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排序方式: 共有617条查询结果,搜索用时 31 毫秒
41.
Fraser Goff Sue J. Goff Sharad Kelkar Lisa Shevenell Alfred H. Truesdell John Musgrave Heinz Rüfenacht Wilmer Flores 《Journal of Volcanology and Geothermal Research》1991,45(1-2)
Results of drilling, logging, and testing of three exploration core holes, combined with results of geologic and hydrogeochemical investigations, have been used to present a reservoir model of the Platanares geothermal system, Honduras. Geothermal fluids circulate at depths ≥ 1.5 km in a region of active tectonism devoid of Quaternary volcanism. Large, artesian water entries of 160 to 165°C geothermal fluid in two core holes at 625 to 644 m and 460 to 635 m depth have maximum flow rates of roughly 355 and 560 l/min, respectively, which are equivalent to power outputs of about 3.1 and 5.1 MW(thermal). Dilute, alkali-chloride reservoir fluids (TDS ≤ 1200 mg/kg) are produced from fractured Miocene andesite and Cretaceous to Eocene redbeds that are hydrothermally altered. Fracture permeabillity in producing horizons is locally greater than 1500 and bulk porosity is ≤ 6%. A simple, fracture-dominated, volume-impedance model assuming turbulent flow indicates that the calculated reservoir storage capacity of each flowing hole is approximately 9.7 × 106 l/(kg cm−2), Tritium data indicate a mean residence time of 450 yr for water in the reservoir. Multiplying the natural fluid discharge rate by the mean residence time gives an estimated water volume of the Platanares system of ≥ 0.78 km3. Downward continuation of a 139°C/km “conductive” gradient at a depth of 400 m in a third core hole implies that the depth to a 225°C source reservoir (predicted from chemical geothermometers) is at least 1.5 km. Uranium-thorium disequilibrium ages on calcite veins at the surface and in the core holes indicate that the present Platanares hydrothermal system has been active for the last 0.25 m.y. 相似文献
42.
43.
S. Kaul 《洁净——土壤、空气、水》1983,11(1):47-57
The mineral content was investigated in the below-ground biomass, the above-ground biomass and the litter of the macrophytes in five wetlands in the valley of the river Jehlum. In different seasons, the concentrations of calcium, magnesium, sodium, potassium, phosphorus and nitrogen in the dry matter were determined. Sodium, phosphorus, potassium and calcium showed decreasing concentraions from spring to autumn. The sodium and magnesium concentrations showed an irregular trend. As a whole, the incorporated mass of substances per unit of area increases, however, in the course of the period of vegatation for the below-ground biomass as well as the above-ground biomass. Due to washing-out, the litter always shows considerably reduced concentrations. 相似文献
44.
Recent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data, and in particular data describing the size distribution of the weathered rock fragments. To enable future development of rock breakdown models for use in landscape evolution and soil production models, laboratory work was undertaken to extend existing schist/salt weathering fragmentation studies to include an examination of the breakdown of sub‐millimetre quartz chlorite schist particles in a seasonally wet tropical climate. Laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution. The results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown. The fragmentation of the schist is characterized by splitting of the larger fragments into mid‐sized product with finer material produced, possibly from the breakdown of mid‐sized fragments when weathering is more advanced. Salinity, the salt addition method and temperature were all found to affect weathering rates. Subtle differences in mineralogy also produce variations in weathering patterns and rates. It is also shown that an increase in drying temperature leads to accelerated weathering rates, however, the geometry of the fracture process is not significantly affected. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
45.
The increased frequency of wildfires in the United States has become a common prediction associated with the build-up of greenhouse gases. In this investigation, variations in annual wildfire data in Yellowstone National Park are compared to variations in historical climate conditions for the area. Univariate and multivariate analytical techniques reveal that (a) summer temperatures in the Park are increasing, (b) January-June precipitation levels are decreasing, and (c) variations in burn area within the Park are significantly related to the observed variations in climate. Outputs from four different general circulation model simulations for 2 × CO2 are included in the analyses; model predictions for increasing aridity in the Yellowstone Park area are generally in agreement with observed trends in the historical climate records. 相似文献
46.
