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1.
城市地表灰尘的分形特性分析 总被引：4，自引：1，他引：3
城市地表灰尘在城市环境中无处不在,其对人体和环境造成危害的程度与灰尘颗粒物的粒径有着直接关系.本文运用分形和多重分形的方法探讨了采样区地表灰尘粒径分布特征,发现城市地表灰尘颗粒分布较分散,但也存在颗粒分布相对集中且较粗的特点;地表灰尘粒径分布、pH值以及有机质含量受城市功能区划影响;熵维数D1和熵维数/容量维数D1/D0与城市地表灰尘的pH值成负相关,与有机质含量成正相关,分维数D与pH值及有机质含量之间无相关性.多重分形参数比简单的分维数更能表征地表灰尘颗粒的分布特征,能够提供更多的信息. 相似文献
2.
环洞庭湖区两种典型红土理化特性比较研究 总被引：1，自引：0，他引：1
通过环洞庭湖区两种典型成因红土的野外勘察与取样、室内磁化率、粒度、微量元素(Li、Rb、Sr、Ba)分析,进行两种不同成因的红土理化性质的比较。研究结果表明,风成成因的红土粒度比基岩风化成因红土明显较细,风成成因红土以粉砂为主,基岩风化型红土为砂和粉砂为主;两种成因红土受到长江中游地区高温高湿的气候条件影响,磁化率均显示为低值,明显低于黄土高原黄土和长江下游下蜀黄土;微量元素Li/Ba、Rb/Sr比值显示为高值,显著高于黄土高原黄土和长江中下游地区下蜀黄土,表明两种红土均经历了强烈的风化淋溶过程,但基岩风化型红土的风化成壤强于风成成因红土,可能基岩风化型红土经历了更长的风化成壤过程。 相似文献
3.
通过对黄河中游晋陕峡谷段的深入调查研究,在山西省大宁县平渡关基岩峡谷河段左岸沟口岩棚内发现了全新世古洪水滞流沉积层剖面。根据野外宏观特征及沉积环境,鉴别出平渡关(PDG)剖面夹有4层古洪水滞流沉积物。结合粒度成分、磁化率、烧失量、CaCO3含量等室内分析测定结果,确定为河流悬移质和跃移质在高水位滞流环境当中的沉积物,是典型的古洪水滞流沉积物。不同层次沉积物是不同古洪水事件的客观记录,既有细沙质粉沙,也有细沙或者中沙,反映出其物质来源的不同或者水动力大小的差异。粒度自然分布频率曲线为正偏和极正偏,主峰高且尖锐,表明其分选良好,其粒度概率累积分布曲线为典型的两段式。沉积物磁化率和烧失量均低于全新世风成黄土和古土壤,CaCO3含量介于古土壤和黄土之间,说明在黄河晋陕峡谷段,洪水所携带的悬移质泥沙是流域内黄土区和风沙区水土流失物质的混合物。 相似文献
4.
黄土高原沙尘暴时空分布格局及变化趋势分析 总被引：1，自引：0，他引：1
研究了黄土高原地区沙尘暴的时空分布格局和变化趋势,主要的工作包括利用黄土高原地区253个旗县市气象站20世纪50年代至1984年沙尘暴的多年平均值做空间插值,结合遥感影像,分析了沙尘暴的空间分布格局,呈现出从西北向东南先增多后减少,北多南少的分布。利用1961-2000年沙尘暴记录分析了沙尘暴年内的季节分布,发现沙尘暴主要发生在春季,尤其是4月。最后,对40 a间沙尘暴进行了趋势分析,发现该区沙尘暴有明显的减少趋势,在1984年发生了明显转折,这种减少趋势在空间上不具有明显差异。 相似文献
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6.
