The factors influencing the abrasion efficiency of saltating grains on a clay‐crusted playa     

Christopher A. Houser  William G. Nickling 《地球表面变化过程与地形》2001,26(5):491-505

The entrainment and subsequent transport of PM₁₀ (particulate matter <10 µm) has become an important and challenging focus of research for both scientific and practical applications. Arid and semi‐arid environments are important sources for the atmospheric loading of PM₁₀, although the emission of this material is often limited by surface crusts. It has been suggested that the primary mechanisms through which PM₁₀ is released from a crusted surface are abrasion by saltating grains or disturbance by agricultural and recreational activities. To examine the importance of saltation abrasion in the emission of PM₁₀, a series of field wind tunnel tests were conducted on a clay‐crusted surface near Desert Wells, Arizona. In a previous part of this study it was found that the emission rate varies linearly with the saltation transport rate, although there can be considerable variation in this relationship. This paper more closely examines the source of the variability in the abrasion efficiency, the amount of PM₁₀ emitted by a given quantity of saltating grains. The abrasion efficiency was found to vary with the susceptibility of the surface to abrasion, the ability of the sand to abrade that surface and the availability of material with a caliper size <10 µm within the crust. Specifically, the results of the study show that the abrasion efficiency is related to the crust strength, the amount of surface disturbance and the velocity of the saltating grains. It is concluded that the spatial and temporal variability of these controls on the abrasion efficiency imposes severe contextual limitations on experimentally derived models, and can make theoretical models too complex and impractical to be of use. Copyright­© 2001 John Wiley & Sons, Ltd.  相似文献   

贵州中三叠统上部垄头组的沉积性质——再论其钙结壳的成因   总被引：4，自引：0，他引：4       下载免费PDF全文

范嘉松  吴亚生 《地质学报》2004,78(2):149-155

钙结壳是土壤层之下的岩石在出露地表渗流带环境内受大气雨水的溶解,并通过上覆土壤层的淋滤而成的产物。由于雨水的不断的溶解,使原始的岩石或沉积物发生破裂,从而形成各种大小的砾块或砾石。随着雨水不断的溶解,雨水逐渐增加 CaCO_3的含量。这些富含碳酸钙的雨水,当它流到位于潜水面之上的下渗流带时,就在土壤层之下、原来岩石之上沉积了特殊的、层纹状方解石胶结物。它们往往覆盖岩石表面或沿着砾石的外缘、呈包覆状沉积,从而形成典型的层纹状钙结壳。渗滤豆粒的外皮也属于层纹状钙结壳的性质,这些外皮有向下方加厚的趋势,这表明渗流带的含碳酸钙的雨水,受重力作用影响下,具有往下悬垂现象,类似于洞穴内的钟乳石。豆粒之间的相互衔接呈多边形构造,也表明它是受重力作用而形成的构造。  相似文献   

毛乌素沙地藓、藻结皮生态功能对比   总被引：1，自引：0，他引：1  

李亚红  卜崇峰  郭琦  韦应欣 《中国沙漠》2021,41(2):138-144

生物结皮在荒漠生态系统中发挥着重要的生态功能,不同类型生物结皮有机体组成和比例不同,生态功能差异巨大。针对毛乌素沙地发育稳定阶段的藓、藻结皮,通过野外调查监测及室内指标测算,深入分析了两类生物结皮对土壤含水量、风蚀量和养分含量的影响尺度,并采用综合指标评价模型定量比较了二者的生态功能差异。结果表明：（1）两类生物结皮下土壤含水量随着土层深度呈现出先增大后波动下降的趋势,0—100 cm深度两类生物结皮下的土壤含水量差异显著（P<0.05）,在0—80 cm深度,藓结皮的土壤含水量大于藻结皮,在90—100 cm则相反;（2）相比裸地,藓结皮和藻结皮影响下土壤风蚀量分别降低了156.0%和136.6%,但二者未达到显著差异;（3）两类结皮影响下土壤养分含量差异显著（P<0.05）,表现为藓结皮下土壤全氮、全磷、有机质含量分别为藻结皮的3.3、3.5、2倍;（4）生物结皮生态功能综合得分藓结皮>藻结皮>裸地（1.60>-0.64>-9.78）。本研究证实了荒漠生态系统中不同类型生物结皮生态功能的差异及其在保持水土和营养物质循环方面贡献程度的优劣,突出了在生物结皮探索工作中关于其类型或组成精准细分的重要性。  相似文献   

