Patterns of estuarine use by juvenile English sole (Parophrys vetulus) and Dungeness crab (Cancer magister)     

Donald R. Gunderson  David A. Armstrong  Yun-Bing Shi  Robert A. McConnaughey 《Estuaries and Coasts》1990,13(1):59-71

Extensive trawl surveys were conducted in two large estuaries (Grays Harbor and Willapa Bay) on the Washington coast during 1983–1987, and in adjacent areas of the open coast. These surveys have shown that both English sole and Dungeness crab rely heavily on these estuaries as nursery areas, although the pattern of utilization differs substantially. Juvenile migration patterns can show substantial interannual variability and can only be delineated by concurrent surveys in both coastal and estuarine areas, conducted over a period of several years. English sole eggs and Dungeness crab larvae are released in coastal waters. Larvae of both species transform to the benthic stage in both coastal and estuarine areas, but most English sole eventually migrate into the estuaries during the first year of life, even if initial settlement is along the open coast. By the time English sole have attained a length of 55 mm (TL), most of them are found in estuaries. English sole begin emigrating from the estuaries at about 75 mm, and few remain there during the second year of life. In contrast, Dungeness crab appear to remain in the area of initial settlement throughout the first year of life. Growth is substantially faster in estuaries where 0+ crab reach a mean size of about 40 mm carapace width (CW) by September, with those off the coast are only about 14 mm CW. Juveniles remain in the area of settlement over their first winter but, in contrast to English sole, most coastal 1+ crab immigrate to estuaries to join siblings that settled there the previous year. By September of the second year, crab at about 100 mm CW emigrate to the open coast where they reach maturity. Advantages to juvenile stages that reside in estuaries are discussed in terms of accelerated growth at higher temperatures and potentially greater food supplies than found nearshore along the coast.  相似文献   

Mechanisms associated with the erosion of sand dune cliffs,Magilligan, Northern Ireland   总被引：1，自引：0，他引：1  

R. W. G. Carter  Gregory W. Stone 《地球表面变化过程与地形》1989,14(1):1-10

A fifteen year history of coastal dune recession at Magilligan, Northern Ireland has revealed both time and space contrasts in processes and morphology. Since 1968 ‘storm’ frequency has increased, while dune retreat reached a peak (5·4 m) in 1978–1979. Three types of dune eroding events are noted, resulting from particular wave/wind/tide combinations. The spatial variability in dune scarping is associated with vegetation and soil development, and slope failures range from granular avalanches to retrogressive rotational slumps.  相似文献   

Development of lava tubes in the light of observations at Mauna Ulu,Kilauea Volcano,Hawaii     

Donald W. Peterson  Robin T. Holcomb  Robert I. Tilling  Robert L. Christiansen 《Bulletin of Volcanology》1994,56(5):343-360

During the 1969–1974 Mauna Ulu eruption on Kilauea's upper east rift zone, lava tubes were observed to develop by four principal processes: (1) flat, rooted crusts grew across streams within confined channels; (2) overflows and spatter accreted to levees to build arched roofs across streams; (3) plates of solidified crust floating downstream coalesced to form a roof; and (4) pahoehoe lobes progressively extended, fed by networks of distributaries beneath a solidified crust. Still another tube-forming process operated when pahoehoe entered the ocean; large waves would abruptly chill a crust across the entire surface of a molten stream crossing through the surf zone. These littoral lava tubes formed abruptly, in contrast to subaerial tubes, which formed gradually. All tube-forming processes were favored by low to moderate volume-rates of flow for sustained periods of time. Tubes thereby became ubiquitous within the pahoehoe flows and distributed a very large proportionof the lava that was produced during this prolonged eruption. Tubes transport lava efficiently. Once formed, the roofs of tubes insulate the active streams within, allowing the lava to retain its fluidity for a longer time than if exposed directly to ambient air temperature. Thus the flows can travel greater distances and spread over wider areas. Even though supply rates during most of 1970–1974 were moderate, ranging from 1 to 5 m³/s, large tube systems conducted lava as far as the coast, 12–13 km distant, where they fed extensive pahoehoe fields on the coastal flats. Some flows entered the sea to build lava deltas and add new land to the island. The largest and most efficient tubes developed during periods of sustained extrusion, when new lava was being supplied at nearly constant rates. Tubes can play a major role in building volcanic edifices with gentle slopes because they can deliver a substantial fraction of lava erupted at low to moderate rates to sites far down the flank of a volcano. We conclude, therefore, that the tendency of active pahoehoe flows to form lava tubes is a significant factor in producing the common shield morphology of basaltic volcanoes.  相似文献   

