Climate Change and Soil Erosion in Holocene in Xi'an Area
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National Natural Science Foundation of China(Nos.41930641, 41771215), Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences(No.KLACP-1904)and the State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences (No. SKLLQG2013)

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    Abstract:

    [Objective] This paper is oriented to reveal changes in climate, monsoon and sandstorm activity in Holocene in Xi'an area, to explore impacts of cold dry climate and warm wet climate on loess erosion and to define erosion period of the loess strata.[Method] Field surveys were carried out to investigate how loess and paleosol eroded in Holocene. Of the loess and paleosol, chemical compositions were determined with an X-ray fluorescence analysis instrument, CaCO3 content with the gas volume method, and magnetic susceptibility with a magnetic susceptibility instrument.[Results] Through the field investigation of 13 sample sites points at Bailuyuan of Xian, it is found that the mid-Holocene paleosol, rarely discovered in the loess plateau in the past, can be divided into three layers, including one layers of loess and two layers of paleosol. The loess and paleosol in the entire Holocene profile can be divided into five layers. The Holocene profile in Milucun displayed apparent changes in chemical composition and magnetic susceptibility and its loess and paleosol can also be divided into five layers, of which two paleosol layers are high and three loess layers low in SiO2, Fe2O3, Al2O and K2O, and the five layers exhibit reverse trends in soil CaO. In the early mid-Holocene S02 paleosol layer, Fe2O3 content varied in the range of 56.8~62.4 g·kg-1, and in the lower part of the paleosol it has been enriched up to 8.0 g·kg-1and Al2O3up to 15.0 g·kg-1. The two paleosol layers are high in Rb, Ba, Ni, Sr and V (five trace elements) and the three loess layers are just the opposite, except in Sr. In the Holocene loess profile, CaCO3 varies similarly to CaO in content. The S02 paleosol layer is very low in CaCO3, demonstrating the feature of leaching soil being low in CaCO3. The two paleosol layers are high in low frequency magnetic susceptibility, while the three loess layers are low.[Conclusion] Various environmental indices indicate that in Beiluyuan the Holocene climate change and sandstorm activity can be divided into five stages. In the mid-Holocene, the period between 8 500-6 000 aB.P and 5 000-3 100 aB.P when paleosol was developing witnessed stronger summer monsoon activity, higher precipitation, more humid climate, and weaker sandstorm activity than the period from 10 000-8 500aB.P to 6 000-5 000 aB.P when paleosol was developing in Bailuyuan. During the five climatic stages of Holocene, the five soil layers display an order of paleosol S02> paleosol S01> loess Lx > loess L0 > loess Lt in terms of thermohumidity and a reverse order in terms of intensity of sandstorm activity. The mid-Holocene S02 paleosol developed during 8 500-6 000 aB.P experienced moderate and moderate on the strong side chemical weathering, and enriched Fe2O3 and Al2O3 to some extent, hence the soil could be sorted into a type of soil similar to subtropical yellow brown forest soil, which indicates that the average annual precipitation at that time is about 150 mm more than it is today. Although the interglacial period with weak sandstorm activity is the theoretical erosion period of loess strata, in fact, the soil erosion in the interglacial period was very weak. The Holocene loess erosion happened mainly during the period under a cold dry climate instead of under a thermohumid climate. Between the period of 6 000-5 000 aB.P in the mid-Holocene when the thin-layered loess was developing, the climate became dry and cold, thus leading to degradation of the vegetation and intensification of loess erosion. The loess in most areas of Xi'an got lost through erosion more than it accumulated during this period, and so was the case in most areas of the Loess Plateau, too, which is the main reason for the absence of thin-layered loess in the Holocene from 6 000 to 5 000 years in most areas of Loess Plateau.

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ZHOU Qi, ZHAO Jingbo, SU Min, WANG Xiaoning, MA Yandong, CHU Chunjie. Climate Change and Soil Erosion in Holocene in Xi'an Area[J]. Acta Pedologica Sinica,2021,58(6):1404-1415.

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History
  • Received:February 20,2020
  • Revised:November 10,2020
  • Adopted:January 06,2021
  • Online: January 14,2021
  • Published: November 11,2021