古尔班通古特沙漠生物结皮的分布特征   总被引：47，自引：1，他引：47  

张元明  陈晋  王雪芹  潘惠霞  辜智慧  潘伯荣 《地理学报》2005,15(1):53-60

新疆古尔班通古特沙漠是我国最大的固定和半固定沙漠，其间广泛发育着以地衣植物为主的生物结皮，是除种子植物以外的固定沙面的重要生物因子。研究表明，选择适当的时段，应用遥感技术并结合地面调查来研究沙漠生物结皮的空间分布格局是可行的，遥感制图与地面调查的结果基本一致。该沙漠南部是生物结皮最为丰富的区域，各种类型的生物结皮均有充分发育，呈连续分布，但其分布模式向北、向西和向东变得破碎。通过统计生物结皮像元的面积，得到生物结皮覆盖率超过33％的像元面积占研究区总面积的28．7％。生物结皮的分布对地貌部位有较强的选择性，生物结皮的不同发育阶段种类组成亦有较大的差别。  相似文献   

Contrasting hydrological response of coastal and desert biocrusts          下载免费PDF全文

Giora J. Kidron  Burkhard Büdel 《水文研究》2014,28(2):361-371

Biocrusts abound in southern Israel, covering the Hallamish dune field near Nizzana (NIZ) in the Negev (mean annual precipitation of 95 mm) and the coast of Nizzanim (NIM) near Ashdod (mean annual precipitation of 500 mm). While the hydrological response of the NIZ crust to natural rain events was thoroughly investigated, no data is available on the hydrological response of the NIM crust. Runoff was monitored in runoff plots during the years 2005–2008, and in addition, sprinkling experiments were carried out on NIM and NIZ crusts. For the evaluation of the possible factors that may control runoff initiation, fine content of the parent material, crust thickness, compressional strength, hydrophobicity, surface microrelief, organic matter, biomass (chlorophyll a and total carbohydrates) and the crust's species composition of NIM were studied and compared to that of NIZ. The data showed that in comparison to the NIZ crust that readily generated runoff, no runoff was produced by the NIM crust. This was so despite the fact that (1) Microculeus vaginatus predominated in both crusts, (2) the substantially higher rain intensities in NIM, (3) the greater thickness and higher chlorophyll content and (4) the lower microrelief at NIM in comparison to NIZ. The lack of runoff in NIM was explained by its low amounts of exopolysaccharides that did not suffice to affectively clog the surface and in turn to facilitate runoff initiation. The absence of runoff and its consequences on the NIM ecosystem are discussed. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

The effect of conservation practices in sloped croplands on soil hydraulic properties and root‐zone moisture dynamics          下载免费PDF全文

Lirong Lin  Jiazhou Chen 《水文研究》2015,29(9):2079-2088

Rain‐induced erosion and short‐term drought are the two factors that limit the productivity of croplands in the red soil region of subtropical China. The objective of this study was to estimate the effects of conservation practices on hydraulic properties and root‐zone water dynamics of the soil. A 3‐year experiment was performed on a slope at Xianning. Four treatments were evaluated for their ability to reduce soil erosion and improve soil water conditions. Compared with no practices (CK) and living grass strips (GS), the application of polyacrylamide (PAM) significantly reduced soil crust formation during intense rainfall, whereas rice straw mulching (SM) completely abolished soil crust formation. The SM and PAM treatments improved soil water‐stable aggregates, with a redistribution of micro‐aggregates into macro‐aggregates. PAM and SM significantly increased the soil water‐holding capacity. These practices mitigated the degradation of the soil saturated hydraulic conductivity (Ks) during intense rainfalls. These methods increased soil water storage but with limited effects during heavy rainfalls in the wet period. In contrast, during the dry period, SM had the highest soil water storage, followed by PAM and CK. Grass strips had the lowest soil water storage because of the water uptake during the vigorous grass growth. A slight decline in the soil moisture resulted in a significant decrease in the unsaturated hydraulic conductivity (Ku) of the topsoil. Therefore, the hydraulic conductivity in the field is governed by soil moisture, and the remaining soil moisture is more important than improving soil properties to resist short‐term droughts. As a result, SM is the most effective management practice when compared with PAM and GS, although they all protect the soil hydraulic properties during wet periods. These results suggest that mulching is the best strategy for water management in erosion‐threatened and drought‐threatened red soils. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Seasonal variations in infiltrability of moss‐dominated biocrusts on aeolian sand and loess soil in the Chinese Loess Plateau     

