Sources, distribution and storage of heavy metals in the Río Pilcomayo, Bolivia     

Karen A. Hudson-Edwards  Mark G. Macklin  Jerry R. Miller  Paul J. Lechler 《Journal of Geochemical Exploration》2001,72(3)

The Río Pilcomayo rises on the Cerro Rico de Potosí precious metal-polymetallic tin deposits of Bolivia, and flows in a southeasterly direction for ca. 600 km to Bolivia's southern border with Argentina. Mining of the Potosí deposits has occurred continuously since 1545, generating large quantities of waste materials in the headwater of the basin. In addition, a tailings dam breach at the Porco mine in 1996 released an estimated 235 000 m³ of tailings and fluid into the upper reaches of the Río Pilaya, the largest tributary to the Pilcomayo.Concentrations of As, Sb, Cd, Cu, Pb, Hg, Ag, Tl and Zn in contemporary channel sediments upstream of the Pilaya confluence are significantly elevated above background values. Elevated levels appear to be associated with pyrite- and other sulphide mineral-bearing tailings materials transported more than 200 km downstream of the Potosí mines. Significant downstream declines in elemental concentrations occur within 15 km, and again between 150 and 200 km, from the mines. The initial decrease in concentrations is due to the rapid dilution of nearly pure tailings effluent released to the river from milling facilities near Potosí. The latter decrease results from a combination of geomorphic processes including the storage of sediment-borne metals within the channel bed and the influx of ‘clean’ sediment from several large tributaries. Downstream of the Pilaya confluence, concentrations of Cu, Pb, Hg and Zn are only slightly elevated above background values, and Ag, Cd, Sb and Tl cannot be distinguished from background levels. These data suggest that while the Porco tailings spill may have had a significant short-term impact on sediment and water quality along the lower reaches of the Río Pilcomayo, its longer-term impacts were limited. Metals stored and eroded from alluvial deposits of historical age in upstream reaches appear to be an important source of metals to the river today. An additional, and perhaps more significant source, is the release of tailings effluent to the river from modern milling operations. The transport of these contaminants downstream of Icla (203 km from Potosí) appears to be restricted by aggradational processes occurring in the vicinity of Puente Sucre. In addition, downstream of the confluence of the Río Pilaya, inputs of large amounts of ‘clean’ sediment have caused dilution of the metal contaminants. Data from other studies where similar geomorphic processes have occurred suggest that the metals in the upper Pilcomayo may eventually be moved downvalley as the aggradational processes are reversed and channel stabilisation occurs. Thus, the most significant impacts of metal contamination may not be realised in downstream areas for decades.  相似文献   

Monitoring Networks in Fractured Rocks: A Decision Analysis Approach   总被引：1，自引：0，他引：1  

Karen Jardine  Leslie Smith  Tom Clemo 《Ground water》1996,34(3):504-518

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Teaching GIS in Geography*   总被引：2，自引：0，他引：2  

Karen K. Kemp  Michael F. Goodchild  Rustin F. Dodson 《The Professional geographer》1992,44(2):181-191

Although numerous courses in geographic information systems (GIS) have been introduced into the geography curriculum over the past few years, there has been remarkably little debate over the issues involved. This paper first discusses the arguments for geography as an appropriate disciplinary setting for GIS teaching at the undergraduate level. This is followed by a discussion of the nature of GIS courses and their appropriate place in the undergraduate geography curriculum. The final section of the paper describes the NCGIA Core Curriculum project and examines its significance in this broader context.  相似文献   

Risk-Based Evaluation of Ground-Water Contamination by Agricultural Pesticides   总被引：1，自引：0，他引：1  

Peeyush Varshney  U. Sunday Tim  Carl E. Anderson 《Ground water》1993,31(3):356-362

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Effects of the 7 march 1970 solar eclipse on atmospheric electricity,a contribution to the boundary layer discussion     

H. Dolezalek  R. V. Anderson  A. K. Kamra  H. W. Kasemir  D. J. Latham  R. Markson  D. E. Olson 《Meteorology and Atmospheric Physics》1972,21(2-3):221-245

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Stability of the lead (II) chloride complexes at elevated temperatures     

J.O. Nriagu  G.M. Anderson 《Chemical Geology》1971

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Zoning in garnets—Diffusion models     

David E. Anderson  Glenn R. Buckley 《Contributions to Mineralogy and Petrology》1973,40(2):87-104

When reference frames and diffusing components are properly selected, the flux equations for diffusion of the major components in natural garnets may often be approximated by: J DC. In such cases it is shown that, for reasonable diffusion coefficients and boundary conditions, observed zoning profiles in natural garnets may be explained with pure diffusion models. These models allow for original inhomogeneities in the host rock and may be used to explain why single hand specimens may show such a variety of zoning profiles within a single mineral species.  相似文献   

The sorption of silver by poorly crystallized manganese oxides     

B.J. Anderson  E.A. Jenne  T.T. Chao 《Geochimica et cosmochimica acta》1973,37(3):611-622

The sorption of silver by poorly crystallized manganese oxides was studied using synthesized samples of three members of the manganous manganite (birnessite) group, of different chemical composition and crystallinity, and a poorly organized γ-MnO₂. All four oxides sorbed significant quantities of silver. The manganous manganites showed the greatest sorption (up to 0.5 moles silver/mole MnO_x at pH 7) while the γ-MnO₂ showed the least (0.3 moles silver/ mole MnO_x at pH 7). Sorption of silver was adequately described by the Langmuir equation over a considerable concentration range. The relationship failed at low pH values and high equilibrium silver concentrations. The sorption capacity showed a direct relationship with pH. However, the rate of increase of sorption capacity decreased at the higher pH values.Silver sorption maxima. were not directly related to surface area but appeared to vary with the amount of occluded sodium and potassium present in the manganese oxide. The important processes involved in the uptake of silver by the four poorly crystallized manganese oxides ara considered to be surface exchange for manganese, potassium and sodium as well as exchange for structural manganese, potassium and sodium.  相似文献   

The composition and origin of the moon     

Don L. Anderson 《Earth and Planetary Science Letters》1973,18(2):301-316

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Pacific Science Association Congress     

A. Grant Anderson 《The Professional geographer》1983,35(4):476-476

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