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71.
XueYing Li FengFeng Zheng YuFei Chen WenTing Guo TingTing Zhang AnYi Hu ChangPing Yu ChuanLun Zhang 《中国科学:地球科学(英文版)》2016,59(7):1317-1328
Archaea play an important role in global carbon and nitrogen cycles. Archaeal lipids, such as isoprenoid glycerol diakyl glycerol tetraethers (iGDGTs), are important biomarkers tracing change in archaeal community structure and biogeochemical processes in the natural environments. In this research, the spatial distributions of archaeal lipids in the surface sediments of the Jiulong River (JR) and the Jiulong River estuary (JRE) were examined. GDGT-0 (containing zero cyclopentyl ring) and crenarchaeol were the most abundant iGDGTs in the JR and JRE. From the rivers to the estuary, the total iGDGTs, GDGT-0, crenarchaeol and archaeol concentrations showed significant spatial variation; in particular, GDGT-0 and archaeol in the river may be predominantly derived in situ from methanogens, whereas crenarchaeol in the estuary mainly derived in situ from Thaumarchaeota. We inferred that archaeal community was dominated by methanogens in the Jiulong River and by Thaumarchaeota in the Jiulong River estuary, which are consistent with change in archaeal community structure observed in other estuarine environments. 相似文献
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74.
Yuanming Guo Chase Holton Hong Luo Paul Dahlen Paul C. Johnson 《Ground Water Monitoring & Remediation》2019,39(2):43-52
Groundwater elevation fluctuation has been recognized as one mechanism causing temporal indoor air volatile organic chemical (VOC) impacts in vapor intrusion risk assessment guidance. For dissolved VOC sources, groundwater table fluctuation shortens/lengthens the transport pathway, and delivers dissolved contaminants to soils that are alternating between water saturated and variably saturated conditions, thereby enhancing volatilization potential. To date, this mechanism has not been assessed with field data, but enhanced VOC emission flux has been observed in lab-scale and modeling studies. This work evaluates the impact of groundwater elevation changes on VOC emission flux from a dissolved VOC plume into a house, supplemented with modeling results for cyclic groundwater elevation changes. Indoor air concentrations, air exchange rates, and depth to groundwater (DTW) were collected at the study house during an 86-d constant building underpressurization test. These data were used to calculate changes in trichloroethylene (TCE) emission flux to indoor air, during a period when DTW varied daily and seasonally from about 3.1 to 3.4 m below the building foundation (BF). Overall, TCE flux to indoor air varied by about 50% of the average, without any clear correlation to changes in DTW or its change rate. To complement the field study, TCE surface emission fluxes were simulated using a one-dimensional model (HYDRUS 1D) for conditions similar to the field site. Simulation results showed time-averaged surface TCE fluxes for cyclic water-table elevations were greater than for stationary water-table conditions at an equivalent time-averaged water-table position. The magnitudes of temporal TCE emission flux changes were generally less than 50% of the time-averaged flux, consistent with the field site observations. Simulation results also suggested that TCE emission flux changes due to groundwater fluctuation are likely to be significant at sites with shallow groundwater (e.g., < 0.5 m BF) and permeable soil types (e.g., sand). 相似文献
75.
利用反映震级-频度关系的参量C值,η值,b值和b值谱以及反映地震空间分布的森下指等研究了近海地震活动的一些主要特征,发现近海强震前地震活动性指标及图象的变化特征与陆地上强震前的特征存在一定差异;给出了新研究的可用于近海及滨海地区强震预报的短期和临震 相似文献
76.
北极阿拉斯加巴罗地区Elson湖长60cmAB—67钻孔岩芯提供了过去450年连续的高分辨环境变化记录。综合分析210Pb测年、沉积物粒度、有机质、化学元素和微体古生物化石等资料,一致反映出巴罗地区过去450年的气候、环境变化过程存在如下3个阶段:1)大约1540~1740年,为低海面寒冷时期;2)1740~1827年,为气候转暖-海侵过渡时期;3)1827年至今,为继续海侵-气候波动变暖时期。其中1800年前后和1940年前后,气温较高。1921~1993年巴罗的气温记录说明,北极地区气温不仅有明显的10a和60a周期变化,而且年平均温度变幅极大,达4.5℃。显示极地气候变化特别强烈并不反映大幅度升温。近20年来的变暖趋势是1827年以来自然的气候波动变暖的继续。 相似文献
77.