Bo Xiao  Fuhai Sun  Xiaomeng Yao  Kelin Hu  Giora J. Kidron 《水文研究》2019,33(18):2449-2463

Biocrust effects on soil infiltration have attracted increasing attention in dryland ecosystems, but their seasonal variations in infiltrability have not yet been well understood. On the Chinese Loess Plateau, soil infiltrability indicated by saturated hydraulic conductivity (K_s) of biocrusts and bare soil, both on aeolian sand and loess soil, was determined by disc infiltrometer in late spring (SPR), midsummer (SUM), and early fall (FAL). Then their correlations with soil biological and physiochemical properties and water repellency index (RI) were analysed. The results showed that the biocrusts significantly decreased K_s both on sand during SPR, SUM, and FAL (by 43%, 66%, and 35%, respectively; P < .05) and on loess (by 42%, 92%, and 10%, respectively; P <.05). As compared with the bare soil, the decreased K_s in the biocrusted surfaces was mostly attributed to the microorganism biomass and also to the increasing content of fine particles and organic matter. Most importantly, both the biocrusts and bare soil exhibited significant (F ≥ 11.89, P ≤ .003) seasonal variations in K_s, but their patterns were quite different. Specifically, the K_s of bare soil gradually decreased from SPR to SUM (32% and 42% for sand and loess, respectively) and FAL (29% and 39%); the K_s of biocrusts also decreased from SPR to SUM (59% and 92%) but then increased in FAL (36% and 588%). Whereas the seasonal variations in K_s of the biocrusts were closely correlated with the seasonal variations in RI, the RI values were not high enough to point at hydrophobicity. Instead of that, the seasonal variations of K_s were principally explained by the changes in the crust biomass and possibly by the microbial exopolysaccharides. We conclude that the biocrusts significantly decreased soil infiltrability and exhibited a different seasonal variation pattern, which should be carefully considered in future analyses of hydropedological processes.  相似文献   

Supraglacial weathering crust dynamics inferred from cryoconite hole hydrology          下载免费PDF全文

Joseph Mitchell Cook  Andy J. Hodson  Tristram D. L. Irvine‐Fynn 《水文研究》2016,30(3):433-446

Water levels in cryoconite holes were monitored at high resolution over a 3‐week period on Austre Brøggerbreen (Svalbard). These data were combined with melt and energy balance modelling, providing insights into the evolution of the glacier's near‐surface hydrology and confirming that the hydrology of the near‐surface, porous ice known as the ‘weathering crust’ is dynamic and analogous to a shallow‐perched aquifer. A positive correlation between radiative forcing of melt and drainage efficiency was found within the weathering crust. This likely resulted from diurnal contraction and dilation of interstitial pore spaces driven by variations in radiative and turbulent fluxes in the surface energy balance, occasionally causing ‘sudden drainage events’. A linear decrease in water levels in cryoconite holes was also observed and attributed to cumulative increases in near‐surface ice porosity over the measurement period. The transport of particulate matter and microbes between cryoconite holes through the porous weathering crust is shown to be dependent upon weathering crust hydraulics and particle size. Cryoconite holes therefore yield an indication of the hydrological dynamics of the weathering crust and provide long‐term storage loci for cryoconite at the glacier surface. This study highlights the importance of the weathering crust as a crucial component of the hydrology, ecology and biogeochemistry of the glacier ecosystem and glacierized regions and demonstrates the utility of cryoconite holes as natural piezometers on glacier surfaces. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Shape of pinch and swell structures as a viscosity indicator: Application to lower crustal polyphase rocks     

《Journal of Structural Geology》2016

Pinch and swell structures occur where a more competent layer in a weaker matrix is subjected to layer-parallel extension. In this contribution, we use numerical models to explore the use of pinch and swell structure shape symmetry and asymmetry as a determinant of relative viscosity between layers. Maximum asymmetry is attained when the matrix viscosity on one side is subtly weaker than the competent layer, while the other side is significantly weaker.Our numerical results are directly applied to asymmetrically developed pinch and swell structures in exposed lower continental crust. Here, shape geometries observed in a shear zone comprised of plagioclase-dominated, garnet-dominated and mixed amphibole-plagioclase-dominated bands, reveals that the plagioclase-dominated band is the most competent band and is marginally stronger (2×) and significantly stronger (10–40×) than the fine grained garnet-dominated and mixed amphibole-plagioclase-dominated band, respectively. Based on the experimentally determined viscosity of a plagioclase-dominated material and quantitative microstructural analysis, the viscosity range of the natural rock bands is 2.8 × 10¹⁵ to 1.1 × 10¹⁷ Pa s. Consequently, the assumption that the experimentally-derived plagioclase flow law is an appropriate proxy for the middle to lower continental crust may lead to a viscosity over-estimation by up to forty times.  相似文献   

