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71.
The origin and chemical nature of micron-sized spheres found as suspended particles in Lake Kivu are examined. It can be shown that the hollow spheres, with a wall thickness of 500 Å, consist of a complex polymeric resinous material which has little functionality, except for hydroxyl groups. The spheres arise in the process of degassing of water samples at depth. Tiny gas bubbles, about 1 micron in size, act as scavengers of dissolved resinous material. The newly created resinous membrane promotes the selective coordination of zinc dissolved in the water column. In the prevailing H2S regime, formation of sphalerite crystals in induced. The size range of the crystals, 5 to 50 Å, corresponds to 1 to 10 unit cells and suggests that the resinous membrane also acts as a template in sphalerite growth processes. The sources of the zinc and dissolved gases (CO2, CH4, H2S) are hydrothermal springs seeping from the lake bottom into the basin. Water discharge is substantial; about 100 years are required to fill the lake to its present level (ca. 550 km3 water). The average Kivu water contains 2 ppm zinc. Thus, 1 million tons of zinc are contained in Lake Kivu in the form of sphalerite.
Zusammenfassung Harzkügelchen von etwa 1 Durchmesser treten in suspendierter Form im Kivusee auf. Die Kügelchen sind hohl und besitzen eine äußere Membrane von rund 500 Å Dicke. Sie sind das Ergebnis von Entgasungsvorgängen die sich in einer Wassertiefe von mehreren hundert Metern abgespielt haben. Die Oberfläche kleiner Gasblasen diente als Kristallisationszentrum für die im Wasser gelösten Harze, die ihrerseits eine selektive Koordinierung von gelöstem Zink bewirkten. Die Anwesenheit von H2S führte zur Bildung von Zinkblende mit Kristallgrößen zwischen 5 und 50 Å. Gase (CO2, CH4, H2S) und Zink entstammen salinaren hydrothermalen Lösungen, die im Gefolge vulkanischer Tätigkeit dem Seeboden auch heute noch entweichen. Der Durchschnittsgehalt von Zink im Kivusee beträgt 2 ppm, was mehr als einer Million Tonnen an Zink für den Gesamtsee entspricht.相似文献
72.
Ammonium Ion, Humic Materials, and Trihalomethane Potential in Northeastern Kansas Ground Waters 总被引:1,自引:0,他引:1
Glacial buried-valley aquifers serve as primary sources of potable ground water in northeastern Kansas. A long known problem, however, is that a large percentage of well waters in this region exceed the U.S. Environmental Protection Agency (EPA) limits for nitrate (NO−3). A detailed study of the hydrogeology and water quality of the buried valleys has confirmed the nitrate problem and led to a recognition that some well waters with low ( 5 mg/l) NO−3 concentrations have anomalous ( 0.5 mg/l) ammonium ion (NH+4) levels, with an NH+4 range from <0.1 to 4.8 mg/l. The extractable NH+4 concentrations in related glacial sediments range up to approximately 75 mg/kg, and the amounts generally increase from an average of 2 mg/kg in the topsoil downward to bedrock. Migration of brines from subjacent Permian or Pennsylvanian bedrock into the unconsolidated sediments locally may cause desorption of NH+4 and an increase in its levels in the associated ground waters. Numerous test holes drilled in the study area showed a black scum on the fluid and cuttings, which may be from buried humic materials. Recently measured total organic carbon (TOC) contents of the ground waters confirm a significant level in some areas, with a range from 0.1 to 2.4 mg/l as C. Chlorination of water with dissolved organics may lead to production of halogenated compounds. Two public-water-supply well waters contained total trihalomethane (TTHM) levels close to the maximum contaminant level (MCL) of 100 /μg/l in chlorinated samples quenched after one week. The presence of NH+4 inhibits the formation of THMs, but it also can give rise to odor and taste problems in the finished water. The inhibition of THM formation by NH+4 is achieved by reactions which compete with the organics for combination with chlorine. These reactions make maintaining appropriate chlorine residuals difficult and also may lead to production of undesirable side products. Present efforts to evaluate the regional water-quality problems are focused in Nemaha County, Kansas. 相似文献
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A fractal analysis using the classical Hurst method has been applied to artificial data, simulated sunspot magnetic field data, and to data acquired with NASA/Marshall Space Flight Center's vector magnetograph. The main goals of this study are to quantify the complexity of an active region and to determine if significant changes in complexity are associated with flare activity. We tested the analysis using three basic types of two-dimensional synthetic data: (1) data composed of gaussians with various types of superimposed features, (2) random data, and (3) synthetic sunspots created from a basic, simple configuration on which are placed increasingly smaller structures. Our results confirm that the Hurst method of analysis is sensitive to the presence of large-scale structures within a two-dimensional image. When the large-scale structure has been removed, the value of the Hurst exponent is inversely proportional to increasing complexity in the image. The Hurst exponent of magnetograph data with the large-scale structure of the sunspot removed, shows a tantalizing variation in the shear parameter five minutes prior to a flare. 相似文献
76.
了解植被物候与城市化之间的关系对于认识人类活动对生态系统的影响至关重要。基于呼和浩特市近20 a MODIS的两种植被指数数据,利用动态阈值法提取了植被物候,结合城市化指标,研究了2001—2020年呼和浩特市植被物候对城市化的响应。研究表明:森林和灌木地返青期(Start of growing season,SOS)发生较早(平均值第132 d),但其枯黄期(End of growing season,EOS)也较早(第265 d)。SOS较晚的是耕地(第168 d),EOS较晚的是草地(第275 d),表明研究区木本植物SOS和EOS均早于草本植物。人造地表植被物候年际变化较大,在SOS和EOS的物候变化率分别为每10 a提前4.1 d和推迟0.7 d。此外,以人造地表比率和城乡梯度信息(即从城市核心到周边农村地区的同心环)为城市化指标,探讨了呼和浩特市中心城区植被物候对城市化的响应。研究发现SOS随人造地表比率上升而提前,EOS则出现相反的趋势。从城乡梯度上看,在特定范围内,远离城市中心SOS波动上升,即距城市中心越远植被SOS越晚,而EOS逐渐下降,即距城市中心越远植被EOS越早。总之,不同的城市化指标显示了植被物候对城市化的非线性响应。 相似文献
77.
丹凤地区光石沟铀矿床大毛沟岩株锆石U-Pb同位素定年及其地质意义 总被引:3,自引:0,他引:3
丹凤地区是我国伟晶岩型铀矿床的重要产区,光石沟铀矿床是该区最大的铀矿床之一,大毛沟岩株与光石沟铀矿床有密切的空间关系与成因联系。本文采用锆石LA-ICP-MS定年方法测定了大毛沟岩株的U-Pb同位素年龄,获得了代表大毛沟岩株形成年龄的锆石谐和曲线加权平均值年龄为418.3±8.8 Ma,与光石沟铀矿床的成矿年龄相当,说明光石沟铀矿床的成矿作用在时间上与该岩株的形成时间相当。同时,残留锆石中1980.5±19.47 Ma年龄的发现,说明大毛沟岩株白岗质花岗岩的物源可能与中下地壳秦岭群有关;E颗粒内核465Ma的年龄则可能代表灰池子岩体片麻状二长花岗岩的形成年龄,表明大毛沟岩株与灰池子岩体的形成年龄之间存在约30 Ma的时差。 相似文献