One of the goals for paleaoenvironmental research is to predict the tendency of future climate and environmental changes based on the understanding of the past. The key approach is to find similar pictures which happened in the past. By understanding the background and mechanism of the paleaoenvironmen- tal changes, reliable parameters and verifications can be provided for the numerical model to predict the tendency of future climate and environmental changes. The Mid-Holocene as the nearest … 相似文献
Magnetic and non-magnetic mineral analyses were conducted on a lacustrine sequence from Lago Verde in the tropical coast along the Gulf of Mexico that covers the last 2000 years. The site witnessed the transformation of the environment since the early Olmec societies until forest clearance in the last century. Through these analyses we investigated the processes that affected the magnetic mineralogy in order to construct a model of past environmental changes, and compare this model with the archeological record and inferred climatic changes in the northern hemisphere of tropical America. Volcanic activity has played a major influence on sediment magnetic properties, as a purveyor of Ti-magnetites/Ti-maghemites, and as a factor of instability in the environment. Anoxic reductive conditions are evident in most of Lago Verde's sedimentary record.
Direct observations of magnetic minerals and ratios of geochemical (Fe, Ti), and ferrimagnetic (χf) and paramagnetic (χp) susceptibility (χ) data, are used as parameters for magnetite dissolution (χp/χ, Fe/χf), and precipitation (χf/Ti) of magnetic minerals. Intense volcanic activity and anoxia are recorded before A.D. 20, leading to the formation of framboidal pyrite. Increased erosion, higher evaporation rates, lower lake levels, anoxia and reductive diagenesis in non-sulphidic conditions are inferred for laminated sediments between A.D. 20–850. This deposit matches the period of historical crisis and multiyear droughts that contributed to the collapse of the Maya civilization. Dissolution of magnetite, a high organic content and framboidal pyrite point to anoxic, sulphidic conditions and higher lake levels after A.D. 850. Higher lake levels in Lago Verde broadly coincide with the increased precipitation documented during the Medieval Warm Period (A.D. 950–1350) in the northern tropical and subtropical regions of the American continent. For the Little Ice Age (A.D. 1400–1800), the relatively moist conditions inferred are in concordance with the glacial advances recorded in central Mexico. Higher erosion rates reflect destruction of the rainforest over the last 40 years. 相似文献
Solid phases, such as surface coatings (SC), suspended particulate matter (SPM) and deposited sediments (DS), contribute to the pool of heavy metals in natural waters. Their existing and forming conditions lead to potential differences in enrichment capacity of pollutants, chemical compositions and crystals. In this study, the contents of heavy metals in SC, SPM and DS were determined by GF-AAS after digestion with a mixture of concentrated HNO3 and HClO4. The selective extraction method was employed to remove Fe, Mn oxides and organic matters and associated heavy metals (Cu, Pb, Zn). X-ray diffraction analyses were performed to characterize the crystals in the samples. The results showed that no significant difference in the contents of Fe-oxides in DS, SPM and SC was found, but the contents of Mn-oxides and organic matter follow the order of SC〉SPM〉DS. The significant crystal characters were observed in DS, SPM and SC, and the kinds of minerals and crystallization degree follow the order of DS〉SC〉SPM. In addition, quartz was the most important matter of crystals in the solid phases. Enrichment capacity follows the order of SPM〉SC〉DS for Pb, Cu and Zn. Organic matter was the major sorbent for Cu, and Mn oxides and organic matter played an important role in the enrichment of Zn. However, Pb was absorbed mainly by Fe oxides. Moreover, compared with Fe oxides and organic matter, Mn oxides had a great enrichment capacity for these metals. Although DS, SPM and SC were formed in the same water system, contents of chemical components, crystals and enrichment capacities to heavy metals were obviously different. 相似文献
The bed and suspended (slime) sediment phases associated with effluent water that are produced from phosphate-ore-upgrading process at Al-Abyad mine in the southern part of Jordan were analyzed chemically and mineralogically. The results show that the effluent water is highly oxic and mildly alkaline in nature. The geochemical behavior of each phase was controlled by the effluent water physicochemical parameters, sediment particle size, mineralogical constituents of the studied phases, and the prevailing climatic nature of the area. Bed sediments have higher concentrations of many elements than slime. Accordingly, the bed sediments can be considered as a sink rather than a pool for many elements. The geochemical dissociation of major oxides and trace elements between bed and slime sediments was evident using t test, particularly between P2O5, SiO2, CaO, K2O, Mn, Sr, Y, and Co, and to lesser extent, V, U, Zn, and Cr. This might be attributed to effluent water characteristics, mineralogy, and the presence of fine-grained materials. The spatial distribution of major oxide and trace element concentrations along the stream drainage exhibited a slight increase with distance either in bed or slime sediment phases. However, they increased suddenly at the last three sampling sites, which might be due to the abundance of fine-grained materials that are mainly composed of clay minerals (montmorillonite) that would enhance the adsorption process. Moreover, the XRD results confirmed the existence of elemental geochemical dissociation as a function of mineral control. 相似文献
