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781.
782.
210Po and 210Pb measurements of soils delineated uranium anomalies at three out of four test sites in Ontario, Canada. Measurements were made of 210Po in solutions produced by both complete digestion and partial leaching of soil samples. Direct plating of 210Po onto metal plates was followed by measuring the alpha activity. Subsequent plating of 210Po in-grown from 210Pb in solution several months later confirmed the anomalies.The 210Po and 210Pb anomalies at three of the test sites coincided with 226Ra and 222Rn anomalies. Samples from the fourth uranium occurrence associated with a known 222Rn anomaly failed to show either a 226Ra anomaly on the one hand, or 210Po or 210Pb anomalies on the other. This suggests that the 210Po and 210Pb anomalies were probably produced by the decay of 226Ra contained within secondary dispersion haloes.Although anomalies due to the 210Po and 210Pb products of 222Rn have now been documented, prospecting methods based on their use as direct tracers of the migration paths of 222Rn require much further development. 相似文献
783.
William W. Carothers Robert H. Mariner Terry E.C. Keith 《Journal of Volcanology and Geothermal Research》1987,31(1-2)
Isotopic compositions were determined for hydrothermal quartz, calcite, and siderite from core samples of the Newberry 2 drill hole, Oregon. The δ15O values for these minerals decrease with increasing temperatures. The values indicate that these hydrothermal minerals precipitated in isotopic equilibrium with water currently present in the reservoirs. The δ18O values of quartz and calcite from the andesite and basalt flows (700–932 m) have isotopic values which require that the equilibrated water δ18O values increase slightly (− 11.3 to −9.2‰) with increasing measured temperatures (150–265°C). The lithic tuffs and brecciated lava flows (300–700 m) contain widespread siderite. Calculated oxygen isotopic compositions of waters in equilibrium with siderite generally increase with increasing temperatures (76–100°C). The δ18O values of siderite probably result from precipitation in water produced by mixing various amounts of the deep hydrothermal water (− 10.5 ‰) with meteoric water (− 15.5 ‰) recharged within the caldera. The δ13C values of calcite and siderite decrease with increasing temperatures and show that these minerals precipitated in isotopic equilibrium with CO2 of about −8 ‰.The δ18O values of weakly altered (<5% alteration of plagioclase) whole-rock samples decrease with increasing temperatures above 100°C, indicating that exchange between water and rock is kinetically controlled. The water/rock mass ratios decrease with decreasing temperatures. The δ18O values of rocks from the bottom of Newberry 2 show about 40% isotopic exchange with the reservoir water.The calculated δ18O and δD values of bottom hole water determined from the fluid produced during the 20 hour flow test are −10.2 and −109‰, respectively. The δD value of the hydrothermal water indicates recharge from outside the caldera. 相似文献
784.
Keith Beven 《地球表面变化过程与地形》1987,12(1):69-82
A further development of a topography-based model of catchment hydrology (TOPMODEL) is described and applied to the problem of predicting flood frequency characteristics. The model can simulate infiltration excess, saturation excess, and subsurface runoff contributions to peak flows. Catchment geomorphology plays a central role in predicting the nature of the hydrological response. Using stochastic rainfall and initial condition inputs based on measured data, the model satisfactorily reproduces the mean hourly flow flood frequency growth curve for the Wye catchment, but not the mean number of peaks greater than 3mm h?1 each year. Suggestions for further improvements are made. 相似文献
785.
Benthic invertebrate populations at the Surry power plant on James River, Virginia and the C. P. Crane power plant on Saltpeter Creek, Maryland exhibited large spatial and temporal variations. At C. P. Crane, where the cooling water is pumped between two tidal creeks, populations in the receiving creek exhibited five response patterns: 1) mitigation of a winter dieoff (Rangia cuneata, a brackish water clam), 2) acceleration of growth or development (R. cuneata; Scolecolepides viridis, a polychaete;Leptocheirus plumulosus, an amphipod; Tubificidae; andCoelotanypus sp., a dipteran), 3) importantion of larvae from the source water creek (S. viridis andCoelotanypus sp.), 4) extension of creek-dwelling species into the adjacent river (Coelotanypus sp. and other dipterans), and 5) increased severity of late summer population depressions (S. viridis andL. plumulosus). At Surry, where the cooling was no confined creek system at the discharge, and effects were less pronounced. The community in the Surry discharge zone resembled the community at downriver stations more closely than at upriver reference stations. TheL. plumulosus population near the Surry discharge was depressed, while theMytilopsis leucophaeta population was enhanced. No major ecological damage was attributed to either power plant, due in part to the resilience of estuarine endemic populations, but the unique features exhibited by each of the two sites support the argument that oligohaline estuarine zones should not be designateda priori for unregulated industrial development. 相似文献
786.
