The significance of lake sediments geochemistry in environmental reconstruction of south Hongshan Lake, northwestern Tibetan Plateau during the past 150 years

1 IntroductionPast Global Changes (PAGES) is one of the important IGBP (International Geo-Biosphere Program) core programs, of which the objectives are to obtain and interpret all kinds of palaeoclimate records, understand the history of environment and ecological change, and provide basic material and necessary test for the establishment and improvement of climate forecasting models. Because the research of climatic and environmental changes on short time scale is the key connection bet…     

History of a presently slightly acidic lake in northeastern Alberta,Canada as determined through analysis of the diatom record

The Holocene sedimentary diatom record from Otasan Lake, Alberta, has been analyzed to determine the development of this presently slightly acidic lake. The changes in the lake have been linked to the development of the Sphagnum-dominated catchment. Analysis of the stratigraphic data revealed four distinct zones. The lake record began ca. 8200 yrs BP with a benthic and alkaline diatom assemblage dominated by Ellerbeckia arenaria (Moore) Crawford. At ca. 7300 yrs BP planktonic species began to increase and dominate indicating increased water levels, decreased turbidity, and increased nutrient levels. Throughout the Holocene the peatland in the catchment encroached toward the modern lake margin and by ca. 5000 yrs BP lake acidity had changed sufficiently such that acidic diatom species dominated. Tabellaria flocculosa (Roth) Kütz.v. flocculosa Strain IIIp sensu Koppen dominated the record from ca. 5000 to ca. 3100 yrs BP. The lowest lake water pH was inferred for this zone. From ca. 3100 yrs BP to the present Fragilaria species, primarily F. construens v. venter (Ehr.) Hustedt, dominated the diatom assemblage. Diatom productivity and inferred pH were interpreted as stable. From correspondence analysis of the fossil samples, and from species assemblages, underlying gradients of pH, nutrient level, and water depth were inferred. The change from alkaline to slightly acidic conditions took place between ca. 8200 and ca. 5000 yrs BP. From ca. 3000 yrs BP to the present, lake water pH has remained fairly constant. Nutrient levels and water depth were inferred to have altered together. After ca. 8200 yrs BP, nutrients and water level began to increase until ca. 6000 yrs BP. Then, there was a gradual decline in these variables over the most acidic zone until ca. 3000 yrs BP, after which they, too, have remained fairly constant. Dominant Boreal Upland Vegetation was established by ca. 7200 yrs BP, and it was inferred that dominant climate patterns had been established at that time, but small changes in climate have occurred and the landscape in northeastern Alberta has only been stable for the last 3000 years.     

Chemostratigraphy of Lago Albano sediments (Central Italy):geochemical evidence of palaeoenvironmental changes in lateQuaternary

The results of the geochemical investigation on bulk sediment fromthree cores collected in Albano crater lake (Central Italy) are reported, andthe main markers of the palaeoenvironmental changes in the last 26ka are discussed. The sediment of Lago Albano consists of greysilt and mud, and is made of volcanogenic, calcareous, siliceous and organicmaterial. Some tephra layers provide a chronological framework for thesequence. The chemical features of the sediments are strongly impacted by theAlban Hills volcanism (Roman volcanic area), but there are also strong changesof organic/inorganic matter ratios, owing to variations in biologicalproductivity and terrigeous supply from the catchment. Six chemostratigraphiczones record the main steps of the transition from the cold and dry climate ofGlacial Maximum to the warmer and more humid Holocene climate. The most usefulgeochemical indices are: biogenic silica, CO₂, Br and organiccontent (OM) for biological productivity; Al, Y, CIA (Chemical Index ofAlteration), Al/Rb, Ti/Zr and Y/Al ratios for terrigenous clasticmaterial; OM/Al ratio for organic/terrigenous ratio; S/Fe andMo/Fe ratios and Authigenic U for redox diagenetic conditions of the lakesediment. The geochemical records agree rather well with those of thelithological and paleomagnetic studies, and despite the information obtainedare less detailed than those acquired by the study of biological remains, thepalaeoenvironmental significance inferred is consistent. A comparison of thechemostratigraphic results of Lago Albano with those obtained on coevalsediments from Central and Southern Italy lakes supports the role of thegeochemical investigation as important complement to more sophisticatedtechniques in the palaeoenvironmental reconstructions.     

