Spatial Evolution Characteristics Of The Yellow River Sediments And The Significance Of Provenance Tracing

As written in�The History of the Han Dynasty�Annals of Rivers and Canals�,�China is home to hundreds of river sources,the most famous rivers are four great rivers,the Yellow River is the crown�,the Yellow River is highly rated as the�Crown of four great rivers�.The control over the Yellow River Basin has been the targeted focus of China along the history.However,the control of the Yellow River has been a headache due to special river condition.The proposal of the�Ecosystem Protection and High-Quality Development of the Yellow River Basin�means that the environmental studies of the Yellow River has been brought up to the national strategic research project.The key to the problem of the Yellow River lies in sediment.The efforts to identify the source of the Yellow River sediments might provide certain theoretical guidance for river siltation,and soil and water conservation in the basin,which in turn drives the high-quality development of the Yellow River Basin.This paper is supported under the NSFC to focus on the sedimentary environment of the Yellow River sediments with reference to a lot of related works.Floodplain sediments from Jiuzhi County,Qinghai in the upper reach of the Yellow River to the estuary in the lower reach are collected at an interval of 50km,and the sediments obtained at Maqu borehole(7m),Liujiaxia borehole(5m)in the upper reach,Liulin-Wubao borehole(7m)in the middle reach and Kaifeng borehole(4m)in the lower reach are observed for the sedimentary environment of the Yellow River.The evolution and source information of the sedimentary environment of the Yellow River sediments are revealed,the hierarchical clustering-based granular end-member model and the end-member hybrid model are constructed,and the transport mode of the Yellow River sediments and the contribution rate of source area sediments are induced,the source analysis system applicable to the Yellow River sediments is proposed,which is expected to provide a theoretical reference for the soil and water conservation and the high-quality development in the Yellow River Basin.This paper leads to the innovative findings below:1.The change of the sediments of the Yellow River in granularity components reflects the difference of geological environmental and the influence of water conservancy project.Based on the analysis of C-M diagram,granulometric facies,granulometric frequency curve and sedimentary discriminant function of the sediments in flood plain and borehole,the sedimentary characteristics of the sediments in the Yellow River are further expounded.The granularity end-element model is established to obtain the dynamic combination information and transport mode of the Yellow River sediments:the far source dust is carried to the river,the coastal desert or the Loess Plateau,the wind sand is carried into the Yellow River,and the coastal erosion products are transported to the sediments by the river for a long distance.It is suggested that the main reason for the obvious changes of hydrodynamic conditions and sediment environment along the Yellow River should be the joint influence of the selective transport of the river,the inflow of tributaries,the change of river geomorphology and human activities.2.Based on the changes along the course of loss of ignition,reddening rate and magnetic susceptibility of sediments in the Yellow River,a systematic clustering analysis method was used to determine the formation conditions and interrelationships of sediments in different river sections.The results show that the loss on ignition,reddening rate and magnetic susceptibility can be used as the basic indicators for the analysis of the source of the Yellow River sediment,which can effectively reflect the changes of the sediment environment of the Yellow River under the interference of human activities;the source of the Yellow River sediments is the erosion along the river,the wind sand into the Yellow River and the sand carried into the Yellow River by tributaries.3.The quartz granules in the sediments of the Yellow River are mainly sub-angular.The sediments flowing through the Loess Plateau and Liujiaxia borehole in the upper reaches develop V-shaped impact crater,underwater polished surface and pockmarks and other composite structures,which indicates that the sediments in this section are related to the effective input of aeolian sand land such as Hedong sand land of Ningxia,Ulanbuhe Desert and Kubuqi Desert.Based on the Euclidean distance between the floodplain and the micro morphology of quartz grains in the borehole sediments,it can be concluded that the mode of wind sand flowing into the Yellow River changes from the near source erosion of the upstream river which does not flow through the Loess Plateau to the tributary which carries the sand into the Yellow River in the middle reaches.4.The mineral association of floodplain and borehole sediments is mainly detrital minerals,successively followed by clay minerals and carbonate minerals,and ferrites only detected at some points.Based on the cluster analysis of mineral content of sediments in different drilling points,it is concluded that due to flood control,residential water use and irrigation,the regular regulation of reservoir drainage and water storage is an important factor that leads to periodic change of mineral content in different depths of drilling holes.According to the comparison between the change of mineral content along the river and the coastal geology and topography,it is inferred that the sediments in Shizuishan-Bayannur section of the Yellow River mostly come from the flowing sand in Ulanbuhe Desert due to the northwest wind,while the sediments in Bayannur-Tuoxian-Sanjiangkou section mostly come from the Kubuqi Desert,the Loess Plateau,the tributaries along the river and the littoral debris into the Yellow River due to the large-scale seasonal rainfall.5.The sediments in the Yellow River are chemically mainly composed of Si O₂ and Al₂O₃,and the situation that the indexes such as Sr,V,Ni,V/Ni and Sr/Ba are applied to identify sedimentary environment is more in line with the actual situation.The contents of Zr elements in the coarsening section of the floodplain sediments increase obviously;the contents of Ca O and Ti are higher near the Qingshui River,and the contents of K₂O and Sr are higher near Ten great Gullies.Therefore,the regional distribution of Sr/Ca and Ti/K values can be used to distinguish the influence of Hedong sand land of Ningxia,tributaries,Kubuqi Desert and Ulanbuhe Desert on the Yellow River sediments.6.According to the discriminant results of sediment sources of the Yellow River,an end-element mixed model is established to determine the randomness of sediment sources of the Yellow River and the quantitative research method of calculating the contribution rate of the source area,and solve the problem of inaccurate information caused by the qualitative conclusions in the traditional evaluation of sediment sources of the Yellow River.Only 52.4%of the sediments in the upper reaches of the river without flowing through the Loess Plateau is carried into the vicinity of Liujiaxia by the Yellow River;the Ningmeng section in the upper reaches is mainly the aeolian sand from Tengger Desert and Ulanbuhe Desert flowing into the Yellow River,and more than 75%of the floodplain sediments is carried into the lower reaches;the two rivers of Zuli and Qingshui running through the Loess Plateau also carry a large amount of sediments into the Yellow River,with the sedimentary contribution rate of 71.9%to the adjacent areas;the sediments in the middle reaches are mainly carried by the Kuye River,Fenhe River,Wuding River and Weihe River;the sediments in the lower reaches are mostly those flowing to the flat area from the upper and middle reaches.At the same time,it is necessary to consider natural factors such as runoff,tributary watershed area,coastal topography,climate and source rock in order to perfect the sediment source analysis model of the Yellow River.In view of the characteristics of the natural environment and social functions of the Yellow River,the targeted measures for soil and water conservation and regional development are proposed,which can guarantee the ecological protection and high-quality development of the Yellow River Basin.