The interplay and effects of deformation and crystallized melt on the rheology of the lower continental crust,Fiordland, New Zealand     

《Journal of Structural Geology》2016

Microstructural, electron backscatter diffraction (EBSD), and misorientation analyses of a migmatitic granulite-facies orthogneiss from the exhumed lower crust of a Cretaceous continental arc in Fiordland, New Zealand show how deformation was accommodated during and after episodes of melt infiltration and high-grade metamorphism. Microstructures in garnet, omphacite, plagioclase, and K-feldspar suggest that an early stage of deformation was achieved by dislocation creep of omphacite and plagioclase, with subsequent deformation becoming partitioned into plagioclase. Continued deformation after melt infiltration resulted in strain localization in the leucosome of the migmatite, where a change of plagioclase deformation mechanism promoted the onset of grain boundary sliding, most likely accommodated by diffusion creep, in fine recrystallized plagioclase grains. Our results suggest three distinctive transitions in the rheology of the lower crust of this continental arc, where initial weakening was primarily achieved by deformation of both omphacite and plagioclase. Subsequent strain localization in plagioclase of the leucosome indicates that the zones of former melt are weaker than the restite, and that changes in deformation mechanisms within plagioclase, and an evolution of its strength, primarily control the rheology of the lower crust during and after episodes of melting and magma addition.  相似文献   

天气尺度波列对长江中下游6月梅雨的影响   总被引：2，自引：2，他引：0       下载免费PDF全文

黄海燕  王亚非  何金海  陈圣劼  秦坚肇 《大气科学学报》2016,39(1):28-36

采用1979—2007年6月NCEP/NCAR2.5°×2.5°逐日再分析资料和中国743站逐日降水资料,利用相关分析、合成分析等方法,分析了天气尺度波列的特征及其对长江中下游6月梅雨的影响。结果表明:当长江中下游6月梅雨较少时,东亚及西太平洋区域存在一个天气尺度波列;该波列的延伸距离较短(从黄河河套地区经过长江中下游至南海、菲律宾海一带),维持时间也很短,且仅仅在500 h Pa以下较强。诊断及个例分析表明,当该波列异常显著时,长江中下游梅雨降水明显减少,而其南部区域降水则增多,说明该波列对预报长江中下游降水具有重要的指示意义。  相似文献   

