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971.
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974.
The use of radioactive isotopes to measure the transfer of materials in aquatic food chains 总被引:5,自引:0,他引:5
Radioisotopes have been misused extensively by ecologists in transfer studies within food chains. Unless it is known that no recycling of isotope has occurred during the experiment, the assumption of linear uptake when in fact the system is not linear, even over short periods, can lead to significant errors in the estimation of ingestion or feeding. If recycling occurs, at least a 3 or 4-compartment, hydraulic-type model is necessary to even approximate the complicated kinetics of isotopic transfer in a simple aquatic feeding experiment. In any event, it is essential to follow the uptake or loss of an isotope (change in specific activity) as a function of time in at least 1 compartment before deciding on an appropriate model. If experiments are designed so that the maximum number of rate processes are summed or integrated by the animal, the kinetics can be considerably simplified. If the food supply is uniformly labelled, the rate of change of tracer can be used to give a rate of ingestion (grazing). If the predator is labelled with a suitable isotope before starting the experiment, the rate of loss of its isotope burden under different experimental conditions can be used to determine respiration or excretion rates, turnover rates, ingestion, and the size and number of major compartments in the transfer system.Bedford Institute Contribution. Woods Hole Oceanographic Institution Contribution No. 2690. 相似文献
975.
Howard M. Prichard Thomas F. Gesell Charles T. Hess Conrad V. Weiffenbach Philip Nyberg 《Environment international》1982,8(1-6)
Radon concentrations were measured in several locations in each of approximately 100 dwellings in central Maine and in Houston, TX. Integrated samples were taken during the heating (or cooling) seasons with commercially available passive alpha track devices, while grab samples were taken at the time of integrated sampler deployment. It was found that both indoor and outdoor measurements in both areas were distributed log normally, and that the geometric mean of indoor measurements in Maine was three times higher than that of corresponding measurements in the Houston area. It was also noted that the mean of the indoor grab sample measurements was not significantly different from the mean of the indoor integrated measurements, and that the degree of correlation between the grab samples and a given indoor integrated sample was nearly as good as between integrated samples taken at different living area locations. 相似文献
976.
D. F. Soule M. Oguri F. Shahrokhi N. L. Jones L. A. Sharver M. S. Connor R. W. Howarth R. W. Yeung G. C. Christodoulou J. J. Connor B. R. Pearce D. A. Rice R. D. Anderson J. W. Anderson N. V. Alisov E. B. Valev A. V. Doncheva V. N. Kalutskov Paul E. Lydolph Philip P. Micklin N. T. Kuznetsov 《Environmental management》1977,1(6):549-555
977.
978.
For natural water bodies there are many models of biochemical oxidation of organic pollutants, from simple to complicated ones. For the artificial conditions of waste water treatment plants there are numerous models of oxidation processes too. The authors believe that a better understanding of these processes in nature would be gained if the oxidation processes in more simple artificial conditions were understood.An attempt has been made to explain the variety of types of models of waste treatment in an activated sludge system or a biofilm reactor by the diffusion mechanism of oxidation of single substrates on the one hand, and by superposition of the kinetics of oxidation of single substrates in measurements of the dynamics of oxidation of a complex pollutant on the other hand.The conditions in which zero- and first-order models are valid in the oxidation of single substrates are derived. Respective formulae for rate constants are given. Monod's model is valid in a broader range of substrate concentration variations. An approximate formula for the half-saturation constant is proposed. Satisfactory agreement with experimental data for glucose and ammonia substrates is shown.The formal character of models being used at present is claimed for multicomponent substrates. The accuracy of the calculation is largely governed by the number of model coefficients. Similar results obtained by Monod's and Grau's models, often used in practice, are emphasized. 相似文献
979.
980.