The spatial distribution patterns of biological soil crusts in the Gurbantunggut Desert, Northern Xinjiang, China   总被引：8，自引：0，他引：8  

Y.M. Zhang  J. Chen  L. Wang  X.Q. Wang  Z.H. Gu 《Journal of Arid Environments》2007,68(4):599-610

The Gurbantunggut Desert, the largest fixed and semi-fixed desert in China, is characterized by a predominant coverage of lichen-dominated biological soil crusts, which serve an indispensable role in sand fixation. Two findings of biological soil crusts have been disclosed from previous field observations: first, distribution of biological soil crusts is selective upon locations; second, species composition varies significantly for the biological soil crusts that are at different developing stages. In this study, a strategy was developed to investigate the spatial distribution of biological soil crusts by coupling remote sensing data and field measurements. A crust index for the Landsat ETM+ data has been developed and applied to detect the lichen-dominated biological soil crusts in the Gurbantunggut Desert. The results indicated the South of the desert encompassed the most abundant biological soil crusts. Besides, biological soil crusts were distributed in uniform density in the South of the desert whereas their distribution patterns become patchier in the rest of the desert. Finally, statistics from the classification revealed that biological soil crusts covered 28.7% of the land in the whole study area. However, it is worth mentioning that the crusts coverage may be underestimated given the fact that detection of crusts from the Landsat ETM+ imagery is viable only if crusts constitute more than 33% of the instantaneous field of view (IFOV) of the Landsat ETM+ sensor.  相似文献   

中太平洋海山富钴结壳中水羟锰矿的超结构          下载免费PDF全文

叶瑛 韩杰邬黛黛  陈雪刚沈忠悦 王步清 《地质学报》2007,81(6):814-819

采自中太平洋海山富钴结壳主要由水羟锰矿组成,在XRD衍射图谱上,该矿物缺少(001)和(002)底面衍射,其原因是水羟锰矿包含了两种对称型的八面体层,即三斜对称和六方对称的八面体层,它们沿c轴方向无序排列。部分样品中的水羟锰矿在低角度区具有d>2.0nm的超结构衍射峰,它在实质上反映了矿物结构层的长程有序性,即两种层片的排列具有某种周期性或规律性。部分样品原先没有,但在加热后出现超结构衍射峰,可能是因为样品在空气中加热,使三斜层片中的Mn(III)被氧化成Mn(IV),从而转变为六方层片,继而改变了水羟锰矿的有序性。富钴结壳中水羟锰矿的超结构,在一定程度上反映了矿物形成环境的变化。  相似文献   

He,Ne and Ar isotopic composition of Fe-Mn crusts from the western and central Pacific Ocean and implications for their genesis   总被引：1，自引：0，他引：1  

