Exploring the stemflow dynamics and driving factors at both inter- and intra-event scales in a typical subtropical deciduous forest     

Haixia Zhang  Congsheng Fu  Aimin Liao  Can Zhang  Jiufu Liu  Niu Wang  Bin He 《水文研究》2021,35(3):e14091

Numerous efforts have been made to understand stemflow dynamics under different types of vegetation at the inter-event scale, but few studies have explored the stemflow characteristics and corresponding influencing factors at the intra-event scale. An in-depth investigation of the inter- and intra-event dynamics of stemflow is important for understanding the ecohydrological processes in forest ecosystems. In this study, stemflow volume (F_V), stemflow funnelling ratio (F_R), and stemflow ratio (F_%) from Quercus acutissima and Broussonetia papyrifera trees were measured at both inter- and intra-event scales in a subtropical deciduous forest, and the driving factors, including tree species and meteorological factors were further explored. Specifically, the F_V, F_R and F_% of Q. acutissima (52.3 L, 47.2, 9.6%) were lower than those of B. papyrifera (85.1 L, 91.2, 12.4%). The effect of tree species on F_V and F_% was more obvious under low intensity rainfall types. At the inter-event scale, F_V had a strong positive linear correlation with rainfall amount (G_P) and event duration (D_E) for both tree species, whereas F_R and F_% had a positive logarithmic correlation with G_P and D_E only under high-intensity, short-duration rainfall type. F_R and F_% were mainly affected by wind speed and the maximum 30-min rainfall intensity under low-intensity, long-duration rainfall type. At the intra-event scale, for both tree species, the mean lag time between the start of rainfall and stemflow was the shortest under high-intensity, short-duration rainfall type, while the mean duration and amount of stemflow after rain cessation were the greatest under high-amount, long-duration rainfall type. The relationship between stemflow intensity and rainfall intensity at the 5-min interval scale also depended greatly on rainfall type. These findings can help clarify stemflow dynamics and driving factors at both inter- and intra-event scales, and also provide abundant data and parameters for ecohydrological simulations in subtropical forests.  相似文献   

How soil texture,channel shape and cross-sectional area affect moisture dynamics and water loss in irrigation channels     

Zhifan Mu  Tianxiao Li  Dong Liu  Qiang Fu  Renjie Hou  Qinglin Li  Yi Ji  Song Cui  Mo Li 《水文研究》2021,35(4):e14155

To enhance the utilization efficiency of farmland irrigation water and reduce the leakage of water conveyance channels, the leakage process of channels was simulated dynamically. The simulated results were compared with data measured in laboratory experiments, and the performance of the model was evaluated. The results indicated that the simulated values of the model were consistent with the observation values, and the R² values varied between 0.91 and 0.99. In addition, based on the laboratory experiments, a water supply system (Mariotte bottles) and soil box were built using plexiglass. Three influencing factors, namely, the channel form, soil texture and channel cross-sectional area, were varied to observe and calculate the resulting cumulative infiltration amount, infiltration rate and wetting front migration distance. HYDRUS-3D software was used to solve the three-dimensional soil water movement equation under different initial conditions. The results demonstrated that the U-shaped channel was more effective than the trapezoidal channel in increasing the utilization efficiency of the water resources. A U-shaped channel with a small channel cross-sectional area should be adopted and the soil particle size should be prioritized in the construction of water conveyance channels for farmlands. The simulation results were in agreement with the observed results, which indicates that HYDRUS-3D is a reliable tool that can accurately simulate the soil moisture movement in water conveyance channels. The research results can provide a reference for the design and operation of farmland irrigation systems.  相似文献   

Orbital control on cyclical organic matter accumulation in Early Silurian Longmaxi Formation shales     

Siding Jin  Hucheng Deng  Xing Zhu  Yan Liu  Sibing Liu  Meiyan Fu 《地学前缘(英文版)》2020,(2):533-545

High resolution(939 samples)total organic carbon content(TOC)analyses were conducted on the Shuanghe Section of^152.6 m in the Changning area,Sichuan Basin.The sampling section was divided into two units considering the distinct-different deposit environment and sediments accumulation rate.The lower part(Unit 1)and the peer part(Unit 2)with high resolution sample spacing(0.08–0.4 m)enables the identification of the precession cycle in two sedimentary sequences with distinct different sedimentary accumulation rate.MTM Power spectral analyses on untuned TOC series reveals significant peaks exceeding above the 95%confidence level and shows that both Unit 1 and Unit 2 have recorded Milankovitch cycles of 405 kyr long eccentricity,short eccentricity,obliquity and precession.The floating astronomical time scale(ATS)was constructed on the Shuanghe Section in the Early Silurian(~439.673–444.681 Ma),and which was calibrated by 405 kyr long eccentricity cycles.The total duration of the Wufeng and Longmaxi shales is 5.01 Myr.The floating ATS used for estimating the duration of the graptolite zones and each stage in the study interval.Finally,we postulated two models that could verify the linkage between orbital cycle and organic accumulation.To make sure whether productivity or preservation is the main factor that under long eccentricity control,the phase correlation between the obtained filtered signal and the theoretical orbital solution should be made clear in the further research.  相似文献   

