Composition And Distribution Of Soluble Salts Of The Loess Soil In The Jingyang Xiushidu Profile Of Shaanxi Province

The study of the soluble salt components of the loess section can not only supplement the paleoclimate characteristics,but also play an active role in the understanding of the engineering mechanical properties of loess and the natural disasters in the loess area.After conducting a field investigation on the Nanyuan of Jiyang,this paper carefully selected the Xiushidu loess section and systematically sampled it.For the first time in this area the water chemistry characteristics of the leachate were analyzed for the eight ions,pH,TDS and other indicators in the loess-paleosol profile leaching solution,using Phreeqc software.The possible mineral phases in the process of loess leaching were analyzed.Combined with particle size analysis and mineral composition analysis,the basic characteristics and distribution of soluble salt components in loess section were studied.The following conclusions were obtained:（1）Pre-experiments show that when 2:1 was chosen as the experimental soil-soil ratio,and 3 days was used as the experimental days,the results of experiment was more ideal.（2）The pH of the sample leaching solution is alkaline.Due to the different content in calcium carbonate,magnesium carbonate,calcium carbonate and sodium bicarbonate,the change trend of pH is divided into two parts:rising zone L₀-L₄ and stable zone S₄-S₉.EC can be divided into four parts:L₀,S₀-S₂,L₃-S₄ and L₅-S₉ in the loess section.Rainfall and human activities have a certain impact on the changes.（3）Due to the defferent content of the eight major ions in the profile,the water chemistry type of the section sample leaching solution can be divided into three types,L₀:Cl·SO₄·HCO₃-Ca·Na type water,S₀-S₂:HCO₃·Ca-Na type water,L₃-S₉:HCO₃·Na-K type water.（4）The cation content of the sample leaching solution were Na⁺,Ca²⁺,Mg²⁺and K⁺from high to low;the anion content were HCO₃^-,SO₄^2-,CO₃^2-and Cl^-from high to low.The types of soluble salt in L₀ are NaHCO₃+CaSO₄;The types of soluble salt in S₀-S₂ are NaHCO₃+CaSO₄+CaCO₃;The types of soluble salt in L₃-S₉ are NaHCO₃+Na₂CO₃+CaSO₄。（5）Possible mineral phase simulation results show that the calcium ions in the leachate were derived from the dissolution of calcite and gypsum.The main source of chloride ions was the dissolution of rock salt,the source of sulfate ion was gypsum dissolution,and the magnesium ion was related to dolomite.There should also be cation exchange in the system.（6）Correlation of main ions in the leaching solution of the profile sample shows that due to the low degree of weathering of various minerals during dry deposition of loess,and the high degree of weathering of various minerals during warm and humid deposition of paleosol.Therefore,compared with paleosol,gypsum minerals,dolomite and calcite in loess may be more.While in paleosol,there were more sodium bicarbonate than loess.（7）The principal component analysis and Q-type cluster analysis showed that Whether it is the loess or the paleosol,the trend from top to bottom has obvious segmentation,the salt content and salt types in each segment is close.The trend of the readily soluble salt in the whole section is not related to the paleosol or loess type.