G. P. GLASBY 《中国科学D辑(英文版)》2007,50(6):857-868

The noble gas nuclide abundances and isotopic ratios of the upmost layer of Fe-Mn crusts from the western and central Pacific Ocean have been determined. The results indicate that the He and Ar nu- clide abundances and isotopic ratios can be classified into two types: low 3He/4He type and high 3He/4He type. The low 3He/4He type is characterized by high 4He abundances of 191×10-9 cm3·STP·g-1 on average, with variable 4He, 20Ne and 40Ar abundances in the range (42.8―421)×10-9 cm3·STP·g-1, (5.40―141)×10-9 cm3·STP·g-1, and (773―10976)×10-9 cm3·STP·g-1, respectively. The high 3He/4He samples are characterized by low 4He abundances of 11.7×10-9 cm3·STP·g-1 on average, with 4He, 20Ne and 40Ar abundances in the range of (7.57―17.4)×10-9 cm3·STP·g-1, (10.4―25.5)×10-9 cm3·STP·g-1 and (5354―9050)×10-9 cm3·STP·g-1, respectively. The low 3He/4He samples have 3He/4He ratios (with R/RA ratios of 2.04―2.92) which are lower than those of MORB (R/RA=8±1) and 40Ar/36Ar ratios (447―543) which are higher than those of air (295.5). The high 3He/4He samples have 3He/4He ratios (with R/RA ratios of 10.4―12.0) slightly higher than those of MORB (R/RA=8±1) and 40Ar/36Ar ratios (293―299) very similar to those of air (295.5). The Ne isotopic ratios (20Ne/22Ne and 21Ne/22Ne ratios of 10.3―10.9 and 0.02774―0.03039, respectively) and the 38Ar/36Ar ratios (0.1886―0.1963) have narrow ranges which are very similar to those of air (the 20Ne/22Ne, 21Ne/22Ne, 38Ar/36Ar ratios of 9.80, 0.029 and 0.187, respectively), and cannot be differentiated into different groups. The noble gas nuclide abundances and isotopic ratios, together with their regional variability, suggest that the noble gases in the Fe-Mn crusts originate primarily from the lower mantle. The low 3He/4He type and high 3He/4He type samples have noble gas characteristics similar to those of HIMU (High U/Pb Mantle)- and EM (Enriched Mantle)-type mantle material, respectively. The low 3He/4He type samples with HIMU-type noble gas isotopic ratios occur in the Magellan Seamounts, Marcus-Wake Seamounts, Marshall Island Chain and the Mid-Pacific Sea- mounts whereas the high 3He/4He type samples with EM-type noble gas isotopic ratios occur in the Line Island Chain. This difference in noble gas characteristics of these crust types implies that the MagellanSeamounts, Marcus-Wake Seamounts, Marshall Is- land Chain, and the Mid-Pacific Seamounts originated from HIMU-type lower mantle material whereas the Line Island Chain originated from EM-type lower mantle material. This finding is consistent with varia- tions in the Pb-isotope and trace element signatures in the seamount lavas. Differences in the mantlesource may therefore be responsible for variations in the noble gas abundances and isotopic ratios in the Fe-Mn crusts. Mantle degassing appears to be the principal factor controlling noble gas isotopic abundances in Fe-Mn crusts. Decay of radioactive isotopes has a negligible influence on the nuclide abundances and isotopic ratios of noble gases in these crusts on the timescale of their formation.  相似文献   

藻类结皮自然恢复后抗风蚀特性研究   总被引：6，自引：2，他引：4  

张正偲  赵爱国  董治宝  李宏 《中国沙漠》2007,27(4):558-562

从风沙物理学的角度出发,通过风洞实验研究藻类结皮对起动风速、摩阻风速、空气动力学粗糙度等的影响,探讨未破坏藻类结皮和一定程度破坏后自然恢复藻类结皮抗土壤风蚀特性。实验结果表明:无论是完好结皮还是自然恢复后的结皮,都可以提高结皮的起动风速、摩阻风速和空气动力学粗糙度长度。结皮的起动风速大于17 m·s^-1,摩阻风速在0.62~1.21 m·s^-1之间,空气动力学粗糙度长度在0.03~0.13 cm之间。同时给出了摩阻风速和风速之间以及空气动力学粗糙度长度和摩阻风速之间的经验公式。  相似文献   

