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111.
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Catastrophic events reveal the dynamic nature of salt-marsh vegetation in Southern California 总被引:1,自引:0,他引:1
Joy B. Zedler Jordan Covin Chris Nordby Phil Williams John Boland 《Estuaries and Coasts》1986,9(1):75-80
Recent hydrological disturbances, including flooding, dry-season streamflow, and drought, greatly altered coastal wetland habitats in sourthern California. At Tijuana Estuary, a six-year study of salt-marsh vegetation patterns during these rare conditions documented substantial temporal variability in plant growth and distribution. Important to cordgrass (Spartina foliosa Trin.) dynamics were the amount and timing of streamflows, which reduced soil salinity and alleviated stresses on plant growth. Poorest growing conditions occurred in 1984 when both river and tidal flows were lacking; soils had low moisture and extreme salinities (avg.=104‰ in September). Plant stress was documented in 1984 as high mortality (62% fewer stems than in 1983) and reduced height (19% less than in 1983). Cordgrass height was greatest in 1980 following winter flooding (20% increase over 1979); densities were greatest in 1983 with summer freshwater influxes (60% increase over 1982). A carbon allocation model is proposed to explain the varied responses. 相似文献
113.
Chris C.Y. CHAN 《Geostandards and Geoanalytical Research》1986,10(2):131-134
The carbonate-carbon (CO2 ) content of forty-one geochemical reference samples has been determined by coulometric method following acid treatment of the sample for releasing CO2 . The method is superior to the conventional methods in speed, accuracy, sensitivity, specificity, and the coverage of CO2 range. The results on NBS limestone samples agree well with the certified values. The precision of the method is 0.5 % r.s.d., and the practical detection limit is 10 ppm C. 相似文献
114.
A detailed study of the subsurface thermal regime at the Upper Stillwater dam site, Uinta Mountains, northeast Utah, has been made. Temperature measurements were made in 36 drillholes located within a 1 km2 area and ranging in depth from 20 to 97 m. Holes less than about 40 m deep were used only to obtain information about spatial variations in mean annual surface temperature. Several holes in or near talus slopes at the sides of the canyons have temperature minima approaching 0°C between 10 and 20 m indicating the presence of year-round ice at the base of the talus. Another set of holes show transient thermal effects of surface warming resulting from clearing of a construction site 3.5 years prior to our measurements. Most of the remaining holes show conductive behavior and have gradients ranging from 13° to 17°C km−1. Measurements made on 44 core samples yield a thermal conductivity of 5.6 (std. dev. 0.35) W m−1 K−1 for the Precambrian quartzite present. Surface heat flow estimates for these holes range from 70 to 100 mW m−2. However, the local disturbance of the thermal field by topography and microclimate is considerable. A finite difference method used to model these effects yielded a locally corrected Upper Stillwater heat flow of about 75 mW m−2. A final correction to account for the effects of refraction of heat from the low conductivity sedimentary rocks in the Uinta Basin into the high conductivity quartzite at the dam site, produced a regionally corrected Upper Stillwater heat flow between 60 and 65 mW m−2. This value is consistent with the observed heat flow of 60 mW m−2 in the Green River Basin to the north and the Uinta Basin to the south. 相似文献
115.
The ongoing human-induced emission of carbon dioxide (CO2) threatens to change the earth's climate. One possible way of decreasing CO2 emissions is to apply CO2 removal, which involves recovering of carbon dioxide from energy conversion processes and storing it outside the atmosphere. Since the 1980's, the possibilities for recovering CO2 from thermal power plants received increasing attention.In this study possible techniques of recovering CO2 from large-scale industrial processes are assessed.In some industrial processes, e.g. ammonia production, CO2 is recovered from the process streams to prevent it from interfering with the production process. The CO2 thus recovered can easily be dehydrated and compressed, at low cost. In the iron and steel industry, carbon dioxide can be recovered from blast furnace gas. In the petrochemical industry CO2 can be recovered from flue gases, using low-temperature heat for the separation process.Carbon dioxide can be recovered from large-scale industrial processes and in some cases the cost of recovery is significantly less than CO2 recovery from thermal power plants. Therefore this option should be studied further and should be considered if carbon dioxide removal is introduced on a wide scale. 相似文献
116.
The delay coordinate technique is examined as an indicator of the regime of particle dynamics for the system of single charged particle motion in magnetic reversals. Examples of numerically integrated trajectories in both static (zero electric field) and time dependent (corresponding nonzero induction electric field) simple models for magnetic reversals are considered. In the static case, the dynamics can in principle be directly classified by constructing Poincaré surfaces of section; here we demonstrate that whilst the Poincaré surface contains the relevant information to classify the dynamics, the corresponding delay coordinate plot can provide a far more sensitive indication of the onset of nonregular behaviour. In the case of nonperiodic time dependence considered here Poincaré plots cannot in general be constructed directly. Nevertheless, delay coordinate plots can still reveal details of the phase space portrait of the system, and here are shown to indicate whether segments of stochastic motion exist in a given trajectory. It is anticipated that the delay coordinate plot technique as realized here will be a valuable tool in characterizing the behaviour in large numbers of trajectories that are evolved in time-dependent systems, thereby giving us insight into the evolution of the distribution function as a whole, either in prescribed fields or in self-consistent numerical simulations. 相似文献
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The experimental programme of Southard and Mackintosh (1981) provides a definitive refutation of the autosuspension criterion as it was originally defined. A simple energy budget for dilute two-phase flow is derived from continuum theory of mixtures; it shows that Bagnold's criterion is based on an arbitrary comparison of two elements of the complete two-phase system. It is recommended that facile, ab hoc criteria for the behaviour of such complex flows be avoided in favour of analyses based on fundamental equations of motion. 相似文献
120.
G.P. Chapman 《Geoforum》1983,14(3):267-275
India's drive to improve agricultural performance includes a major commitment to develop many new large-scale irrigation systems. But existing systems perform far below design capacity. Analysis and correction of the problems in existing systems may help increase production and may also lead to improvements in the design of new schemes, particularly if there is improved understanding of the relationship between physical and social systems and improved management techniques. Analysis of the problems leads practising geographers into applied use of theories and models of systems-with-uncertainty. 相似文献