黄河北岸兰州段丘陵区土壤生态化学计量与空间变异北大核心CSCD

为探究黄河北岸兰州段丘陵区土壤碳、氮、磷含量及化学计量比的空间变异特征,基于12个样地数据,采集1 m剖面内不同发生层土壤进行土壤含水率(SWC)、pH、有机碳(SOC)、全氮(STN)和全磷(STP)的测定。分析了研究区土壤碳、氮、磷含量及其生态化学计量特征在植被和土层上的差异及空间变异特征。结果表明:(1)研究区SOC、STN、STP均值分别为4.53、0.74、0.13 g·kg^(-1),C∶N、C∶P、N∶P均值分别为7.85、55.17、8.40;(2)研究区SOC、STN、C∶N和N∶P的块基比C_(0)/(C_(0)+C)<0.25,主要受气候、植被、地形等自然因素影响;STP、C∶P则C/(C+C)>0.75,主要受退耕还草等人为因素影响;(3)研究区土壤整体受到氮限制,与此同时有机碳更为匮乏,磷则在短期内不会成为限制因子。在黄河流域兰州段北岸丘陵区北岸的生态治理与恢复中,应重视有机肥和氮肥的配置与施加,同时需减少人为干扰,这对于植被的快速恢复与养分的固定具有重要意义。     

1993年咸宁地震群震害损失及发震成因探讨

1993年7~8月,湖北省咸宁地区发生了一系列ML≤4.1的地震。从地震系列、地表破坏状况和地震宏观等烈度线展布特征出发,深入研究了地震与地质构造及地下水动态变化的关系,得出结论地震群可能为抽取地下水引起的构造变动而诱发。     

冰碛扇型砂金矿床特征及其成矿初探

成生于冰碛扇内，经一定的生物、物理、化学成矿作用，以砂金形态分布而富集成矿的金矿称为冰碛扇型砂金矿床。它具有沿造山带一定标高范围成群、成带分布，沉积物为近源且半胶结，砂金呈面状分布，并以粒金、块金为主，具胶状、浑圆状、包块状构造形态，分布极不均匀等特征。冰碛扇型砂金矿床的成矿作用与河成砂金矿床有本质的区别。它的成矿作用模式是：造山带下地壳富含的活化金通过新构造运动活化的断裂运移地表，经地下流体和地表流体的迁移聚集到冰碛扇这一封闭稳定的生物、物理、化学障环境中，主要经高效聚金微生物有机胶体成矿作用沉淀、再生加大形成砂金，逐步富集成矿床。而红色磨拉石建造中风化离解的Ｆｅ，Ｍｎ物质对沉淀环境ｐＨ值起着一定的调节作用。冰碛扇型砂金矿床在我国西部造山带内广泛分布，具有一定的工业价值，是砂金矿床中一重要类型，应予以重视     

Influencing factors of seed long-distance dispersal on a fragmented forest landscape on Changbai Mountains,China

Seed long-distance dispersal(LDD) events are typically rare, but are important in the population processes that determine large-scale forest changes and the persistence of species in fragmented landscapes. However, previous studies focused on species dispersed via animal-mediated LDD, and ignored those dispersed by wind. The aim of this study was to assess the effects of canopy openness, edge, seed source, and patch tree density on the LDD of seeds by wind in forest. We collected birch seeds, a typical wind-dispersed species, throughout a larch plantation. We then assessed the relationship between birch LDD and each factor that may influence LDD of seeds by wind including distance to edge, canopy openness size, distance to mature forest, and the tree density of the larch plantation. We used univariate linear regression analysis to assess the influence of those factors on birch LDD, and partial correlations to calculate the contribution of each factor to LDD. The results showed that both canopy openness and edge had significant influences on birch LDD. Specifically, a negative relationship was observed between distance to edge and birch LDD, whereas there was a positive correlation between canopy openness size and LDD. In contrast, the distance to the mature forest was not correlated with birch LDD. Our results suggest that patch tree density could potently affect the probability of LDD by wind vectors, which provides novel and revealing insights regarding the effect of fragmentation on wind dynamics. The data also provide compelling evidence for the previously undocumented effect of habitat fragmentation on wind-dispersed organisms. As such, these observations will facilitate reasonable conservation planning, which requires a detailed understanding of the mechanisms by which patch properties hamper the delivery of seeds of wind-dispersed plants to fragmented areas.     

Introduction to the solar space telescope

The design of the space solar telescope (SST) (phase B) has been completed. The manufacturing is under development. At the end of 2000, it will be assembled. The basic aspect will be introduced in this paper.     

