of salt-water intrusion due to the operation of one discharge well taking into account various conditions of aquifer properties, pump capacities, natural flows, time effects, and well locations. Dimension-less solutions for specific conditions have been obtained by means of a simple computer program. Range of most common conditions is discussed. One of the main findings of this study was that salt water may be pumped out of a well even if it is located in an initially totally fresh-water zone beyond the natural salt/fresh-water interface. 相似文献
775.
Douglas V. Smith 《Journal of the American Water Resources Association》1972,8(6):1225-1234
Recent progress in operations research has refined stochastic programming with recourse sufficiently to significantly increase its potential for use in water resource planning. To demonstrate its strengths and weaknesses this paper considers an irrigation planning problem and illustrates how more and more refined variants of this problem are successively cast into stochastic programming with recourse forms. The result is an outline of the state of the art with method limitations and demands on model formulation clearly indicated. 相似文献
776.
The known degradation products and degradative pathways involving selected volatile aliphatic chlorinated hydrocarbons in soil-groundwater systems are summarized. Current data indicate that the most commonly found products of microbial degradation of these compounds come from reductive dehalogenation, while nonmicrobial degradations tend to involve hydrolysis and/or oxidation. However, conclusions must be regarded as tentative, since most of the available studies have involved model systems and extrapolations, rather than direct studies of compounds in groundwater systems. Other potentially complicating factors, such as mobility and volatilization, are mentioned. Current knowledge is discussed in the context of data that would be desirable to obtain in future studies. 相似文献
777.
Deborah R. Smith 《Behavioral ecology and sociobiology》1982,11(3):149-154
Summary
Philoponella oweni (Uloboridae) is a facultatively communal orb-web spider found in arid regions in the southwestern United States. Within one habitat solitary adult females and communal groups of adult females coexist.This study compared the reproductive output (egg production) and reproductive success (production of live offspring) of solitary and communal females. There was no significant difference in the mean number of egg-cases produced by solitary and communal females, but communal females produced significantly more eggs per egg-case. However, communal females suffered significantly higher rates of egg-case parasitism from the pteromalid wasp Arachnopteromalus dasys. As a result, the mean number of liver offspring produced by solitary and communal females did not differ. Thus, both strategies led to roughly equal reproductive success. The advantages of aggregation of adults may be significant in the evolution of social behavior in spiders. 相似文献
778.
Hose JE Cross JN Smith SG Diehl D 《Environmental pollution (Barking, Essex : 1987)》1989,57(2):139-148
White croaker (Genyonemus lineatus), collected from a highly contaminated site in San Pedro Bay and from a reference site 80 km away (Dana Point), were induced to spawn in the laboratory. Forty-one per cent of San Pedro Bay females and 54% of Dana Point females spawned. Examination of the ovaries of non-spwaning females revealed that spawning was imminent in the remainder of Dana Point fish but only in 16% of the San Pedro Bay fish. The remainder of the San Pedro Bay fish (43%) contained only immature, yolky oocytes. No croakers containing more than 3.8 ppm ovarian total DDT could be induced to spawn whereas 36% of a contemporaneous San Pedro Bay sample had ovarian total DDT residues in excess of 4 ppm. This suggests that the inability to induce spawning in white croaker may be associated with an ovarian total DDT threshold of about 4 ppm. These data, coupled with observed decreases in fecundity (32%), fertility (14%), and early oocyte loss (30%) relative to reference fish, could partially explain the population declines observed for many southern California fishes since the 1940s. 相似文献
779.
Inorganic carbon uptake by photosynthetically active protoplasts of the red macroalga Chondrus crispus 总被引:1,自引:0,他引:1
Photosynthetically active protoplasts were isolated from Chondrus crispus Stackh. by treating thalli with -carrageenase produced from batch culture of Pseudomonas carrageenovora. Using the silicone oil centrifugation technique, it was found that the protoplasts: (1) did not generally accumulate inorganic carbon (Ci) above the concentration in their incubation medium; (2) were saturated at Ci concentrations of 3 to 4 mM; (3) had an intracellular pH of 7.50 when incubated at pH 7.5; and (4) their initial carbon fixation rate was reduced by carbonic anhydrase inhibitors. Although the carbon fixation rate of the protoplasts was about 30% that of thallus fragments, presumably due to the relatively harsh protoplast isolation treatment, the behavior of the protoplasts was similar to that of fragments. This similarity indicates that the protoplasts are photosynthetically active and behave as thallus fragments. Further, the data are consistent with the hypothesis that C. crispus acquires Ci for photosynthesis by the diffusion of CO2 across the plasma membrane. 相似文献
780.