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171.
172.
In evaluating potential impacts of climate change on water resources, water managers seek to understand how future conditions may differ from the recent past. Studies of climate impacts on groundwater recharge often compare simulated recharge from future and historical time periods on an average monthly or overall average annual basis, or compare average recharge from future decades to that from a single recent decade. Baseline historical recharge estimates, which are compared with future conditions, are often from simulations using observed historical climate data. Comparison of average monthly results, average annual results, or even averaging over selected historical decades, may mask the true variability in historical results and lead to misinterpretation of future conditions. Comparison of future recharge results simulated using general circulation model (GCM) climate data to recharge results simulated using actual historical climate data may also result in an incomplete understanding of the likelihood of future changes. In this study, groundwater recharge is estimated in the upper Colorado River basin, USA, using a distributed-parameter soil-water balance groundwater recharge model for the period 1951–2010. Recharge simulations are performed using precipitation, maximum temperature, and minimum temperature data from observed climate data and from 97 CMIP5 (Coupled Model Intercomparison Project, phase 5) projections. Results indicate that average monthly and average annual simulated recharge are similar using observed and GCM climate data. However, 10-year moving-average recharge results show substantial differences between observed and simulated climate data, particularly during period 1970–2000, with much greater variability seen for results using observed climate data. 相似文献
173.
Stephen E. Davis Daniel L. Childers John W. Day David T. Rudnick Fred H. Sklar 《Estuaries and Coasts》2001,24(4):610-622
We used enclosures to quantify wetland-water column nutrient exchanges in a dwarf red mangrove, (Rhizophora mangle L.) system near Taylor River, an important hydraulic linkage between the southern Everglades and eastern Florida Bay, Florida, USA. Circular enclosures were constructed around small (2.5–4 m diam) mangrove islands (n=3) and sampled quarterly from August 1996 to May 1998 to quantify net exchanges of carbon, nitrogen, and phosphorus. The dwarf mangrove wetland was a net nitrifying environment with consistent uptake of ammonium (6.6–31.4 μmol m−2 h−1) and release of nitrite +nitrate (7.1–139.5 μmol m−2 h−1) to the water column. Significant flux of soluble reactive phosphorus was rarely detected in this nutrient-poor, P-limited environment. We did observe recurrent uptake of total phosphorus and nitrogen (2.1–8.3 and 98–502 μmol m−2 h−1, respectively), as well as dissolved organic carbon (1.8–6.9 μmol m−2 h−1) from the water column. Total organic carbon flux shifted unexplainably from uptake, during Year 1, to export, during Year 2. The use of unvegetated (control) enclosures during the second year allowed us to distinguish the influence of mangrove vegetation from soil-water column processes on these fluxes. Nutrient fluxes in control chambers typically paralleled the direction (uptake or release) of mangrove enclosure fluxes, but not the magnitude. In several instances, nutrient fluxes were more than twofold greater in the absence of mangroves, suggesting an influence of the vegetation on wetland-water column processes. Our findings characterize wetland nutrient exchanges, in a mangrove forest type that has received such little attention in the past, and serve as baseline data for a system undergoing hydrologic restoration. 相似文献
174.
B.L.N. Kennett A.W.H. Bunch J.A. Orcutt R.W. Raitt 《Earth and Planetary Science Letters》1977,34(3):439-444
Systematic travel time inversion techniques have been applied to first arrival travel times from a number of seismic refraction profiles on the crest and flanks of the East Pacific Rise to generate bounds on the possible velocity-depth distributions. The greatest variability in structure occurs within 5 Myr of the rise crest. The generally similar character of the bounds on the velocity distributions for ages greater than 5 Myr indicates that the most rapid aging occurs within 5 Myr of the crest, though the mantle velocity increases systematically with age. The nature of the bounds on the velocity distribution for the range of velocities associated with layer 3 requires that the velocity distribution within layer 3 increase with depth. 相似文献
175.
Tidal triggering of reservoir-associated earthquakes 总被引:1,自引:0,他引:1
If the effect of a reservoir is to bring a fault zone gradually to failure and trigger an earthquake, then it is reasonable that rapidly fluctuating tidal stresses may influence the time of the induced earthquakes. An examination of earthquakes from eight reservoirs shows that earthquakes at six sites occur at preferred times in the semidiurnal tidal cycle. Tidal-stress orientations and the phase within the semidiurnal tidal cycle were calculated for only the largest earthquakes occurring at each site. This insures the elimination of aftershocks and selects earthquakes which are independent of each other. Sites of a significant earthquake/tide correlation with less than a 3% chance of occurring randomly include Hebgen Lake, Mont., U.S.A.; Kariba, Rhodesia; Kerr Dam, Mont., U.S.A.; Kremasta, Greece; Lake Mead, Nev., U.S.A.; and Monteynard, France. Each data set includes from about ten to twenty earthquakes. In most of the above cases earthquake triggering seems to occur when tidal stress enhances slip, i.e., when tidal stresses are oriented to enhance the tectonic stress. 相似文献
176.