Discharge characteristics in six adjacent mountainous watersheds in northern New Mexico, U.S.A., vary substantially between basins underlain by different lithologies. Relatively resistant gneisses and granites underlie two basins (drainage areas: 43 and 94 km2) that have high unit discharge (0·010 to 0·14 m3s?1 km?2), high bankfull discharge, and sustained high discharge. Less resistant sandstones and shales underlie four basins (drainage areas: 96 to 215 km2) that have relatively low unit discharge (0·001 to 0·005 m3s?1 km?2), relatively low bankfull discharge, and peak discharges that are not sustained as long as those in the crystalline terrane. Analysis of snowmelt-runoff water budgets suggests that three factors control hydrologic conditions in the basins. First, area-elevation distributions appear to control the timing and amounts of water input. These distributions probably reflect the erosional resistance of the different lithologies. Second, lithology appears to control runoff production in areas having minor amounts of storage. Third, glacial deposits in headwater regions control discharge duration and timing via storage and return flow releases. The amount of return flow released by glacial deposits, however, is probably controlled by the permeability of underlying bedrock. Therefore it appears that the duration, timing, and magnitude of discharge events in the study area are controlled both directly and indirectly by lithology. Stream power and shear stress estimates derived from bankfull discharge and bed-material size data suggest that higher bedload transport rates and larger bedload particle sizes exist in streams draining crystalline rocks than in streams draining sedimentary terrane. It appears that source-area lithology, by controlling discharge production, also influences stream power, bedload transport capabilities, and therefore total amounts of bedload transport. 相似文献
787.
788.
A rhodamine dye tracer study was conducted over eight tidal cycles to investigate mixing and tidal exchange processes in Perch Pond, a Cape Cod embayment subject to recurrent blooms of the toxic dinoflagellate, Gonyaulax tamarensis. Dye injected at the inlet to Perch Pond during flood tide became well-mixed within the pond in one day and was removed at an effective first order rate of 0.36 d?1, equivalent to a 70% utilization of the maximum possible tidal exchange. This relatively high flushing efficiency can be attributed to a density-driven circulation within the pond, consisting of a subsurface inflow of high salinity dense water on the flood tide followed by removal of lighter surface layers through the shallow inlet during ebb tide. The formation of a frontal convergence near the inlet on flood tide is consistent with the observed distribution of G. tamarensis cysts and shelifish toxicity. It is also clear that phytoplankton like G. tamarensis, whose maximum growth rates approximate the rate of tidal flushing, can only bloom within the embayment by avoiding the outflowing surface waters. Mixing within the pond is probably less efficient and population losses greater during dry periods when the pond salinity is higher and the stratification weaker. 相似文献
789.
Initial Sr87/Sr86 ratios and rubidium and strontium contents have been measured in 83 specimens from 8 suites of alkalic and ultrabasic rocks. The range of initial Sr87/Sr86 ratio observed and the number of specimens (in parentheses) analysed for each suite are: West Kimberley, Australia (8), 0.7125–0.7215; Jumilla, Spain (6), 0.7136–0.7158; Bearpaw Mountains, Montana (9), 0.7062–0.7086; Highwood Mountains, Montana (10), 0.7072–0.7087; Hopi Buttes, Arizona (8), 0.7038–0.7094; Leucite Hills, Wyoming (17), 0.7055–0.7070; Montana diatremes (13), 0.7034–0.7073; Navajo Province, Arizona and New Mexico (12), 0.7052–0.7099.The initial Sr87/Sr86 ratios of the West Kimberley and Jumilla rocks are the highest yet found in strontium-rich basic rocks. Some of the individual specimens from West Kimberley have initial ratios as high as some estimates of the present Sr87/Sr86 ratio of average crustal material. This is interpreted to mean that the West Kimberley and Jumilla rocks contain substantial amounts of radiogenic strontium, and possibly other elements, from a crustal source. 相似文献
790.
The crustal structure of the Hawaiian Archipelago, northern Melanesia, and parts of the Central Pacific Basin have been studied by seismic refraction methods. The systematic variation found in crustal thickness in the Hawaiian Islands is explainable by a hypothesis of differential subsidence. The crustal structure of northern Melanesia points to tensional forces in an east-west direction and compressional forces in a north-south direction. In the Central Pacific Basin, a 7.4 km/sec layer in the lower crust seems to be present over a wide area. 相似文献