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71.
Assessment of nutrient sources and paleoproductivity during the past century in Longgan Lake,middle reaches of the Yangtze River,China 总被引:3,自引:0,他引:3
Total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) were determined in combination with stable isotope
ratios of carbon and nitrogen (δ13COrg, δ15N) in a 63 cm sediment core from Longgan Lake, located in the middle reaches of the Yangtze River, China. These geochemical
and isotopic records provide a continuous history of lake productivity and trophic state of Longgan Lake since 1890. Variations
of δ13COrg, TOC, TN and TP indicate that primary productivity of Longgan Lake increased continuously during the last century and that
the trophic state of the lake shifted from oligotrophic to mestrotrophic conditions accordingly. Anthropogenic sources of
organic carbon (OC), nitrogen (N) and phosphorus (P) were distinguished from their natural background in the sediments using
mass accumulation rates. Element mass accumulation rates suggested increased human activities in the lake’s catchment since
1950s, were especially the utilization of artificial fertilizers amplified the anthropogenic input of N and P into the lake.
In the course of the improved availability of dissolved nutrients also primary productivity of Longgan Lake increased, resulting
in an increase of the Suess-effect corrected organic carbon isotope ratios. δ15N of bulk sediments show a marked shift towards lower values around 1950 that has been attributed to the input of nitrogen
from chemical fertilizers characterized by relatively depleted isotopic signatures into the lake. 相似文献
72.
杨赤中推估法是一种对空间域复合变量通过连续的几何滤波过程来建立核函数的最小二乘推估法,建模过程简便且能基于少量已知数据点取得好的建模效果。针对地质勘查中离散、稀疏而不规则分布的地质特征点数据难以构建地质体三维模型的难点问题,提出了一种基于杨赤中推估法的三维地质空间插值与模型建立的自动化方法。该方法首先以地质特征点数据库为基础,选用负幂指数函数模型建立适合三维地质空间插值的杨赤中推估法估值数学模型;在此基础上,构建一套基于杨赤中推估法的三维地质空间插值计算和地质体隐式建模的自动化实现流程与程序;最后以实例矿化插值数据为基础,采用基于移动立方体算法的三维隐式建模方法,快速构建实例矿体三维模型。与人工交互圈定地质体边界和进行矿体推断的三维地质显式建模相比,这种方法能快速直观地分析地质特征并处理样品分析数据,方法可行且高效。 相似文献
73.
Antioxidative capacity and enzyme activity in Haematococcus pluvialis cells exposed to superoxide free radicals 总被引:1,自引:1,他引:0
The antioxidative capacity of astaxanthin and enzyme activity of reactive oxygen eliminating enzymes such as superoxide dismutase
(SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were studied in three cell types of Haematococcus pluvialis exposed to high concentrations of a superoxide anion radical (O2−). The results show that defensive enzymes and astaxanthin-related mechanisms were both active in H. pluvialis during exposure to reactive oxygen species (ROS) such as O2−. Astaxanthin reacted with ROS much faster than did the protective enzymes, and had the strongest antioxidative capacity to
protect against lipid peroxidation. The defensive mechanisms varied significantly between the three cell types and were related
to the level of astaxanthin that had accumulated in those cells. Astaxanthin-enriched red cells had the strongest antioxidative
capacity, followed by brown cells, and astaxanthin-deficient green cells. Although there was no significant increase in expression
of protective enzymes, the malondialdehyde (MDA) content in red cells was sustained at a low level because of the antioxidative
effect of astaxanthin, which quenched O2− before the protective enzymes could act. In green cells, astaxanthin is very low or absent; therefore, scavenging of ROS
is inevitably reliant on antioxidative enzymes. Accordingly, in green cells, these enzymes play the leading role in scavenging
ROS, and the expression of these enzymes is rapidly increased to reduce excessive ROS. However, because ROS were constantly
increased in this study, the enhance enzyme activity in the green cells was not able to repair the ROS damage, leading to
elevated MDA content. Of the four defensive enzymes measured in astaxanthin-deficient green cells, SOD eliminates O2−, POD eliminates H2O2, which is a by-product of SOD activity, and APX and CAT are then initiated to scavenge excessive ROS. 相似文献
74.
发射信号不完善性对卫星导航系统内及系统间干扰的影响分析 总被引:1,自引:1,他引:0
研究了3种典型的卫星发射信号不完善性——载波泄漏、互调失真和杂散辐射对于卫星导航信号的接收所带来的干扰,通过信号建模以及谱分离系数、码跟踪谱灵敏度系数和等效载噪比的解析计算对干扰效果进行量化分析;针对GPS和Galileo系统L1/E1频段的信号进行了多层次的仿真计算,给出了综合考虑噪声、信号损耗、外源干扰、GNSS系统内和系统间干扰,以及3种信号不完善性单独作用、两两组合和综合作用下的结果,其中对于GPS L1C/A短码考虑了电文调制对线谱的影响。结果表明,当总的不完善干扰功率水平达到一定程度后,其对接收机信号捕获跟踪和解调的影响大于系统间干扰,不能忽略。 相似文献
75.
