Diver-operated piston corer for nearshore use     

Francis J. Sansone  James T. Hollibaugh  Sue M. Vink  Randoph M. Chambers  Samantha B. Joye  Brian N. Popp 《Estuaries and Coasts》1994,17(3):716-720

A diver-operated piston corer suitable for collecting cores of >3 m length from fine-grained nearshore sediment has been developed. The corer uses a platform that rests on the sediment surface supporting both the operators and a derrick that maintains the piston at the sediment-water interface. The core is insected into and recovered from the sediment manually. The technique offers several advantages; low cost, minimal disruption of the sediment-water interface, little compaction of the sediment, the ability to collect longer length cores than is possible with gravity corers, and the ability to be deployed from relatively small boats. Dissolved ammonium and inorganic carbon data are presented from a 3.3-m core collected by this technique from Tomales Bay, California.  相似文献   

Early use by fish of a mitigation salt marsh,Humboldt Bay,California     

Robert H. Chamberlain  Roger A. Barnhart 《Estuaries and Coasts》1993,16(4):769-783

Fish numbers and biomass in a mitigation salt marsh, Humboldt Bay, California, were examined from July 1981 to October 1982 and were compared with a nearby established marsh to determine whether the restored marsh provided adequate mitigation for habitat lost due to construction of a nearby marina. The use by fish of channels adjacent to the two marshes and the channel at the Woodley Island Marina construction site, for which mitigation was required, were also compared. The mitigation marsh, adjacent to Freshwater Slough channel, was 5.2 km from the marina site. Fishes were sampled by otter trawl, ichthyoplankton net, fixed channel nets, drop traps, and beach seines. Thirty-one fish species and two crab species were collected. Wide ranges in seasonal salinities and water temperatures, and differences in marsh elevation influenced fish use of the mitigation marsh area. The intertidal area of the mitigation marsh, dominated by euryhaline sticklebacks and topsmelts, did not replace intertidal and subtidal habitat lost by marina construction, which had more stable salinities and water temperatures and was used extensively by juvenile English sole.  相似文献   

Flood control failures in a Third World City: Benin City,Nigeria — some environmental factors and policy issues     

Odemerho  Francis O. 《GeoJournal》1993,29(4):371-376

GeoJournal - Inspite of step-up efforts at controlling flood hazards in Third World cities, the frequency and magnitude of the flood problem have more than doubled in recent years. A survey of the...  相似文献   

Phase transformations and inherited lattice preferred orientations: implications for seismic properties     

David Mainprice  Michel Humbert  Francis Wagner 《Tectonophysics》1990,180(2-4):213-228

In phase transitions via either the martensitic (diffusionless shear) or nucleation and growth mechanism a specific orientation relationship may exist between the two phases. In cases where the orientation relationship is known, the lattice preferred orientation (LPO) inherited by the new phase may be calculated from the LPO of the old phase. The method of calculation is presented in a form suitable for the spherical harmonic method of texture analysis using the orientation distribution function (ODF). Examples are presented for the -β-quartz, calcite-aragonite, orthopyroxene-clinopyroxene and olivine-spinel transformations.

The seismic properties of the transformed and untransformed phases are calculated from the ODF and the single crystal elastic constants. In particular the -β quartz transformation is considered in detail. The quartz polycrystal is very anisotropic in the alpha field (V_p anisotropy coefficient, A = 8.1%) and almost isotropic in the β-field (A = 2.1%). The transition is accompanied by V_p velocity increase of 0.6 km/s. In the other example discussed, olivine-β-spinel, there is also a decrease in V_p anisotropy coefficient from 11.1% (olivine) to 4.0% (β-spinel). The estimate of the volume fraction of olivine at the 400 km discontinuity (associated with this phase transition) is shown to depend on the direction of wave propagation.  相似文献   

Calculated mineral equilibria in the greenschist-blueschist-eclogite facies in Na2O−FeO−MgO−Al2O3−SiO2−H2O     

Michel Guiraud  Tim Holland  Roger Powell 《Contributions to Mineralogy and Petrology》1990,104(1):85-98