The cumulative characteristics of PAEs in PM2.5 in Changji,Northwest China     

Yuyan Liu  Caiye Ji  Bo Fu  Yongxin Yu  Haofeng Liu  Yaxing Shen 《自然地理学》2020,41(4):332-342

ABSTRACT

This paper discusses characteristics of the seasonal variation in phthalate acid esters (PAEs) in the PM_2.5 in the city of Changji, which is located an arid area of Xinjiang Province, northwest China. Samples were collected using a Laoying 2030 median discharge intelligent total suspended particulate (TSP) sampler and analyzed by a Shimadzu GC-2010 gas chromatograph. The results showed that PAEs in PM_2.5 were mainly composed of phthalic acid dibutyl phthalate (DBP) and phthalic acid (2-)ethyl hexyl ester (DEHP). DBP and DEHP are the most commonly used plasticizers, accounting for the majority of plasticizers used, and have large environmental emissions. Compared with the proportions of TSPs, proportions of DBP and DEHP in the PM_2.5 were lower, while the proportions of DMP and DEP were higher. A correlation exists between the distribution of PAEs and the particle size and concentration of atmospheric particulates. Seasonal variations in DBP and DEHP were the same, with lowest concentrations in the summer. Although seasonal variation in DMP was not the same as those of DBP and DEHP, the general trend was similar. Seasonal variation in DEP was different from those of other PAEs. This pattern is related to PAE characteristics and seasonal variations in their sources.  相似文献   

Progress in Danube Loess and Paleoenvironment Study     

Xuechao Wu  Qingzhen Hao  B Marković Slobodan  Yu Fu  Namira  Yang Song  Zhengtang Guo 《地球科学进展》2020,35(4):363-377

Danube loess, located at the westernmost part of the widespread Eurasian loess belt, is one of the most well-preserved aeolian dust deposits in Europe with the basal age dating back over 1 Ma. Owing to its unique location and formation processes, Danube loess plays an important role in understanding the linkage of climate changes in different climate regimes over Eurasian continent and paleoclimatic changes in middle-high northern latitudes. Major research advances of the Danube loess, including compositions, provenance, chronology, stratigraphy and paleoenvironment changes were systematically reviewed and the focuses of future research were suggested. To better understand loess provenance, the compositions of sediments in all the potential source areas should be investigated, and methodological study of provenance indicators and application of multi-proxies approaches need to be carried out. Chronologically and stratigraphically, feldspar luminescence dating and tephrochronology methods should be widely used, and the establishment of a uniform stratigraphic framework and correlation scheme should be constrained by precise chronology. In terms of the paleoenvironment, it is necessary to conduct high-resolution multi-proxies reconstruction of paleoenviroment for the entire loess-paleosol sequence, extending from the last interglacial period (130 ka to present) to interval of last 1 Ma. The future progress in Danube loess is crucial to improving the study of continental paleoclimate comparison and paleoclimate dynamics over the Eurasian loess region.  相似文献   

生态地理学概念界定及其经典案例分析     

傅声雷  傅伯杰 《地理科学》2019,39(1):70-79

对生态地理学的概念进行了详细讨论和辨析,并将它与相近学科如生物地理学、生态地理区划、宏生态学等进行了比较分析,界定了生态地理学的概念。研究认为：生态地理学是生态学和地理学的交叉学科,是研究生态系统各组分关系和生态过程的地理空间分布格局或/和时间演变规律及其与地理环境耦合机制的学科。生态地理学的目的是揭示不同环境梯度下或不同时间尺度上生态系统各组分关系和生态过程的普适性规律及其成因。同时,结合国内外野外实验平台介绍,在全球变化等研究领域列举了经典案例进行分析：① 全球不同气候带森林凋落物分解和碳汇功能的研究;② 中国不同陆地生态系统碳通量和碳汇功能研究;③ 中国东北样带和南北样带陆地生态系统的脆弱性与适应性研究;④ 中国北方草地样带尺度的生态系统生态学研究。主要目的是在辨析生态地理学概念的基础上指出未来发展方向,推动生态地理学的发展。  相似文献   