随着GPS技术的飞速前进,利用网络RTK技术建立的连续运行卫星定位系统已成为GPS应用的发展热点之一。通过对胜利油田单基站CORS系统的组成、功能及在胜利油区石油天然气井位测量中的应用方式及精度分析的论述,对单基站CORS系统在石油天然气井位测量中的现实意义和应用前景进行了展望。 相似文献
76.
A number of studies have revealed that the climate in the eastern margin of the Tibetan Plateau and Northeast China is sensitive
to postglacial changes. Unfortunately, the link of the past climate evolution between the two regions is not well understood.
In this study, two cores are analyzed to determine this link directly. The high-resolution n-alkanol distribution patterns from two typical peat sequences covering the past 16,000 cal years in the northeastern margin
of the Tibetan Plateau and Northeast China, respectively, are closely examined by gas chromatograph–mass spectrometry analysis.
In combination with other palaeoclimatic proxies, it is proposed that the n-alkanol average chain length and (C22 + C24)/(C26 + C28) ratio could reflect past climate changes in the two peat sequences. The n-alkanol proxies reveal several climatic intervals in the period from the last deglaciation through the Holocene. A comparison
of n-alkanol records between the northeastern margin of the Tibetan Plateau and Northeast China indicates that the start and end
of the warm Holocene Optimum differed at the two locations. The spatially asynchronous pattern of climatic change is possibly
a result of different responses to change in solar radiation. The evolution of the Holocene paleoclimate is more consistent
with changes in Northern Hemisphere solar radiation in Northeast China than on the Tibetan Plateau. The Holocene Optimum began
and terminated earlier in Northeast China than in the northeastern margin of the Tibetan Plateau. Thus, the two n-alkanol proxies provide valuable insights into the regional Holocene climate and local environmental conditions. 相似文献
77.
Accumulation of heavy metals in the lacustrine sediment of Longgan Lake, middle reaches of Yangtze River, China 总被引:1,自引:0,他引:1
Haijian Bing Yanhong Wu Wook-Hyun Nahm Enfeng Liu 《Environmental Earth Sciences》2013,69(8):2679-2689
Spatial and temporal distribution of heavy metals (Chromium, Copper, Nickel, Lead, and Zinc) in the sediment of Longgan Lake, middle reaches of Yangtze River, China were analyzed to discuss their enrichment characteristics and history in combination with geochronological data and to identify anthropogenic effects. The results showed that the enrichment state of heavy metals was higher in the western versus eastern lake area, although their concentrations behave in the opposite case, which demonstrated that stronger human activities existed in the western lake catchment. The enrichment history of heavy metals pointed out that prior to 1950, the enrichment state was lower in the ambient lake areas illustrating the natural effect on the lake; thereafter the human activities in the catchment enhanced markedly causing an increasing heavy metal enrichment. The increase of heavy metal enrichment in the 1970s occurred in the central lake areas. The temporal difference between the ambient and central areas elucidated that the heavy metal accumulation might be buffered by the lake before they entered the sediment. Correlation analysis revealed that there was a significant correlation between heavy metals in the sediment suggesting their similar sources. Heavy metals were distinctly related to aluminum, calcium, lithium, iron, and organic matters, which could denote their forms in the sediment. 相似文献
78.
文章利用Vulcan和Datamine三维可视化软件建立了虎头崖铅锌多金属矿床矿体的三维实体模型、块体模型及地层三维实体模型;运用地质统计学方法分析了虎头崖矿区67线以东和117线以西矿体的Pb,Zn品位空间变化结构,得出搜索椭球体,实现了虎头崖铅锌多金属矿床矿体、地层形态和铅锌品位变化形态的空间分布展示;结合三维建模结果和铅锌矿体空间变化结构,总结出矿体空间分布规律,并用三维可视化软件对矿体分布规律进行显示,指导隐伏矿体的预测,寻找有利的找矿部位。 相似文献
79.
80.
滇西三江地区中生代盆—山动力学耦合初论 总被引:4,自引:0,他引:4
盆地和相邻造山带在动力学机制上的耦合关系是当前大陆动力学研究的热点,滇西三江地区中—新生代盆山格局是开展这一研究的典型实例。晚三叠世思茅盆地从前陆盆地向裂谷盆地的转换过程,与造山带演化的主碰撞阶段和后碰撞阶段相关,是研究的切入点。通过分析研究区中—新生代盆—山耦合过程及其沉积响应、地球物理和岩浆岩地球化学特征来探讨其深部动力学过程的一致性和连续性。研究表明三江地区中—新生代盆山演化经历了"盆转山"(T1—T2)、"山控盆"(T3—E1)以及盆—山共变(E2—Q)三个阶段;思茅陆相断陷湖盆通过盆地内沉积相迁移、层序建造、基底变形,尤其是沉积旋回来响应深部动力学过程;岩石圈速度结构剖面揭示出思茅盆地的下地壳和岩石圈地幔P波速度增大,莫霍面加深;结合思茅盆地两侧中生代岩浆岩活动期次和地球化学特征,底侵作用、拆沉作用和俯冲板片断离作用可能是盆山动力学耦合的深部作用模式。 相似文献