Constraints of authigenic carbonates on trace elements (Sr, Mg) of lacustrine ostracod shells in paleoenvironment reconstruction and its mechanism     

Guang Hu  ZhangDong Jin  Fei Zhang 《中国科学D辑(英文版)》2008,51(5):654-664

Molar ratios of Mg/Ca and Sr/Ca were measured in two species of ostracod shells preserved in the upper core (15-55 m) of the Heqing Basin in Yunnan Province, southwest China. By correlating the molar ratios between Mg/Ca and Sr/Ca and comparing them with Sr concentrations of the sediments, we suggested that: (1) the molar Mg/Ca and Sr/Ca ratio variations in respective ostracod primo re- flected the changes in its ambient water composition and ecology; (2) the molar Sr/Ca ratios responded better to the salinity change linearly than Mg/Ca without aragonite precipitation in the system, and otherwise there was no linear relation between them; and (3) the molar Sr/Ca ratios were mainly con- trolled by salinity and authigenic carbonate precipitation, whereas the molar Mg/Ca ratios were related to both salinity and temperature. In fact, the rate of ostracod growth owing to temperature controls the fluctuation of Mg/Ca in shells. Here, more attentions should be paid to the constraint of authigenic mineral precipitation processes on the trace elements in ostracod shells and to the correlation between these trace elements in biogenic carbonates and compositions of the sediments in systems and in fu- ture in vitro experiments.  相似文献   

藏北色林错流域的水文特征   总被引：4，自引：0，他引：4  

陈毅峰  陈自明  何德奎  蔡斌  巴珠 《湖泊科学》2001,13(1):21-28

本文报道了1997年降1998年夏季对藏北色林错等水体水文特征的考察情况,结果表明,色林错是一个大型深水湖泊,表层水温在下午4：30左右达到最高,清晨7：30左右时最低,浅水区域表层湖水在6月份的极端最高水温为21．2℃,极端最低水温为11．0℃,而日平均水温变幅仅5．6℃,其幅度大于在同一时段湖区内不同区域之间表层水温的变化,色林错湖水的pH值较高咪9．19－9．66;表层水的pH昼夜变化较小,仅0．15,最高值出现在凌晨,同时水体不同区域及深度的pH值基本一致,其溶解氧变化在4．62－5．12mg/L,而且不同深度水层之间的变幅较小,仅0．03－0．35mg/L;但其湖汊浆东如瑞溶解氧的昼认变幅为4．58－5．59mg/l;盐度的日变幅为1．60％－2．20％,考察表明,藏北水体的盐分有一个从河流到湖泊、以及由流水向静水富集的趋势;鱼类的分布与水体盐分的含量密切相关,即鱼类随着水体盐分的增加而消失,代之以嗜盐性卤虫的出现及大量繁衍。  相似文献   

Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient     

J.E. Ferguson  G.M. Henderson  M. Kucera  R.E.M. Rickaby 《Earth and Planetary Science Letters》2008,265(1-2):153-166

The Mg/Ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures. Used in conjunction with δ¹⁸O of foraminiferal calcite it allows deconvolution of temperature and ice-volume signals to infer past ocean temperatures and salinities (assuming the relationship between seawater δ¹⁸O and salinity is known). Such work assumes that temperature is the only, or at least the dominant, environmental controller of foraminiferal Mg/Ca. The semi-enclosed Mediterranean Sea, where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 °C to 8 °C, provides a relevant setting to test this assumption outside the laboratory. In this study, planktonic foraminifera (O. universa, G. siphonifera, G. bulloides and G. ruber (white) and (pink)) were picked from 11 box core tops spanning the Mediterranean salinity gradient and analysed for their trace-element concentrations. Mg/Ca ratios are higher, for the associated calcification temperatures, than in other regions where calibrations have been conducted and correlate poorly with calcification temperature. Mg/Ca ratios are particularly high for samples from the Eastern Mediterranean where salinity is unusually high. Correlations of Mg/Ca with the calcification salinity are statistically significant with Mg/Ca changing by 15–59% per psu, suggesting that salinity may act as a control on Mg/Ca ratios in addition to the dominant temperature control. We show that contamination by non-carbonate material and diagenetic high-Mg carbonate overgrowths cannot account for the observed trend of increasing Mg/Ca with salinity. A relationship between Mg/Ca and salinity is also suggested by re-analysis of calibrations from open-ocean settings. These new Mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the Mg/Ca palaeothermometer should be considered even in open-ocean settings, particularly where large salinity changes occurred in the past.  相似文献   

