Fractal dimensions of suspended solids in streams: comparison of sampling and analysis techniques     

Dirk H. de Boer  Mike Stone 《水文研究》1999,13(2):239-254

Fluvial suspended sediment typically consists of a variety of complex, composite particles referred to as flocs. Floc characteristics are determined by factors such as the source, size and geochemical properties of the primary particles, chemical and biological coagulation processes in the water column and shear stress and turbulence levels in the stream. Studies of floc morphology have used two contrasting methods of sampling and analysis. In the first method, particles settle on a microscope slide and are observed from below using an inverted microscope. The second method uses filtration at no or low vacuum and particles deposited on the filter are observed with a microscope. Floc morphology can be quantified using fractal dimensions. The aims of the present study were to examine the effect of the two sampling methods on the fractal dimensions of particle populations, and to evaluate for each method how well the fractal dimensions at the various sampling sites reflect basin conditions. Suspended solids were collected in triplicate on inverted microscope slides and on 0·45 μm Millipore HA filters in two southern Ontario streams with contrasting riparian zones during a minor runoff event resulting from the melt of a freshly fallen snowpack. An image analysis system was used to determine area, longest axis and perimeter of particles. The morphology of the particle population of each sample was characterized using four fractal dimensions (D, D₁, D₂ and D_K). Systematic differences in fractal dimensions obtained with the two methods were observed. For the settling method, outlines of larger particles were frequently blurred because of the distance between the focal plane (the top of the inverted microscope slides) and the plane of the particle outline. In this method, the blurring of large particles can cause an increase in the projected area and length of the particle. The effect on the particle perimeter is unpredictable because it depends on the amount of detail lost through blurring and its effect on the apparent increase in particle size. Because of blurring, D and D₁ tend to be systematically lower for the settling method, whereas the net effect on D₂ is unpredictable. Particle size distributions derived from settling are typically coarser because small, low density particles may remain in the water column and all particles may not deposit on the slides. This loss of fines results in systematically lower D_K values for the settling method compared with the filtration method. Fractal dimensions and particle size distributions obtained with the filtration method were sensitive to and clearly indicated differences between drainage basins and between sites within each basin. These differences were explained by basin characteristics and conditions. Fractal dimensions and particle size distributions obtained with the settling method were less sensitive to drainage basin characteristics and conditions, which limits their usefulness as process indicators. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Mapping of groundwater potential zones in the drought-prone areas of south Madagascar using geospatial techniques     

《地学前缘(英文版)》2020,11(4):1403-1413

The southern regions of Madagascar have the country’s lowest water supply coverage and are highly vulnerable to drought. Access to potable drinking water is a major challenge for the local population. Chronic droughts lead to annual emergency appeals to save the lives of acute malnourished children. UNICEF’s response consisting in providing potable drinking water through the drilling of boreholes has been challenged by the complex hydrogeology, the low yield of boreholes and high-level salinity of water, the lack of reliable groundwater data and the weak capacity of the drilling sector. These constraints result in a high rate of drilling failure. To improve drilling success and provide more potable drinking water to local communities, it is vital to undertake reliable groundwater investigation.UNICEF Madagascar and the European Union delegation in Madagascar collaborated on the use of satellite imagery to improve sector knowledge and access to safe and clean water for local communities in southern Madagascar. The methodology relies on produce thematic layers of groundwater potential areas. Later, these thematic layers were overlaid with ground-based hydrogeological data to map the groundwater potential zones (GWP) and identify the most suitable sites for borehole siting and drilling. Findings of this study are very encouraging, and the integrated approach used has proven its applicability in mapping groundwater potential areas in the eight drought-affected areas of south Madagascar. The groundwater potential zone map is being used by UNICEF and partners to plan water supply projects and identify the best sites for positioning new boreholes and reduce the likelihood of drilling failure. Additionally, the project developed a database of groundwater resources, which will improve knowledge of the regional hydrogeological context and strengthen the capacity of the water sector. Lessons learnt from this study show that an integration of the groundwater potential zone map with demographics and water demand information will help identifying priority areas for detailed studies. Moreover, a capacity building activity is required for knowledge/technology transfer to the Ministry of Energy, Water and Hydrocarbons (MEEH), allowing the possibility of scaling-up this integrated approach to the rest of Madagascar. Finally, strengthening the capacity of the MEEH and refining this approach as suggested above will certainly help in the pursuit to improve equitable access to safe and clean water for households located in the drought-affected areas of southern Madagascar, allowing them to be more resilient to the effects of climate change.  相似文献   

Exploring Placer Gold Deposits through Integrated Geophysical and Geochemical Techniques at the Confluence of the Indus and Kabul Rivers, NW Pakistan     

