Evolution of soil properties on stabilized sands in the Tengger Desert, China

The spatial and temporal patterns of pedogenesis on stabilized dunes at Shapotou, northwestern China, were studied on the time sequences of 0, 18, 35 and 43 years. The spatial pattern of soil formation was estimated by measuring the thickness of accumulated sand fractions on the stabilized dune surface and by analyzing the characteristics and properties of soil. The results showed that the environment of soil formation and circulation of soil material were influenced in the processes of shifting-sand fixation, and the mean soil particle size changed from >0.2 to <0.08 mm in 0–20 cm soil depth with the succession from cultivated plants to natural vegetation. The capacity of available soil water increased fivefold. Deep infiltration of water in soil no longer occurred due to the increase in soil water capacity and the change of redistribution of soil water in profiles. Soil microorganisms evolved from simple to complex. Interaction of these processes obviously brought about accumulation of soil fertility, evolution of soil profiles and development of the profiles towards aripsamments. The difference of micro-topography is closely related to redistribution of material and energy in soil formation.     

五道梁大气气溶胶的化学组成和浓度及其季节变化

利用１９９３年９－１０月和１９９４年４－５月及７－８月在青藏高原五道梁采集的大气气溶胶元素浓度资料，分析了气溶胶化学组成的总体特征和浓度及其季节变化。结果表明：五道梁低层大气中气溶胶在总体上保持自然大气的组成，以地壳土壤元素为主，由人类活动造成的污染轻微，春季的气溶胶浓度约为秋季的１．７５倍，夏季可能与秋季接近，基本上反映了五道梁低层大气气溶胶浓度的季节变化特征。按元素质量深度的季节变化特征可将其     

塔里木沙漠公路沿线的起沙风与输沙强度

塔里木沙漠公路绝大部分路段穿越流沙地段，风沙活动十分强烈，因此，机械防沙带的设置显得十分关键。由于起沙风的统计分析和输沙强度的定量计算是防沙工程设计中的最主要依据之一。该文在大量统计起沙风和野外实地观测的基础上，进行输沙强度的数值计算及分析后指出：由沙漠边缘向内部深入，起沙风更加东偏，输沙强度更大和更为集中。     

Simulation on sand grain/bed collision mechanism: Cascade collision and ejection (1)

Ejection of sand grains from a sand surface is assumed to result from cascade collision caused by the impact of a saltating particle. Allowing for only two-body cascade collision and introducing new quantities such as the cross-section for sand grain–grain collisions and sand surface binding energy, the theoretical model for the cascade collision of ion particles is applied to simulate sand grain/bed collision processes. The results of simulations indicate that the collision cascade events caused by impacting particles can eventually lead to the ejection of grains taking place from the sand surface. The number of ejected grains at any surface point is found to be proportional to the fractional energy deposited at that point and inversely proportional to the sand surface binding energy. This cascade collision model also confirms that the peak in the spatial distribution of ejected grains does not appear at the impact point but is located downwind, and that the speed distribution of ejected grains at a fixed angle exhibits a peak having a value directly related to the ratio of surface binding energy to the mass of the ejected grain. The angular distribution at a certain ejection speed also exhibits a maximum at an ejection angle near 90°. The model also offers a new interpretation for the observed variability in the number of ejected grains under constant impact velocity; this variability is directly related to the wide distribution of the energy deposition in the surface layer of the sand bed.     

Contributions of climate,vegetation and soil to the alpine sediment carbon accumulation rate in central China since the Middle Holocene

Large amounts of carbon in alpine sediments have been expected to be sensitive to climate change, but how carbon accumulation responds to climate change remains unclear. Thus, we explored the impact of different factors on the carbon accumulation rate (CAR) of alpine sediments by combining a variety of climatic variables, vegetation data and erosion indicators based on two alpine sediment successions on Taibai Mountain, the highest peak in central and eastern mainland China. One succession is near the modern treeline (Paomaliang Swamp, PML) and the other is located at the upper forest line (Sanqing Chi, SQC, a small lake). We used our previously published organic carbon content data and for the first time calculated the CAR, and further used pollen and physicochemical indicators to quantify the contributions from climate, vegetation and soil. We found that their contributions varied during different periods and between the two sediment successions. For the PML succession, from 5850 to 4000 calendar years before present (cal. a BP), the CAR was low, which was related to low annual temperatures, low vegetation cover and strong soil erosion. From 4000 to 2400 cal. a BP, a high CAR coincided with high annual temperatures, high vegetation cover and weak soil erosion. From 2400 to 200 cal. a BP, the CAR decreased, mainly attributed to low vegetation cover. Local vegetation cover had major impacts on the CAR in the SQC succession during the Middle–Late Holocene. In general, the local factor interpretation rate in SQC (83%) was higher than that of PML (47%), related to the vegetation stability of continuous forest and the treeline. This study highlights the important role of the local environment in determining carbon accumulation in the alpine region.     

