Study On The Formation Age And Evolution Process Of Nitraria Tangutorum Nebkhas In The Gonghe Basin

Nebkhas is a typical type of dune landform where sand,silt and other mobile debris are blocked by bushes and deposited around bushes without moving with wind and sand flow.The emergence of nebkhas can block the deposition of particulate matter and avoid it becoming a new source of sand.It can also enrich water and nutrients and protect biodiversity,thereby improving the ecological environment in desert areas.Nitraria tangutorum nebkhas is widely distributed in the western Gonghe Basin,but its growth and evolution process is not clear,so we can not make full use of existing vegetation windbreak and sand fixation.In this paper,the western republic basin as the research area,select the study area of different stages of development of 13 nebkhas sampling,7 of them were studied systematically.Through field investigation,sample analysis and other methods,the spatial distribution,morphological characteristics and development types of Acanthopanax senticosus shrub sandpile in western Gonghe Basin were studied.Based on the comparative analysis of OSL dating,grain size,organic carbon and magnetic susceptibility,the formation and evolution process of Nitraria tangutorum nebkhas were discussed,and the response relationship between nebkhas and climatic and hydrological conditions was analyzed,so as to better apply Nitraria tangutorum to prevent desertification.The main conclusions are as follows: 1.The nebkhas in the west of Gonghe Basin show the trend of northwest-southeast,L is between 270-1710 cm,W is between140-540 cm,H is between 60-230 cm,Fc is between 20-80 %.The L,W,H and Fc of sand piles gradually increase in the embryonic stage,reach the maximum in the development stage,and gradually decrease from recession stage to extinction stage.2.Different stages of development in the western Gonghe basin of the bayonet bush nebkhas are relatively young,concentrated between 0.2-0.4 ka,that is,the medieval glacial period;3.The sediment samples of Nitraria tangutorum nebkhas in the west of Gonghe Basin showed bimodal characteristics,indicating that the sediment was subjected to complex force in the process of transport.Among them,the coarser sand is the main one,supplemented by fine sand content,and the sediments of nebkhas are mostly transported near the source.4.The TOC of sandpile profile of Nitraria tangutorum nebkhas in the western part of Gonghe Basin showed a decreasing trend with depth.The reason was that Nitraria tangutorum and other vegetation were grown on the top of sandpile.The litter and roots of vegetation could provide good conditions for the storage of TOC,so that the TOC content at the top of sandpile was the highest.5.The formation of the shrub sand heap in the west of Gonghe Basin is related to the distance between groundwater and sand source.The west side of the study area is close to the Yingdehai Lake,the groundwater level is higher,and the distance from the sand source is closer.The nebkhas is well developed.The east side is farther and farther from the Yingdehai Lake,the groundwater level is also reduced,and the distance from the sand source is also farther and farther.Therefore,the volume of the nebkhas is becoming smaller and smaller.