The Morphology,Sediments Characteristics And Evolution Law Of Vitex Trifolia Nebkhas In The Houtian Sandy Land,Nanchang City

In order to explore the nebkhas developed in subtropical humid regions,this study took the Houtian sandy land on the west side of the Ganjiang River in Nanchang City,Jiangxi Province as the study area,and carried out research on the Vitex trifolia nebkhas developed in the sandy land.Through the process of field investigation,field survey,sample collection,experimental processing and data analysis,this paper analyzes the morphological characteristics,morphological parameters,evolution stages,sediments and spatial distribution patterns of the Vitex trifolia nebkhas in Houtian sandy land.The formation mechanism of the nebkhas in this area and the changes of various characteristics in the process of evolution are discussed preliminarily.This study is not only of great significance to the understanding of the nebkhas developed around rivers and lakes in subtropical humid regions,but provides a theoretical basis for the management of sandstorm environment in Houtian sandy land.In addition,this study compared with the nebkhas developed with different vegetation types in arid-semi-arid regions,the similarities and differences between the nebkhas developed in different regional environments and different vegetation types were analyzed,it is of great value to explore the nebkhas developed in different climatic environments.The research yielded the following insights:(1)In the Houtian sandy land,the shape of the Vitex trifolia nebkhas is mostly shieldshaped,with a large horizontal range,short height and gentle slope.The overall correlation between the morphological parameters shows that,except for the height of the shrub,there is a significant correlation between the other morphological parameters(P<0.01),the characteristics of the coordinated development among the morphological parameters of nebkhas,and the size of the nebkha is mainly affected by the area covered by the shrub.According to the evolution stage,the nebkhas are mainly in the stable stage,accounting for58.82%,36.90% in the decline stage,and only 4.28% in the development stage,the morphological changes during the evolution of sand piles are low cone-shield-irregular shapes.In different evolution stages,the morphological parameters in the developmental stage of nebkha have less significant correlation,the morphological parameters in the stable stage of nebkha have more significant correlation and the correlation is more significant,and the recession stage is in the middle.Due to different wind conditions,sand source abundance and vegetation types,there are certain differences in the morphological characteristics and morphological changes in the evolution process of the nebkhas between the Houtian sandy land and those in the arid-semi-arid regions.(2)The sediments on the surface of the nebkhas are mainly medium sand and the average particle size is 1.52 Φ,the overall sorting of sand particles is poor,and the particle size distribution curve shows a positive skewness and narrow kurtosis distribution.From the bottom of the windward slope to the bottom of the leeward slope,the average particle size of the sediments showed a tendency of finer first and then coarser,reflecting the mechanism of blocking sand of nebkhas.The average particle size of nebkhas surface sediments in each evolution stage showed that the coarsest is the developing stage,the finest is the stable stage,and the middle in the recession stage.Nebkha sediments mainly come from nearby areas and flat sandy land,which are near-source sediments,different from the sources of nebkha sediments in arid-semi-arid areas.But the sedimentary rules of the surface sediments at various slope positions are consistent,all of them reflect the characteristics of wind-breaking and sand-fixing of the nebkhas.(3)The nebkhas generally show a state of aggregated distribution,and the degree of aggregation is most obvious when the distance scale is 14 m,the nebkhas are mostly concentrated in areas with more soil moisture,more nutrients and less human activities,reflecting the environmental heterogeneity of the Houtian sandy land under the double effects of natural environment and human activities.The spatial correlation between nebkhas in different evolution stages is shown as follows: there is no obvious spatial correlation between nebkhas in the developing stage and other stages,and the nebkhas in the stable and recession stages are positively correlated at the medium and small scales.Reflects the characteristics of interdependence among the main nebkhas and exerts their group effect in the Houtian sandy land,which plays an important role in enhancing the ability of nebkha groups to resist wind and sand damage.