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971.
The conditional acid dissociation constants (pKa′) of two sulfonephthalein dyes, thymol blue (TB) and m-cresol purple (mCP), were assessed throughout the estuarine salinity range (0<S<40) using a tris/tris–HCl buffer and spectrophotometric measurement. The salinity dependence of the pKa′ of both dyes was fitted to the equations (25 °C, total proton pH scale, mol kg soln−1):The estimated accuracy of pH measurements using these calculated pKa′ values is considered to be comparable to that possible with careful use of a glass electrode (±0.01 pH unit) but spectrophotometric measurements in an estuary have the significant advantage that it is not necessary to calibrate an electrode at different salinities. pH was measured in an estuary over a tidal cycle with a precision of ±0.0005 pH unit at high (S>30) salinity, and ±0.002 pH unit at low (S<5) salinity. The pH increased rapidly in the lower salinity ranges (0<S<15) but less rapidly at higher salinities. 相似文献
972.
Amvrakikos Gulf is a Neogene basin, formed during a late extensional tectonic phase within the Plio-Quaternary period. It is a semienclosed embayment, separated from the Ionian Sea by a shallow (< 10 m) channel. The analysis of 3.5-kHz seismic reflection profiles shows that, during the last (Würm) glacial period, the parts of the Gulf that lie at water depths >41 m (below present sea level) were a paleo-lake while the rest were exposed to subaerial erosion. Subsequent offshore depositional sequences accumulated at rates of 1.2–2.3 m/ka. 相似文献
973.
Dowty RA Shaffer GP Hester MW Childers GW Campo FM Greene MC 《Marine environmental research》2001,52(3):195-211
Research was conducted to assess the impact of oiling on fresh-marsh plant communities and to test the efficacy of techniques that may be used to enhance the bioremediation of crude oil spills in these environments while minimizing secondary anthropogenic impacts. To emulate field conditions, a mesocosm facility was used that houses 120 mesocosm vessels, each of 200-1 capacity. A five-way factorial treatment arrangement was used that included two substrates (inorganic, organic), two nutrient regimes (fertilized, not fertilized), two aeration levels (substrate aeration, no aeration), three oiling concentrations (0-, 5-, 10-1 m(-2) of South Louisiana Sweet Crude oil), and four vascular plant species (Alternanthera philoxeroides, Panicum hemitomon, Phragmites australis, Sagittaria lancifolia, and an unplanted control). Under the 5- and 10-1 m(-2) oiling concentrations, S. lancifolia displayed a short-term response of increased productivity, whereas P. hemitomon had the highest biomass production and photosynthetic rates at the end of the 18-month experiment. Overall plant growth and productivity, as well as oil degradation, were significantly higher in the inorganic substrate, indicating that biodegradation of oil spills in organic substrates may require a longer time period. Time-released fertilizer also stimulated plant productivity and resulted in higher soil respiratory quotients, suggestive of greater microbial activity, particularly in aerated mesocosms. The amount of oil remaining after 18 months was lowest in aerated and fertilized mesocosms containing either P. hemitomon or S. lancifolia and a substrate of low organic matter content. 相似文献
974.
Video assessment of environmental impacts of salmon farms 总被引:1,自引:0,他引:1
975.
A phase-resolving wave transformation module is combined with an intra-wave sediment transport module to calculate the on-/offshore sediment transport rates. The wave module is based on the Boussinesq equations extended into the surf zone. The vertical variation of the mean undertow and the intra-wave sediment concentrations are calculated. The net sediment transport rates are calculated, and the equation for conservation of sediment is solved to predict the beach profile evolution. The results of the present paper showed that the undertow contribution to the sediment transport rates is not dominating in all parts of the surf zone, even for eroding beaches, suggesting that other contributions should not be neglected. The present model also showed that for the same offshore wave energy the time series of the oscillatory motion is important and that the effect of wave groups cannot be disregarded. 相似文献
976.
G. H. Sutton F. K. Duennebier B. Iwatake J. D. Tuthill B. T. R. Lewis J. Ewing 《Marine Geophysical Researches》1981,5(1):3-34
The purpose of the experiment was to determine the effects of coupling and bottom currents on ocean bottom seismometers. Twelve operational OBSs, three specially designed three-component systems, and a hydrophone were compared with each other. Unlike seismometers placed on hard rock at land stations, ocean bottom seismometers can be affected by soft sediments (which act as lossy mechanical springs) and by buoyancy. Coupling through soft sediments can modify the response to ground motion much as a low pass filter does, and high buoyancy tends to counteract this effect. These effects are observed in the Lopez data, which consist of signals from mechanical transient tests, cap shots, airgun pulses, and general background noise. The modification of response is pronounced for some instruments and barely noticeable in others. Instruments that stand high in the water relative to their base width tend to be susceptible to rocking motion that shows up as a mechanical cross coupling between horizontal and vertical motion. Correlation of Lopez results with coupling theory suggests that it is possible to design ocean bottom seismometers that will couple well to any sediment. Current levels at the Lopez site (<5 cm s-1) were too small to produce noticeable effect on any of the instruments; however, the same design criteria that will minimize coupling problems will also lessen problems caused by ocean currents.Hawaii Institute of Geophysics Contribution No. 1171. 相似文献
977.
978.
Measurements of 226Ra and 210Pb in barite samples separated from different depths of a piston core from the eastern equatorial Pacific are reported. 226Ra is enriched in the barite as would be expected from the chemistries of Ra and Ba; the ratio centers around 1.5 · 1014 atoms/mole. The results suggest that barite is concentrating Ra at a rate comparable to its decay rate, viz. 5.78 · 10?3 yr?1. The gross 210Pb depletion with respect to 226Ra is indicative of 222Rn loss due to the smallness of the barite crystals. 相似文献
979.
980.
A stochastic prognostic model of the atmospheric precipitation in the tropical area of the Atlantic Ocean is developed on the basis of a large data array. The data represent a series of monthly precipitation rates for 31 towns in the Republic of Guinea covering a period of 35–64 years as well as satellite data on the meridional displacement of the Intertropical Convergence Zone during 11 years. The model takes into account major regularities of the tropical precipitation: their impulsive periodic regime, trends, and the modulation of the stochastic component by the determined variability.Translated by Mikhai M. Trufanov. 相似文献