巢湖南淝河口黑水团区流速和溶解氧与Fe²⁺、S^2-浓度的空间关联性     

王玉琳  汪靓  华祖林  丁士明 《湖泊科学》2016,28(4):710-717

黑臭现象在我国东部地区浅水湖泊频繁发生,已经严重影响环湖地区的社会经济发展.厌氧环境和高浓度Fe~(2+)、S~(2-)是引起黑臭现象的必要条件.本文解析巢湖南淝河口区黑臭水团范围内Fe~(2+)、S~(2-)与DO、流速的分布特性;基于空间计量模型重点探讨了流速、DO和Fe~(2+)、S~(2-)分布的空间关联性.结果发现,水体流动在黑臭水团中主要有两个作用:使Fe~(2+)、S~(2-)和DO彼此产生空间相关性以及通过分散作用改变局部Fe~(2+)、S~(2-)浓度分布;同时流速通过增强复氧间接影响Fe~(2+)及S~(2-)总体浓度的作用较小.流速与Fe~(2+)、S~(2-)之间均满足线性空间滞后模型;而线性回归模型中流速对Fe~(2+)的影响低估了约7%,对S~(2-)的影响则低估了12%.  相似文献   

High-pressure phase equilibria in a garnet lherzolite,with special reference to Mg²⁺Fe²⁺ partitioning among constituent minerals     

M. Akaogi  S. Akimoto 《Physics of the Earth and Planetary Interiors》1979,19(1):31-51

Phase equilibria in a natural garnet lherzolite nodule (PHN 1611) from Lesotho kimberlite and its chemical analogue have been studied in the pressure range 45–205 kbar and in the temperature range 1050–1200°C. Partition of elements, particularly Mg²⁺Fe²⁺, among coexisting minerals at varying pressures has also been examined. High-pressure transformations of olivine(α) to spinel(γ) through modified spinel(β) were confirmed in the garnet lherzolite. The transformation behavior is quite consistent with the information previously accumulated for the simple system Mg₂SiO₄Fe₂SiO₄. At pressures of 50–150 kbar, a continuous increase in the solid solubility of the pyroxene component in garnet was demonstrated in the lherzolite system by means of microprobe analyses. At 45–75 kbar and 1200°C, the Fe²⁺/(Mg + Fe²⁺) value becomes greater in the ascending order orthopyroxene, Ca-rich clinopyroxene, olivine and garnet. At 144–146 kbar and 1200°C, garnet exhibits the highest Fe²⁺/(Mg + Fe²⁺) value; modified spinel(β) and Ca-poor clinopyroxene follow it. When the modified spinel(β)-spinel(γ) transformation occurred, a higher concentration of Fe²⁺ was found in spinel(γ) rather than in garnet. As a result of the change in the Mg²⁺Fe²⁺ partition relation among coexisting minerals, an increase of about 1% in the Fe₂SiO₄ component in (Mg,Fe)₂SiO₄ modified spinel and spinel was observed compared with olivine.These experimental results strongly suggest that the olivine(α)-modified spinel(β) transformation is responsible for the seismic discontinuity at depths of 380–410 km in the mantle. They also support the idea that the minor seismic discontinuity around 520 km is due to the superposition effect of two types of phase transformation, i.e. the modified spinel(β)-spinel(γ) transformation and the pyroxene-garnet transformation. Mineral assemblages in the upper mantle and the upper half of the transition zone are given as a function of depth for the following regions: 100–150, 150–380, 380–410, 410–500, 500–600 and 600–650 km.  相似文献   

Management of sustainable ecological water levels of endorheic salt lakes in the Inner Mongolian Plateau of China based on eco-hydrological processes     

Ziqiang Xing  Huojian Huang  Yuanyuan Li  Shanshan Liu  Ding Wang  Yong Yuan  Zhongnan Zhao  Lisheng Bu 《水文研究》2021,35(5):e14192

