Food habits and distribution of wintering canvasbacks,Aythya valisineria,on Chesapeake Bay     

Matthew C. Perry  Francis M. Uhler 《Estuaries and Coasts》1988,11(1):57-67

Baltic clams (Macoma balthica) were the predominant food items of 323 canvasbacks (Aythya valisineria) collected throughout Chesapeake Bay during 1970–1979. Natural vegetation constituted 4% of the food volume. Widgeongrass (Ruppia maritima) and redhead grass (Potamogeton perfoliatus) constituted the greatest percent volume and frequency of occurrence among the plant species, whereas wild celery (Vallisneria americana) constituted only a trace of the food volume. These results contrast with historical records of food habits of canvasbacks in Chesapeake Bay. Canvasback population estimates during the 1970’s were examined to detect annual and seasonal changes in distribution. Linear regression analyses of winter canvasback populations in the bay showed a significant decline in the upper-bay and middle-bay populations, but no significant changes in the lower-bay and Potomac River populations. The changes in winter distribution and abundance of the canvasback appear related to changes in natural food availability, which is the result of altered environmental conditions.  相似文献   

Subsidence, extension and thermal history of the West African margin in Senegal     

Marie Vronique Latil Brun  Francis Lucazeau 《Earth and Planetary Science Letters》1988,90(2)

The subsidence of the Atlantic margin in Senegal clearly shows two rapid stages related to the formation of (1) the Central Atlantic during the early Jurassic (around 200 Ma), and (2) the Equatorial Atlantic during the Cretaceous (100 Ma). A simple model of extension is used to interpret the subsidence history and to derive the thermal evolution of this basin. The present-day gravity, bathymetry, bottom hole temperatures (BHT) in oil exploration boreholes and heat flow density are used to control the validity of the model. Two cross sections from the outcropping basement to oceanic crust are used, one in Casamance and the other one at the south to latitude of Dakar. The model can fully explain the first-order subsidence history as well as the present-day observations, and therefore can provide valuable information about the thermal evolution of sediments and about the structure of the continental crust along the margin. Comparisons with the opposite margin in North America (Blake Plateau and Carolina trough) indicate a rather different evolution (the North American margin did not undergo the second stage of rifting) and a different crustal structure (crustal thinning is less important on the African margin).  相似文献   

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   

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   

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   

A reduced-rank prediction model of stream-channel size response to traditional agricultural land-use practices in southwestern Nigeria     

Francis O. Odemerho 《Journal of Hydrology》1984,70(1-4):85-100

Stream-channel morphologic responses are found to be related to different parameters measuring traditional agricultural land-use patterns and practices in 50 small headwater basins in southwest Nigeria. The problem of intercorrelations among these parameters made it initially difficult to establish their precise channel enlargement effects and to calibrate an impact prediction model. Through factor analysis of the 22 land-use and morphometric parameters, six factors identified as measures of traditional land-use practice, farm size, planting activities, shortened fallow, relief and overland flow, were found to account for 86% of the variance in the data. The factor-defining variables are length of cropping period, areas in short fallow, farm-plot size, length of farm preparation, relief ratio and overland flow. In a multiple regression analysis, only the first three variables were found to be statistically significant in explaining stream-channel morphologic responses. Thus, areas in short fallows, average farm size and length of cropping period adequately described those aspects of the traditional farming practices that affect basin hydrologic and channel responses. Since these variables were orthogonally derived, they formed the basis for the evaluation of the channel impact status of traditional land-use activities. The duplication of information and effects in the original 22-variable full-rank model were removed while utilizing the three-factor reduced model.  相似文献   

Paragenetic relationship of thermal maturation (coalification) and tectonic framework of some Canadian Rocky Mountain coals     

Francis T.C. Ting 《Organic Geochemistry》1984,5(4):279-281

Use of the attitude of the optical axis of vitrinite as an indicator of paragenetic relationship of thermal maturation/coalification and tectonics is discussed. A constant angular relationship between the optical axis and bedding plane of coals is observed in seven coal mines in the Canadian Rocky Mountain coal fields. This constant relationship suggests that thermal maturation predated tectonic structures.  相似文献   

Evidence for Enhanced Mineral Dissolution in Organic Acid-Rich Shallow Ground Water   总被引：3，自引：0，他引：3  

Peter B. McMahon  Don A. Vroblesky  Paul M. Bradley  Francis H. Chapelle  Cheryl D. Gullett 《Ground water》1995,33(2):207-216

Total concentrations of formate, acetate, and isobutyrate varied from less than 5 to greater than 9,000 μmol/l over distances of < 3 m in ground water from a shallow hydrocarbon contaminated aquifer. Laboratory incubations of aquifer material indicate that organic acid concentrations were dependent on the amount of hydrocarbon loading in the sediment and the relative rates of microbial organic acid production and consumption. In heavily contaminated sediments, production greatly exceeded consumption and organic acid concentrations increased. In lightly contaminated sediments rates were essentially equal and organic acid concentrations remained low. Concentrations of dissolved calcium, magnesium, and iron generally were one to two orders of magnitude higher in organic acid-rich ground water than in ground water having low organic acid concentrations. Carbonate and Fe(III)-oxyhydroxide minerals were the likely sources of these elements. Similarly, concentrations of dissolved silica, derived from quartz and k-feldspar, were higher in organic acid-rich ground water than in other waters. The positive relation (r = 0.60, p < .05, n = 16) between concentrations of silica and organic acids suggests that the microbially mediated buildup of organic acids in ground water enhanced quartz/k-feldspar dissolution in the aquifer, although it was not the only factor influencing their dissolution. A model that included organic acid microequivalents normalized by cation microequivalents significantly strengthened the correlation (r = 0.79, p < .001, n = 16) between dissolved silica and organic acid concentrations, indicating that competition between silica and cations for complexation sites on organic acids also influenced quartz/k-feldspar dissolution. Physical evidence for enhanced mineral dissolution in organic acid-rich waters included scanning electron microscopy images of highly corroded quartz and k-feldspar grains from portions of the aquifer containing organic acid-rich ground water. Microporosity generated in hydrocarbon contaminated sediments may adversely affect remediation efforts that depend on the efficient injection of electron acceptors into an aquifer or on the recovery of solutes from an aquifer.  相似文献   

USGS Reference Samples Attapulgite ATT-1 and Bentonite CSB-1     

John W. Hosterman  Francis J. Flanagan 《Geostandards and Geoanalytical Research》1987,11(1):1-9

The U.S. Geological Survey has prepared an attapulgite and a bentonite as reference samples because of their economic importance. The attapulgite (ATT-1) is from the Meigs-Attapulgite-Quincy fuller's earth district of Georgia and Florida, and the bentonite (CSB-1) is from the Northern Black Hills bentonite district of Wyoming, Montana, and South Dakota. The chemical and mineralogical properties of these two samples are quite different. Provisional values calculated from the few analytical data and the X-ray diffraction mineralogy are presented for those who wish to use the clays as reference samples.  相似文献