西安城区黄土冲洪积层CFG桩复合地基承载能力可靠度分析

为西安城区黄土冲洪积层CFG桩复合地基设计和施工更加合理。搜集了西安城区冲洪积地层信息,得到含有黄土层的3种阶地。假设各随机变量之间相互独立,基于3种阶地的6个典型复合地基工程中36根CFG桩的工程信息,建立CFG桩复合地基承载力无量纲极限状态方程,得到各随机变量的分布概率模型,利用Monte-Carlo法计算CFG桩可靠度指标,得到可靠度指标β平均值为3.033 6,低于《建筑结构可靠度设计统一标准》(GB 50068-2001)给出的柔性结构上部平均可靠度指标3.2.结果表明:利用经验公式进行CFG桩复合地基承载力的设计能够满足工程的可靠度要求。研究成果可为西安城区黄土冲洪积层CFG桩复合地基及类似工程的设计和施工提供依据。     

黄土区金盏菊幼苗对Pb/Cd次生非生物胁迫响应的红外光谱研究

植物修复法是重金属污染场地修复的重要手段,这种"绿色修复技术"得到了学者们的广泛关注和期待。在重金属胁迫条件下,植物自身会出现相应的响应反映,进而逐渐适应并有效减缓重金属的直接毒害作用。这种微尺度的调控行为往往多维度和不可见,需要借助精密仪器分析技术加以剖析。现阶段,相关方面的研究还略显欠缺。以黄土修复植物金盏菊幼苗为研究对象,分析Pb/Cd复合胁迫对其表观形貌的影响,采用傅里叶变换红外光谱法(FTIR)识别其地下和地上部分样本的官能团性质,初步推断金盏菊对Pb/Cd胁迫的响应途径和耐受机制。研究表明:随着Pb/Cd胁迫程度的加剧,金盏菊根冠弯曲萎缩,根毛数量明显减少,而其地上部分形貌差异很小。Pb/Cd胁迫对金盏菊幼苗地下和地上部分的FTIR图谱影响较大:3 573cm~(-1)附近的—OH峰强减弱且发生移动,随着Pb/Cd胁迫浓度的增加,峰形更趋复杂化;这表明Pb/Cd与—OH间存在配位结合效应,Pb/Cd胁迫干扰了有机物的合成和分泌。饱和C—H振动峰整体红移,可能与细胞膜的膜脂氧化程度有关。1 631和1 574 cm~(-1)处吸收峰强下降,说明与之关联的蛋白质组分特性可能有异。1 385 cm~(-1)处峰位有所偏移,推测金盏菊通过改变果胶质和油脂的甲基化程度,完成细胞组织对Pb/Cd胁迫的"直接排斥→逐步适应→增强抗逆性"的过程转变。FTIR对于识别土壤重金属的植物修复机制具有重要指导意义。     

湿法消解火焰原子吸收法测定黄土复合污染修复植物金盏菊幼苗中的铅和镉

原子吸收光谱法(AAS)广泛应用于重金属分析检测领域,优化测试过程的操作条件,进而保障分析结果的稳定性和重现性,直接关系到预期研究目标的有效实现,建立精准的检测方法往往成为科学研究的首要任务。以金盏菊为黄土区Pb/Cd复合污染修复植物,采用湿法消解-AAS法测定金盏菊幼苗体内Pb/Cd含量,分析所得结果初步揭示金盏菊幼苗对Pb/Cd的富集效应。研究发现:湿法消解-AAS法对Pb/Cd的检出限分别为0.104和0.007 mg·L~(-1),Pb/Cd回收率对应于94.33%~110.78%和97.73%~107.50%之间,同一样品重复测定(6次)的相对标准偏差(RSD)波动于4.11%~4.75%(Pb)和1.11%~2.77%(Cd),表明该方法准确度较好,精密度较高。金盏菊幼苗对Pb的富集能力不强,这可能与Pb的电负性、植物生长周期较短及环境因子等因素有关;但在黄土Cd浓度为50 mg·k~(-1)时,金盏菊幼苗对Cd的平均富集量已达到104.85 mg·kg~(-1)。此外,黄土Pb的共存一定程度上促进了金盏菊幼苗对Cd的吸收,其间可能存在协同作用。所建立的分析方法可以对金盏菊幼苗Pb/Cd含量进行有效检测,预期能为后续研究提供技术支持和质量保障。     

金盏菊根际圈黄土溶解性有机质对Pb/Cd赋存形态原位调控机制的光谱学证据

在污染场地植物修复过程中,植物根系通过释放活性分泌物主动适应和抵御污染胁迫,直(间)接影响根际圈土壤DOM的结构组成。现阶段,植物修复的关注点主要集中于污染物的吸收、转运、累积和解毒行为,对于根际圈土壤DOM的探讨略显不足。以Pb/Cd复合污染黄土区金盏菊幼苗为研究对象,分析根际圈黄土Pb/Cd赋存形态、金盏菊生长状况等宏观差异,借助紫外可见光谱(UV)、傅里叶变换红外光谱(FTIR)和三维荧光光谱(3D-EEMs)明确Pb/Cd胁迫前后根际圈黄土DOM的微观性质。结果表明:根际圈黄土Pb/Cd以残渣态和可交换态为主,金盏菊生长周期结束后可交换态Pb/Cd含量有所升高。Pb/Cd胁迫抑制了金盏菊株高和出苗率,其生长周期有助于改善黄土理化性质。胁迫后金盏菊根部呈现细长、弯曲且萎缩的迹象;DOM紫外光谱最大吸收区间位于200~240nm,但胁迫后的图谱波峰更加尖锐,峰强更大。Pb/Cd胁迫导致DOM红外吸收峰分别从3 444和1 637cm-1移动至3 440和1 645cm-1,其中存在重金属离子与OH和C=O结合效应。DOM荧光峰集中在λex/em=240/430附近(紫外区类富里酸荧光峰),Pb/Cd胁迫对荧光峰强干扰较大,而对荧光峰位基本没有影响。金盏菊根际圈黄土DOM能够提供重要的微生态环境信息,光谱学手段能够一定程度上揭示其与Pb/Cd赋存形态的构效关系。     

