Organic pollutants associated with macromolecular soil organic matter: Mode of binding   总被引：2，自引：0，他引：2  

H. H. Richnow  R. Seifert  J. Hefter  M. Link  W. Francke  G. Schaefer  W. Michaelis   《Organic Geochemistry》1997,26(11-12)

A study of ether-linked moieties in macromolecular bound residues of polycyclic aromatic hydrocarbons (PAH) generated in bioremediation experiments was performed using high temperature hydrolysis degradation with subsequent analysis of the products by GC-MS. This hydrolysis reaction was specifically designed to cleave ether bonds including relatively stable diarylether structures. Among the reaction products, aromatic alcohols representing typical microbiologically derived metabolites of PAH were found in addition to natural compounds. Thus, parts of the bound residues appeared to be linked within the macromolecular material by ether bonds. Model experiments with an oxidoreductase enzyme and aromatic alcohols indicate the formation of these ether bonds to be an enzyme-catalysed process.  相似文献   

ELNES spectroscopy of mixed Si coordination minerals     

B. Poe  F. Seifert  T. Sharp  Z. Wu 《Physics and Chemistry of Minerals》1997,24(7):477-487

 Si K- and L-edge ELNES spectroscopy and multiple-scattering (MS) calculations are used to examine mixed Si coordination compounds varying in Si^VI:Si^IV ratio. As in previous studies, the edges are influenced mainly by silicon coordination (tetrahedral vs. octahedral), as supported by the MS calculations. We demonstrate two methods semi-quantitatively to extract the value of Si^VI/(Si^VI+Si^IV): (1) A linear relationship between the L_2,3-L₁ splitting and Si^VI/(Si^VI+Si^IV) is observed, (2) a fitting method based on the coaddition of reference tetrahedral and octahedral Si spectra is applied to both Si K- and L-edge ELNES spectra. Received: February 10, 1997 / Revised, accepted: May 23, 1997  相似文献   

On the 70 birthday of Wilfried Schönborn     

Günther Friedrich  Heike Zimmermann-Timm  Anita Lange  Rainer Koschel 《Limnologica》2004,34(3):173-175

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Floodgate Operations and Fish Communities in Tidal Creeks of the Lower Fraser River (British Columbia,Canada)     

Rebecca E. Seifert  Jonathan W. Moore 《Estuaries and Coasts》2018,41(4):1206-1221

Tidal creeks in large coastal deltas can be important habitat for fish but are often highly modified by human activities. Connectivity between tributary creeks and mainstem channels is often constrained by structures such as dikes and floodgates, designed to protect urban and agricultural areas from flooding. While they play important roles in flood mitigation, floodgates can diminish habitat quality and block fish from accessing tidal creeks. It is likely that floodgates differ in their operations and may consequently open for different amounts of time; however, floodgate operations and their effects are not well quantified. We asked the question: how does the mechanical functioning of these floodgates affect fish communities in tidal creeks? We used time-lapse cameras and quantified the timing of gate openings for 22 tributaries of the Lower Fraser River in British Columbia, Canada, and related these operational data to differences in fish communities above and below floodgates. Floodgate operations varied substantially, with some floodgates opening daily while others opened less than 20% of the day, on average. Sites with floodgates that seldom opened were associated with greater differences in fish communities and with reduced upstream native species richness by about one species on average. Where floodgates opened infrequently, we also found lower upstream dissolved oxygen concentrations than at sites where floodgates opened for longer periods of time. Thus, floodgate operations can influence fish communities as well as water quality. These data indicate a large scope for improving floodgate operations for connectivity.  相似文献   

Effect of polychromatic X‐ray microtomography imaging on the amino acid content of the Murchison CM chondrite     

Jon M. Friedrich  Hannah L. McLain  Jason P. Dworkin  Daniel P. Glavin  W. Henry Towbin  Morgan Hill  Denton S. Ebel 《Meteoritics & planetary science》2019,54(1):220-228

X‐ray microcomputed tomography (μCT) is a useful means of characterizing cosmochemical samples such as meteorites or robotically returned samples. However, there are occasional concerns that the use of μCT may be detrimental to the organic components of a chondrite. Small organic compounds such as amino acids comprise up to ~10% of the total solvent extractable carbon in CM carbonaceous chondrites. We irradiated three samples of the Murchison CM carbonaceous chondrite under conditions akin to and harsher than those typically used during typical benchtop X‐ray μCT imaging experiments to determine if detectable changes in the amino acid abundance and distribution relative to a nonexposed Murchison control sample occurred. After subjecting three meteorite samples to ionizing radiation dosages between ~300 Gray (Gy) and 3 kGy with bremstrahlung X‐rays, we analyzed the amino acid content of each sample. Within sampling and analytical errors, we cannot discern differences in the amino acid abundances and amino acid enantiomeric ratios when comparing the control samples (nonexposed Murchison) and the irradiated samples. We conclude that a polychromatic X‐ray μCT experiment does not alter the abundances of amino acids to a degree greater than how well those abundances are measured with our techniques and therefore any damage to amino acids is minimal.  相似文献   

Geochemistry and mineralogy of laterites in the Sula Mountains greenstone belt, Lake Sonfon gold district, Sierra Leone     

T.C. Davies  G. Friedrich  A. Wiechowski 《Journal of Geochemical Exploration》1989,32(1-3)