The new, greatly expanded internally-consistent dataset of Holland and Powell includes thermodynamic data for a wide range of mineral end-members in common rock-forming minerals, in particular, including FeMg_-1 substitutions in glaucophane, garnet, chloritoid and carpholite, and FeMg_-1 and MgSiAl_-1Al_-1 substitutions in talc and chlorite. Moreover, we have the uncertainties and correlations for these data. With the data, we have calculated the full pressure-temperature phase diagram for the system Na₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O (NFMASH) for quartz (or coesite) and H₂O in excess, in the range 300°–800°C and 5–50 kbars. By solving the set of non-linear equations formed by the equilibrium relationships for an independent set of equations between the end-members in an assemblage in NFMASH, the compositions of the minerals (and PT) can be calculated. Thus the changes in MgSiAl_-1Al_-1 along NMASH reactions, and FeSiAl_-1Al_-1 along NFASH reactions, are calculated, and the changes in FeMg_-1 and MgSiAl_-1Al_-1 along NFMASH reactions are calculated. From this information it is straightforward to generate PT diagrams for specific rock compositions. Mineral assemblages and mineral compositional changes in the phase diagram are discussed in relation to greenschist, blueschist and eclogite facies assemblages in metapelitic rocks. It is found that the correspondence between the predictions of the phase diagrams and the observations on rocks is remarkably good. When semiquantitative extensions of the phase diagram to include Ca(MgFe)_-1, NaSiCa_-1Al_-1, Fe³⁺Al_-1 and KNa_-1 substitutions are taken into account the agreement is essentially complete.  相似文献   

On the general character of coastal flow     

Roger L. Hughes 《Pure and Applied Geophysics》1990,133(4):665-689

It is well-known that some coastal currents such as the Florida Current have a recirculating region on their coastal side, while other currents such as the East Australian Current have no such region. Under the hypothesis that the form drag on a coastal current by an irregular coastal topography reduces the momentum transport of the current to a minimum for the given flow within the current, the hydraulic theory of coastal currents is used to explain this behaviour.  相似文献   

The application of cellular automata to the erosion of landforms     

Roger Smith 《地球表面变化过程与地形》1991,16(3):273-281

Two approaches to modelling surface erosion are described which can be used to explain the development of geomorphological features. The first approach uses non-linear wave theory and shows how surface gradient discontinuities can arise as the erosion of an initially smooth surface proceeds. For isotropic erosion, surface shapes may be predicted by a simple application of the Huyghens wavefront construction and Snell's law at media boundaries. A second approach uses a computational cellular method. The general shapes predicted by the computer simulations are shown to agree with those determined from the wave approach. The application of the cellular method to problems of geomorphological interest are discussed.  相似文献   

The effect of Tschermak's substitution on assemblages in aluminous dolomites     

Judy Baker  T. J. B. Holland  Roger Powell 《Contributions to Mineralogy and Petrology》1994,118(1):48-59

A calculated petrogenetic grid for the system CaO-MgO-Al₂O₃-SiO₂-CO₂-H₂O (CaMASCH), incorporating Tschermak's substitutions in amphibole, chlorite, talc and clinopyroxene, is used to examine phase relationships in aluminous marbles. A series of diagrams illustrating the effect upon stable mineral assemblages of increasing the aluminium content of a bulk composition is used to show the way aluminous minerals enter mineral assemblages in progressively more aluminous rocks. The effects of changing pressure and the incorporation of Fe into the bulk composition on the stable mineral assemblages are also examined. The calculated equilibria are shown to be in reasonable agreement with natural assemblages, and the incorporation of new experimental data on amphiboles into the existing dataset is shown to improve the agreement between observed and natural amphibole compositions.  相似文献   

210Pb dating of scottish lake sediments,afforestation and accelerated soil erosion     

Richard W. Battarbee  Peter G. Appleby  Kevin Odell  Roger J. Flower 《地球表面变化过程与地形》1985,10(2):137-142

Changes in the rate of soil erosion in lake catchments can be identified from changes in the rate of sediment accumulation in lakes. Here we compare recently afforested sites with non-afforested sites in the Galloway area of Southwest Scotland. We show that lakes with non-afforested catchments have slow, constant sediment accumulation rates, whereas lakes with recently afforested catchments have changes in accumulation that parallel the known history of afforestation. For Loch Grannoch the sediment accumulation rate increases from 0.1 cm yr^?1 to over 2 cm yr^?2 during the disturbance period. Data from L. Skerrow, however, suggest that the rate might decline to predisturbance levels after approximately 10 years as the forest canopy closes and drainage channels stabilize.  相似文献   

River basin management and food crisis in Nigeria     

Francis C. Okafor   《Geoforum》1985,16(4):413-421

River Basin Development is one of the key agricultural programmes embarked upon by Nigeria to meet the challenges of escalating import bills on food. This paper takes a critical look at the various efforts made by the management of the River Basin Authorities in responding to the current food crisis. The rationale for the huge financial allocation made to the Authorities is questioned, and the management lapses in their key areas of operation, such as irrigation, mechanization and extension services, are discussed. It is found that despite the huge financial investments made in the river basins, their impact is hardly felt, not only in terms of food production capacity but also in the production performance of the peasant farmers. The paper argues that the problem of food crisis in Nigeria could be solved by strengthening the ability of the peasant farmers and farmers co-operatives through financial aid and extension services, and not by huge financial investments on high technology agricultural projects, characterized by centralized administration and expatriáte management.  相似文献