The prevailing theory for the formation of trona [Na3(CO3)(HCO3) · 2(H2O)] relies on evaporative concentration of water produced by silicate hydrolysis of volcanic rock or volcaniclastic sediments. Given the abundance of closed drainage basins dominated by volcanics, it is puzzling that there are so few trona deposits and present-day lakes that would yield dominantly Na–CO3 minerals upon evaporation. Groundwater in the San Bernardino Basin (southeastern Arizona, USA and northeastern Sonora, Mexico) would yield mainly Na–CO3 minerals upon evaporation, but waters in the surrounding basins would not. Analysis of the chemical evolution of this groundwater shows that the critical difference from the surrounding basins is not lithology, but the injection of magmatic CO2. Many major deposits of trona and Na–CO3-type lakes appear to have had “excess” CO2 input, either from magmatic sources or from the decay of organic matter. It is proposed that, along with the presence of volcanics, addition of “excess” CO2 is an important pre-condition for the formation of trona deposits. 相似文献
177.
178.
In scintillometry Monin–Obukhov similarity theory (MOST) is used to calculate the surface sensible heat flux from the structure parameter of temperature (CT2){(C_{T^2})} . In order to prevent saturation a scintillometer can be installed at an elevated level. However, in that case the observation level might be located outside the atmospheric surface layer (ASL) and thus the validity of MOST questioned. Therefore, we examine two concepts to determine the turbulent surface sensible heat flux from the structure parameter at elevated levels with data obtained at 60-m height on the Cabauw tower (the Netherlands). In the first concept (MOSTs) CT2{C_{T^2}} is still scaled with the surface flux, whereas in the second (MOSTl) CT2{C_{T^2}} is scaled with the local sensible heat flux. The CT2{C_{T^2}} obtained from both concepts is compared with direct observations of CT2{C_{T^2}} using a sonic anemometer/thermometer. In the afternoon (when the measurement height is located within the ASL) both concepts give results that are comparable to the directly observed values of CT2{C_{T^2}} . In the morning (data outside the ASL), our data do not unequivocally support either of the two concepts. First, the peak in CT2{C_{T^2}} that occurs when the measurement height is located in the entrainment zone disqualifies the use of MOST. Second, during the morning transition, local scaling shows the correct pattern (zero flux and a minimum in CT2{C_{T^2}}) but underestimates CT2{C_{T^2}} by a factor of ten. Third, from the best linear fit a we found that the slope of MOSTl gave better results, whereas the offset is closer to zero for MOSTs. Further, the correlation between the direct observations and MOST-scaled results is low and similar for the two concepts. In the end, we conclude that MOST is not applicable for the morning hours when the observation level is above the ASL. 相似文献
179.
Uncertainty Estimate of Surface Irradiances Computed with MODIS-, CALIPSO-, and CloudSat-Derived Cloud and Aerosol Properties 总被引:1,自引:0,他引:1
Seiji Kato Norman G. Loeb David A. Rutan Fred G. Rose Sunny Sun-Mack Walter F. Miller Yan Chen 《Surveys in Geophysics》2012,33(3-4):395-412
Differences of modeled surface upward and downward longwave and shortwave irradiances are calculated using modeled irradiance computed with active sensor-derived and passive sensor-derived cloud and aerosol properties. The irradiance differences are calculated for various temporal and spatial scales, monthly gridded, monthly zonal, monthly global, and annual global. Using the irradiance differences, the uncertainty of surface irradiances is estimated. The uncertainty (1σ) of the annual global surface downward longwave and shortwave is, respectively, 7?W?m?2 (out of 345?W?m?2) and 4?W?m?2 (out of 192?W?m?2), after known bias errors are removed. Similarly, the uncertainty of the annual global surface upward longwave and shortwave is, respectively, 3?W?m?2 (out of 398?W?m?2) and 3?W?m?2 (out of 23?W?m?2). The uncertainty is for modeled irradiances computed using cloud properties derived from imagers on a sun-synchronous orbit that covers the globe every day (e.g., moderate-resolution imaging spectrometer) or modeled irradiances computed for nadir view only active sensors on a sun-synchronous orbit such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation and CloudSat. If we assume that longwave and shortwave uncertainties are independent of each other, but up- and downward components are correlated with each other, the uncertainty in global annual mean net surface irradiance is 12?W?m?2. One-sigma uncertainty bounds of the satellite-based net surface irradiance are 106?W?m?2 and 130?W?m?2. 相似文献
180.