Early diagenetic influences on iron transformations in a freshwater lake sediment   总被引：4，自引：0，他引：4  

Paul Wersin  Patrick H  hener  Rudolf Giovanoli  Werner Stumm 《Chemical Geology》1991,90(3-4):233-252

Iron transformations in a calcium carbonate rich fresh-water sediment were studied by analyzing the relevant constituents of both interstitial water and solid matter. Analysis of interstitial water shows that the observed redox sequence NO⁻₃/NH⁺₄, MnO₂/Mn(II), FeOOH/Fe(II), SO²⁻₄/S(−II) is roughly in agreement with that predicted by the Gibbs Free Energy for the corresponding reactions. In contrast to marine sediments, these redox transitions occur in the uppermost sediments, i.e., at depths of 0–4 cm.

Deeper in the sedimentary sequence, the depth profile for dissolved iron exhibits a steady non-linear increase up to 400 μmol dm⁻³. In this anoxic zone, according to thermodynamic predictions, iron (II)-minerals such as iron sulfide, siderite, and vivianite should precipitate while Fe(III) oxides should be completely dissolved. However, microscopic analysis showed that Fe(III) oxides were present throughout the studied sediment. Furthermore, scanning electron microscope/energy dispersive spectroscopy analysis suggests the presence of iron sulfide could be verified but not that of siderite or vivianite. These observations indicate kinetic control of iron transformations.

We have investigated the importance of kinetic control of iron distribution in anoxic sediments using a diagenetic model for dissolved iron(II). A rough estimate of time scales for dissolution and precipitation rates was made by imposing limiting boundary conditions. Using the calculated rate constant, we established that more than 1000 years would be required for the complete dissolution of Fe(III) oxides, which is agreement with our observations and experimental data from the literature. Calculated precipitation rates of Fe(II) for a given mineral phase such as siderite yield a maximum value of 3 μg_(FeCO3) g⁻¹_{(dry sediment)} yr⁻¹. Such low rates would explain the absence of siderite and vivianite.

Finally, it can be inferred from the Mn_T/Fe_T ratio in the sediments that this ratio depends on the redox conditions of the sediment-water interface at the time of deposition. Thus, this ratio can be used as “paleo-redox indicator” in lacustrine sediments.  相似文献   

Frequency Domain Electromagnetic Induction Sounding Surveys for Landfill Site Characterization Studies     

John Jansen  Bassem Haddad  Wayne Fassbender  Patrick Jurcek 《Ground Water Monitoring & Remediation》1992,12(4):103-109

A frequency domain electromagnetic induction sounding survey (FDEM) was conducted on a landfill in northern Illinois to determine the depth of fill, locate areas of drum disposal, and locate areas of heavy metal sludge disposal. Sketchy information obtained from interviews of the site personnel identified specific exploration targets and areas of concern. The results of the geophysical survey verified much of the reported disposal history and identified areas suspected to contain hazardous waste.
Based on the results of the survey, the thickness of fill was estimated and two areas with highly conductive fill were located. These areas could represent leachate pockets or sludge disposal areas. An area in which the fill appears to be thicker than expected was identified. This area is thought to represent industrial sludge disposal in trenches excavated into the existing fill and underlying soils. An area with several linear in-phase, quadrature, and conductivity highs was detected. A subsequent magnetometer survey detected linear magnetic anomalies that are believed to be caused by parallel trenches filled with steel drums. This area is believed to be a previously unreported hazardous waste drum disposal cell excavated into the native soil.
As of this writing, the results of this survey have not been verified by traditional intrusive methods. When these investigations begin, we expect that information provided by the FDEM survey will reduce project costs by directing subsequent investigations, thereby reducing the number of borings and test pits required to characterize the site. While there is an unavoidable margin of error and uncertainty in remote sensing methods, the subsurface coverage provided by this geophysical survey could not have been reproduced by traditional methods without substantial expense. This paper presents the results of the survey and discusses application of the FDEM method on landfills.  相似文献   

Atoll island hydrogeology: flow and freshwater occurrence in a tidally dominated system     

June A. Oberdorfer  Patrick J. Hogan  Robert W. Buddemeier   《Journal of Hydrology》1990,120(1-4):327-340

A layered-aquifer model of groundwater occurrence in an atoll island was tested with a solute-transport numerical model. The computer model used, SUTRA, incorporates density-dependent flow. This can be significant in freshwater-saltwater interactions associated with the freshwater lens of an atoll island. Boundary conditions for the model included ocean and lagoon tidal variations. The model was calibrated to field data from Enjebi Island, Enewetak Atoll, and tested for sensitivity to a variety of parameters. This resulted in a hydraulic conductivity of 10 m day⁻¹ for the surficial aquifer and 1000 m day⁻¹ for the deeper aquifer; this combination of values gave an excellent reproduction of the tidal response data from test wells. The average salinity distribution was closely reproduced using a dispersivity of 0.02m. The computer simulation quantitatively supports the layered-aquifer model, including under conditions of density-dependent flow, and shows that tidal variations are the predominant driving force for flow beneath the island. The oscillating, vertical flow produced by the tidal variations creates an extensive mixing zone of brackish water. The layered-aquifer model with tidally driven flow is a significant improvement over the Ghyben-Herzberg-Dupuit model as it is conventionally applied to groundwater studies for many Pacific reef islands.  相似文献   

Regional modelling of groundwater flow and salt and environmental tracer transport in deep aquifers in the Paris Basin     

Huai Fu Wei  Emmanuel Ledoux  Ghislain De Marsily 《Journal of Hydrology》1990,120(1-4):341-358

