Sedimentary Characteristics Of Soil Particles,Carbon And Nitrogen In Check Dam In Typical Erosion Areas Of The Loess Plateau

As a unique engineering measure of the Loess Plateau,the checkdam plays an important role in soil and water conservation and comprehensive management.However,the horizontal and profile distribution of soil particles,carbon?C?and nitrogen?N?in check dam remain largely unclear.To address these problems,we selected four check dams in the Liudaogou watershed of northern wind-water erosion crisscross region and Zhifanggou watershed of the southern water erosion region on the Loess Plateau.We analyzed the holistic distribution,horizontal and profile distribution characteristics of soil particle composition?PSD?,organic carbon?OC?and total nitrogen?TN?in check dams under different erosion types and research scales,and established the relationship of redistribution of OC,TN and PSD in check dam.Our objectives were to provide a scientific basis for the accurate assessment of the C and N source and sink changes of check dam and its response to soil erosion,and to provide a theoretical basis for the evaluation of ecological effects and agricultural production of check dams.The major conclusions were as follows:?1?The soil particle composition of Zhifanggou dam was dominated by silt,with a mean content of 60.10%,Liudaogou dam was dominated by sand,with a mean content of 50.11%.The horizontal distribution of soil particles were not affected by soil depth in the same site,but was affected by sampling sites.The clay and silt content of different soil depths in Zhifanggou dam1 is higher than that of Liudaogou dam1,while the sand content is significantly lower than that of Liudaogou dam1.The profile distribution of soil clay and silt showed that Zhifanggou dam1>Liudaogou dam1,Zhifanggou dam2>Liudaogou dam2,on the contrary,soil sand showed that Zhifanggou dam1>Liudaogou dam1,Zhifanggou dam2<Liudaogou dam2 in different positions.?2?The soil water-stable aggregates in Zhifanggou dam1 and Liudaogou dam1were dominated by 0.25-0.053 mm aggregates,which accounted for 60%-70%of the total soil mass.The proportions of>0.25 mm and 0.25-0.053 mm aggregates in Liudaogou dam1 were significantly higher than those in Zhifanggou dam1,the proportion of<0.053 mm aggregates was lower than Zhifanggou.In the entire profile?0-200 cm?,the average proportions of>0.25 mm and 0.25-0.053 mm aggregates in Liudaogou dam1 were 65.64%and 7.3%higher compared to that of Zhifanggou dam1,respectively,while the average proportion of<0.053 mm aggregates was 35.46%lower than that of Zhifanggou dam1.Furthermore,the proportion of each aggregate fraction were not affected by soil depth in the same site.?3?From dam-tail to dam-head,the profile distribution of soil moisture and nitrate?NO₃^-?varied with sampling site,showed that Zhifanggou dam1>Liudaogou dam1,Zhifanggou dam2>Liudaogou dam2,while ammonium?NH₄⁺?showed that Zhifanggou dam1<Liudaogou dam1,Zhifanggou dam2<Liudaogou dam2 at different depths.?4?The distribution of soil OC and N in the horizontal and vertical directions were significantly affected by soil depth and site.The soil OC and N contents decreased with soil depth in Zhifanggou dam1 and Liudaogou dam1.Moreover,the OC and N were basically higher in Zhifanggou dam1 than Liudaogou dam1 at all soil depths.?5?The distribution of OC and N associated with aggregates of Zhifanggou dam1and Liudaogou dam1 were the highest in>0.25 mm aggregates and the lowest in 0.25-0.053 mm aggregates.Contents of OC and N associated with aggregates were significantly affected by sites and soil depths.Except for some soil depths,the OC and N contents in aggregates decreased with soil depth,and the aggregates associated OC and N of Zhifanggou dam1 were significantly higher than those of Liudaogou dam1 at all soil depths.There was a significant positive correlation between OC and N in bulk soils and in three aggregate fractions in two sites,and the soil OC and N contents mainly depended on the 0.25-0.053 mm aggregates associated OC and N.These results indicated that there were significant differences between two types of soil erosion in the distribution characteristics of PSD,aggregates,soil moisture,mineral N,soil OC and TN in bulk soils and aggregates in the check dam.