简论90年代以色列的经济政策

现代以色列经济是外向型经济。90年代以来,中东和平进程在前进,以色列经济在发展,工党政府和利库德集团政府都把进一步改革开放、奠定以色列的中东经济强国地位作为主要目标,为此,制定了推进私有化、吸引外资、扩大对外贸易的政策以及一系列相关政策,对以色列经济的现状和将来有着重大影响,也对中东区域经济的发展有着促进作用,同时也存在着某些问题。     

深圳农民工集聚空间的演变特征及影响机制

以2000年、2010年人口普查数据和2008年珠江三角洲外来农民工问卷调查为基础数据,以街道为单元,运用数理统计分析和GIS空间技术揭示深圳农民工集聚空间演变特征及其影响机制。研究发现：① 深圳农民工以青年为主体,具有受教育水平高、职业转型模式多样、留城意愿较低和社会空间分异度较高等特征。② 农民工规模呈现西北部最高、中部其次、沿海最低的地带性分布规律,农民工高密度地区主要分布在工业集中区和城市中心区;热点区（高聚集区）集中在西部和北部的宝安区和龙华新区,冷点区（低聚集区）则分布在南部的中心城区,与传统制造业布局相一致。③ 农民工空间演化格局相对稳定,全市农民工分布重心逐步向西北偏移;全市农民工集中度略有上升,热点区基本稳定,冷点区有所扩大;农民工人口密度高值由“1个高中心+1个外围中心”逐步演变为“1个高中心+2个外围中心”;农民工空间变化差异较大,增长演变类型呈多样化。④ 深圳农民工分布的时空演变特征与常住人口存在较为明显的差异。⑤ 农民工集聚空间的分布演变受住房因素、就业机会、交通条件、社会网络、城市规划共同影响。     

Characteristics of mineral element content of alpine vegetation in permafrost region on Qinghai-Tibetan Plateau

The content characteristics of 16 elements (Al, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, and Zn) in 23 plant species collected from the Qinghai-Tibetan Plateau permafrost region were investigated using ICP-OES. Results show that the average contents of Ca, K, Mg, Fe and P were higher than 1,000 mg/kg, those of Al, Na, Zn and Cr ranged between 10–1,000 mg/kg and those of Cu, Li, Pb and Mo were less than 10 mg/kg. The levels of Al, Ca, K, Mg and Na were within the scope of the reported terrestrial plant element content, those of Sr, Fe and Cr were higher than the average of the terrestrial plants and the maximum content of Mn was higher than the upper limit of the reported Mn content. The main character of the element content was of the Ca>K type, however, in terms of Cyperaceae species the element content character was K>Ca type. The contents of Ca, Li, Mg and Sr in Gramineae and Cyperaceae species were higher than those in other species and the contents of Ca, K, Mg, Fe, P, Al and Na in all collected plants were higher than those of other elements. Zn had weak variability with the lowest coefficient (i.e., 7.81%), while other elements had strong variability. The ratio of maximum content to minimum content indicated Ca and K had less change than other elements in the Qinghai-Tibetan Plateau permafrost region. Element content of alpine vegetation in the Qinghai-Tibetan Plateau permafrost region mainly shows a positive correlation, among which the correlation coefficient between Al and Pb, Al and Fe, Mo and Cr, Pb and Fe, Sr and Li were higher than 0.9, and negative correlation had no statistical significance. The correlation between Al and Fe, Mg, Mn in the Qinghai-Tibetan Plateau permafrost region were consistent with that reported in Kunlun Mountains.     

莫高窟PM10浓度与气象要素的关系

采用2018年敦煌莫高窟第16窟窟内与窟区PM₁₀浓度及气象数据,分析PM₁₀时空分布特征及其影响因素。结果表明：（1）两处监测点PM₁₀浓度主要分布在50 μg·m^-3以下,受重污染天气影响较小;春、冬、秋、夏季依次降低,窟区PM₁₀浓度在春、冬季高于窟内,夏、秋季反之。（2）PM₁₀浓度3月最高,9月最低,5—9月窟内月均值高于窟区。PM₁₀污染日数窟内5月最多,而窟区3、5月较多。（3）PM₁₀浓度日变化曲线在春季和秋季呈“双峰”型,夏季和冬季呈“单峰”型。（4）在半封闭环境的洞窟内,沙尘暴发生前后,PM₁₀浓度达到极值及恢复至原来水平的时间均滞后于窟区。（5）在不同季节PM₁₀浓度与气温、风速和降水呈负相关。除秋季外,PM₁₀浓度与相对湿度、气压呈正相关。（6）窟区全年主风向为ESE,在冬春两季,此风向PM₁₀浓度最高,PM₁₀主要来自三危山前的戈壁滩、干涸的大泉河河道以及窟前裸露的地表积尘。     

基于星载激光测高估计南极冰盖高程变化

利用NSIDC公布的ICESat运行期间的19个任务期的观测数据, 采用重复轨迹分析方法估计近年来南极冰盖高程的时空变化。结果表明,南极大陆冰盖整体上呈现消融趋势,基于不同的GIA模型和ICESat激光测高数据的南极大陆冰盖高程变化的趋势约为 -1.17~-1 cm/a。