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   

Warming at 18,000 yr B.P. in the Tropical Andes     

Karin F. Helmens  Peter Kuhry  Nathaniel W. Rutter  Klaas Van Der Borg  Arie F. M. De Jong 《Quaternary Research》1996,45(3):289-299

Palynological, paleopedological, and glacial geomorphological evidence from the area of the high plain of Bogotá in the Colombian Eastern Cordillera indicates a significant climatic warming around 18,000¹⁴C yr B.P. Comparison of dated vegetation changes, pedogenic episodes, and glacier fluctuations provides the basis for defining the so-called “La Laguna Interstadial” that lasted from 19,500 to 17,000 yr B.P. During this interstadial period, mean annual temperatures in the tropical Andes were up to 4°C higher than during the preceding and following stadial periods, when full-glacial conditions prevailed and temperatures were up to 8°C colder than at present.  相似文献   

Modelling of ground acceleration in the near source range: the case of 1976, Friuli earthquake (M = 6.5), northern Italy     

Aldo Zollo  Antonella Bobbio  Antonio Emolo  André Herrero  Giuseppe De Natale 《Journal of Seismology》1997,1(4):305-319

A mixed statistical-deterministic model of earthquake rupture is developed for evaluating the strong ground motion in the near source range (receiver distance comparable to the fault length). The source parametrization is based on the k-square model and the propagation is computed by asymptotic Green's functions. The method is applied to the case of 1976, Friuli earthquake (M = 6.5) in northern Italy which occurred on a low-dip thrusting fault. Acceleration records at 29 stations are computed for 100 simulations of rupture histories. The mean value map of peak ground accelerations shows clearly a maximum to the south due to the inner geometry and directivity of the source. The variation of the estimated PGA versus the epicentral distance is strongly dependent on azimuth and is not decreasing monotonically. The comparison of these curves with those predicted by empirical acceleration–distance relationships shows discrepancies in the near source distance range. This study shows the importance of considering the complexity of the source rupture process for strong motion estimate in the near source range.  相似文献   

Constraints on the shallow crustal model of the Northern Apennines (Italy) from the analysis of microearthquake seismic records   总被引：1，自引：0，他引：1  

Aldo Zollo  Raffaella De Matteis  Paolo Capuano  Flora Ferulano  Giovanni Iannaccone 《Geophysical Journal International》1995,120(3):646-662

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Book reviews     

Lluis Cabera  Patrick De Deckker  Robert S. Webb 《Journal of Paleolimnology》1995,14(2):225-230

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Scaling of peak ground motions from digital recordings of small earthquakes at Campi Flegrei,southern Italy   总被引：2，自引：0，他引：2  

Giuseppe De Natale  Ezio Faccioli  Aldo Zollo 《Pure and Applied Geophysics》1988,126(1):37-53

The dependence of peak ground acceleration and velocity on seismic moment is studied for a set of small earthquakes (0.7<M _L<3.2) recorded digitally at distances of a few km in the Campi Flegrei volcanic area near Naples, Italy, during the ground uplift episode of 1982–1984. Numerical simulations, using the -square spectral model with constant stress drop and ane ^–kf high frequency decay, fit well both the velocity and acceleration data for an averagek=0.015. The observed ground motions in the 1–24 Hz frequency band appear to consist of radiation from simple sources modified only slightly by attenuation effects. Moreover, the scaling of peak values agrees closely with those determined in nonvolcanic areas, once the difference in stress drop is taken into account.  相似文献   

Determination of total vertical water vapor in the atmosphere     

V.E. Cachorro  A.M. De Frutos  J.L. Casanova 《Atmospheric Research》1986,20(1)

The comparison between the precipitable water vapor w obtained by classical sounding and that obtained by high resolution measurements of spectral solar direct irradiance in the 400–1000 nm spectral range is shown. Three different water vapor absorption functions in the πστ band are used to determine the water vapor w by optical measurements. An episode of attenuation of direct solar irradiance by cirrus clouds is also shown.  相似文献   