青岛近海物理-生物地球化学过程及其生态响应     

韦钦胜  王保栋  姚庆祯  于志刚  傅明珠  孙俊川  许博超  谢琳萍  辛明 《海洋学报(英文版)》2019,38(2):11-23

近些年来，夏季黄海浒苔大规模暴发，并在青岛近岸海域大面积聚集，引起了广泛的关注。本文基于在夏季和冬季所获得的多学科调查资料，重点研究了青岛近海的水文-生物地球化学过程及其生态影响，阐明了该海域物理-化学-生物等多参数之间的耦合响应。研究显示，夏季黄海冷水团的边界可扩展至青岛近岸海域，并在局部涌升至上层水体，形成沿岸上升流；该上升流可对上层营养盐产生一定的补充，进而促进浮游植物的繁殖，并于底层海域对应形成溶解氧（DO）和pH的低值。夏季青岛近海的上升流可能还有利于随南风漂移至此的浒苔的生长，并在一定程度上引起浒苔的局地旺发；同时，夏季该海域特定的锋面系统对浒苔聚集的影响也不容忽视。冬季黄海暖流在苏北浅滩外侧向山东半岛南部海域延伸，扩展至青岛近海的暖水舌与近岸低温水之间的锋面特征明显，而且在向岸暖水与近岸冷水间还对应形成了明显的营养盐和叶绿素（Chl-a）锋面。该项研究从多学科交叉的视角，增进了对青岛近海物理、化学和生物过程之间耦合关系的认识。  相似文献   

经济地理学制度理论的发展与建构的重要方向     

傅沂  赵子奇 《热带地理》2019,39(5):711-720

在中国制度差异显著与目前区域发展不平衡不充分的现实下,经济地理学与制度相结合的研究显得尤为必要。通过系统地梳理经济地理学与制度的关系发现,经济地理学与制度在历史上存在先分离后融合的情况,并且目前经济地理学与制度研究结合态势不容乐观,制度研究在本体论、方法论、时间维度、空间尺度、研究方法等方面仍然存在不足。通过文献梳理与理论分析,认为经济地理学的制度理论应基于演化经济地理学进行建构,并提出了建构的方向：1）以系统论、层级观为指导,注重构建制度的层级结构;2）以反还原论为基础,寻求方法论的突破;3）借助演化的思想与路径依赖理论,强调时间在制度系统中的作用;4）加强对各空间尺度的制度研究;5）注重工具方法的借鉴与创新。  相似文献   

Human-induced changes in recent sedimentation rates in Bohai Bay,China: Implications for coastal development     

Fu Wang  Lizhu Tian  Xingyu Jiang  William Marshall  Hong Wang 《中国科学:地球科学(英文版)》2018,61(10):1510-1522

In many countries, coastal planners strive to balance the demands between civil, commercial strategy and environmental conversation interests for future development, particularly given the sea level rise in the 21 st century. Achieving a sustainable balance is often a dilemma, especially in low-lying coastal areas where dams in inland river basin are trapping significant amounts of fluvial sediments. We recently investigated the shore of Bohai Bay in northern China where there has been a severe increase in sea level following a program of large-scale coastal reclamation and infrastructure development over the last five decades. To investigate this trend, we obtained sediment cores from near-shore in Bohai Bay, which were dated by ~(137)Cs and ~(210)Pb radionuclides to determine the sedimentation rates for the last 50 years. The average sedimentation rates of Bohai Bay exceeded 10 mm yr~(-1) before 1963, which was much higher than the rate of local sea-level rise. However, our results showed an overall decreasing sedimentation rate after 1963, which was not able to compensate for the increasing relative sea-level rise in that period. In addition, our results revealed that erosion occurred after the 1980 s in the shallow sea area of Bohai Bay. We suggest that this situation places the Bohai Bay coast at a greater risk of inundation and erosion within the next few decades than previously thought, especially in the large new reclamation area. This study may be a case study for many other shallow sea areas of the muddy coast if the sea level continues to rise rapidly and the sediment delivered by rivers continues to decrease.  相似文献   

Precise Location of Earthquakes at the Eastern Boundaries of the Sichuan-Yunnan Rhombic Block     

Fu Ying  Hu Bin  Long Feng  Wang Shiyuan 《中国地震研究》2018,32(4):470-481

Based on the seismic station data sets from Sichuan and Yunnan provinces, we employed a multi-step seismic location method (Hypo2000 + Velest + HypoDD) to precisely locate the 7,787 earthquakes that occurred during 2010-2015 along the eastern boundaries of the Sichuan-Yunnan rhombic block, namely from southern Dawu to the Qiaojia segment. The final results show that location precision is greatly advanced and epicenter distribution exhibits good consistency with the linear distribution of the seismic faults. Earthquake distribution is quite intensive at the intersection region in the southern segment of the Xianshuihe fault, the Anninghe fault zone, the Xiaojinhe fault zone and the Daliangshan fault zone to the east. The depth profile of seismicity shows a clear stepwise activity along the active seismic fault zones. The profile crossing the faults of the Xianshuihe, Anninghe, and Daliangshan presents a complex interaction among faults near the multiple faults intersection region, Shimian, where the earthquakes are obviously divided into two groups in depth. Earthquakes are very rare at the depth of 15km-20km, which is consistent with the region of the plastic rheology between 14km-19km calculated by Zhu Ailan et al.,(2005).  相似文献