该文主要讨论了在陕、甘、宁境内作为黄土风成成因的主要颗粒组成从北向南或从西向东的分布规律,以砂粒、粗粉粒、粘粒及物理性粘粒四种粒级作为黄土风成成因的主要指标粒级,并讨论了随着土壤颗粒的变化,而产生的土壤一系列物理性质的变化:土壤比重愈向南愈大;土壤容重则是最南部及最北部最大,而中间过渡地带较小;对于破坏土壤(无结构的土壤),土壤质地愈粘重,渗透性能愈差,质地愈轻则渗透性能愈好,而对于有结构的原状土壤则恰好相反。另外,黄土地区的土壤水分常数如最大吸湿水、凋萎湿度、自然含水量及田间持水量亦是从北向南相应的逐渐递增变大,然而毛管持水量则是最南部及最北部较小,而中间过渡地带最大,和土壤粗粉粒分布规律恰相吻合。 相似文献
7.
黄土高原的形成与整治对策 总被引：20，自引：4，他引：20
本文以雨土和雨尘等泥质“细粒团”的形成和细小矿粒楔入粗粒等现象,作为只有经过风力吹扬搬运才能形成的“专一”特征,来检查250万年以来黄土高原各期黄土后,发现黄土确系西来黄尘在黄土高原上空与东来湿气相遇不断降落、堆积增厚所成。这样堆积以颗粒支架式接触为主的黄土层,本来就具有良好的通透性能,后来因植被的繁生,尤其是禾本科草本植物根系的作用,而更加提高和巩固。这是在自然环境下,黄土高原堆积厚达100m以上完整的黄土——古土壤系列的唯一背景和根源。目前黄土高原水土流失剧烈进行,其主要原因就是人为活动对天然植被的无情破坏,从根本上破坏了土壤的入渗和抗冲性能。当前黄土高原整治的对策也只有按照“全部降水就地入渗拦蓄”为战略目标,采取“米粮下川上塬;林果下沟上岔;草灌上坡下坬”,并与社会经济需求紧密结合,来安排土地合理利用和具体生产措施。 相似文献
8.
五华河中游的乌陂河流域水上流失严重,人为恢复植被的速度仍赶不上自然水土流失的速度。本文在分析植被的作用,植被工程的特征与作用等问题的基础上,提出了实施植被工程的三条基本原则和两个不容忽视的问题,最后讨论了植被工程的开发利用问题。 相似文献
9.
长江中游地区第四纪红土的二元结构及古环境意义 总被引：3，自引：0，他引：3
在长江中游地区的湖南和湖北两省,选择宜昌、咸宁、常德、长沙、株洲5个第四纪红土剖面,分析第四纪红土的粒度组成特征,研究红土的成因及南方古环境的演变。结果表明,这些地区第四纪红土的粒度组成呈明显的二元结构:剖面上部(宜昌剖面0～320 cm,咸宁剖面0～220 cm,常德剖面0～270 cm,长沙剖面0～280 cm,株洲剖面0～150 cm)粒度细小而均匀,砂粒含量低,大部分小于1%;粗粉砂(又称风尘"基本粒组")相对富集,平均含量分别为34.38%、32.29%、32.48%、31.69%和31.86%。而且土壤样品粒度频率分布曲线与安徽宣城第四纪红土很相似,与镇江下蜀黄土也有明显继承性。这些特性均反映了剖面上层红土的风成特性。但研究剖面下部红土,粒度组成有明显不同:含有砾石,砂粒含量较高,不同粒度组分垂向变化明显,粒度频率分布曲线与宣城红土和下蜀黄土有显著差异,表现出明显的冲、洪积相特性。第四纪红土的"二元结构",反映了研究区域第四纪古环境的多变性和复杂性:早期红土形成后,因受间冰期湿热气候的影响,多受流水作用改造;而晚期红土更多地受风尘堆积的影响,沉积后虽经过了强烈的原位风化,但仍保留了风尘沉积的特性。 相似文献
10.
