黄河三角洲土壤氯离子空间变异特征及其控制因素

为了解黄河三角洲地区土壤盐渍化发生与发展的主要控制因素,通过采集土壤样品及潜水样,运用地统计学等方法,分析样品中优势离子Cl^-含量的空间分布特征及成因。结果表明:① 土壤Cl^-含量与潜水Cl^-质量浓度的空间分布表现出高度的相似性和相关性。② 潜水借助包气带自身的水势梯度或植物蒸腾作用向土壤输送水分,进而控制着土壤Cl^-的空间分布与变异。③ 地形地貌通过对水、气、热的再分配控制着包气带土层中Cl^-的迁移方向和富集区域。水文地质条件是对区域"饱和带-包气带"盐分迁移富集起决定作用的内部因素,而地形地貌条件是起控制作用的外部因素。

Spatial Variability of Soil Chloride Content and Its Driving Factors in the Huanghe River Delta

To understand the main controlling factors of the soil salinity in the Huanghe River Delta, multi-layer soil samples, phreatic water samples and typical vadose column were collected in this study. Spatial distributions of the content of Cl^- were analyzed by using traditional statistics and geostatistical method. Results show that: 1) ranges of the content of Cl^- at the soil depths of 0-20 cm, 30-50 cm and 50-100 cm were 0.08-35.23, 0.04-15.22 and 0.07-11.67 g/kg, respectively. Random variations at these three soil depths were 50.0%, 24.0% and 60.4% respectively. The content of Cl^- at 30-50 cm depth was mainly affected by structural factors or non-human factors (e.g., vegetation, climate and topography). The content of Cl^- at other soil depths was influenced by both random factors (e.g., management practices) and structural factors. The spatial pattern of the content of Cl^- at each soil depth showed a substantial plaque-strip-plaque shape, which indicates the continuity and direction to some extent. It is also noted that the content of Cl^- in soils positively correlated with that in phreatic water. 2) the groundwater level (0.50-2.50 m) was relatively shallow in the study area, while the groundwater level was generally less than 1.0 m in the coastal inshore. Due to the fact that the embedded depth of the groundwater did not change much, the spatial variation of groundwater level was significantly weaker than that of the content of Cl^- in phreatic water. In that case, with respect to the key factor of the content of Clin phreatic water, difference of soil salinity caused by embedded depth of groundwater can be ignored to some extent. Under the condition of little changes in groundwater depth, similar the lithology and structure of the vadose zone, and roughly similar phreatic aquifer permeability, water in the phreatic zone was easy to transport to the vadose zone due to the plant transpiration and the water potential gradient in the unsaturated zone. Therefore, the pattern of the content of Cl^- in phreatic water driven was similar to that of Cl^- in soils; and 3) the average value of the content of Cl^- in surface soils was smallest for the higher fluvial highlands (0.09) and flood land highlands (0.26 g/kg). However, the average value of the content of Cl^- in surface soils was as high as 4.34 g/kg for coastal lowland. Through the redistribution of water, gas and heat, Topography controlled the direction of the migration of Cl^- in the unsaturated zone and enrichment region. As a result, the content of Cl^- in soils varied with the topography. Hydro-geology condition was the internal factor that determines salt migration and enrichment between the groundwater and the vadose zone. In addition, topography was the external factor that plays a key role of controlling in the Huanghe River Delta.