δ13CSC values of the loess-paleosol sequence in Dali area, Shaanxi Province, China, and paleoenvironmental implications

The carbon isotopic ratios of carbonate in the two profiles of the Dali area were analyzed and some new understandings on the influencing factors of the δ^13Csc value of the Iocss-paleosol sequence and its paleoenvironmental implications were discussed preliminarily in this report. The δ^13Csc value of the Dali Ioess-paleasol sequence is synchronizing with the variance of magnetic susceptibility basically and the negative peaks of the δ^13Csc curves are corresponding to the different developmental periods of the paleosol. It is believed that the intervention of the CO2 produced by plants will cause the decrease of the δ^13Csc value, the amplitude of which may be relevant to the paleovegetation density and the ancient humidity. The relative biomass of C4 plants in the vegetation will affect the sublevel change of the δ^13Csc. Low δ^13Csc value by and large indicates the environmental conditions of the relatively abundant vegetation and humid climate. During the last 250000 years, the period with the sparsest vegetation and the most arid climate is the phase of the loess in L2 depositing and the period with the most abundant vegetation and the most humid climate is the last interglacial period. The δ^13Csc curves of Dali also show that the High Temperature and Large Precipitation Event of the Qinghai-Tibetan Plateau during 40-30 kaBP had affected the Central Shaanxi Plain with relatively humid climate, and had apparent influence on the local vegetation and humidity.     

A study on responses of soil erosion and sediment yield to closing cultivation on sloping land in a small catchment using ^137Cs technique in the Rolling Loess Plateau, China

By comparison of volumes and ^137Cs Contents of the deposited sediments before and after 1993,changes of specific sediment yields and relative sediment contributions from the gully area and from the inter gully area after closing cultivation on the later area on a small catchment of Zhaojia Gully,in the Rolling Loess Plateau,are analyzed in this paper.Closing cultivation in a large scale has not resulted in decrease but increase of specific sediment yield and the relative sediment contribution of the inter-gully area,and in increase of the sediment yield and the contribution of the gully area,for a short term.The mean specific sediment yield of 29650 t km^-2a^-1 of 1994-1996 in the catchment was 2.2 times the average value of 13413 t km^-2 a^-1 for a long term.The specific sediment yield of the inter-gully area decreased from the 14335t km^-2a^-1 in 1994 to 7034 t km^-2 a^-1 in 1995 and 3517 t km^-1a^-1 in 1996 which was much greater than the value of 21118 t km^-2 a^-1 before 1993.The relative sediment contribution from the inter-gully area decreased form 23% in 1994 to 15% in 1995 and 6% in 1996,while the contribution from the gully area increased form 77% in 1994 to 85% in 1995 and 94% in 1996.It is suggested that compacting of ploughed soils resulted in increasing of the erosion resistance but in decreasing of the precipitation infiltration,therefore,the soil erosion reduced but the runoff amount increased on the inter-gully area.Increase of delivering runoff from the inter-gully area to the gully area should result in activeness of gully erosion and mass movements,consequently,in increase of the total sediment yield from the catchment.     

Paleoclimatic significance of mineral magnetic properties of loess sediments in northeastern Qinghai-Tibetan Plateau

Loess deposit in the northeastern Qinghai-Tibetan Plateau offers an excellent record of climate and environment changes in this region.We have conducted multiparameter mineral magnetic analyses of smaples of loess deposits from the Dongchuan,Lalakou and Panzishan sections.The methods used include magnetic susceptibility,fre-quency-dependent suceptibility,temperature-dependent susceptibility,isothermal remanent magnetization acquisibility.Maghemite and hematite is also present in the loess layers and paleosol horizons.The higher concentration of maghemite in paleosols suggests that the formation of maghemite occurred during in situ pedogenesis,which plays an important role in the enhancement of the magnetic susceptibitily.Similar to that in the Chinese Loess Plateau lying to the east of the Liupan Mountains,magnetic granulometry in the studied loess and paleosols is predominantly pseudo-single-domain(PSD). However,the mean grain-size of the ferrimagnetic minerals in loess is evidently coarser (larger PSD and multiomain-like) than in paleosols (mainly PSD).The magnetic susceptibility of loess and paleosols is positively correlated with the content of ultrafine magnet-ite/maghemite grains,and hence with the intensity of in situ pedogenesis.Therefore,the enhanced magnetic susceptibility in the studied loess-paleosol sequences can be interpreted as being due to climatically induced in situ pedogenesis.     

黄土地区高等级公路的边坡绿化

文章论述了黄土地区高等级公路边坡绿化的意义、主要形式及植物的选择。     

2.5 Ma以来黄土高原灵台剖面黄土-古土壤87Sr/86Sr比值的变化

研究提出了2．5MaB．P．以来黄土高原灵台剖面黄土-古土壤序列的酸不溶物^87Sr/^86Sr、Rb/Sr、Zr/Rb、平均粒径和磁化率的变化曲线．黄土和古土壤酸不溶物^87Sr/^86Sr、Rb/Sr、Zr/Rb和磁化率的变化具有类似的阶段性．研究证明，黄土和古土壤酸不溶物^87Sr/^86Sr比值是化学风化强度的替代指标。Zr/Rb是物理风化强度的替代指标．自2．5MaB．P．以来大陆化学风化强度在总体上呈下降趋势,而物理风化强度呈上升趋势．