The grassland of Qinghai-Tibet Plateau (QTP) and Inner Mongolia Plateau (IMP), accounting for 73.9% of the total grassland area in China, is significant to food and ecological safety. Due to climate change and irratio...The grassland of Qinghai-Tibet Plateau (QTP) and Inner Mongolia Plateau (IMP), accounting for 73.9% of the total grassland area in China, is significant to food and ecological safety. Due to climate change and irrational human activities, grasslands on the two plateaus have severely degraded over recent decades. Understanding the dynamic changes of grassland and its driving forces is necessary to make effective measurements to prevent grassland degradation. Here, we selected the net primary productivity (NPP) as an indicator to quantitatively assess the dynamic variation of grassland and the relative roles of climate change and human activities on QTP and IMP from 2000 to 2016. The results found significant spatial variability of grassland on QTP. 28.3% of the grassland experienced degradation and was mainly distributed in the southern QTP, versus 71.7% of the grassland was restored and mainly distributed in the central and northern QTP. In contrast, grassland on IMP didn’t show significant spatial variability. Most of the grassland on IMP was restored during the study period. Climate change (i.e. increased precipitation) was the dominant factor and could explain 72.8% and 84.4% of the restored grassland in QTP and IMP. Irrational human activities (i.e. overgrazing) were the main driving factors and could explain 72.9% and 100.0% of the degraded grassland on the two plateaus during the study period. Ecological restoration projects were favorable for grassland restoration on the two plateaus, and they contributed to 27.2% and 15.6% of the restored grassland in QTP and IMP, respectively. Therefore, climate changes on IMP were more favorable for grassland restoration, and human activities have a greater impact on the grassland variation on QTP.展开更多
Lakes are important ecological water sources in the Bashang Plateau. Its expansion or shrinkage directly affects the ecological security of the plateau and its surrounding areas. In this study, Landsat images from 198...Lakes are important ecological water sources in the Bashang Plateau. Its expansion or shrinkage directly affects the ecological security of the plateau and its surrounding areas. In this study, Landsat images from 1984 to 2015 were selected to monitor the area of lakes in the Bashang Plateau and to analyze the spatiotemporal evolution and driving forces of lakes in the Bashang Plateau. The results showed that there were 47 lakes in the Bashang Plateau in 2015, with a total area of 37.63 km2, mainly distributed in the central and western regions of the region. From 1984 to 2015, the lakes in Bashang Plateau showed a shrinking trend. At the same time, there are obvious stage differences in lake changes. During 1984-1996, the number of lakes increased by 99 and the total area increased by 124.43 km2. From 1996 to 2015, the number of lakes decreased by 142, and the total area decreased by 183.96 km2. Before 1996, climate change was the dominant factor. However, the shrinkage of lakes after 1996 is the result of climate change and human activities. Among them, the large-scale planting of water consuming crops such as vegetables is the main human activity mode leading to lake shrinkage. This study will help to understand the expansion and contraction factors of the Bashang Plateau lakes in Hebei province and provide a reference for the future protection and management of the lakes.展开更多
目的建立动态三磁场塞曼背景校正石墨炉原子吸收法测定工作场所空气中铅及其化合物的分析方法。方法用微孔滤膜采集空气样品,使用高氯酸—硝酸(1∶9,V∶V)消解,以1%硝酸定容至25 m L,在283.3 nm波长下,使用动态三磁场塞曼背景校正模式...目的建立动态三磁场塞曼背景校正石墨炉原子吸收法测定工作场所空气中铅及其化合物的分析方法。方法用微孔滤膜采集空气样品,使用高氯酸—硝酸(1∶9,V∶V)消解,以1%硝酸定容至25 m L,在283.3 nm波长下,使用动态三磁场塞曼背景校正模式进行测定。结果使用动态三磁场模式,同时得到2-磁场和3-磁场模式下的吸光值及校正曲线,在0~800μg/L质量浓度范围内有较好的线性关系,其中0~100μg/L浓度范围采用二磁场模式校正曲线,曲线方程为A=2.76×10^(-3)C+2.08×10^(-2),r=0.9975,特征浓度1.58μg/L;100μg/L^800μg/L浓度范围采用三磁场模式校正曲线,曲线方程A=(4.05×10^(-3)+9.67×10^(-4)C)/(1+6.50×10^(-4)C),r=0.9970,特征浓度4.51μg/L,方法最低检出浓度为2.6μg/L,加标回收率为95.1%~104.8%,RSD为2.4%~4.5%。结论本法操作简单,兼具两种磁场模式的优点,有效扩展了线性范围,准确灵敏,适用于不同浓度级别空气中铅及其化合物的同时测定。展开更多