采用粒级-标准偏差方法对黄土高原西部、河西走廊及河南西部等6个剖面末次间冰期-冰期旋回的黄土-古土壤粒度进行了系统分析，提取了对环境变化敏感的粒度组分。各剖面的环境敏感粒度组分主要分为粗细两个组分，并显示出一定的区域性差异和不同的沉积学意义。敏感组分主要受物源和沉积后成壤作用的影响：冰沟和罗家湾剖面可能受源区的影响更大而使敏感组分偏粗，暖和湾和扣马剖面可能由于后期风化的影响较大而使敏感组分偏细。对扣马剖面末次冰期旋回堆积的L1和S1的粒级一标准偏差分析表明，L1的敏感组分与全剖面相似；而S1的敏感组分与全剖面存在较大差异，可能与成壤作用有关。 相似文献
11.
Samples of drift were studied by mechanical analysis and scanning electron microscopy of individual grains and compared with nearby fixed dunes and present-day pedisediment. Results indicate that the drift is well sorted and has the textural characteristics of a loess (modal grain size + 4 − + 5 Ø, 62-31 μm), this differs markedly from the fixed dunes (modal grain size + 2 − + 3 Ø, 250-125 μm), SEM micrographs show that the drift contains grains with a wide variety of morphologies, although they are predominantly angular to sub-angular with only limited evidence of abrasion by aeolian and/or fluvial transport and some ovegrowths of secondary silica. This suggests that much of the drift material is of local origin, and was deposited by aeolian reworking of alluvium and coarse surface soil horizons when sand dunes were forming further north. It is envisaged that concomittant with aeolian activity was periodic reworking of the drift by slopewash associated with individual storms and a wet season of reduced duration and intensity. 相似文献
12.
渭河咸阳段非饱和层状沉积物中水分分布特征 总被引：2，自引：0，他引：2
层状结构是河流相松散沉积物中最常见的沉积结构,通常表现出一些特有的水力学性质,对水分运动过程及沉积物的持水性能产生影响.本文通过对渭河陕西咸阳段河漫滩一个层状沉积物剖面的含水率分布特征进行原位观测,讨论层状沉积物中含水率的分布特征,及其与粒度和毛细壁垒效应的关系.结果表明:在以水平层理和交错层理为主的粗细相间的层状河流沉积物中,天然含水率也呈干润相间的层状分布特征,各层含水率的大小主要与粒度成负相关;沉积物粗细相间的层状分布为毛细壁垒的形成提供条件,在降雨入渗和土壤水蒸发过程中,毛细壁垒效应对水分运动的控制会导致细粒层中含水率高于粗粒层.层状松散沉积物中水分的这种分布规律,为理解土壤持水性能提供了新的思路,对研究土壤含水率与降雨入渗、蒸发等水文过程的关系具有重要意义. 相似文献
13.
黄土高原土壤颗粒组成及质地分区研究 总被引：7，自引：0，他引：7
黄土高原土壤颗粒组成主要以细沙粒和粗粉沙为主 ,此二者是土壤的骨架部分 ,其含量占颗粒总量的 5 0 %以上。该区土壤颗粒组成具有高度的均一性 ,分布具有一定的规律性。按照土壤物理性黏粒含量 ,区内土壤质地可分为松沙土带、紧沙土带、沙壤Ⅰ带、沙壤Ⅱ带、轻壤Ⅰ带等 10个条带 相似文献
14.
风成黄土是研究古气候变化的良好载体,在全球陆地分布广泛,而不同区域地理环境差异显著,其记录气候变化的机制亦有所不同。以色列南部黄土区地处亚热带沙漠边缘,为探究该区域黄土磁性特征及其对区域环境的响应机制,对内盖夫沙漠边缘黄土区进行野外考察并测试系统环境磁学及粒度参数。结果表明,Har Keren(HK)剖面中磁性矿物主要为碎屑磁铁矿和磁赤铁矿,磁性矿物含量较少,磁性颗粒主要为粗单畴(SD)和多畴(MD),磁性特征与中国西北干旱区黄土较为相似。HK剖面常温磁学参数整体变化范围较小,仅在剖面亚表层有所升高,可能是受现代成土作用影响。HK剖面中值粒径自底部至顶部呈减小趋势,但粒度整体偏粗,其频率分布曲线显示为正偏态,分选较差,反映出多种搬运方式的混合特征,与典型风成黄土有所差异。 相似文献
15.
