IDENTIFYING AND ASSESSING PROBLEM AREAS IN SOIL EROSION SURVEYS USING AERIAL PHOTOGRAPHS     

R. G. B. Jones  M. A. Keech 《The Photogrammetric Record》1966,5(27):189-197

Gully erosion has for many years been a problem in Rhodesia1s Tribal Trust Lands. This paper describes how Soil Conservation Service staff, with no previous ground knowledge of these areas, used good quality 1/25,000 scale aerial photographs to measure the extent of the gully erosion and to pinpoint erosion “black spots.” This enabled quick and reliable estimates of the cost of reclamation work to be made without the need for time-consuming field survey. The survey method discussed is capable of wide application wherever gully erosion occurs and needs to be brought under control.  相似文献   

Ion-exchange reactions on clay minerals and cation selective membrane properties as possible mechanisms of economic metal concentration     

A. Weiss  G. C. Amstutz 《Mineralium Deposita》1966,1(1):60-66

A series of exploratory experiments on the concentration of base metals through ion exchange reactions on clay minerals show promising results. The extraction of Pb, Zn and Cd from bentonite, illite, kaolinite and montmorillonite was successful and megascopic quantities of PbS, CdS and ZnS could be obtained at specific loci, depending essentially on the flow velocity, and the other cations present. These or similar exchange reactions are tentatively proposed as possible mechanisms of economic metal concentration during diagenesis.

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Zusammenfassung Es werden experimentelle Resultate zur Anreicherung von Schwermetallen durch Tonminerale (Montmorillonite, Illite und Kaolinite) mitgeteilt. Eine erste Anreicherung kann über den Kationenaustausch bewirkt werden. In dem darauffolgenden zweiten, sehr viel wirksameren Schritt werden die Schwermetallionen aus den Tonlagern extrahiert und in deren Nähe als schwerlösliche Sulfide oder Carbonate gefällt. Die Extraktion beruht darauf, daß Tonschichten als Kationen-permeable Membranen wirken können. Sie wird von der Art der Tonminerale und der Kationen, den Lösungsgenossen, den Konzentrationsverhältnissen, dem pH-Wert, der Reaktionstemperatur, dem Porenvolumen und der Porenverteilung im Sediment beeinflußt.

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SOME INTRODUCTORY NOTES ON REGIONAL DIVISION AND SET THEORY     

Reginald G. Golledge  Douglas M. Amadeo 《The Professional geographer》1966,18(1):14-19

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Electrochemical strengthening of clayey sandy soils     

Lucas G. Adamson  Donald W. Quigley  H. Ross Ainsworth  George V. Chilingar 《Engineering Geology》1966,1(6):451-459

Most previous studies and applications of electrochemical stabilization of soils through electroosmosis have been made on clayey soils. The object of this investigation was to find out if relatively small amounts of clay (1.5%–3.5%, by weight) present in a sandy soil would be enough for stabilization and strengthening to be possible. The results indicate increases of cohesion of the order of 100–200 lb./sq.ft. X-ray analyses of treated soils indicate that sheet structures of clays are reduced and silicates destroyed upon treatment by electroosmosis. Newly-formed minerals also cement the soil. These neoformations include gibbsite, limonite, calcite, hydrohematite, hydrogoethite (hydrolepidocrocite), hisingerite, allophane, allophanoid, gypsum, hematite, magnetite, nontronite, trona and natron (Na₂ CO₃, 10H₂O). The process seems to be irreversible.  相似文献   

Isotopic variation of fishes in freshwater and estuarine zones of a large subtropical coastal lagoon     

A.M. Garcia  D.J. Hoeinghaus  J.P. Vieira  K.O. Winemiller 《Estuarine, Coastal and Shelf Science》2007,73(3-4):399-408

We used stable C and N isotope ratios of tissues from 29 fish species from a large subtropical lagoon in southern Brazil to examine spatial variability in isotopic composition and vertical trophic structure across freshwater and estuarine habitats. Nitrogen isotope ratios indicated a smooth gradation in trophic positions among species, with most fishes occupying the secondary and tertiary consumer level. Fish assemblages showed a significant shift in their carbon isotopic signatures between freshwater and estuarine sites. Depleted carbon signatures (from −24.7‰ to −17.8‰) were found in freshwater, whereas more enriched signatures (from −19.1‰ to −12.3‰) were obtained within the estuarine zone downstream. Based on our survey of the C₃ and C₄ plants and isotopic values for phytoplankton and benthic microalgae reported for ecosystems elsewhere, we hypothesized that the observed δ¹³C differences in the fish assemblage between freshwater and estuarine sites is due to a shift from assimilating organic matter ultimately derived from C₃ freshwater marsh vegetation and phytoplankton at the freshwater site (δ¹³C ranging from −25‰ to −19‰), to C₄ salt-marsh (e.g. Spartina) and widgeon grass (Ruppia maritima), benthic microalgae and marine phytoplankton at the estuarine sites (from −18‰ to −12‰). Our results suggested that fish assemblages are generally supported by autochthonous primary production. Freshwater fishes that likely were displaced downstream into the estuary during periods of high freshwater discharge had depleted δ¹³C values that were characteristic of the upper lagoon. These results suggest that spatial foodweb subsidies can occur within the lagoon.  相似文献   