设计了一种胶体光子晶体修饰的光纤. 采用恒温快速蒸发法直接在经切割刀处理后的光纤端面生长胶体晶体,再与另一根切割后的光纤在毛细玻璃管中完成对接,制备成胶体光子晶体修饰的光纤. 用扫描电子显微镜和光谱分析仪对样品的形貌、结构以及光学特性进行分析. 实验结果表明,粒径为640 nm、体积分数约为0.5%的SiO2胶体微球溶液在60 ℃的情况下沉积,大约12 h后可得到质量较高的胶体光子晶体. 在SEM下,观察到端面的胶体晶体为面心立方(fcc)结构. 透射光谱证明,该结构在(111)面上 相似文献
78.
An-Yi Tsai Gwo-Ching Gong Kuo-Ping Chiang Chien-Fu Chao Herng-Ru Guo 《Journal of Oceanography》2011,67(6):725-737
The spatial distribution of heterotrophic ciliates, environmental factors and potential food items (bacteria, Synechococcus spp. and nanoflagellates) were measured in the East China Sea to examine which variables contributed importantly to the long-term
distribution of ciliates between 1998 and 2007. In July 1998 and June 2003, heterotrophic ciliates were found to be abundant
(1,000–2,000 × 103 cells m−3) in regions where surface salinity <32 but extremely low (<500 × 103 cells m−3) in shelf waters of surface salinity >32. After August 2003, shortly after the completion of the Three Gorges Dam, we found
no significant areal differences in the abundance of heterotrophic ciliates (HC). However, we found a significantly negative
correlation between temperature and HC abundance of surface water after the completion of the dam, suggesting that temperature
had a greater influence on HC abundance, once the original saline state had changed. For the long-term trends on the vertical
distribution of HC, their abundance was significantly higher in the upper 50 m of the water column than at either 75 or 100 m.
Abundance of Synechococcus spp. at these levels varied significantly in regions of surface salinity <32, suggesting that ciliates and picophytoplankton
contribute greatly to mediating the transfer of organic matter to higher trophic levels in this marine ecosystem. 相似文献
79.
台风是我国东南沿海区域每年发生的严重自然灾害之一。本文分别采用传统的Monte-Carlo模拟方法以及较为先进的经验路径模拟方法预测中国东南沿海区域台风的极值风速(10 m高度处10 min平均值),并对两种方法的预测结果进行了对比。本文将东南海岸线向内陆扩展约200 km的区域划分为0.25°×0.25°的网格,以每个网格点作为研究点。首先采用Monte-Carlo模拟方法产生每个研究点1 000年间的虚拟台风事件。然后采用经验路径模型方法构建了西北太平洋1 000年的热带气旋事件集,采用模拟圆方法从中提取对各个研究站点有影响的台风事件。接着采用Yan Meng风场模型计算每个研究点台风的最大风速,构成极值风速序列。最后采用极值分布模型预测每个研究点不同重现期的极值风速,并对两种不同方法预测的结果进行了对比。研究发现在研究区域的内陆侧经验路径方法预测的风速略高于Monte-Carlo模拟方法预测的结果,而在海岸沿线一带经验路径方法预测的结果略低,这主要是由两种方法构造的虚拟台风的中心压强存在差异以及模型本身的不确定性造成的。本文的研究结果可以为防灾减灾系统提供有益的参考。 相似文献
80.
Qiao Ling Yu Jie Li Ying Guo Haobing Zhen Yu Zhang Lingling Mi Tiezhu Zhang Fuchong Bao Zhenmin 《Ocean Science Journal》2019,54(3):375-392
Ocean Science Journal - Brown tides caused by Aureococcus anophagefferens have occurred frequently in the coastal waters of Qinhuangdao since 2009. The Changli coast is the area most strongly... 相似文献