黄土高原褐土和黑垆土剖面中Rb和Sr分布与全新世成土环境变化 总被引：5，自引：0，他引：5
对黄土高原 3个土壤剖面Rb和Sr分布规律的研究表明 ,全新世不同阶段的黄土和土壤中Rb和Sr分布存在明显的差异 ,Rb/Sr比值的变化反映了成土环境和成土作用强度的变化。全新世早期 ,气候比较温和干燥 ,风尘堆积速率降低 ,土壤发育表现为边沉积边成土 ;全新世中期 ,气候温暖湿润 ,沙尘暴很少发生 ,风尘堆积速率极低 ,生物风化成土作用达到最强 ,以至于在黄土高原面发育黑垆土 ,在关中盆地形成褐土。到了 3 10 0多年前 ,气候恶化变干 ,风尘堆积速率加快 ,土壤严重退化。从区域上看 ,冬季风对黄土高原南部的环境效应比夏季风对北部的环境效应要强 ;黄土高原南部季风场强的变化较北部大。 相似文献
16.
《Geoderma》2006,130(1-2):108-123
Rock-derived nutrients in soils originate from both local bedrock and atmospheric dust, including dust from far-distant sources. Distinction between fine particles derived from local bedrock and from dust provides better understanding of the landscape-scale distribution and abundance of soil nutrients. Sandy surficial deposits over dominantly sandstone substrates, covering vast upland areas of the central Colorado Plateau, typically contain 5–40% silt plus clay, depending on geomorphic setting and slope (excluding drainages and depressions). Aeolian dust in these deposits is indicated by the presence of titanium-bearing magnetite grains that are absent in the sedimentary rocks of the region. Thus, contents of far-traveled aeolian dust can be estimated from magnetic properties that primarily reflect magnetite content, such as isothermal remanent magnetization (IRM). Isothermal remanent magnetization was measured on bulk sediment samples taken along two transects in surficial sediment down gentle slopes away from sandstone headwalls. One transect was in undisturbed surficial sediment, the other in a setting that was grazed by domestic livestock until 1974.Calculation of far-traveled dust contents of the surficial deposits is based on measurements of the magnetic properties of rock, surficial deposits, and modern dust using a binary mixing model. At the undisturbed site, IRM-based calculations show a systematic down-slope increase in aeolian dust (ranging from 2% to 18% of the surface soil mass), similar to the down-slope increase in total fines (18–39% of surface soil mass). A combination of winnowing by wind during the past and down-slope movement of sediment likely accounts for the modern distribution of aeolian dust and associated nutrients. At the previously grazed site, dust also increases down slope (5–11%) in sediment with corresponding abundances of 13–25% fines. Estimates of the contributions of aeolian dust to the total soil nutrients range widely, depending on assumptions about grain-size partitioning of potential nutrients in weathered bedrock. Nevertheless, aeolian dust is important for this setting, contributing roughly 40–80% of the rock-derived nutrient stocks (P, K, Na, Mn, Zn, and Fe) in uppermost soil over most of the sampled slope at the undisturbed site, which shows no evidence of recent wind erosion. 相似文献
17.
Jiongxin Xu 《CATENA》2002,49(4)
According to the yearly maximum suspended sediment concentrations (SSC) in the Yellow River and its tributaries, the rivers are divided into three types of more than 300, 20–300, and less than 20 kg/m3. The middle Yellow River basin is located in the transitional zone from subhumid to semiarid climates, and covered by a thick loess mantle. Neighboring on the desert areas to the northwest, the surface material of the Loess Plateau exhibits some marked areal differentiation in grain size and forms three zones covered by sandy loess, (typical) loess and clayey loess from northwest to southeast. Controlled by these physico-geographical conditions, the grain size of river-transported sediment shows some particular characteristics; at small water discharge or SSC, the grain size of suspended sediment abruptly decreases to a minimum with increasing water discharge or SSC. At water discharge of more than ca. 40 m3/s or at SSC of more than ca. 40 kg/m3, the grain size increases with water discharge or SSC.During the low-stage season, the relatively clear baseflow may scour the coarse bed materials, so the suspended sediment is relatively coarse. In the rainy season, rainstorm runoff washes out fine loess materials to the river, making suspended sediment fine. During relatively strong rainstorms, there often occur hyperconcentrated flows at SSC of more than 300 kg/m3. The relatively coarse grains could then remain suspended in the mixture of water and fine suspended sediment. 相似文献
18.
