| Exploring the surface characteristics and dust release law of typical grassland lakes in the process of drying up is an important scientific issue in the study of grassland ecosystems in semi-arid areas,and it is also the key to lake management in grassland source areas.In this study,the surface types of typical steppe lakes in semi-arid areas at different stages of drying up were taken as the research object.The spatial distribution of water,salt and particle size along the lake center to natural grassland was analyzed by statistical and geostatistical methods.Four typical surfaces（crust surface,broken crust surface,activated surface and desertification surface）were selected to study the near-surface wind-sand transport law of different drying stages of steppe lakes,and the salt content and particle size characteristics of sand and dust were analyzed.The purpose of this study is to reveal the characteristics of surface salinization desertification and its dust release mechanism during the drying up of typical steppe lakes in semi-arid areas.In order to provide data support and theoretical basis for ecological risk prediction and ecological management of typical grassland dry lakes in semi-arid areas.The main conclusions are as follows:（1）The dry surface of the lake in the study area can be divided into intermittent dry area,permanent dry area and grassland area.Horizontally,the soil water content tends to decrease gradually from the center of the lake to the natural grassland,and the soil salinity and p H are highest in the center of the lake,decrease gradually with the increase of distance from the center of the lake to the lowest at the intermittent-permanent dry junction,and then increase gradually to the lake shore;In vertical distribution,soil water content increases with the increase of soil depth,and the main ions of salinity are Na+,Cl-and SO42-.In the intermittent-dry zone,the water-salt transport action causes the soil surface layer to collect salt,and the salinity decreases with the increase of soil depth.（2）The average particle size parameters of the soils in the study area were 0.56～8.52φ,which belonged to coarse sand to clay soils with poor sortability.The particle size frequency curves show multi-peakedness.According to the cumulative frequency curves,leapfrog particles account for about 10%～90%and creep particles account for about 4%～88%.Under the influence of long-term wind and water external forces,the surface particles gradually become coarser along the lake center toward the lake shore.The dominant particle size of soil particles in the lake core area is 0-63μm,and the particles in the grassland area are mainly>250μm.（3）The fluctuating wind speed of four typical surfaces（crust surface,broken crust surface,activated surface,and desertification surface）in the study area increases or decreases synchronously within 2 m height,and all conform to the normal distribution,and the fluctuation frequency is relatively stable.The fluctuating wind speed increases with the increase in height,and the correlation between fluctuating wind speeds at adjacent heights is significant.With the increase in wind speed,the friction velocity of the crust surface increases,and the roughness decreases.When the wind speed is greater than 11.5 m/s,the friction velocity and roughness of the crust surface are greater than those of the other three surface types.（4）The total horizontal sediment transport flux of the four typical surfaces is broken crust surface>desertification surface>activated surface>crust surface under different wind speeds,and the total horizontal sediment transport flux of the crust surface is linear with the increase of wind speed and height.The relationship between the total horizontal sediment transport flux of the other three surfaces and the increase of wind speed is a power function,and the distribution with height is a piecewise function.The linear model is within10 cm height and the exponential model is within 10～50 cm height.The sediment transport rate decreased with the increase of height.The sediment transport rate of crust surface at 0～10 cm height was 30.73%～63.76%,which decreased with the increase of wind speed.The sediment transport rate of other surface types was 60%～79%at 10 cm height,which changed little with wind speed.（5）The salt dust concentration and horizontal flux increase with the increase of wind speed of the four typical surfaces in the study area.When the wind speed was less than 13.4m/s,the salt dust flux of the broken crust surface was the largest.With the increase in wind speed,the amount of salt dust released by the activated surface and the desertification surface was higher than that of the broken crust.The concentration of salt dust varies in height,but the flux of salt dust decreases with the increase in height.The distribution of salt dust flux on the crust surface with height is a linear function;the surface of the broken crust was an exponential function below the wind speed of 13.4 m/s and a linear function above 13.4 m/s.The activated surface is a linear function and an exponential function at low wind speed and becomes an exponential function with the increase of wind speed.（6）The main ions are Na+,Cl-and SO42-in the salt dust.The concentration of each ion varies with height.The ion flux decreases with the increase of height,and is mainly distributed in the range of 20 cm of the surface,reaching more than 87%.On the whole,the concentration of all ions was activated surface>desertification surface>broken crust surface>crust surface.The particles in salt dust were mainly<63μm,and the content of fine particles increases with the increase of height.With the increase of wind speed,the coarse particles in the height of 0～10 cm increased,and the proportion of fine particles in the height of 10～50 cm increased.On the whole,the particle size parameters of salt dust show that with the increase of height,the average particle sizeΦbecomes larger,the sorting becomes better,the extreme negative bias develops,and the kurtosis becomes sharp and narrow. |
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