全球冥古宙的研究进展和存在问题   总被引：1，自引：0，他引：1  

沈其韩  耿元生  宋会侠 《地质学报》2016,90(9):2083-2099

冥古宙是地球上最老的一个地质历史时期,由于缺少可靠的岩石记录一直没有得到国际地学界的重视和承认,到2004年才在建议的国际地层表中使用了冥古宙这一术语,定义从地球形成到出现地球最老岩石这段地球历史。但冥古宙与太古宙没有明确的地质界线,一些研究者提出了不同的年代界线(3.85Ga,4.0Ga,4.03Ga),目前还存在较大分歧。目前已知残存的冥古宙岩石只有两处,一处是加拿大的阿卡斯塔片麻岩(Acasta gneiss)中两个英云闪长岩和一个变质花岗闪长岩。前者锆石U-Pb年龄为4002±4Ma和4012±6Ma,后者为4031±1Ma。另一处是东南极索尼山(Mount Sones)的麻粒岩相英云闪长质片麻岩,已获得U-Pb年龄为3927±10Ma。世界上最老的表壳岩(≥3870Ma)出露在格陵兰。冥古宙年代久远,地球形成最初的600~700Ma的初始岩石经历了陨石撞击、地壳再循环、重熔等改造,甚至再循环到地幔,几乎已经消失殆尽。目前主要以年轻岩石中的碎屑锆石或继承锆石作为桥梁,来追索这些古老锆石原来母岩的类型、特征及成因。3800Ma的碎屑锆石已在全球十多个地区发现,而以西澳伊尔岗克拉通的杰克山最多最全,从3800Ma到4404Ma都有,在3840Ma,3900~3920Ma,4000~4200Ma,4260~4300Ma和4404Ma显示峰值,其中以3900~4200Ma最为发育,4404Ma是目前世界公认的最老碎屑锆石。此外在北美克拉通、南非克拉通、华北克拉通等古老克拉通以及一些年轻造山带中都发现有冥古宙的碎屑锆石,这些锆石是追索冥古宙地质事件的重要桥梁。通过对冥古宙碎屑锆石的研究提出了很多值得重视和进一步研究的课题和内容。包括早期地壳的性质,一些锆石具有与太古宙之后岩浆锆石特征相似的环带结构,因此这些碎屑锆石的母岩大部分被认为相当花岗质,来自老地壳的重熔。冥古宙碎屑锆石的Hf同位素等综合分析表明这些碎屑锆石来源于中性熔岩的结晶,或许表明早期地壳具有中性成分特征。冥古宙锆石的成因也是一个重要的课题,根据锆石中钛的含量、锆石Ti饱和温度计计算的温度以及锆石的一些结构特征,有的研究者提出冥古宙相当一部分碎屑锆石是陨石撞击导致的岩石熔融结晶产生的,是追溯地球早期撞击事件的重要手段。在4300Ma的碎屑锆石中包裹有金刚石和石墨晶体,前者表明锆石的母岩曾处于高压条件,而后者石墨的碳同位素接近有机碳,有人认为可能为生命起源的迹象。多个地区的碎屑锆石的边部Th/U比值低,U-Pb年龄为4000Ma左右,属于变质作用的产物,表明当时地壳已具有一定厚度。冥古宙碎屑锆石的研究提出了很多重要的问题,但是由于资料有限,有些认识还存在矛盾,还需要获得更多实际资料,才能对冥古宙的地质事件过程取得更可靠的科学认识。因此今后应加强可能赋存古老碎屑锆石地区的寻找,并发现更多古老碎屑锆石。对现有的古老碎屑锆石加强综合研究以及各地区的对比研究。  相似文献   

长江中下游庐枞火山岩盆地南侧钾质侵入岩带的成因   总被引：1，自引：0，他引：1  

薛怀民  马芳  曹光跃  王一鹏  郭秀艳 《地质学报》2016,90(9):2233-2257

庐枞火山岩盆地南侧的钾质侵入岩带由正长岩-石英正长岩-正长花岗岩组成,以石英正长岩为主。它们的形成时间介于123"130 Ma之间,峰值约为126 Ma,其中正长岩和石英正长岩的形成时间稍早,而正长花岗岩的形成时间略晚。整个钾质侵入岩带的侵位时间晚于庐枞盆地内的橄榄玄粗质火山作用约4"7 Ma,也是长江中下游地区除最东段的宁镇地区外中生代最晚的岩浆活动产物之一。地球化学上,该钾质侵入岩带以高钾、富碱、富集Rb、Th、U、K等强不相容元素和轻稀土元素、亏损高场强元素Nb、Ta和Ti为特征。它们的母岩浆主要是由富集型上地幔部分熔融形成的,从正长岩经石英正长岩到正长花岗岩的演化主要受矿物的分离结晶作用控制,地壳物质同化所起的影响不大。但与同样来自富集型上地幔部分熔融的庐枞盆地内火山杂岩的母岩浆相比,前者的母岩浆来源深度可能更大些或其中包含了更多来自软流圈地幔的组分。两者的演化路径也完全不同,钾质侵入岩带的母岩浆除经历过高压下的分离结晶作用外,晚期在低压下还经历过长石为主,可能还有黑云母的分离结晶,甚至上地壳物质一定程度的混染作用;而盆地内火山杂岩的母岩浆低压下矿物的分离结晶作用及上地壳物质的混染都不明显。庐枞盆地南缘的富钾侵入岩与盆地内的火山杂岩一样,地球化学上都具有明显的大陆弧的特征,暗示它们的岩浆源区可能形成于俯冲带环境,意味着扬子地块北缘先前(推测为古元古代晚期)曾发生过俯冲作用,上地幔的交代富集可能就与这次的俯冲作用有关。  相似文献