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Airborne pollen is indicative of vegetation and climatic conditions. This study investigates airborne pollen trapping in the Betula microphylla-dominated wetland of Ebinur Lake in Northwestern China from September 2012 to August 2015 using Pearson correlation analysis and the Hybrid Single-particle Lagrangian Integrated Trajectory model. Higher temperatures and moderate precipitation during the flowering period facilitated an increase in birch pollen with more exotic spruce pollen carried from the Tianshan Mountains by airflows, leading to the highest arbor pollen concentrations from September 2012 to August2013. Peak pollen concentrations from September 2013 to August 2014 were possibly due to an increase in herbaceous pollen resulting from higher temperatures, lower precipitation and more exotic pollen from the desert of southwest Ebinur Lake and Central Asia in summer and autumn. Between September 2014 and August 2015, unfavorable climate conditions in summer and autumn decreased the pollen dispersal of xerophytes such as Artemisia and Chenopodiaceae, with little pollen transported from the Kazakh hilly area in late summer, resulting in the lowest pollen concentrations. Climatic parameters and air mass movements both greatly affected the atmospheric pollen concentration. The results provide information concerning the dispersion and distribution of birch pollen, paleoenvironmental reconstruction and wetland conservation. 相似文献
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To interpret past vegetation and climate changes from pollen data, we need to reveal the degree of similarity between modern analogues and fossil pollen spectra, which would help us predict the future climate and vegetation. Ninety surface pollen samples across six vegetation zones along an altitudinal gradient from 460 to 3510 m and 44 fossil samples at Caotan Lake were collected in the central Tianshan Mountains, northern Xinjiang, China. Discriminant analyses results, fossil pollen and phytolith assemblages were then used to reconstruct palaeovegetation and palaeoclimate in the area. The 90 surface samples were divided into six pollen zones (alpine cushion, alpine and subalpine meadow, montane Tianshan spruce forest, forest-steppe ecotone, Artemisia desert, typical desert), corresponding to the major vegetation types in the area. These zones follow a climatic gradient of increasing precipitation with increasing elevation. Paleovegetation reconstructed from 44 fossil pollen assemblages through discriminant analysis reflects the regional vegetation shifted from typical desert to Artemisia desert since 4640 cal. year BP in the Caotan Lake wetland. The fossil pollen and phytolith record also reveal the arid climate has not fundamentally changed in the period. But a dry-wet-dry local climate oscillation since 2700 cal. year BP has a fundamental influence on local wetland vegetation dynamics and peat accumulation of the Caotan wetland. Modern wetland landscape and surface pollen assemblages from the Ebinur Lake Wetland Nature Reserve provide further evidence for ferns and Betula growing in the Caotan Lake wetland during the historical period. 相似文献