Geochemical and mineralogical investigations have been carried out on laterite profiles developed in the Lake Sonfon Au district of northern Sierra Leone. The area is underlain by Archean metavolcanics and constitutes part of the Sula Mountains greenstone belt, which is mineralized in Au. Extensive lateritization has affected the rocks of this region, resulting in a profile which from bottom to top consists typically of a decomposed bedrock zone, a pisolitic laterite layer and a duricrust layer. Both the pisolitic and duricrust layers of the laterite are sometimes punctuated by lenses of ironstones containing high amounts of Cu, Zn, Ni, Co and Ce. Gold occurs as small grains within the heavy mineral fraction recovered from the decomposed rock zones and pisolitic layers of the profiles and also in gravels of streams draining the area. The mineralogy of the duricrust and pisolitic layers is dominated by goethite, gibbsite and quartz, with minor amounts (<5% by volume) of ilmenite, magnetite, haematite, rutile and kaolinite. The kaolinite content increases towards the decomposed rock zone, where talc, vermiculite and other layer lattice silicates become abundant. The heavy-mineral fraction of stream sediments is composed essentially of ilmenite, magnetite, haematite, and traces of rutile, zircon, tourmaline and Au. The Au grains are often characterized by a 10–200-μm-wide rim having a much lower content of Ag (0.3 wt.% or lower) than the grain interior (about 5 wt.% on average). Dissolution effects are also observed on the grain surfaces. It is considered that Au derived from the amphibolite parent rock is dissolved, transported, and redeposited during laterization.The duricrust cover of the laterite profiles is characterized by high contents of Fe₂O₃ (ca. 60 wt.%) and Al₂O₃ (ca. 32wt.%) and low content of SiO₂ (ca. 9 wt.%). In comparison, the pisolitic layer is higher in SiO₂ (ca. 18 wt.%) as well as a slightly higher in Al₂O₃ (ca. 34 wt.%). Lateritic weathering has resulted in the removal of CaO, Na₂O, MgO and SiO₂, with relative enrichment of Fe₂O₃ and Al₂O₃. The geochemical distribution of the trace elements in the laterite profiles can be related to the occurrence of the auriferous mineralization. The significance of these observations is discussed in relation to the origin of the lateritic Au and the role of the associated trace elements as indicators of the mineralization.  相似文献   

Acceptance speech for the 1984 Alfred E. Treibs Award     

Dr.Wolfgang Seifert 《Geochimica et cosmochimica acta》1985,49(7):1672-1673

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Volume relaxation of compacted SiO₂ glass: a model for the conservation of natural diaplectic glasses     

Sabine Höfler  Friedrich Seifert 《Earth and Planetary Science Letters》1984,67(3):433-438

Relaxation experiments on vitreous SiO₂, densified at 900°C, 20 kbar to a permanent density of 2.36 g cm^?3 yield an activation energy of69 ± 5kcal mol^?1 in the temperature range 700–800°C. The data can be used to estimate minimum cooling rates, maximum depositional temperatures or maximum thicknesses of shock-metamorphosed rocks containing diaplectic glasses, if relaxation of a glass densified under dynamic conditions is assumed to be similar to that of statically densified glass.  相似文献   

Structure proof and significance of stereoisomeric 28,30-bisnorhopanes in petroleum and petroleum source rocks     

J.Michael Moldowan  Wolfgang K. Seifert  Edward Arnold  Jon Clardy 《Geochimica et cosmochimica acta》1984,48(8):1651-1661

Two C₂₈H₄₈-pentacyclic triterpanes were isolated from Monterey shale. X-ray crystallography of a crystal containing both compounds proved their structures as 17β,18α,21α(H)-28,30-bisnorhopane and 17β,18α,21β(H)-28,30-bisnorhopane. Several differences are found between 28,30-bisnorhopanes and the regular hopanes. Unlike the regular hopane epimers, for practical purposes the three epimeric 28,30-bisnorhopanes [17α,21β(H)-, 17β,21α(H)-, and 17β,21β(H)-]cannot be distinguished by their mass spectra. Special conditions are needed to separate them by gas chromatography. The diagenetically first-formed epimer is thought to be 17α,21β(H)- because it predominates in immature shales. The order of thermodynamic stability is 17β,2lα(H) < > 17α,21β(H) > 17β,21β(H), and all three epimers are present in petroleum. 25,28,30-Trisnorhopanes can be analyzed in similar fashion and are found to have similar thermodynamic characteristics. The percent of the ring D/E cis epimer of 28,30-bisnorhopane and/or 25,28,30-trisnorhopane is a useful maturation parameter similar to the 20S/20R sterane ratio. Evidence indicates 25-demethylation of 28,30-bisnorhopane to 25,28,30-trisnorhopane during advanced stages of biodegradation. Hence, percent ring $\text{D}\text{E}$cis 25,28,30-trisnorhopane has an application to maturation assessment in heavily biodegraded oils.  相似文献   

Development and changes in the Eastern Province of Saudi Arabia     

Barth  Hans Karl  Quiel  Friedrich 《GeoJournal》1986,13(3):251-259

Due to a particularly favourable geologic and tectonic setting in the Eastern Province, Saudi Arabia has the world largest oil reserves and is the third largest oil-producing nation in the world. Based on oil and gas revenues, the Kingdom experienced an overwhelming development during the last few decades, changing a desert country into a modern industrialized nation. Main characteristics of spatial changes are based on processes of urbanization and industrialization, on agricultural reclamations and infra-structural developments. Since the natural environment of deserts and semi-deserts in the Eastern Province is determined by an extremely sensitive equilibrium, environmental impacts, shortages in water resources, as well as limited human resources are causing basic problems, which will influence future developments.  相似文献