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601.
Estuarine nursery areas are critical for successful recruitment of tautog (Tautoga onitis), yet they have not been studied over most of this species' range. Distribution, abundance and habitat characteristics of young-of-the-year (YOY, age 0) and age 1+juvenile tautog were evaluated during 1988–1992 in the Narragansett Bay estuary, Rhode Island, using a 16-station, beach-seine survey. Estuary-wide abundance was similar among years. Greatest numbers of juveniles were collected at northern Narragansett Bay stations between July and September. Juvenile abundances varied with density of macroalgal and eelgrass cover; abundances ranged from 0.03 fish per 100 m2 to 8.1 fish per 100 m2. Although juveniles use eelgrass, macroalgae is the dominant vegetative cover in Narragansett Bay. Macroalgal habitats play a previously unrealized, important role and contribute to successful recruitment of juvenile tautog in Narragansett Bay. Juvenile abundances did not vary with sediment type or salinity, but were correlated with surface water temperature. Fish collected in June were age 1+ juveniles from the previous year-class (50–167 mm TL) and these declined in number after July or August. The appearance of YOY (25–30 mm TL) in July and August was coincident with the period of their greatest abundances. A precipitous decline in abundance occurred by October because of the individual or combined effects of mortality and movement to alternative habitats. Based on juvenile abundance, a previously unidentified spawning area was noted in Mount Hope Bay, a smaller embayment attached to the northeastern portion of Narragansett Bay. In August 1991, Hurricane Bob disrupted juvenile sise distribution and abundance, resulting in reduced numbers of YOY collected after the storm and few 1+ juveniles in 1992. 相似文献
602.
Barbara Soloducha 《Astrophysics and Space Science》1991,177(1-2):139-143
Local seasonal terms of latitude variations were determined on the basis of data of 17 BIH/IPMS stations andx, y, z data of the BIH global solution during the years 1967–1978. Some models for local correctionsR to the latitude introduced by the BIH are created. The correctionsR obtained from the least squares adjustment from one year data appear to be the best. The present study shows that it is necessary to determine these more frequently than once a year or to compute them for all stations simultaneously with the ERP. This will be particularly important in view of the future re-reduction of past astrometric data. 相似文献
603.
604.
An examination of the feasibility of passive transport from coastal spawning grounds to estuarine nursery areas for English sole 总被引:1,自引:0,他引:1
Christopher N. Rooper Donald R. Gunderson Barbara M. Hickey 《Estuarine, Coastal and Shelf Science》2006,68(3-4):609
English sole recruitment has been linked to environmental conditions occurring during their 6–10 week pelagic egg and larval stages, prior to their appearance in nursery estuaries during their first summer. The purpose of this study was to predict the spawning locations of juvenile English sole observed in estuaries to assess the feasibility of passive transport of egg and larval stages. Current meter data were used to back-calculate the transport trajectories of 19 cohorts of English sole observed as juveniles during estuarine trawl surveys. Only six of these cohorts were predicted to be spawned outside the Oregon–Washington shelf system, assuming passive transport of eggs and larvae. Predicted egg and larval trajectories indicate that most of the English sole found in Oregon and Washington estuaries were spawned off the coast of Washington, with some spawning off northern California and central Oregon. Although these results are not consistent with the presumed spawning locations for the Oregon and Washington shelf, they indicate that passive transport assumptions may be adequate to preserve the larvae in the coastal system until settlement. 相似文献
605.
606.
Barbara Zakrzewska 《The Professional geographer》1971,23(4):351-354
607.