A hydrodynamic model which takes into account the aquitard storage effect was developed for the deep multilayered system including the Dogger aquifer and its surroundings in the Paris Basin. It provides a good explanation for a series of observations in the Dogger concerning, for instance, the hydraulic head, the salinity and the transmissivity. The calibration of the model also makes it possible to estimate some unmeasured parameters such as the aquifer and aquitard storage coefficients. Finally, the results of simulations of the transport of ⁴He and ¹⁴C strengthen the representativeness of the model. The Darcy average horizontal velocity in the Dogger, obtained with the model, is of the order of 0.33m year⁻¹.  相似文献   

Chemical structural models for coalified wood (vitrinite) in low rank coal     

Patrick G. Hatcher 《Organic Geochemistry》1990,16(4-6)

Examination of a series of coalified gymnospermous woods ranging in rank from brown coal to subbituminous coal by solid-state ¹³C NMR and analytical pyrolysis has provided sufficient information to construct structural models depicting the changes that occur to lignin, the primary precursor of vitrinite, during coalification. Progressive changes in the chemistry of coalified wood suggest the following series of reactions: (1) demethylation to form catechol-like structures that are dominant components of brown coal and lignite A; (2) cleavage of aryl ether linkages to form phenols and reactive carbocations that alkylate the catechol rings; (3) dehydration of the catechol rings; (3) dehydration of the catechol-like structures to form the structures of subbituminous coal dominated by alkylphenols; and (4) reduction of the 3-carbon alkyl side chain derived from lignin to form propyl substituents. The models developed for each stage of coalification are derived from chemical modifications of the structure of lignin.  相似文献   

Structural Geology, principles, concepts, and problems: Hatcher, R. D. 1989. Merrill Publishing Co., Columbus, Ohio, U.S.A. 531 pp. Price $49.95 (hardback)     

Declan G. De Paor 《Journal of Structural Geology》1990,12(8)

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Nonlinear kinetic Alfvén wave with Poisson equation correction in the low aurora     

De Yu Wang  Guang Li Huang  C. -G. Fälthammar  P. A. Lindqvist  L. Blomberg  Li Ting Song 《Astrophysics and Space Science》1996,240(2):175-186

Nonlinear kinetic Alfvén waves where m _e /m _i , have been solved both with and without the Poisson equation correction. It is found that the ratio of the perpendicular electric field and magnetic field, and the ratio of parallel and perpendicular electric field increase with deepening of the depressive density soliton. The former ratio may be larger than the Alfvén velocity in the case of a large amplitude solitary kinetic Alfvén wave. The Poisson equation correction is important for the nonlinear kinetic Alfvén wave propagating along the magnetic field, which solves a puzzle of Sagdeev potential to approach infinity in the limit ofK _x 0. This correction causes the solitary KAW possessing an electrostatic character along the direction of wave moving frame. These results have been compared with the observations from the Freja satellite in the low aurora.  相似文献   

Observing molecular clouds in halo dark clusters through absorption lines     

F. De Paolis  G. Ingrosso  Ph. Jetzer  M. Roncadelli 《Astrophysics and Space Science》1996,235(2):329-335

In addition to Massive Astrophysical Compact Halo Objects (MACHOs), as detected by microlensing, cold molecular clouds (mainly ofH ₂) may well contribute substantially to the galactic halo dark matter. Here, we argue that the existence of such halo clouds can be inferred from the observation of absorption lines (due to heavy molecules located in the clouds themselves) towards stars of the Large Magellanic Cloud, which lie very close, within 1, to a previously microlensed one.The possibility of clusters of MACHOs has been investigated by several authors (see e.g. Carr and Lacey, 1987; Ashman, 1990; Eichler and Silk, 1992 and Wasserman and Salpeter, 1994).  相似文献   

Why we study the geological record for evidence of the solar oscillation about the galactic midplane     

John J. Matese  Patrick G. Whitman  Kimmo A. Innanen  Mauri J. Valtonen 《Earth, Moon, and Planets》1995,71(3):7-12

The Solar System oscillates about the plane defined by the disk of matter in our Galaxy. This oscillatory motion gives rise to a substantial modulation in the tidally induced flux of Oort cloud comets. An observational determination of the quasi-periodicity of this motion carries with it significant information about the population, distributions, dynamics and origins of short-period and long-period comets. An additional incentive for emphasizing such a study is the information about dark disk matter that a period can yield. If dark disk matter is completely negligible, the amplitude of the solar motion will be sufficiently large that the peak-to-trough flux ratio will be 2.5 and the plane-crossing period will exceed 40 Myr. Dark disk matter comparable in mass to bright disk matter and distributed in any manner is inconsistent with K-dwarf distributions and can be rejected as a working hypothesis. But if a modest fraction of the disk matter is dark and distributed like the interstellar medium, as is consistent with limits deduced from K-giant and K-dwarf velocity distributions, the peak-to-trough flux ratio can increase to a factor of 4 even though the solar z amplitude is decreased. In that case the period can be as little as 30 Myr and the implied Oort population is smaller by a factor of 3. We should carefully reconsider the geological record as a potential discriminator of these options.  相似文献   

The Intermittently Embedded Herbig Ae/Be Stars ISO and Ground-Based IR Observations     

C.A. Grady  M.R. Pérez  K.S. Bjorkman  M.L. Sitko  P.S. Thé  D. De Winter  V.P. Grinin  R.W. Russell  D.K. Lynch  M.S. Hanner 《Astrophysics and Space Science》1997,255(1-2):35-41

We discuss silicate emission profiles observed with the ISO SWS and ground-based IR observations in a population of intermittently embedded Herbig Ae/Be stars which are viewed edge-on to their polarimetrically identified dust and gas disks. The ISO SWS observations confirm the lack of a simple correlation between system age and the profile shape. Comparison with laboratory silicates suggests that much of the observed variation is due to different annealing histories of the grains. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献