Spatial distribution and transport characteristics of river and sediment pollen in the middle and lower reaches of the Yellow River
Clarifying the modern process of alluvial pollen is the foundation for reconstructing the ancient environment of the watershed.Although research on the transport of pollen in rivers has started early both domestically and internationally,further research is needed on how pollen is transported and what factors affect it after entering rivers.This paper selects sampling sections for the main stream and tributaries of the middle and lower reaches of the Yellow River,collects river water and sediment samples during the flood season for pollen analysis,and uses methods such as geographic detectors to explore the distribution characteristics and influencing factors of pollen.The results show that:(1)The vegetation composition varies in different watersheds,and there are significant differences in the percentage and concentration of pollen types.The pollen concentration in the main stream of river water is higher than that in the tributaries,while the percentage and concentration of sediment pollen in the main stream are generally lower than those in the tributaries.(2)The concentration of suspended solids is the main factor affecting the concentration of pollen in the Yellow River,and it is particularly prominent outside the Shanxi-Shaanxi Gorge.Furthermore,excessive coarse sand and rapid flow velocity may be the reasons for the high concentration of suspended solids and low concentration of pollen in the main stream of the Shanxi-Shaanxi Gorge.(3)The sediment clay content is the main factor affecting the pollen content of sediment,and the interaction between clay and silt,clay and flow velocity is more prominent.After the Yellow River exited the Shanxi-Shaanxi Gorge,the concentration of sediment pollen and clay particles significantly increased.(4)The changes in pollen concentration in the river water before and after the reservoir are consistent with those in suspended solids,while the changes in sediment pollen concentration are consistent with those in clay particles.Compared to water samples,the decrease in pollen concentration in sediment after the reservoir is more pronounced.(5)There is a good correspondence between river pollen and topsoil pollen,which can better reflect the overall vegetation landscape of the watershed.The results can provide support for paleoenvironmental reconstruction using alluvial deposits or lake sediment pollen injected by rivers.
river pollensediment pollenspatial distributiontransmission mechanismthe middle and lower reaches of the Yellow River
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