Petrogenesis of Monte Vulture volcano (Italy): inferences from mineral chemistry,major and trace element data     

M. De Fino  L. La Volpe  A. Peccerillo  G. Piccarreta  G. Poli 《Contributions to Mineralogy and Petrology》1986,92(2):135-145

The paper presents major and trace element data and mineral compositions for a series of foiditic-tephritic to phonolitic rocks coming from Monte Vulture, Southern Italy, and investigates their origin, evolution and relationship with the other centres of the Roman province.Major and trace element variation in the foiditic to tephritic suite agrees with a hypothesis of evolution by simple crystal/liquid fractionation, whereas the early erupted phonolitic trachytes and phonolites have geochemical characteristics which do not support their derivation from tephritic magma by crystal fractionation. Foiditic and phonolitic rocks have mineral compositions which are interpreted as indicating magma mixing. However geochemical evidence shows that this process did not play an important role during the magma evolution.The Vulture rocks have compositional peculiarities such as high abundance of Na₂O, CaO, Cl and S, when compared with other Roman volcanics. Instead, the distribution of incompatible elements is similar to those of Roman rocks, except for a lower content of Rb and K, higher P and lower Th/Ta and Th/Nb ratios which are still close to the values of arc volcanics.The high contents of Na, Ca and of volatile components are tentatively attributed to the interaction of magma with aqueous solutions, rich in calcium sulphate and sodium chloride, related to the Miocene or Triassic evaporites occurring within the sedimentary sequence underlying the volcano. The distribution pattern of the incompatible elements is interpreted as indicative of magma-forming in a subduction modified upper mantle and of the peculiar location of M. Vulture.  相似文献   

Immunological studies on microbial mats from Solar Lake (Sinai)— A contribution to the organic geochemistry of sediments     

G. Muyzer  S. De Koster  Y. Van Zijl  J.J. Boon  P. Westbroek 《Organic Geochemistry》1986,10(4-6)

Immunological and biochemical techniques were used to investigate organic matter in microbial mats from Solar Lake (Sinai, Egypt). Antibodies, elicited in rabbits against samples taken at different depths from a core of these mats, were used for the detection of immunological determinants preserved in these samples. Special attention was given to an antiserum directed against a top mat fraction (3–10 mm depth) and an antiserum against a fraction from a lower section of the core (380–390 mm depth). Both antisera, tested in a dot-blot immunobinding assay, were found to give positive reactions with organic matter from different depths of the sediment. An immunohistochemical experiment with the antisera points to antigenic determinants on Recent and subfossil sheaths of Microcoleus. In addition, extracts of sediment samples were submitted to electrophoresis in polyacrylamide gels in order to characterize the separated macromolecules by immunological means. The results showed a rapid decrease in the number of antigenic determinants from Recent to subfossil samples. However, even in the deepest layers of the sediment (690–700 mm depth) intact biopolymers were detected.  相似文献   

On the origin and age of the Steep Rock buckshot, Ontario, Canada     

A.De Barros Machado 《Chemical Geology》1987,60(1-4):337-349

The Steep Rock buckshot is a brecciated pisolithic ferruginous bauxite found in the Errington iron mine, Steep Rock Lake, Ontario, Canada. It occurs within the almost vertical ore zone included in the Archean Steep Rock Group, reaching a depth in excess of 1100 ft. (335 m). Successive authors considered its age as Precambrian. The biological observations now presented deny this supposed Precambrian age. Treatment of the concretions by HCI, followed by staining, put in evidence abundant microscopic figurate animal and vegetal remains, namely shreds of insect integument and varied fragments of vascular plant material. Comparable results were obtained by casting and by scanning electron miscroscopy (SEM) of the surface of the concretions and by thin sections. All these remains are Phanerozoic and one of them is probably not anterior to the Late Cretaceous. The macro- and micromorphology of the concretions obey models of termite constructions and the spectrum of organic remains is identical to the one found in tubulo-alveolar laterites and in termite constructions. The presence in the matrix of canaliculi attributable to thin roots gives force to the idea that the buckshot was originated near the soil surface.  相似文献