Hydrologic regime plays an important role in maintaining aquatic ecosystem structures and biogeochemical processes of endorheic salt lakes. Due to joint influences of regional climate change, runoff regulation and water withdrawal, ecological water deficiency has been increasingly prominent in endorheic salt lakes in Northwest China, especially in the Inner Mongolian Plateau. Previous studies mainly focused on establishing and applying methods to determine ecological water levels of lakes, while much less attention was paid to a more important problem – how such water levels could be reached under changed watershed hydrological processes. Solutions of this gap were explored in this study using the Dalinuoer Lake as an example. This lake is a typical endorheic salt lake located in the Inner Mongolian Plateau. It is a critical source to provide important ecological services and economic values for locals. Its ecological water level to maintain the optimum salinity threshold was first calculated by applying a statistical analysis of relationships between the phytoplankton biomass, salinity and water level of the lake. Potential measures to preserve the ecological water level of the lake were subsequently evaluated based on a hydrological process analysis of the watershed. The results indicated that the optimum salinity threshold was 5.7 g/L. This value should be also valid for other endorheic salt lakes in this region. According to a function between the water storage and the mean water depth of this lake, the ecological water level was determined to be 10.28 m with an ecological water deficit of 2.5 × 10⁸ m³. A basin water balance analysis using the results proposed measures to maintain a sustainable ecological water level, including controlling local water consumption and infusing ecological water. The results of this study could be extrapolated to other similar conditions to provide guidance for policy-makers, so that better decisions could be hopefully forged to protect eco-hydrological processes of endorheic salt lakes in the Mongolian Plateau, as well as other comparable scenarios.  相似文献   

Characterization of biochars produced from seven biomasses grown in three different climate zones     

《Acta Geochimica》2015,(4)

The characterization of biochars produced from seven feedstocks(four crop straws: cotton stalks, wheat stalks, rape stalks and corn stalks; three hardwoods: Salix babylonica Linn, Platanus orientalis and Robinia pseudoacacia) grown in three different climate zones(arid,semiarid and humid regions) were investigated for their potential as soil amendments. The results show that ash content, K+, Ca2+, Mg2+, CEC, Cl-, p H, and salinity are generally higher in the straw biochars(STR-BCs) than the hardwood biochars(HW-BCs). However, there is no significant distinction between the two categories of biochars in terms of surface acidity, surface basicity, TC, available phosphorus(A-P) or NH4+-N. The contents of K+, Na+,Ca2+, Mg2+, EC, Cl-of all 21 biochars increase in semiarid and arid regions in comparison to humid regions, while ash content, TC, CEC, p H, surface acidity, surface basicity,A-P and NH4+-N show no correlation to the climate. From the perspective of K+, CEC and the remediation of acidified soils, STR-BCs are preferable over HW-BCs as a soil amendment, while HW-BCs are more suitable than STRBCs in soils with a saline problem. EC, Na+and Clincrease with the water stress of the climatic regions, and the high saline ions of biochar in the arid regions indicate that biochars produced from local biomass, especially from crop residues, are at a high risk of exacerbating soil salinization. The big difference in the critical chemical properties, such as the saline ions, stresses that biochar should be taken on a regional basis as well as a biomass basis, with the general assumption that whether biochar as a soil amendment is good or bad is groundless.  相似文献   

Cd²⁺和Cr⁶⁺对慈姑（Sagittaria sagittifolia L.）的毒害效应   总被引：3，自引：0，他引：3  

胡金朝  施国新  丁秉中  陈苏雅  许丙军  赵娟  吴国荣 《湖泊科学》2006,18(2):157-162

以水生经济植物慈姑（Sagittaria sagiuifolia L．）为实验材料,通过模拟水体Cd^2＋和Cr^6＋污染环境,研究了两种单一离子处理对慈姑的毒害影响．结果表明：随着水体Cd^2＋、Cr^6＋浓度增大,慈姑叶绿素含量与根细胞质膜透性先升高后降低;Cd^2＋浓度增大,根和叶的POD活性,叶的SOD活性、丙二醛（MDA）含量及根的超氧阴离子（O2^-）产生速率均是先升后降;根和叶的CAT活性、根的SOD活性、MDA含量和叶的O2^＋产生速率则逐渐升高;而Cr^6＋处理时,MDA含量、根的SOD、CAT、POD活性均随浓度增大而升高,O2^-产生速率和叶的SOD、CAT、POD活性则升高后降低;Cd^2＋和Cr^6＋污染都对慈姑产生毒害,其毒害的效应既有相似性又有差异,同浓度条件下根的受害程度比叶严重．  相似文献   

Hg,Cd对莼菜冬芽茎、叶叶绿素含量及活性氧清除系统的影响     

陆长梅  施国新  吴国荣  陈国祥  常福辰 《湖泊科学》1999,11(4):322-327

利用人工配制的生活污水先进行单胞藻（斜生栅落Ｓｃｅｎｅｄｅｓｍｕｓ ｏｂｌｉｑｕｕｓ Ｔｕｒｐ）的培养,再接种田螺（Ｃｉｐａｎｇｏｐａｌｕｄｉｎａ ｓｐ．）和短钝蚤（Ｄａｐｈｎｉａ ｏｂｔｕｓａ Ｋｕｒｚ）对栅藻密度的经时变化,短钝蚤种群增长及水体中氮,磷,碳在培养过程中的变化作了与分析。  相似文献