The distribution of acidic andalkaline constituents (SO4 2-,NO3 -, Cl-, NH4 +, Na+,K+, Ca2+) between the fine and coarseparticle range has been examined in an urban locationin Thessaloniki, N. Greece over an 8-month period. The chemistry of wet and dry deposition collected overthe same period was also examined. Statisticalassociations between species within each environmentalphase were investigated using correlation analysis.Use of principal component analysis was made toinvestigate compositional similarities betweenaerosol, deposited dust and rain. It was found thatSO4 followed by NO3, NH4 and Caprevailed in fine aerosol. Sulphates and Ca were alsothe prevailing ions in the coarse particle fraction.Wet deposition was found to be the dominant depositionmechanism for all species. The high dry depositionrates observed for Ca and SO4 suggest that mostof the dry deposited sulphate is in the form ofCaSO4. Scavenging ratios of ionic speciesassociated with coarse aerosol were higher than thecorresponding ratios for fine particles. Principalcomponent analysis suggested that variations in ioniccomposition of fine aerosol could be interpretedprimarily by gas-to-particle neutralization reactionsinvolving atmospheric ammonia. In contrast, theinteraction between SO2 and HNO3 with Cacompounds seems to be the most likely factor that canexplain variations in wet and dry deposition ioniccontents. 相似文献
19.
在野外模拟降雨条件下,研究了黄土粒度分布和微结构在降雨前后的变化及其对泥流启动的影响.结果表明,采自径流沉积物的降雨后土样中的细黏粒、粗黏粒体积含量分别相对增加了22％和18％,而粗粉粒、微砂体积含量分别相对减少了7.6％和3.3％.坡面残余土的粒度“粗化”,降雨后土骨架连接松散,这些由降雨引起的黄土的粒度和微结构变化说明降雨后黄土的抗剪强度和抗压能力将降低,导致泥流启动的可能性增加.随着降雨入渗,当沿坡面的黄土重力分力与抗剪强度间的平衡被打破,黄土开始滑移并发展成泥流.有效防止坡面土粒度“粗化”是遏制水土流失的关键. 相似文献
20.
Formation and movement of groundwater in the thick loess-palaeosol sequences of the Chinese Loess Plateau 总被引：1，自引：0，他引：1
Permeability and water-bearing space are important hydrological characteristics of the loess strata. In this study a systematic experiment was conducted to measure the magnetic susceptibility, grain size, porosity, and infiltration rate of the loess and palaeosol layers on a loess tableland of the central Chinese Loess Plateau, in order to investigate the differences in hydrological conditions between the loess and palaeosol layers. The magnetic susceptibility of the loess layer was lower than that of the palaeosol layer, but the average quasi-steady infiltration rate was about 0.31 mm min~(-1) higher, the coarse silt and very fine sand contents were about7.1% greater, and the porosity was about 5.7% higher. These differences were mainly due to pedogenesis, which was affected by the Quaternary climate. The pedogenesis differences between the loess and palaeosol layers resulted in hydrological property differences in terms of permeability and water-bearing space. The loess layer had a higher permeability and more water-bearing space than the palaeosol layer, which meant that the loess layer is more likely to form aquifers and the palaeosol layer is more prone to form aquitards.The groundwater in the loess strata had a multilayered characteristic, which depended on the relative impermeability of palaeosol layer and the alternate deposition of loess-palaeosol layers. The hydrological characteristics of the loess strata demonstrated that the Quaternary climate had an important control function on the formation and movement of groundwater. This knowledge provides a reliable theoretical basis for water resource development and utilization on the Chinese Loess Plateau, and this study extends the application of Quaternary climate change theory to hydrological systems in loess deposits. 相似文献