目的:探讨定量三维能量多普勒超声(three-dimensional power Doppler ultrasonography,3D-PDU)球体模式记录局部胎盘与整个胎盘血管指数的相关性与一致性,为了解胎盘血流灌注提供一种方法。方法:对154例11~14周单胎妊娠胎盘进行3D-PDU检...目的:探讨定量三维能量多普勒超声(three-dimensional power Doppler ultrasonography,3D-PDU)球体模式记录局部胎盘与整个胎盘血管指数的相关性与一致性,为了解胎盘血流灌注提供一种方法。方法:对154例11~14周单胎妊娠胎盘进行3D-PDU检查,应用虚拟器官计算机辅助分析(virtual organ computer aided analysis,VOCAL)球体模式和手动模式分别记录4处球形感兴趣区及整个胎盘血管化指数(vascularization index,VI)、血流指数(flow index,FI)、血管化-血流指数(vascularization flow index,VFI),分析4处球形感兴趣区平均与整个胎盘相应指数的相关性与一致性。结果:球体模式获得局部胎盘(VI:38.60±14.31;FI:29.49±6.17;VFI:12.53±6.34)与手动模式获得整个胎盘(VI:38.93±13.86;FI:31.79±5.49;VFI:12.90±6.50)的血管指数均显著相关[r分别为0.978(P<0.001)、0.677(P<0.001)、0.963(P<0.001)];VI差异无统计学意义,VFI和FI差异有统计学意义(P<0.05)。结论:三维球体血管计算模式可作为评价整个胎盘血流灌注的有效替代。展开更多
文摘The grassland of Qinghai-Tibet Plateau (QTP) and Inner Mongolia Plateau (IMP), accounting for 73.9% of the total grassland area in China, is significant to food and ecological safety. Due to climate change and irrational human activities, grasslands on the two plateaus have severely degraded over recent decades. Understanding the dynamic changes of grassland and its driving forces is necessary to make effective measurements to prevent grassland degradation. Here, we selected the net primary productivity (NPP) as an indicator to quantitatively assess the dynamic variation of grassland and the relative roles of climate change and human activities on QTP and IMP from 2000 to 2016. The results found significant spatial variability of grassland on QTP. 28.3% of the grassland experienced degradation and was mainly distributed in the southern QTP, versus 71.7% of the grassland was restored and mainly distributed in the central and northern QTP. In contrast, grassland on IMP didn’t show significant spatial variability. Most of the grassland on IMP was restored during the study period. Climate change (i.e. increased precipitation) was the dominant factor and could explain 72.8% and 84.4% of the restored grassland in QTP and IMP. Irrational human activities (i.e. overgrazing) were the main driving factors and could explain 72.9% and 100.0% of the degraded grassland on the two plateaus during the study period. Ecological restoration projects were favorable for grassland restoration on the two plateaus, and they contributed to 27.2% and 15.6% of the restored grassland in QTP and IMP, respectively. Therefore, climate changes on IMP were more favorable for grassland restoration, and human activities have a greater impact on the grassland variation on QTP.
文摘Lakes are important ecological water sources in the Bashang Plateau. Its expansion or shrinkage directly affects the ecological security of the plateau and its surrounding areas. In this study, Landsat images from 1984 to 2015 were selected to monitor the area of lakes in the Bashang Plateau and to analyze the spatiotemporal evolution and driving forces of lakes in the Bashang Plateau. The results showed that there were 47 lakes in the Bashang Plateau in 2015, with a total area of 37.63 km2, mainly distributed in the central and western regions of the region. From 1984 to 2015, the lakes in Bashang Plateau showed a shrinking trend. At the same time, there are obvious stage differences in lake changes. During 1984-1996, the number of lakes increased by 99 and the total area increased by 124.43 km2. From 1996 to 2015, the number of lakes decreased by 142, and the total area decreased by 183.96 km2. Before 1996, climate change was the dominant factor. However, the shrinkage of lakes after 1996 is the result of climate change and human activities. Among them, the large-scale planting of water consuming crops such as vegetables is the main human activity mode leading to lake shrinkage. This study will help to understand the expansion and contraction factors of the Bashang Plateau lakes in Hebei province and provide a reference for the future protection and management of the lakes.
文摘目的建立动态三磁场塞曼背景校正石墨炉原子吸收法测定工作场所空气中铅及其化合物的分析方法。方法用微孔滤膜采集空气样品,使用高氯酸—硝酸(1∶9,V∶V)消解,以1%硝酸定容至25 m L,在283.3 nm波长下,使用动态三磁场塞曼背景校正模式进行测定。结果使用动态三磁场模式,同时得到2-磁场和3-磁场模式下的吸光值及校正曲线,在0~800μg/L质量浓度范围内有较好的线性关系,其中0~100μg/L浓度范围采用二磁场模式校正曲线,曲线方程为A=2.76×10^(-3)C+2.08×10^(-2),r=0.9975,特征浓度1.58μg/L;100μg/L^800μg/L浓度范围采用三磁场模式校正曲线,曲线方程A=(4.05×10^(-3)+9.67×10^(-4)C)/(1+6.50×10^(-4)C),r=0.9970,特征浓度4.51μg/L,方法最低检出浓度为2.6μg/L,加标回收率为95.1%~104.8%,RSD为2.4%~4.5%。结论本法操作简单,兼具两种磁场模式的优点,有效扩展了线性范围,准确灵敏,适用于不同浓度级别空气中铅及其化合物的同时测定。
