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461.
Particulate trace metal speciation in stream sediments and relationships with grain size: Implications for geochemical exploration 总被引:1,自引:0,他引:1
Sediment samples were collected from streambeds in an undisturbed watershed in eastern Quebec (Gaspé Peninsula). Two sampling sites were located on a stream draining an area of known mineralization (Cu, Pb, Zn) and two on a control stream. The sediment samples were separated into 8 distinct size classes in the 850 μm to <1 μm size range by wet sieving, gravity sedimentation or centrifugation. Each sediment subsample was then subjected to a sequential extraction procedure designed to partition the particulate heavy metals into five fractions: (1) exchangeable; (2) specifically adsorbed or bound to carbonates; (3) bound to Fe-Mn oxides; (4) bound to organic matter; (5) residual. The following metals were analyzed in each extract: Cu, Pb, Zn; Fe, Mn.Comparison of samples from the mineralized area with control samples revealed the expected increase in total concentrations for Cu, Pb and Zn. Non-detrital metals were mainly associated with Fe oxides (specifically adsorbed; occluded) and with organic matter or resistant sulfides. For a given sample, variation of trace metal levels in fractions 2 and 3 with grain size reflected changes in the available quantities of the inorganic scavenging phase (FeOx/MnOx); normalization with respect to Fe and Mn content in fraction 3 greatly reduced the apparent dependency on grain size.The results of this study suggest that a single reducing extraction (NH2OH.HCl) could be used advantageously to detect anomalies in routine geochemical surveys. A second leaching step with acidified H2O2 could also be included, as the trace metal concentrations in fraction 4, normalized with respect to organic carbon content, also showed high {anomaly/background} ratios. 相似文献
462.
Alfons Zehnder Dr. J. Komárek Prof. Dr. S. Golubić Prof. Dr. R. Y. Stanier Dr. J. Komárek Dr. J. Ludvík Dr. L. Kováčik Dr. Asta Almestrand Prof. Dr. P. Compère Dr. D. Mollenhauer Dr. F. Hindák Dr. T. P. Chang Dr. Nagaraj Jeeji Bai C. V. Seshadri Dr. M. -E. Meffert Dr. R. Oberhäuser Dr. J. Overbeck Dr. F. Hindák Susan E. Campbell Dr. Jaroslava Komárková Dr. U. Uehlinger Dr. F. Schanz Dr. Alfons Zehnder 《Aquatic Sciences - Research Across Boundaries》1983,45(1):267-310
The 8th Symposium of the International Association for Cyanophyte Research IAC was attended by 29 specialists from 11 countries.
The 19 oral presentations and discussions centered on the following themes: The basic principles of cyanophyte taxonomy (3
lectures), systematic problems of certain taxonomic groups (5 lectures), morphology (6 lectures) and ecology (5 lectures).
The intensive discussions between representatives of the classical (european) taxonomic treatment of cyanophytes (based on
morphological and ecological characteristics) and those representing the bacteriological study of ‘cyanobacteria’ were especially
valuable. The central theme of the meeting was, however, the mutual microscopic study and discussion of problematic blue-greens
from natural habitats, that were mostly collected during the three field trips into different areas of central Switzerland
(Grimsel-Gotthard-Nufenen. Klewenalp. Gerzensee).
相似文献
463.
Does perception match reality when people judge the flatness of large areas, such as U.S. states? The authors conducted a geomorphometric analysis of the contiguous United States, employing publicly available geographic software, Shuttle Radar Topography Mission (SRTM) elevation data, and a new algorithm for measuring flatness. Each 90‐meter cell was categorized as not flat, flat, flatter, or flattest, and each state was measured in terms of percentage flat, flatter, and flattest as well as absolute area in each category. Ultimately, forty‐eight states plus the District of Columbia were mapped and ranked according to these values. Keywords: flatness, U.S. states, slope, Kansas, Florida. 相似文献
464.
Ian A. Simpson Sophia Perdikaris Gordon Cook John L. Campbell William J. Teesdale 《Geoarchaeology》2000,15(8):743-763
The development of specialized and commercial fishing activity in the island archipelago of Lofoten and Vesterålen in northern Norway is a critical foundation from which to understand the subsequent spread of commercial fishing across the north Atlantic region during the medieval and early modern period. One little understood aspect of this development is the relationship between medieval commercial fishing stations (fiskevaer) and earlier fishing activity. In this article, cultural sediment deposits at Langenesværet, Vesterålen, Northern Norway provide an opportunity to examine this relationship and its implications for current historical models of fishing development in northern Norway and the north Atlantic region. Conventional and AMS radiocarbon dating techniques are used to establish a chronology for the deposits, while activities associated with the sediments are characterized using thin‐section micromorphology supported by proton induced X‐ray emission spectrometry (PIXE). The results suggest that the site commenced formation as early as ca. 3000 B.C. and that the site was first used for specialized fishing activity from the early centuries A.D. The medieval commercial fiskevaer settlement at Langenesværet was introduced to an area that had a longstanding tradition of specialised fishing activity. © 2000 John Wiley & Sons, Inc. 相似文献