As evidenced by catastrophic cadmium and mercury poisonings in Japan, heavy metals belong to the most toxic environmental pollutants. Through the investigation of sediments, the extent, distribution, and provenance of heavy-metal contamination in rivers and lakes can be determined and traced. Eight heavy metals (Cd, Hg, Pb, Zn, Cu, Cr, Ni, Co) in the clay fraction of sediments from major rivers within the Federal Republic of Germany (Rhine, Danube, Ems, Weser, Elbe) were determined by means of atomic adsorption spectrometry. The addition of the eight metals results in average values higher than 1,000 ppm for each river; in the Elberand Weser over 2,000 ppm are found. The zinc concentration in each river is higher than the other seven heavy metals together. Heavy metals known for their high toxicity are most enriched--mercury, lead, and zinc by a factor of 10; cadmium by a factor of 50--compared with the natural background of these elements. A geochemical reconnaissance survey on extreme cadmium concentrations in the sediments of the Neckar river (tributary of the Rhine) led to (a) the detection of extreme cadmium concentrations in the river water, (b) the detection of fish highly polluted with cadmium, and (c) the discovery of the source of the cadmium: a factory producing cadmium pigments. The potential danger of the heavy-metal accumulation in river sediments lies in the possibility that, under certain circumstances (changes in eH-pH within the sediment), a dissolution or desorption might lead to a release of metals into the river water. The mobilization of heavy metals from the suspended load and from the sediments--as is observed in rivers approaching the marine environment--could endanger marine organisms, thus negatively influencing the aquatic food chain. End_of_Article - Last_Page 1844------------
ABSTRACT Semi‐quantitative clay. mineral analysis was carried out on the clay and silt fractions of approximately three hundred Black Sea core samples. Relative abundance of montmorillonite, illite, kaolinite and chlorite was determined. Illite is the most frequent clay mineral in the Black Sea surface sediments. Highest values are obtained in the northern and central Black Sea. Approaching the Anatolian coast, the illite portion gradually decreases at the expense of montmorillonite. Chlorite and kaolinite occur generally only in small quantities. The lateral changes in the composition of the clay minerals can easily be traced back to the petrology of a northern (rich in illite) and a southern (rich in montmorillonite) distributive area. In almost all cores a periodical fluctuation of the montmorillonite/illite ratio with depth could be observed which may be related to the changing influence of the two distributive provinces during the Holocene and Late Pleistocene (Würm). Higher montmorillonite contents indicate arctic and subarctic climate periods in the northern distributive area during which the illite supply was diminished to a large extent.
Abstract In 1900 the position of the mouth of the Rhine (Alpenrhein) was artificially changed so that the river flowed into Fussach Bay in the eastern part of Lake Constance. The average water flow from 1931 to 1960 was 223.6 m3/sec; the average suspended load was 349.5 cm3/m3, or 454.1 g/m3. Thus, the river supplies an average annual suspended load of 2.571 million m3 which is mainly deposited in Lake Constance. The amount of bed load is about 40,000 m3 per year. Seasonal deviations from the average are extreme; during the peak of the thaw period in the Alps, water flow can be ten times greater and the amount of suspended load can increase more than twenty times. Through extension of the delta out into Fussach Bay, the area of Lake Constance has decreased by approximately 1.2 km2 in 50 years, and the average depth of Fussach Bay has decreased from 17.2 to 4.06 m. The Rhine Delta is composed primarily of silty sands; clean sands and pebble deposits are extremely rare. The average grain size decreases from top-set beds (silty sands) through fore-set beds (silty sands and silt) to bottom-set beds (silt to clayey silt which grades into silty clay away from the delta). The mineral constituents of the sediments are quartz, feldspars (orthoclase and sodic plagioclase), fragments of carbonate rocks (limestone and dolomite), and micas and clay minerals (kaolinite, illite, ledikite, chlorite). The clay mineral content increases with decreasing grain size. The amount of organic substance present is small, but it also clearly increases with the decreasing grain size. The heavy mineral content is characterized by the association garnet-epidote-staurolite-apatitekyanite.
Compared with modern carbonate environments associated with or derived from the marine milieu, the study of nonmarine carbonate depositional environments has been neglected, although these offer a much wider range of conditions under which carbonate formation and diagenesis can occur. During the past years I have studied the following environments: (1) lakes and ponds, (2) springs and rivers, (3) caves (speleothems), (4) soils (especially caliche, and (5) technical incrustations (scale). My investigations clearly reveal that the formation of primary carbonate minerals (calcite, high-magnesium calcite, aragonite, hydrous magnesium carbonates) and of secondary carbonates (dolomite, huntite, and magnesite) in these various environments having different hydrochemistry, salinity, climatic conditions, etc., is mainly dependent on the Mg/Ca ratio of the solution in which the formation or transformation occurs. By loss or extraction of carbon dioxide, evaporation concentration or mixing of different water bodies, calcite, high-magnesium calcite, aragonite, and hydrous magnesium carbonates precipitate in an order of increasing Mg/Ca ratios. Dolomite formation takes place only at elevated Mg/Ca ratios (> 7) if high-magnesium calcite is available. The reactions leading to the formation of huntite and magnesite at very high (> 30) Mg/Ca ratios are not fully understood; from observations in Turkish lakes, it seems evident that dolomite is the precursor of huntite and huntite is the precursor of magnesite. A comparison between inorganic carbonate minerals deposited in the marine and nonmarine environments shows that the only significant difference in carbonate mineralogy is that (low-magnesium) calcite does not form under marine (or marine-derived) conditions. The explanation is that the high Mg/Ca ratio of the seawater (about 5) does not allow the formation of (low-magnesium) calcite. End_of_Article - Last_Page 1844------------
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