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2021, 13 (4) Online: 31 August 2021 Previous issue
  • Progress, problems and prospects of palynology in reconstructing environmental change in inland arid areas of Asia
  • YongTao Zhao,YunFa Miao,Yan Lei,XianYong Cao,MingXing Xiang
  • DOI: 10.3724/SP.J.1226.2021.20049.
  • 2021, Vol.13 (4): 271–291 Abstract ( 133) HTML ( 21) PDF (5371 KB) ( 180 )
  • Studying the climatic and environmental changes on different time scales in inland arid regions of Asia can greatly improve our understanding of climatic influences for the Qinghai-Tibet Plateau in the context of global change. Pollen, as a remnant of seed plants, is sensitive to environmental factors including precipitation, temperature and altitude, and is a classic proxy in environmental reconstruction. In the last two decades, great progress in the application of palynology to inland areas of Asia has highlighted the role of palynology in paleoclimatic and paleoenvironmental research. The main progress is as follows. (1) On the tectonic time scale of the late Cenozoic, the palaeoclimatological sequence has been established on the basis of pollen percentage, concentration and taxon. Pollen data have revealed a continuous enhancement of drought in the inland arid region of Asia, in contrast to evidence acquired based on other proxies. (2) In the late Quaternary, an increase in herbaceous plants further supports the intensification of drought associated with global cooling. In more detail, the palynological record shows a glacial-interglacial pattern consistent with changes in global ice volume. (3) The Holocene pollen record has been established at a high resolution and across a wide range of inland areas. In general, it presents an arid grassland environment in the early Holocene, followed by the development of woody plants in the mid- to late-Holocene climate optimum. This pattern is related to moisture changes in areas dominated by the westerlies. There are also significant regional differences in the pattern and amplitude of vegetation response to the Holocene environment. (4) Modern pollen studies based on vegetation surveys, meteorological data and statistics show that topsoil palynology can better reflect regional vegetation types (e.g., grassland, meadow, desert). Drier climates yield higher pollen contents of drought-tolerant plants such as Chenopodioideae, Ephedra, and Nitriaria, while contents of Artemisia and Poaceae are greater under humid climates. Besides these achievements, problems remain in palynological research: for example, pollen extraction, identification, interpretation, and quantitative reconstruction. In the future, we encourage strengthened interdisciplinary cooperation to improve experimental methods and innovation. Firstly, we should strengthen palynological classification and improve the skill of identification; secondly, laboratory experiments are needed to better constrain pollen transport dynamics in water and air; thirdly, more rigorous mathematical principles will improve the reliability of reconstructions and deepen the knowledge of plant geography; and finally, new areas and methods in palynology should be explored, for example DNA, UV-B and isotopic analysis. It is expected that palynology will continue to develop, and we hope it will continue to play an important role in the study of past climatic and environmental changes.

  • 10Be exposure ages of Quaternary Glaciers in Antarctica
  • WangJing Ni,ZhiGang Zhang,JingXue Guo,XueYuan Tang
  • DOI: 10.3724/SP.J.1226.2021.20043.
  • 2021, Vol.13 (4): 292–298 Abstract ( 43) HTML ( 2) PDF (2909 KB) ( 107 )
  • In situ terrestrial cosmogenic nuclides (TCN) have been widely applied to date the ages of Quaternary glacial deposits in Antarctica and plays an important role in reconstructing the glacial evolution and climate change. It helps to understand the Antarctic ice sheet's evolution process in Quaternary and shed light on the application of Cosmogenic Nuclide exposure dating technique in glacial geomorphology. In this paper, we retrieved 495 10Be age samples in Antarctica from literature published between 2004 and 2020 and recalculated the TCN ages using version 3.0 online calculator of Cosmic-Ray Produced Nuclide Systematics on Earth (CRONUS-Earth). Several conclusions can be drawn from the results: (1) 75% of the exposure ages are younger than 400 ka, and 91% younger than 1,100 ka. Northern Antarctic Peninsula exposure result is visibly younger than the main glaciers area in East Antarctica due to climate change and geological evaluation since the LGM (Last Glacial Maximum). (2) TCN ages are relevant to the samples' relative positions in the Antarctic continent, but a relationship between their ages and elevations is yet to be determined based on the collected data.

  • Ground temperature variation and its response to climate change on the northern Tibetan Plateau
  • GuoNing Wan,MeiXue Yang,XueJia Wang
  • DOI: 10.3724/SP.J.1226.2021.20024.
  • 2021, Vol.13 (4): 299–313 Abstract ( 56) HTML ( 13) PDF (12729 KB) ( 89 )
  • Ground temperature plays a significant role in the interaction between the land surface and atmosphere on the Tibetan Plateau (TP). Under the background of temperature warming, the TP has witnessed an accelerated warming trend in frozen ground temperature, an increasing active layer thickness, and the melting of underground ice. Based on high-resolution ground temperature data observed from 1997 to 2012 on the northern TP, the trend of ground temperature at each observation site and its response to climate change were analyzed. The results showed that while the ground temperature at different soil depths showed a strong warming trend over the observation period, the warming in winter is more significant than that in summer. The warming rate of daily minimum ground temperature was greater than that of daily maximum ground temperature at the TTH and MS3608 sites. During the study period, thawing occurred earlier, whereas freezing happened later, resulting in shortened freezing season and a thinner frozen layer at the BJ site. And a zero-curtain effect develops when the soil begins to thaw or freeze in spring and autumn. From 1997 to 2012, the average summer air temperature and precipitation in summer and winter from six meteorological stations along the Qinghai-Tibet highway also demonstrated an increasing trend, with a more significant temperature increase in winter than in summer. The ground temperature showed an obvious response to air temperature warming, but the trend varied significantly with soil depths due to soil heterogeneity.