Diurnal changes in the bio-optical properties of the phytoplankton in the Alborán Sea (Mediterranean Sea)     

Jesús M. Mercado  Teodoro Ramírez  Dolores Corts  Marta Sebastin  Andreas Reul  Begoa Bautista 《Estuarine, Coastal and Shelf Science》2006,69(3-4):459

The changes in the phytoplankton absorption properties during a diurnal cycle were investigated at one station located in the north-western area of the Alborán Sea. The experiment was performed in spring when the water column was strongly stratified. This hydrological situation permitted the establishment of a deep chlorophyll a (chl a) fluorescence maximum (DFM) which was located on average close to the lower limit of the mixed layer and the nutricline. The relative abundance of pico-phytoplankton (estimated as its contribution to the total chl a) was higher in the surface, however, micro-phytoplankton dominated the community at the DFM level. Chl a specific absorption coefficient (a*(λ)) also varied with optical depth, with a* (the spectrally average specific absorption coefficient) decreasing by 30% at the DFM depth with respect to the surface. A significant negative correlation between the contribution of the micro-phytoplankton to the total chl a and a* was obtained indicating that a* reduction was due to changes in the packaging effect. Below the euphotic layer, a* increased three-fold with respect to the DFM, which agrees with the expected accumulation of accessory pigments relative to chl a as an acclimation response to the low available irradiance. The most conspicuous change during the diurnal cycle was produced in the euphotic layer where the chl a concentration decreased significantly in the afternoon (from a mean concentration of 1.1 μg L⁻¹ to 0.7 μg L⁻¹) and increased at dusk when it averaged 1.4 μg L⁻¹. In addition, a* and the blue-to-red absorption band ratio increased in the afternoon. These results suggest that a*(λ) diurnal variability was due to increase in photo-protective and accessory pigments relative to chl a. The variation ranges of a*(λ) at 675 and 440 nm (the absorption peaks in the red and blue spectral bands, respectively) in the euphotic layer were 0.01–0.04 and 0.02–0.10 m² mg⁻¹ chl a, respectively. Approximately 30% out of this variability can be attributed to the diurnal cycle. This factor should therefore be taken into account in refining primary production models based on phytoplankton light absorption.  相似文献   

Nonlinear effects of the distribution of amplitudes of sea waves     

M.Aziz Tayfun 《Ocean Engineering》1984,11(3):245-264

The effect of nonlinearities, such as wave-breaking and vertical asymmetry associated with sea waves, on the distribution of wave amplitudes is explored. Semiclosed theoretical expressions are derived to describe the distributions of breaking-limited crest and trough amplitudes for Stokes-type nonlinear sea waves. These are compared with the conventional Rayleigh distribution appropriate to linear wave amplitudes. The construction of nonlinear wave envelopes with the fast Fourier transform technique is described. The technique can be utilized to enlarge the data base in empirical analyses of field records which typically contain limited information on amplitude characteristics. The theoretical distributions and the proposed data enlargement technique are demonstrated with the analysis of a nonlinear wave record.  相似文献   

Numerical simulation of undersea cable dynamics   总被引：7，自引：0，他引：7  

C.M. Ablow  S. Schechter 《Ocean Engineering》1983,10(6):443-457

A fully three-dimensional code has been written to compute the motion of a towed cable. The code is based on a robust and stable finite difference approximation to the differential equations derived from basic dynamics. A 3500-ft (1.07 km) cable pulled at 18.5 knots (34.3 km hr⁻¹) through a circular turn of 700 yd (0.64 km) radius has been computed in about half of the real time of the maneuver. The computed displacements are close to the measured ones; the changes in depth are within 2%.  相似文献   

Lagrangian diffusion equation and its application to oceanic dispersion     

Akira Okubo  Curtis C. Ebbesmeyer  Brian G. Sanderson 《Journal of Oceanography》1983,39(5):259-266

The Lagrangian diffusion equation appropriate for the dispersion of current followers (e. g., floats, drogues, drifters) is proposed. The analytical solution to the equation is obtained for a uniform deformation field, characterized by Lagrangian deformations and anisotropic eddy diffusivities both varying with time. Expressions are derived for the patch area and its elongation and rotation. For small values of elapsed time after the initial release the patch area can be accounted for by the exponential of the cumulative value of the horizontal divergence; the relative rate of change of the patch area can be accounted for by the horizontal divergence.  相似文献   

The heave response of a spar buoy     

M.J. Tucker 《Ocean Engineering》1982,9(3):259-270

The vertical response of spar buoys to waves is examined. The response is the product of a rather complex wave forcing function and the resonant response of the buoy. With compound spar buoys (that is, consisting of more than one section of different diameters) the forcing function has a zero at a frequency which is usually close to the resonant frequency, but which can be arranged to be somewhat higher with beneficial effects on the response. Only the effects of pressure and inertia are considered, since this paper is mainly concerned to clarify some specific general principles and it is difficult to include the effects of drag, which are complex.  相似文献