Measurement of water content as a control of particle entrainment by wind     

Cheryl McKenna Neuman  Greg Langston 《地球表面变化过程与地形》2006,31(3):303-317

Of all controls on particle transport by wind, which include texture, crusting, vegetation cover and roughness, the role of water content is one of the most difficult to parameterize because of its high degree of spatial and temporal variability and its operation at a particle‐scale level directly at the surface. This study demonstrates that measurement of the distribution of brightness for all pixels in an image, now routinely employed in digital photography, is strongly correlated with gravimetric water content. Wind tunnel experiments further suggest that measurement of the distribution of β, as normalized against the brightness of the dry sand surface, is very useful in determining the order of magnitude of the mass transport rate (q). Finer resolution will likely never be achieved because of the heterogeneity of the particle transport phenomenon. Analysis of the variability in surface brightness does suggest that q is governed by the partitioning of momentum to particle motion that terminates in adhesion to surrounding areas of the surface that remain relatively wet. The proportion of surface particles that becomes dry appears to be of less importance. Preliminary work suggests that field application of digital photography in tracking spatial and temporal changes in the water content of beach deposits looks promising. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Paleoclimatic Significance of Late Quaternary Lacustrine and Alluvial Stratigraphy, Animas Valley, New Mexico     

P.Reed Krider 《Quaternary Research》1998,50(3):283-289

Lacustrine and alluvial stratigraphic sequences in the southern Animas Valley of New Mexico allow reconstruction of late Quaternary climates. Four separate stands of late Quaternary Lake Cloverdale in the southern Animas Valley are recorded by lacustrine shoreline deposits. Soils and stratigraphic evidence show that three young lake highstands occurred during the Holocene and that a higher lake stand occurred 18,000 to 20,000¹⁴C yr B.P. Fluvial systems aggraded the southern Animas Valley during the middle to late Holocene. The late Quaternary stratigraphy shows that several periods during the late Holocene were characterized by higher effective precipitation than at any time since the last glacial maximum.  相似文献   

Effect of hydrologic management on marsh surface sediment deposition in coastal Louisiana     

Denise J. Reed  Nina De Luca  A. Lee Foote 《Estuaries and Coasts》1997,20(2):301-311

High rates of coastal land loss in Louisiana have prompted efforts to maintain or restore coastal wetland habitats, and structural management of marsh hydrology is one of a number of approaches that has been adopted. The aim of this study was to determine the effect of hydrologic management measures on marsh-surface sediment deposition in the Mississippi deltaic plain. Four impoundments, ranging in size from 50 ha to 177 ha and similarly sized control sites were included in the study. At each site, marsh-surface sediment traps were collected approximately biweekly for 3.5 yr to measure changes in sediment deposition. There was no significant difference in sediment deposition between any of the impoundment and control sites during the premanagement period. The results show no significant difference in marsh-surface sediment deposition between management year 1992–1993 and management year 1994–1995, but management year 1993–1994 had significantly lower sediment deposition than either the first or the last year of the study. Management year 1992–1993 showed the highest sediment deposition when it was assessed across all basins, areas, and sites, and this high rate of deposition is accounted for by the impact of Hurricane Andrew. For all management years there were significant differences between impoundment and control sites, with control sites showing higher rates of marsh surface sediment deposition than impoundments. No clear pattern was identified concerning the influence of various types of hydrologic management on rates of sediment deposition. This reduction in sediment deposition indicated that the areas under management in this study are receiving insufficient inorganic sediment deposition to keep pace with sea-level rise.  相似文献   

A natural resource damage assessment model for coastal and marine environments     

Thomas A. Grigalunas  James J. Opaluch  Deborah French  Mark Reed  Dean Knauss 《GeoJournal》1988,16(3):315-321

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Backfill settlement of restored strip mine sites — case histories     

S. M. Reed  D. B. Hughes  R. N. Singh 《Geotechnical and Geological Engineering》1987,5(2):161-169

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Patterns of sediment deposition in subsiding coastal salt marshes,Terrebonne Bay,Louisiana: The role of winter storms   总被引：1，自引：0，他引：1  

Denise J. Reed 《Estuaries and Coasts》1989,12(4):222-227

High rates of wetland loss in the Mississippi deltaic plain have been attributed to a combination of insufficient marsh sedimentation and relative sea-level rise rates of over 1.2 cm yr^?1. This study examines contemporary patterns of sediment delivery to the marsh surface by evaluating the contribution of individual marsh flooding events. Strong meteorological effects on water level in Terrebonne Bay often mask the usual microtidal fluctuations in water level and cause flood events to be of unpredictable frequency and duration. Sediment deposited on the marsh surface was collected weekly at two sites. Preliminary results allow the relative contributions of tidal and storm inundations to be calculated. Maximum sedimentation is associated with strong southerly winds both causing increased flooding and mobilizing sediment from open bay areas. Sediment deposition is limited by the availability of suspended sediment and the opportunity for its transport onto the marsh surface.  相似文献   