Experience from one year of operating a boundary-layer profiler in the center of a large city     

R. R. Rogers  S. A. Cohn  W. L. Ecklund  J. S. Wilson  D. A. Carter 《Annales Geophysicae》1994,12(6):529-540

Since May 1992 a small, 915-MHz profiler has been operated continuously in downtown Montreal. It is a five-beam system employing a microstrip array antenna, located atop a 14-story office building that houses several academic departments of McGill University. The data are used for research on precipitation physics and the clear-air reflectivity in addition to wind profiling. We are especially interested in situations in which the reflectivities of the clear air and the precipitation are comparable. This permits the study of interactions between the precipitation and the clear air, a new area of research made possible by wind profilers. On clear days in the summer, 30-min consensus winds can often be measured to an altitude of 3 km, but ground clutter in the antenna sidelobes interferes with measurements below 600 m. Rain when present often permits wind profiling down to 100 m and up to 6 km or higher. On cold winter days there are some periods when the reflectivity is too weak at all levels to permit wind estimation. Falling snow, however, provides readily detectable echoes and serves as a good tracer of the wind and so allows profiling over its full altitude extent. The best conditions for observing interactions between precipitation and the clear air are when light rain falls through a reflective layer associated with a frontal surface or inversion. Unexpectedly, flocks of migrating birds sometimes completely dominate the signal at night in the spring and fall seasons.  相似文献   

A Method of Collecting and Analyzing Lineaments for Regional-Scale Fractured-Bedrock Aquifer Studies   总被引：10，自引：0，他引：10  

Stephen B. Mabee  Kenneth C. Hardcastle  Donald U. Wise 《Ground water》1994,32(6):884-894

  相似文献   

Characterization of Chromium- Contaminated Soils Using Field-Portable X-Ray Fluorescence     

Robert W. Puls  Donald A. Clark  Clark Carlson  James Vardy 《Ground Water Monitoring & Remediation》1994,14(3):111-115

A detailed characterization of the underlying and adjacent soils near a chrome plating shop utilized field-portable X- ray fluorescence (XRF) as a screening tool. XRF permitted real-time acquisition of estimates for total metal content of soils. A trailer-mounted soil coring unit was used to recover soil samples for XRF analyses. This approach minimized the number of samples required for adequate characterization of the chromium distribution in the soils at the site and permitted immediate delineation of source'hot spots.'The nondestructive nature of the XRF analyses permitted correlation analysis using inductively coupled plasma (ICP) techniques. Correlation between XRF and ICP was very good (r²= 0.95) but the XRF analyses underestimated the total chromium concentrations, probably because of inappropriate calibration samples.  相似文献   

Impact of high herbivore densities on introduced smooth cordgrass,Spartina alterniflora,invading San Francisco Bay,California     