A case study was conducted on the potential impacts of climate change on fish habitat in a southeastern reservoir. A reservoir water quality model and one year of baseline meteorologic, hydrologic, and inflow water quality input were used to simulate current reservoir water quality. Total adult striped bass habitat, defined by specific quantitative temperature and dissolved oxygen criteria, was simulated. Daily reservoir volumes with optimal, suboptimal, and unsuitable temperature and DO were predicted for the year. Output from recent runs of atmospheric general circulation models (GCMs), in which atmospheric carbon dioxide concentrations have been doubled, was then used to adjust the baseline inputs to the water quality model. New sets of input data were created for two grid cells for each of three GCMs. All six climate scenarios are predicted to cause overall declines in the available summer striped bass habitat, mostly due to lake water temperatures exceeding striped bass tolerance levels. These predictions are believed to result from the consensus among GCM scenarios that air temperatures and humidity will rise, and the sensitivity of the reservoir model to these parameters. The reservoir model was found to be a promising tool for examining potential climate-change impacts. Some of the assumptions required to apply GCM output to the reservoir model, however, illustrate the problems in using large-scale gridcell output to assess small-scale impacts. 相似文献
47.
Presented is a stochastic method of analysis of offshore towers subjected to strong motion earthquakes. A zero mean ergodic Gaussian process of finite duration is used to characterize horizontal ground acceleration and full fluid structure interaction effects are included. Numerical results for four representative deep water towers having heights of 475, 675, 875 and 1075 ft are compared with corresponding results obtained by the response spectrum method of analysis. Particular emphasis is placed on the maximum or extreme values of total transverse shear and total overturning moment. Comparisons are made with code values and the role of ductility is briefly discussed. 相似文献
48.
49.
Lisa L. Etherington Philip N. Hooge Elizabeth R. Hooge David F. Hill 《Estuaries and Coasts》2007,30(6):927-944
Alaska, U.S.A, is one of the few remaining locations in the world that has fjords that contain temperate idewater glaciers.
Studying such estuarine systems provides vital information on how deglaciation affects oceanographic onditions of fjords and
surrounding coastal waters. The oceanographic system of Glacier Bay, Alaska, is of particular interest ue to the rapid deglaciation
of the Bay and the resulting changes in the estuarine environment, the relatively high oncentrations of marine mammals, seabirds,
fishes, and invertebrates, and the Bay’s status as a national park, where ommercial fisheries are being phased out. We describe
the first comprehensive broad-scale analysis of physical and iological oceanographic conditions within Glacier Bay based on
CTD measurements at 24 stations from 1993 to 2002. easonal patterns of near-surface salinity, temperature, stratification,
turbidity, and euphotic depth suggest that freshwater nput was highest in summer, emphasizing the critical role of glacier
and snowmelt to this system. Strong and persistent tratification of surface waters driven by freshwater input occurred from
spring through fall. After accounting for seasonal nd spatial variation, several of the external physical factors (i.e., air
temperature, precipitation, day length) explained a large mount of variation in the physical properties of the surface waters.
Spatial patterns of phytoplankton biomass varied hroughout the year and were related to stratification levels, euphotic depth,
and day length. We observed hydrographic atterns indicative of strong competing forces influencing water column stability
within Glacier Bay: high levels of freshwater ischarge promoted stratification in the upper fjord, while strong tidal currents
over the Bay’s shallow entrance sill enhanced ertical mixing. Where these two processes met in the central deep basins there
were optimal conditions of intermediate tratification, higher light levels, and potential nutrient renewal. These conditions
were associated with high and sustained hlorophylla levels observed from spring through fall in these zones of the Bay and provide a framework for understanding he abundance
patterns of higher trophic levels within this estuarine system. 相似文献
50.
The growing interest in and emphasis on high spatial resolution estimates of future climate has demonstrated the need to apply
regional climate models (RCMs) to that problem. As a consequence, the need for validation of these models, an assessment of
how well an RCM reproduces a known climate, has also grown. Validation is often performed by comparing RCM output to gridded
climate datasets and/or station data. The primary disadvantage of using gridded climate datasets is that the spatial resolution
is almost always different and generally coarser than climate model output. We have used a Bayesian statistical model derived
from observational data to validate RCM output. We used surface air temperature (SAT) data from 109 observational stations
in California, all with records of approximately 50 years in length, and created a statistical model based on this data. The
statistical model takes into account the elevation of the station, distance from coastline, and the NOAA climate region in
which the station resides. Analysis indicates that the statistical model provides reliable estimates of the mean monthly SAT
at any given station. In our method, the uncertainty in the estimates produced by the statistical model are directly determined
by obtaining probability density functions for predicted SATs. This statistical model is then used to estimate average SATs
corresponding to each of the climate model grid cells. These estimates are compared to the output of the RCM to assess how
well the RCM matches the observed climate as defined by the statistical model. Overall, the match between the RCM output and
the statistical model is good, with some deficiencies likely due in part to the representation of topography in the RCM. 相似文献