  • Application of geodetector in sensitivity analysis of reference crop evapotranspiration spatial changes in Northwest China
  • WenJu Cheng,HaiYang Xi,Sindikubwabo Celestin
  • DOI: 10.3724/SP.J.1226.2021.20038.
  • 2021, Vol.13 (4): 314–325 Abstract ( 48) HTML ( 3) PDF (4642 KB) ( 115 )
  • Reference crop evapotranspiration (ET0) is an important parameter in the research of farmland irrigation management, crop water demand estimation and water balance in scarce data areas, therefore, it is very important to study the factors affecting the spatial variation of ET0. In this paper, the Penman-Monteith formula was used to calculate ET0 which is the dependent variable of elevation (Elev), daily maximum temperature (Tmax), daily minimum temperature (Tmin), daily average temperature (Tmean), wind speed (U2), sunshine duration (SD) and relative humidity (RH). The sensitivity analysis of ET0 was performed using a Geodetector method based on spatial stratified heterogeneity. The applicability of Geodetector in sensitivity analysis of ET0 was verified by comparing it with existing research results. Results show that RH, Tmax, SD, and Tmean are the main factors affecting ET0 in Northwest China, and RH has the best explanatory power for the spatial distribution of ET0. Geodetector has a unique advantage in sensitivity analysis, because it can analyze the synergistic effect of two factors on the change of ET0. The interactive detector of Geodetector revealed that the synergistic effect of RH and Tmean on ET0 is very significant, and can explain 89% of the spatial variation of ET0. This research provides a new method for sensitivity analysis of ET0 changes.

  • Ecophysiological responses to drought stress in Populus euphratica
  • ChunYan Zhao,JianHua Si,Qi Feng,TengFei Yu,Huan Luo,Jie Qin
  • DOI: 10.3724/SP.J.1226.2021.20025.
  • 2021, Vol.13 (4): 326–336 Abstract ( 65) HTML ( 5) PDF (6610 KB) ( 132 )
  • Ecophysiological responses to drought stress of Populus euphratica in Alashan Desert Eco-hydrology Experimental Research Station were investigated. Results show that under mild and moderate drought stress, stomatal length, aperture, area and density is likely to decrease in the early days, but afterwards this is likely to recovery with treatment over the passage of treatment time. Under severe drought stress, these properties appear to decline continuously. However, after 45 days of drought-stress treatment, the decline is not as noticeable as before, indicating that Populus euphratica could possibly reduce water evaporation by shutting down the stoma, leading to an improvement in its water use efficiency with better survival under drought stress conditions. The leaf area first decreases, and then increases under mild and moderate drought stress conditions, with the average values under different degree of stress found to be approximately 129.52, 120.08, 116.63 and 107.28 cm2, respectively. Under moderate stress conditions, the leaf water potential appears to show a continuous decline where the average values under different degree of stress are found to be -1.27, -1.85, -4.29 and -4.80 MPa, respectively. In terms of proline content, the results demonstrate that this factor appears to increase significantly under moderate and severe drought stress conditions. Especially under severe drought stress condition, the content is found to be more than 700 μg/g. Ranging over average values of 14.64 and 15.90 nmol/g under moderate and severe drought stress, respectively, Malondialdehyde content is found to increase quite rapidly under moderate and severe drought stress conditions at first, which then appears to decrease gradually with the treatment over time.

  • The driving force of water resource stress change based on the STIRPAT model: take Zhangye City as a case study
  • Xia Tang,XinYuan Wang,Lei Feng
  • DOI: 10.3724/SP.J.1226.2021.20093.
  • 2021, Vol.13 (4): 337–348 Abstract ( 48) HTML ( 5) PDF (1998 KB) ( 125 )
  • A prominent contradiction between supply and demand of water resources has restricted local development in social and economic aspects of Zhangye City, located in a typical arid region of China. Our study quantified the Water Resource Stress Index (WRSI) from 2003 to 2017 and examined the factors of population, urbanization level, GDP per capita, Engel coefficient, and water consumption per unit of GDP by using the extended stochastic impact by regression on population, affluence and technology (STIRPAT) model to find the key factors that impact WRSI of Zhangye City to relieve the pressure on water resources. The ridge regression method is applied to improve this model to eliminate multicollinearity problems. The WRSI system was developed from the following three aspects: water resources utilization (WR), regional economic development water use (WU), and water environment stress (WE). Results show that the WRSI index has fallen from 0.81 (2003) to 0.17 (2017), with an average annual decreased rate of 9.8%. Moreover, the absolute values of normalized coefficients demonstrate that the Engel coefficient has the largest positive contribution to increase WRSI with an elastic coefficient of 0.2709, followed by water consumption per unit of GDP and population with elastic coefficients of 0.0971 and 0.0387, respectively. In contrast, the urbanization level and GDP per capita can decrease WRSI by -0.2449 and -0.089, respectively. The decline of WRSI was attributed to water-saving society construction which included the improvement of water saving technology and the adjustment of agricultural planting structures. Furthermore, this study demonstrated the feasibility of evaluating the driving forces affecting WRSI by using the STIRPAT model and ridge regression analysis.