The problem of the origin of the enigmatic tektites is still unsolved. The two leading hypotheses - viz., ejecta from terrestrial impacts, and ejecta from lunar volcanoes or lunar impacts, each encounters serious difficulties. The former has ballistic and water content difficulties, while the latter has some compositional difficulties, especially in the trace elements, as determined from the returned samples. It is possible that the latter problem may be met through lunar volcanic ejecta from sites suggesting more differentiation than the majority of the Moon. That such features may exist is suggested from the identity of some granitic material in the returned rocks and soil samples implying fairly sizable source regions on the Moon. The rare terrestrial strewn tektite fields require restrictive ballistic trajectories from the Moon. Calculations reveal that ellipses of varying, decreasing sizes which depend on velocity of vertical ejection from which ejecta will intersect the earth at low-entrance angles occur on the nearside of the Moon. Reasonable velocities were chosen (2.55 to 3.0 km s?1) and these ellipses circumscribe areas with longitudes between 30 and 50° east and latitudes between 7° north and south of the Moon's equator. These areas were searched for evidence of volcanism. As tektites have compositions ranging from acidic (major tektites) to basic (micro-tektites) contents of silica (SiO2) both acidic and basic volcanic features were sought. Since tektites range in age from about 30 million to 700000 yr old, they imply recent volcanism. Lunar Transient Phenomena (LTP) and data from various Apollo missions indicate that mild internal activity may still be occurring on the Moon. LTP sites are logical sources to investigate, of which four occur within the above delimited regions. These and their surroundings were examined and a number of possible explosive volcanism sites were found. These sites are identified and discussed after a review of the manifestations found from the various kinds of terrestrial volcanism for which lunar counterparts were sought. 相似文献
608.
We compare 3-D upper mantle anisotropic structures beneath the North American continent obtained using standard and improved crustal corrections in the framework of Non-linear Asymptotic Coupling Theory (NACT) applied to long period three component fundamental and higher mode surface waveform data. Our improved approach to correct for crustal structure in high-resolution regional waveform tomographic models goes beyond the linear perturbation approximation, and is therefore more accurate in accounting for large variations in Moho topography within short distances as observed, for instance, at ocean–continent margins. This improved methodology decomposes the shallow-layer correction into a linear and non-linear part and makes use of 1-D sensitivity kernels defined according to local tectonic structure, both for the forward computation and for the computation of sensitivity kernels for inversion. The comparison of the 3-D upper mantle anisotropic structures derived using the standard and improved crustal correction approaches shows that the model norm is not strongly affected. However, significant variations are observed in the retrieved 3-D perturbations. The largest differences in the velocity models are present below 250 km depth and not in the uppermost mantle, as would be expected. We suggest that inaccurate crustal corrections preferentially map into the least constrained part of the model and therefore accurate corrections for shallow-layer structure are essential to improve our knowledge of parts of the upper mantle where our data have the smallest sensitivity. 相似文献
609.
Robin E. Nimmer James L. Osiensky Andrew M. Binley Kenneth F. Sprenke Barbara C. Williams 《Hydrogeology Journal》2007,15(5):877-890
Electrical resistance tomography (ERT) was used to monitor a conductive plume dilution experiment that was conducted in fractured basalt in order to assess its applications in this type of fractured-rock environment. Tap water was injected into an injection well for 34 days to dilute a pre-existing potassium chloride (KCl) plume at a site in Idaho, USA. No further fluids were introduced artificially during a 62-day monitoring period. Both surface ERT and cross-borehole ERT were used to monitor dilution and displacement of the plume. A square grid of land-surface electrodes was used with the surface ERT. Three-dimensional images of surface ERT delineated areas of increased and decreased resistivities. Increasing resistivities are attributed to dilution/displacement of the KCl solution by tap-water invasion or the influx of seasonal recharge. Decreasing resistivities resulted from redistribution of residual KCl solution. Cross-borehole ERT was conducted between the injection well and each of seven surrounding monitoring wells. Polar plots of the injection-well resistivity data in the direction of each monitoring well delineate specific locations where tap water seeped from the injection well via preferential flow paths determined by time-dependent resistivity increases. Monitoring-well data indicate locations of clustered and isolated regions of resistivity changes. 相似文献
610.