Asghar ALI  Khaista REHMAN  Owais TAYYAB  Tahir ZAMAN  Mahad JAMEEL  Azeem KHAN  Rafique AHMAD  Muhammad IRFAN 《《地质学报》英文版》2020,94(5):1440-1450

Analysis of the anomalous magnetic mineral intensities and geochemistry for placer gold deposits are presented for those of the Attock area at the confluence of the Indus and Kabul rivers in northwestern Pakistan. Two grids covering an area of 10x18 m2 and 8x10 m2 were analyzed using a G-858 Cesium Vapor Magnetometer. The anomalous zones obtained were plotted on contour maps, 2D and 3D magnetic intensity maps. Based on the magnetic anomalies, grid-1 of the study area was sampled at three different anomalous zones for geochemical analysis. These zones contain gold concentrations, ranging from 2.11 ppm to 6.109 ppm with an average of 4.01 ppm. Increase in gold concentration in the subsurface within the anomalous zones indicates that magnetometer survey followed by a geochemical analysis can potentially narrow down the gold-bearing anomalous zones.  相似文献   

Structural and 40Ar/39Ar mineral age constraints for the tectonothermal evolution of the Green Head Group and Brookville Gneiss,southern New Brunswick,Canada: Implications for the configuration of the Avalon composite terrane     

R. Damian Nance  R. David Dallmeyer 《Geological Journal》1994,29(4):293-322

In the late Precambrian Avalon composite terrane of the Canadian Appalachians, the local juxtaposition of Avalonian successions against gneiss complex–platformal metasedimentary rock associations of uncertain relationship to the Avalonian overstep sequence has raised important questions about the configuration of the composite terrane. Typical of this relationship is the juxtapostion of Avalonian arc-related packages (Caledonia assemblage) with the migmatitic Brookville Gneiss and metacarbonate–quartzite Green Head Group (Brookville assemblage) along the Caledonia Fault in southern New Brunswick. Polyphase deformation of the predominantly greenschist facies Green Head Group accompanied development of a regional ductile shear zone that separates the group from the amphibolite facies Brookville Gneiss. Heterogeneous ductile flow in carbonate rocks and the development of a regional foliation was followed by NW-directed shortening and the local development of a penetrative axial planar fabric that intensifies towards the shear zone. Associated structural elements suggest regional dextral transpression, consistent with the metamorphic contrast across the shear zone. Steeply plunging east–west folds may record younger, sinistral movement on associated NE–SW faults. Deformation coincident with metamorphic culmination in the Brookville Gneiss produced a gneissic foliation that was later deformed to produce widespread minor folds of sheath-like geometry. These folds are best developed proximal to the shear zone where they locally document dextral shear, and probably include several generations that overlap early phases of deformation of the Green Head Group. Kinematic indicators within the gneiss are predominantly dextral. ³⁶Ar/⁴⁰Ar versus ³⁹Ar/⁴⁰Ar isotope-correlation ages recorded by metamorphic hornblende suggest that regional cooling of the Brookville Gneiss through ca. 500°C occurred at ca. 540 Ma, providing a minimum age for initial deformation and concomitant metamorphic culmination in the gneiss. ⁴⁰Ar/³⁹Ar plateau ages for metamorphic muscovite suggest cooling through ca. 375°C at ca. 500–520 Ma, providing a minimum age for progressive deformation in both lithotectonic sequences. Low temperature age discordance in the muscovite spectra suggest partial rejuvenation in the mid- and late Palaeozoic. Protracted Cambrian tectonothermal activity in the Brookville assemblage contrasts with the Avalonian tectonostratigraphic record of the Caledonia assemblage in which late Precambrian arc-related packages are overstepped by Cambrian–Ordovician shallow marine strata. Significant Cambrian separation between the two assemblages is therefore suggested, despite Precambrian similarities in their tectonothermal evolution. Separation as a consequence of terrane dispersal is suggested, and may imply a significant rearrangement of the Avalon composite terrane at this time. Final juxtaposition of the two assemblages pre-dates their shared late Palaeozoic rejuvenation, and may correspond to an earlier, mid-Palaeozoic thermal overprint correlated with tectonothermal activity accompanying accretion of the Avalon and outboard Meguma terranes to more inboard tectonic elements of the northern Appalachians.  相似文献   

现阶段我国开发区几个战略问题的思考   总被引：8，自引：0，他引：8  

王峰玉  吴怀静  魏清泉 《地域研究与开发》2006,25(1):23-27

通过对国内关于开发区相关研究的梳理综述,提出现阶段我国开发区的几个重大战略问题,认为开发区应定位为一个以发展工业为主的具有相对综合功能的新型城区,使外向型和内向型的产业相结合,逐步与周边地区融合、一体化的发展,并发挥开发区在推进城市化方面的作用;同时,应珍惜现有的体制形式,慎重地对待开发区的体制变化,从而适应现阶段国内外的经济环境和实现自身的持续发展。  相似文献   