Curtis C. Daehler  Donald R. Strong 《Estuaries and Coasts》1995,18(2):409-417

Spartina alterniflora, smooth cordgrass, invading San Francisco Bay, California (USA), is attacked by high densities of a plant hopper, Prokelisia marginata, and a mirid bug, Trigonotylus uhleri. Both herbivores are sap-feeders. We investigated the impact of these herbivores on S. alterniflora's growth rate, vegetative spread, and seed production by manipulating herbivore densities in the field and in a greenhouse. Herbivore densities in the field peaked in early fall, with P. marginata averaging more than 300 individuals per mature culm of S. alterniflora (about 100,000 per m²) and T. uhleri densities exceeding 10 per culm (about 3,000 per m²). Field reductions of herbivore densities by approximately 70% with insecticidal soap did not result in greater vegetative growth rates or lateral spread of plants; plants grew vigorously with the highest densities of insects. In the greenhouse study, conducted with seedlings, herbivory significantly reduced plant mass and tiller number in some but not all replicate herbivory treatments. In both field and greenhouse, there were significant differences between some clones' growth rates independent of herbivory. Inflorescence production in the field was not affected by reduced-herbivory treatments. Seed set was low under conditions of both natural and reduced herbivory, averaging 0.4%. Despite densities of P. marginata and T. uhleri that are much higher than typically observed in areas where S. alterniflora is native, herbivory by these particular insects appears to have little impact and in unlikely to limit S. alterniflora’s spread through San Francisco Bay. *** DIRECT SUPPORT *** A01BY070 00009  相似文献   

Book reviews     

Dahl  Carol  Moody  David W.  McCammon  Richard B.  Grybeck  Donald J. 《Natural Resources Research》1994,3(4):341-343

Natural Resources Research -  相似文献   

Numerical models for diagenesis and the Neogene Sr isotopic evolution of seawater from DSDP Site 590B     

Frank M. Richter  Donald J. DePaolo 《Earth and Planetary Science Letters》1987,83(1-4)

A numerical model for the diagenetic exchange of Sr between carbonates and their pore fluids during sedimentation and compaction has been developed. The model has been applied to data from DSDP Site 590B in order to assess the accuracy with which the Sr isotope record in the carbonate sediment reflects that of seawater. The most important process affecting the Sr in the solid carbonate is exchange with the pore fluid due to solution-reprecipitation, but the concentration or isotopic composition of Sr in the solid itself gives little or no information as to the magnitude of this exchange. The key to determining the rate of exchange is the pore fluid, where the variations of Sr²⁺ and⁸⁷Sr/⁸⁶Sr with depth are very sensitive indicators. The logical structure of applying the model to data from DSDP 590B is to find by successive iteration an ocean history (i.e., the initial⁸⁷Sr/⁸⁶Sr and Sr concentration of each increment of carbonate deposited) and a rate of Sr exchange between pore water and solid carbonate such that the model matches the present Sr concentration and⁸⁷Sr/⁸⁶Sr of both pore water and solid carbonate.Once all the data are matched, the model provides an estimate of the rate of Sr exchange due to solution-reprecipitation and the evolution of⁸⁷Sr/⁸⁶Sr in seawater over the past 20 million years. For DSDP 590B we find that solution-reprecipitation decreases rapidly with depth, from a near surface value of about 10% per million years to about 1% per million years below 200 m. This rate of exchange of Sr results in the carbonates of DSDP 590B preserving an accurate record of the Sr isotopic evolution of the ocean over the past 5 million years, but for ages greater than 5 million years the⁸⁷Sr/⁸⁶Sr ratio of the carbonate is systematically displaced from that of the seawater in which it was deposited. The maximum difference is of order 5 × 10⁻⁵.  相似文献   

Anomalous upper mantle beneath the Australian-Antarctic discordance     

Donald W. Forsyth  Richard L. Ehrenbard  Steven Chapin 《Earth and Planetary Science Letters》1987,84(4)

Within the Australian-Antarctic discordant zone, residual depth anomalies approach 1000 m. In sea floor younger than 10 Ma that is more than 500 m deeper than expected, Rayleigh wave phase velocities are significantly faster than in sea floor of comparable age in the Pacific. In this area, the shear wave velocity in the 20–40 km depth range is unusually fast, indicating that the lithosphere develops more rapidly than usual from an asthenosphere that is perhaps cooler than average. In sea floor that is older than 10 Ma, phase velocities are anomalously fast and independent of the residual depth. Beneath this older sea floor, the low-velocity zone in the oceanic mantle is much less pronounced than beneath sea floor of comparable age in the Pacific.  相似文献