Understanding salt-marsh accretion,Scolt Head Island,Norfolk, England     

David R. Stoddart  Denise J. Reed  Jonathan R. French 《Estuaries and Coasts》1989,12(4):228-236

Measurements of surface sediment accretion have been obtained for Hut Marsh, Scolt Head Island, Norfolk, England, using sand marker horizons. More than eighty 1-m² marker sites were deployed in October 1983, and vertical accretion measured at them in April and October 1986 and April 1987. Elevations relative to Ordnance Datum were established by levelling each site at the time of deployment. Data collected by Steers between 1935 and 1957 on the same marsh show a clear relationship between marsh elevation and sedimentation. The results of the current more detailed study, presented as mean annual accretion rates, indicate a complex pattern of sediment distribution at this macrotidal location. These data, together with the results of tidal flow monitoring in the creeks on Hut Marsh, show the importance of spatial and temporal patterns of sediment delivery and variations in depositional processes in determining the distribution of sedimentation across the marsh surface.  相似文献   

Chemical differences between minerals from mineralizing and barren intrusions from some North American porphyry copper deposits   总被引：1，自引：0，他引：1  

D. A. F. Hendry  A. R. Chivas  J. V. P. Long  S. J. B. Reed 《Contributions to Mineralogy and Petrology》1985,89(4):317-329

Major-element analyses (by electron microprobe) and copper contents (by ion-probe) are reported for primary biotite, amphibole, magnetite, pyroxene, ilmenite, sphene and secondary biotite from intrusive rocks from mineralizing and barren stocks. The districts studied include Christmas, Globe-Miami, Sierrita and Tombstone, in Arizona; Bingham and Alta, Utah; Ely, Nevada; and Brenda, British Columbia. Amphiboles from barren rocks are relatively iron-rich and display only minor compositional variation. In contrast, amphiboles from mineralizing rocks span the range from magnesio-hornblende to actinolite, commonly even within one grain. Barren intrusions (type B) that are temporally distinct from mineralizing intrusions, and barren intrusions outside areas of known mineralization have higher Cu contents in their constituent minerals than do mineralizing intrusions. Barren intrusions (type A) that are deep-level temporal equivalents of Cu-bearing porphyritic rocks are depleted in copper. This suggests that copper is abstracted from not only the apical portions of porphyries but from parts of the deeper parent intrusions. The Cu contents of biotites (av. 23 ppm) and magnetites (97 ppm) from barren type B intrusions contrast with those from mineralizing intrusions, with biotites containing 7 ppm Cu and magnetites 3 ppm Cu. Primary amphiboles from all intrusive rock types have low copper contents, typically 2 to 5 ppm. In the continental North American deposits, the amount of copper available by liberation from or non-incorporation into amphibole, biotite and magnetite during magmatic crystallization or the early hydrothermal stage is low, perhaps too low to be the sole source of copper mineralization, unless copper is abstracted from large volumes (∼ 100 km³) of rock. These results contrast with a study of the island-arc porphyry copper at Koloula, Guadalcanal, where it was argued that sufficient copper for mineralization could have been abstracted from relatively small volumes of host rocks that originally contained as much Cu as the contemporaneous barren rock types.  相似文献   

Growth,production, food consumption,and mortality of juvenile spot and croaker: A comparison of tidal and nontidal nursery areas     

Benjamin M. Currin  James P. Reed  John M. Miller 《Estuaries and Coasts》1984,7(4):451-459

As the dominant juvenile finfish in southeast and Gulf of Mexico nursery areas, spot and croaker growth, food consumption, production, and mortality are compared in tidal salt marshes and nontidal brackish systems. Growth rates of spot and croaker from 5 studies ranged from 0.021–0.04 g per g per d. Differences in the annual production and food consumption estimates were primarily due to differences in average biomass. Although mean biomass varied widely, the daily production to mean biomass ratios ranged from 0.021–0.037, suggesting that these systems probably could support more juvenile fish than are present. Spot mortality ranged from 0.023–0.041% per d. Despite large hydrographic differences between tidal and nontidal systems and large differences in the amount of detrital input, the secondary production values and many of the fish population parameters are remarkably similar. This is interpreted as confirmation of the basic trophic similarity of the different systems and the highly adaptable and general nature of juvenile fish. The primary consumers are supported by 50–100% of the algal production. But because the dominant fishes consume only 10–35% of that secondary production, at least in some systems, food does not appear to limit juvenile fish production. Predation on the juveniles is implicated as a limiting factor.  相似文献   

Venus: The 17- to 38-micron spectrum     

R.A. Reed  W.J. Forrest  J.R. Houck  J.B. Pollack 《Icarus》1978,33(3):554-557

The Venus emission spectrum was measured from the NASA Lear Jet on five nights in June 1975. A cooled grating spectrometer with a resolution of γ/δγ ? 25 over the spectral interval 17 to 38μm was used. The main features in the observed spectrum are consisten with the theoretical emission spectrum of a haze of aqueous sulfuric acid droplets suspended in a CO₂ atmosphere.  相似文献