Ordovician and Silurian graptolite assemblages from Cerro del Fuerte,San Juan Province,Argentina     

Barrie Rickards  Edsel Brussa  Blanco Toro  Gladys Ortega 《Geological Journal》1996,31(2):101-122

  相似文献   

金属稳定同位素示踪俯冲带挥发分循环SCIEI北大核心CSCD          下载免费PDF全文

刘盛遨 《岩石学报》2022,38(5):1512-1522

俯冲带挥发分的循环不仅深刻影响着地球各圈层之间的相互作用,而且在成矿金属元素迁移-富集以及全球气候变化等重要地质和环境过程中扮演着重要的角色。近年来,金属稳定同位素示踪俯冲带挥发分循环受到了广泛关注,取得了众多进展,但大多针对单个挥发性元素开展某个特定金属同位素的示踪研究。本文根据不同金属元素的地球化学性质差异及其与多种挥发分之间的结合形式,系统归纳了金属稳定同位素在示踪俯冲带不同挥发分循环方面的特点。整体上讲,镁和锌同位素体系示踪俯冲带碳循环最为有效;锂、镁、钾、钡、钼等金属同位素体系在示踪俯冲带水(流体)循环方面则具有各自的特点;锌同位素在示踪俯冲带硫循环方面有巨大潜力;铬同位素示踪俯冲带氯循环有独特优势;铁、铬、铜等变价金属同位素体系对挥发分的氧化还原状态较为敏感,有望示踪俯冲带氧循环。这些同位素体系对理解俯冲带挥发分循环提供了全新的视角,有望成为未来地球系统科学的重要研究方向。  相似文献   

夏季长江口东北部海域DO的分布及低氧特征   总被引：4，自引：0，他引：4  

韦钦胜  战闰  魏修华  臧家业  王守强  王宗兴 《海洋科学进展》2010,28(1)

基于2006年7月18—23日对长江口东北部海域的大面调查资料,重点分析了该海域DO的分布特征,初步探讨了DO与温度、盐度、叶绿素和营养盐等各要素分布之间的关系。研究显示,2006年7月长江口东北部海域DO的质量浓度范围为1.36~8.81 mg/L,平均值为6.25 mg/L;调查海域(122°~123°E,32°~33°N)底层存在较为严重的DO亏损现象,表明长江口外DO低值区7月份在长江口东北部海域也存在一定程度的扩展;夏季台湾暖流北上引起的海水层化作用、表层生物繁殖引起的大量有机碎屑的沉降和氧化分解,可能是致使调查海域底层出现一定面积的DO低值区和DO亏损现象的2个主要原因。  相似文献   

Late Carboniferous–Early Permian palynology of Baode (Pao‐te‐chou) in Shanxi Province,North China     

Liu Feng  Zhu Huaicheng  Ouyang Shu 《Geological Journal》2008,43(4):487-510

  相似文献   

昆山城市热岛效应特征及其关键影响因子研究北大核心          下载免费PDF全文

季群  包云轩  汪婷  吴俊梅  陈粲 《气象科学》2023,43(2):155-166

昆山地处长三角超大城市群中,在热岛效应上受到了上海、苏州等大、中城市的显著影响。利用2014—2017年昆山气象站网逐小时观测资料分析昆山城市热岛强度时空分布特征的基础上,结合归一化建筑指数(Normalized Difference Built-up Index,NDBI),揭示了城市功能分区和城市扩张对该市热岛强度的影响,并通过一套用于城市气候研究的系统的场地分类方法—局地气候分区体系(Local Climate Zones,LCZ),探讨了不同城市用地的热岛强度特征。研究发现:昆山市热岛强度总体呈现夜间强、白天弱的特征。季节变化上表现为秋季最强,冬季次之,春季和夏季较弱;昆山市城市热岛强度处于逐年增长的过程,各镇中平均年际热岛强度增长率最高可达0.19℃·a^(-1)。高热岛强度范围由东南向西北延伸,湖陆风效应对昼夜热岛强度的分布及其变化有一定的影响,由于水体的作用,昆山市NDBI与夜间热岛强度的相关性较差,而与白天的热岛强度呈高度正相关。各镇不同的功能分区对热岛效应有显著影响,且当各镇的平均NDBI每增加0.1时,白天平均热岛强度会增加0.16℃;不同LCZ类型的热岛强度具有显著的差异,且地块城市化程度越高,热岛效应越强。密集低层建筑区(LCZ 3)和工业厂房(LCZ 10)的热岛强度与人类活动密切相关;开阔低层建筑区(LCZ 6)与茂密树木区(LCZ A)热岛强度表现出相似的变化特征;森林绿地(LCZ A、LCZ B)对热岛效应有缓解作用;水体(LCZ G)在白天有一定的降温效果,在夜间则会加剧热岛效应。  相似文献