The objective of this work is to present an example of environmental impact of barite waste management observed in stream sediments of the western part of the Kupa River drainage basin. It is a significant water resource for Croatia and a part of Slovenia. In addition, it is for both countries a region of tourism, sport and fishing. Sediments (fraction < 63 μm) collected within the whole drainage basin have shown a significant barium anomaly in the western part. The highest concentration of total barium (5790 mg/kg) was determined in Kupica, a tributary of Kupa River. The barium anomaly was traced in Kupa River about 120 km downstream. Looking for the contamination source it was found that the anomaly originates from uncareful waste disposal into an abyss, after barite separation in Homer (Lokve), Gorski Kotar, Croatia. From there barite entered Kupica River subterraneous. Barite and albite were identified by XRD near the source of Kupica River as minor minerals, while quartz and dolomite ferroan were major minerals. This preliminary report does not give yet an answer about barium solubility in river water, about its bioavailability and consequently about barium pollution in the western part of the Kupa River drainage basin, however the possibility is highlighted and discussed. 相似文献
Forms of phosphorus in sediments from 25 lakes in the middle and lower reaches of Yangtze River were analyzed by the sequential extraction procedure. Contents and spatial distrubution of algal available phosphorus (AAP) in sediments of Lake Taihu, the third largest freshwater lake of China, were also studied. Relationships between phosphorus forms in sediment and macrophytes coverage in sample sites, as well as phosphorus forms in sediments and chlorophyal contents in lake water were discussed. Exchangeable form of phosphorus (Ex-P) in surface sediments was significantly positive correlative to total phosphorus (IP), dissolved total phosphorus (DTP) and soluble reactive phosphorus (SRP) contents in the lake water. Bioavailable phosphorus (Bio-P) contents in sediments from macrophytes dominant sites were significantly lower than that in no macrophyte sites. In Lake Taihu, Ex-P content in top 3 cm sediment was highest. However, content of ferric fraction phosphorus (Fe-P) was highest in 4 - 10 cm. Bioavalilble phosphorus (Bio-P) contents in surface sediments positively correlated to Chlorophyll a contents in water of Lake Taihu with significant difference. Therefore, contents of Bio-P and AAP could be acted as the indicators of risks of internal release of phosphorus in the shallow lakes. It was estimated that there were 268.6 ton AAP in top 1 cm sediments in Lake Taihu. Sediment suspension caused by strong wind-induced wave disturbance could carry plenty of AAP into water in large shallow lakes like Lake Taihu. 相似文献
Changes in microfossils (diatoms, chrysophytes, chironomids and cladocera remains), geochemistry and deposition of atmospheric pollutants have been investigated in the sediment records of the alpine lake Gossenköllesee (Tyrol, Austria) spanning the last two centuries. The sediment records were compared with seasonal and annual air temperature trends calculated for the elevation (2417 m a.s.l.) and the geographical position (47° 1346N, 11° 0051E) of the lake, and with precipitation records available since 1866 from Innsbruck. Temperature trends followed a 20–30 year oscillation between cold and warm periods. Regarding long-term changes, temperature trends showed a U-shaped trend between 1780 and 1950, followed by a steep increase since 1975.Physical, geochemical, and organic parameters were not controlled by air temperature. Among the biological records only diatoms and chrysophytes reacted to air temperature changes: the relative abundance of planktonic diatoms increased during warm periods and changes in mean annual alpine air temperature explained 36.5% of their variation. The relation between abundance of seasonal stomatocyst types and air temperature varied on two different time scales: while summer stomatocysts were influenced by short term temperature fluctuations, the autumn stomatocysts were affected only by the long term changes. Other biological parameters exhibited a constant species composition (chironomids, pigments) or changes were small and independent of temperature (cladocera). Spheroidal carbonaceous fly-ash particles, and trends in Pb and Cr indicated increasing deposition of atmospheric pollutants but had no detectable effects on the biological parameters either. In respect to temperature variations over the last 200 years, this alpine lake is much less sensitive than expected and has thus to be regarded as a well buffered site. However, temperature alone is not sufficient to understand changes in species composition and other biogeochemical processes with unknown historical patterns might have affected species composition more strongly. 相似文献