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１ ＩＮＴＲＯＤＵＣＴＩＯＮＳｉｎｃｅｔｈｅ１９８０ｓａｓｅｒｉｅｓｏｆｒｅｓｅａｒｃｈｐｌａｎｉｎｃｌｕｄｉｎｇＩＧＢＰ（ｔｈｅＩｎｔｅｒｎａｔｉｏｎａｌＧｅｏｓｐｈｅｒｅ．ＢｉｏｓｐｈｅｒｅＰｒｏｇｒａｍｍｅ）ｈａｖｅｂｅｅｎｓｅｔｕｐ，ｏｆｔｈｅｍ，ＰＡＧＥＳ（ｔｈｅＰａｓｔＧｌｏｂａｌｃｈａｎｇｅｓ）ｉｓａｎｉｍｐｏｒｔａｎｔｃｏｒｅｐｒｏｊｅｃｔ．Ｔｈｅｎａｔｕｒｅｒｅｃｏｒｄｓｏｆｏｃｅａｎｄｅｐｏｓｉｔ，ｔｅｒｒｅｓｔｒｉａｌ（ｌｏｅｓｓ，ｌａｋｅｓａｎｄｓｗａｍｐ）ｄｅｐｏｓｉ… 相似文献
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This study investigates the initialization of nonlinear free-surface simulations in a numerical wave flume.Due to the mismatch between the linear input wavemaker motion and the kinematics of fully nonlinear waves,direct numerical simulations of progressive waves,generated by a sinusoidally moving wavemaker,are prone to suffering from high-frequency wave instability unless the flow is given sufficient time to adjust.A time ramp is superimposed on the wavemaker motion at the start that allows nonlinear free-surface simulations to be initialized with linear input.The duration of the ramp is adjusted to test its efficiency for short waves and long waves.Numerical results show that the time ramp scheme is effiective to stabilize the wave instability at the start of the simulation in a wave flume. 相似文献
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以黄河源区水文循环过程为主要研究对象,应用TRMM卫星和GPM卫星的日降水产品(TMPA3B42和IMERG-Final)驱动流域分布式水文模型SWAT,将结果进行比较分析,评估了新型卫星降水在黄河源区的适用性及其模拟潜力。研究表明:(1)对于大尺度流域而言,同时对多个子流域进行参数的敏感性分析及率定的结果不适用于每一个站点。因此,本文采用对每个水文站点所对应的子流域依次进行敏感性分析与验证的方式进行订正,最终得到验证期内3个站点径流模拟结果的纳什效率系数均在0.50以上,决定系数都在0.60以上。(2)从模拟结果来看,IMERG-Final产品的模拟结果要优于TMPA3B42产品。两种卫星降水产品均能模拟出黄河源区月径流变化的主要趋势,但均表现为对于径流峰值的模拟偏高。新型卫星产品(GPM)较前任TRMM卫星产品的精度确实有提高,且具备一定的模拟潜力,但对于高海拔地区的模拟能力有待提高,需要进一步订正。 相似文献
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文章依据新疆天山北麓古尔班通古特沙漠东南缘的四厂湖人工剖面进行的孢粉分析、平均粒径、磁化率以及烧失量测定结果,揭示了四厂湖地区最近1000年以来的古环境特征。研究结果表明,在与被称之为"中世纪温暖期(900-1300A.D.)"相当的时段内,淡水的四厂湖湖体周边地区曾经生长着由中旱生的灌木及草本组成的荒漠草原植被,并分布有淡水沼泽隐域植被。当时气候湿润,湖区生物物种多样性增加。结合新疆其他地区的第四纪研究成果,反映出该时期新疆地区气候湿润、湖沼发育、植被生长旺盛,因此本区在中世纪时气候应称之为湿润期或适宜期。而中世纪前后,该区以旱生、超旱生植物花粉占绝对优势,湖区植物种类减少,风沙作用较强,荒漠化景观显著。 相似文献
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采用能量聚焦的方式产生深水破碎波,并通过增加输入波陡使发生不同强度的波浪破碎现象。实验中,沿水槽中心位置布置22个浪高仪,分析波浪传播过程中的波面演化特征。对水槽不同位置处波面数据进行波能谱与小波能谱分析,发现在聚焦波传播过程中,低频能量部分保持相对稳定,而一次谐波高频部分先逐渐拓宽,经过破碎区域后又逐渐恢复。能量在高频部分有所损失,这种现象在破碎时更加明显,且破碎强度越大,越显著。波浪未破碎时,由于波浪传播过程中高频部分拓宽,导致聚焦前后特征频率略有增加,特征群速和特征周期略有减小;当波浪破碎时,由于破碎导致的能量损失比较明显,且卷破时更加明显,导致破碎后特征频率减小,特征群速和特征周期增大。 相似文献
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为了使消能结构在多频率波浪作用下都能有一个较低的反射率,提出一种新型消能结构——双层板与双列开孔结构复合结构。考虑了面积约束条件下结构物边界对波浪反射特性的影响,运用数值模拟方法模拟了波浪与结构物的相互作用,计算了消能结构在不同边界形状下的反射系数,对比波浪反射系数结果获得了最佳的消能结构物边界形状。反射系数研究结果及消能结构周围流场的分析表明:消能结构物的反射特性及流场特性对波候有一定的依赖性,也依赖于消能结构物的边界特性。因此开展消能结构物边界排布及形状的研究是很有必要的。 相似文献
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近年,考古学家发现坚果类植物在农业起源中曾占有很重要的地位。为了对考古器物上附着的淀粉粒进行鉴定,我们对中国北方现代主要坚果类栗属（Castanea）中的板栗（C.mollisima）、栎属（Quercus）中的槲树（Q.dentata）、槲栎（Q.aliena）、麻栎（Q.acutissima）、栓皮栎（Q.viriabilis）、蒙古栎（Q.mongolicus）和胡桃属（Juglans）中的胡桃楸（J.mandshurica）共7个样品进行了淀粉粒形态对比分析,以求为建立北方坚果类淀粉粒的鉴定标准积累资料。实验结果发现,除胡桃楸未发现淀粉物质以外,其他6个样品的淀粉粒不仅可以与其他科、属进行区分,甚至在一定程度上还可以进行种间的区分。板栗的脐点是闭合的,有层纹,无裂隙; 麻栎脐点是偏心的; 槲树栓皮栎的淀粉粒近乎80％都具有裂隙特征,但栓皮栎的淀粉粒中会出现横裂隙和相当数量的星形裂隙而只有槲树的淀粉粒才具有相当数量的纵向裂隙; 蒙古栎的淀粉也大多具有裂隙（70％）而且纵向型裂隙占主要地位,但是蒙古栎淀粉粒表面有细密的放射线; 60％的槲栎淀粉粒不具有裂隙特征。所有样品的淀粉粒均由大小不一的各种卵圆形组成,而且6个样品的长轴最大值（约20μm）和6个样品的平均值（约10μm）都非常接近。 相似文献