Conifer stomata analysis in paleoecological studies on the Loess Plateau: An example from Tianchi Lake, Liupan Mountains

The identification of fossil conifer stomata was conducted from a lake sedimentary sequence on the Liupan Mountains, southwestern Loess Plateau, in order to reconstruct detailed forest history and assess the potential of using stomata as a supplement to pollen analysis to determine the local presence of conifers over the last 3200 years. The pollen has already been analyzed in our previous study. Reference conifer stomata were prepared for the fossil stomata identification and demonstrate that the conifer stomata could be identified to at least genus level. Our stomata and pollen results reveal three clear stages of the forest recession during the late Holocene: mixed conifer-deciduous forest, steppe-forest and steppe. Combined stomata and pollen results confirm the local presence of conifer trees (Abies and Pinus) in the vicinity of the Tianchi Lake. Abundant Abies trees existed during 3200-2200 cal yr BP. Then it decreased and finally demised at ca.210 cal yr BP. Pinus trees have been continuously present with very low abundance throughout the late Holocene. Application of comprehensive studies comprising both stomata and pollen analyses allowed a detailed determination of the stages of conifer trees presence in the vicinity of the Tianchi Lake. Our study suggests that the analysis of fossil stomata is a valuable methodological tool for the provision of unambiguous evidence of the past local presence of the coniferous taxa in this region.     

A Raman investigation on the boron form occurring in salt lake brine during evaporation

Boron resources are abundant in Da Qaidam salt lake of Qaidamu Basin. It has been given great attention for the polyborate species present in brine. In this study, the Raman spectroscopy was applied to investigate the existing-form of boron in brine during evaporation. The prepared solutions of MgO·2B2O3-H2O, MgO·2B2O3-MgCl2 -H2O, and MgO·2B2O3-MgSO4-H2O was also evaporated and recorded to study the influence of boron concentration, pH, and electrolytes on the borate speciation in brine. The mononborates of B(OH)3 and B(OH)4- were found to be the only forms present in the original salt lake brine. Brine evaporation promotes the formation of polyborate anions B3O3(OH)4-, B5O6(OH)4-, and B6O7(OH)62- and also disappearance of the B(OH)4- ion in brine with boron concentration of more than 11 g/L in B2O3. The pentaborate ion of B5O6(OH)4- was sensitive to the solution pH and found to be appeared under the pH value of 8.0. While the hexaborate ion of B6O7(OH)62- was observed more dependent on the electrolyte of magnesium chloride due to its special properties, such as promoting boron accumulation, lowering solution pH, and also the strong af?nity for water molecules, which is beneficial to the polymerization of borate ions in brine. The interaction mechanisms among polyborate anions during evaporation had also been proposed.     

我国西部地区湖泊水资源利用与湖水咸化状况分析

湖泊咸化是指湖水含盐量逐步增加．湖泊由淡水湖向咸水湖、再向盐湖和干盐湖的演化过程,这是我国西部干旱、半干旱地区湖泊普遍存在的一种现象。在大量调查的基础上,分析了我国西部干旱、半干旱地区近几十年来湖泊萎缩咸化的状况,湖泊变化的所产生的原因,并初步提出改善我国西部地区湖泊水资源利用的对策。     

盐湖丰产元素与Zintl化合物(续完)

Zintl化合物是以Edward Zintl命名的化合物,是一类由电正性的碱金属或碱土金属与电负性的13族或14族元素形成的特殊金属间化合物。其价键模式可以是离子键、金属键和共价键共存,其中的准金属可以共价键的形式形成各种形式的离子簇,因而其结构复杂多样。这类化合物的部分阴离子簇不仅具有稳定的笼状、层状和链状结构,并且具有特殊的光、电、磁等性能,使得在半导体、催化、电极材料等方面都有应用的前景和发展潜力。介绍了几个特殊Zintl化合物体系,盐湖丰产元素在Zintl化合物中的作用,指出了含有盐湖丰产元素的Zintl化合物的应用前景和方向。     

The fauna of the Aral Sea in 1989. 2. The zooplankton

Data are presented on the composition and biomass of the Aral Sea zooplankton in August and October, 1989. As salinity gradually increased, a decrease in zooplankton species composition occurred at a salinity of 25–30 g L⁻¹. Because the Aral has now divided into two water-bodies, the zooplankton communities in these lakes have begun to conform with their individual hydrological and biological regimes.     

近30年来西藏那曲地区湖泊变化对气候波动的响应

根据1975年地形图、20世纪80年代至2005年的TM、CBERS卫星遥感资料和近45年的气温、降水量、蒸发量、最大积雪深度和最大冻土深度等气候资料分析得出,西藏那曲地区东南部的巴木错、蓬错、东错、乃日平错等四个湖泊的水位面积在近30年来呈较显著的扩大趋势,2005年与1975年相比,分别增加了48.2 km²、38.2km²、19.8 km² (比2004年)、26.0 km²,增长幅度分别为25.6%、28.2%、16.2%、37.6%。其主要原因与该地区近年来气温的上升、降水量的增加和蒸发量的减少、冻土退化等暖湿化的气候变化有很大关系。