古尔班通古特沙漠生物结皮小尺度分异的环境特征   总被引：12，自引：5，他引：7  

王雪芹  张元明  王远超  万金平  徐曼 《中国沙漠》2006,26(5):711-716

古尔班通古特沙漠广泛存在的生物结皮,对地貌部位有极强的选择性分布,其实质是生物对环境条件综合适应的一种生态表现。2002年3~11月在个体沙丘表面初步开展了生物结皮类型小尺度环境分异规律研究。结果表明:苔藓结皮、地衣结皮和藻类结皮依次分布于垄间、沙垄两坡中部和坡上部,从垄间往垄顶,生物结皮盖度逐渐减小,厚度变薄,抗压性减弱。苔藓结皮分布区的物质组成以细沙和极细沙为主,春季表层土壤水分在5%以上,短命植物广泛发育,基质稳定;坡中部的地衣结皮分布区以细沙为主,春季表层土壤水分在4%左右,短命植物亦有广泛分布,地表受风沙活动影响较小;沙垄上部和顶部的藻类结皮分布区,是沙垄表面活动性最强和土壤水分最差的区域,物质组成以中沙为主,高等植物中白梭梭为优势种,可见藻结皮是三类结皮中最能适应恶劣环境的生物结皮类型。  相似文献   

固定沙丘生物结皮层藓类植物形态结构及其适应性研究   总被引：16，自引：6，他引：10  

田桂泉  白学良  徐杰  张建升 《中国沙漠》2005,25(2):249-255

对腾格里沙漠沙坡头地区及其毗邻区域固定沙丘生物土壤结皮层6种有代表性藓类植物形态解剖结构及其适应性进行了观察和系统分析,结果表明:优势种真藓、土生对齿藓和刺叶赤藓植物体密集丛生,其中真藓和土生对齿藓易于通过茎叶碎片或芽胞进行无性繁殖,其茎的结构中皮部细胞壁明显增厚、中轴分化明显;刺叶赤藓和芦荟藓叶片结构最复杂,刺叶赤藓叶片具两层细胞,细胞密被透明马蹄形细疣,芦荟藓叶片内卷成兜形,中肋扁宽,背部有多层厚壁细胞,腹部着生许多绿色丝体;绿色流苏藓和盐土藓的叶片细胞也发生了明显的分化。藓类植物多样的形态结构特征使其适应沙漠环境中水分缺乏、基质不稳、强光辐射伤害等不利环境因子。植物体集群生长状态是其形态适应性的重要特征,与繁殖过程中植物体的连续分枝和原丝体反复再生及外延生长特性直接相关,个体和种群形态结构上的适应性对减缓细胞内生理条件的剧烈变化,减弱细胞器受损害的程度,加快其生理功能的恢复速度有重要作用。  相似文献   

西北太平洋多金属结核铂族元素地球化学特征   总被引：1，自引：0，他引：1  

邱忠荣  董彦辉  马维林  章伟艳  杨克红  赵宏樵 《海洋学报(英文版)》2020,39(8):34-42

Polymetallic nodules and cobalt (Co)-rich crusts are enriched in platinum-group elements (PGEs),especially platinum (Pt) and may be important sinks of PGEs.At present,little information is available on PGEs in polymetallic nodules,and their geochemical characteristics and the causes of PGEs enrichment are unclear.Here PGEs of polymetallic nodules from abyssal basin in the Marcus-Wake Seamount area of the Northwest Pacific Ocean are reported and compared with the published PGEs data of polymetallic nodules and Co-rich crusts in the Pacific.The total PGEs (ΣPGE) content of polymetallic nodules in study area is 258×10~(–9) in average,markedly higher than that of Clarion-Clipperton Zone (CCZ) nodules (ΣPGE=127×10~(–9)) and lower than that of Co-rich crusts in the Marcus-Wake Seamount (ΣPGE=653×10~(–9)),similar to that of Co-rich crusts in the South China Sea(ΣPGE=252×10~(–9)).The CI chondrite-normalized PGEs patterns in different regions of polymetallic nodules and cobalt-rich crusts are highly consistent,with all being characterized by positive Pt and negative Pd anomalies These results,together with those of previous studies,indicate that PGEs in polymetallic nodules and Co-rich crusts are mainly derived directly from seawater.Pt contents of polymetallic nodules from the study area are negatively correlated with water depth,and Pt/ΣPGE ratios in nodules there are also lower than those of the Corich crusts in the adjacent area,indicating that sedimentary water depth and oxygen fugacity of ambient seawater are the possible important controlling factors for Pt accumulation in crusts and nodules.  相似文献