侵蚀型沙丘:来自火星的启示

风沙地貌分为风积地貌和风蚀地貌两大范畴,风积地貌即指各种沙丘.沙丘地貌虽然是风沙堆积的产物,但其形态和类型是风沙蚀积时空变化规律的表现,在堆积形成之后,风蚀作用在沙丘形态塑造过程中有时会具有重要作用,从而形成独特的侵蚀型沙丘.但由于有悖于传统风积地貌的理解,侵蚀型沙丘长期被忽视.然而,在火星沙丘地貌的形态和分布规律研究中,已发现大量的与地球常见沙丘地貌具有微妙差异的沙丘地貌形态,并将其归咎于沙源供应不充分的发育环境.重温法国学者Mainguet沙丘分类方案中关于侵蚀型沙丘的论述,以及经典风沙地貌学理论关于沙丘形态控制因素的概念框架,明确指出研究侵蚀型沙丘的必要性.系统分析了火星沙丘地貌形态特征后,初步辨认出火星的10种侵蚀型沙丘,分析其形态特征、发育环境及可能的形成机制.地球干旱区广袤的盐碱地是极有可能发育侵蚀型沙丘的地区,具有类似火星沙源供应不足的环境,在中国柴达木盆地沙漠中发现了多种侵蚀型沙丘地貌.据此推断,侵蚀型沙丘在地球上比较普遍,其研究对发展风沙地貌学理论具有重要意义,对中国未来的火星探测与研究具有参考意义.     

伊朗高原及周边地区MS≥7.1地震的时空对称性研究及趋势预判

地震的时空对称性研究对防灾减灾有重要意义.结合可公度理论,利用蝴蝶结构图、可公度结构系,对伊朗高原及周边地区 M_S≥7．1地震的时空对称性进行研究,同时进行二次预测对一次预测结果进行检验.结果显示:研究区时空对称性显著,2023年发生 M_S≥7．1强震的信号最强,且通过二次预测检验;研究区震中在1960年前呈大幅度东西迁移,在1960年后呈大幅度南北迁移, 震中向东南方向迁移,3或4个强震可构成一次回旋,且多为闭合环状;经向震中迁移呈双对称轴形式,在1960年前后对称轴由43°E转为53°E,纬向震中迁移在1960年后沿35．5°N 对称,未来地震可能发生在44°E,37°N 附近.     

敦煌阳关国家级自然保护区湿地植物群落特征与物种多样性

敦煌阳关国家级自然保护区中的湿地是典型的内陆湿地,作为重要的候鸟迁徙驿站,具有脆弱性和特殊性,其植物群落特征与多样性研究对湿地及生物多样性保护有重要意义。通过野外样地调查,对阳关保护区湿地植物区系组成、地理成分和物种多样性进行了分析。结果表明,阳关保护区的湿地中共有74种植物,隶属于26科56属,其中占优势的是禾本科和藜科植物,二者占所有植物总物种数的29.73%;在植物生活型中,草本植物占绝对优势,占总物种数的77.03%;植物区系地理成分以温带分布型为主;用TWINSPAN分析法,将36块样地划分为8个植物群落,不同植物群落的物种多样性指数都较低,且存在较大差异;以重要值计算的Margalef丰富度指数为0~4.2,Simpson多样性指数为0~0.512,Shannon-Wiener多样性指数为0~1.4,Pielou均匀度指数为0.538~1,表明阳关保护区湿地植物种类总体上比较稀少、群落的组成和结构简单、物种多样性水平较低、生态较为脆弱。     

柴达木盆地风况及输沙势特征

利用柴达木盆地13个气象站的风资料,分析了盆地风况和输沙势的变化特征。结果表明：（1）盆地年平均风速2.0~4.4 m·s^-1,自盆地南、北边缘山地到盆地中部逐渐降低。盆地西部主风向为偏西风,风向较集中;东部主风向为偏东风,风向较分散。（2）盆地年平均起沙风速7.0~8.2 m·s^-1,起沙风频率5.1%~26.1%,主要发生在冬、春季,风向以WNW和W为主。（3）盆地输沙势34.0~462.3 VU,盆地西北部属于高风能环境,中部及东南部属于低-中风能环境,方向变率0.45~0.91,风况为窄单峰或宽单峰风况,盆地西北部和东南部差异较大,东部德令哈站与其他地区的合成输沙势方向相反。