Migration characteristics of soil water and salt and their interaction under different groundwater levels

Abstract: Soil salt and water closely related to groundwater depth mainly affect vegetation distribution pattern and community succession of the Yellow River Delta. Thus，it is important to explain the changing process of water and salt in groundwater and soil and their effects on the occurrence of the secondary salinization. This study aimed to understand the response of soil water-salt distribution characteristics to groundwater depth and their interactive effects under saline groundwater conditions. To achieve the objective, a laboratory experiment was carried out in a controllable greenhouse of Shangdong Provincial Key Laboratory of Eco-Environmental Science for Yellow River Delta, Binzhou University, China in 2014. Soils were collected from Yellow River downstream and air-dried. A total of 18 soil columns planted with Tamarix chinensis Lour, a constructive species in the Yellow River Delta were prepared and the soil columns were made of polyvinyl chloride resin. These soil columns were immersed into saline water that simulated groundwater levels of 0.3, 0.6, 0.9, 1.2, 1.5 and 1.8 m. The water-salt parameters (such as relative soil water content, soil salt content and soil solute absolute concentration) of different soil column profiles were measured. The results showed that: 1) Relative soil water content of soil columns was greatly decreased as the level of groundwater increased while soil salt content: soil moisture fluctuated dramatically for treatment of groundwater level 0.9-1.2 m and was stable for groundwater level 0.3-0.6 m; 2) Soil solution absolution concentration increased first and then decreased, and the turning point of soil water and salt content occurred at level of groundwater 1.2 m, under which soil salinity and soil solution absolute concentration of soil profiles were both the highest; 3) The maximum variation of water content, salt content and soil solution absolution concentration occurred for treatments of the level of groundwater 0.9-1.2 m, 0.6 m and 1.5-1.8 m, respectively; 4) As soil depth increased, the relative soil water content also increased, the soil salt content fell first and then rose up to 1.34% at surface layer, while soil solution absolute concentration decreased; From the soil surface down the soil profile, the change range and degree of relative soil water content and soil solution absolute concentration decreased gradually with increasing groundwater level; The groundwater level corresponding to the highest salt content of all soil profiles was 1.2 m; and 5) Soil salt content and relative soil water content had significant negative correlations with level of groundwater at P<0.01 and P<0.05, respectively, and a significant positive correlation (P<0.01) was observed between relative soil water content and soil salt content. Based on changes in soil moisture, salinity and soil solution absolute concentration, the T. chinensis should be planted 20 cm at least of soils, preferably 30-40 cm under saline groundwater conditions. The suitable level of groundwater was between 1.5 and 1.8 m. The results can provide important information for the prevention of soil secondary salinization, and the planting and management of T. chinensis under saline groundwater conditions.