Abstract:

       The middle reach of Heihe River in Gansu Province is faced with serious problem of soil salinization. It is necessary to study the content of salt and the correlation among the soluble ions in salted soils further. Based on the field observation and the GPS technology, the salted soil and the groundwater samples were taken along the Heihe River in Gaotai County, Zhangye District. This study adopted the pit prospecting method. In each pit, the groundwater level was disclosed. Within 5 cm from the surface and when soil particle changed at the vertical profile, the samples were taken. If one single soil layer was more than 50 cm, the samples were taken at 30 cm intervals. After the groundwater reached to the static level, the groundwater samples were taken. The total pits, groundwater samples and the soil samples are 15,15 and 90,respectively. The analysis results of the contents of salt and ions show that the surface soils are intensely salinized, and the primary compound is sulphate, the secondary is chloride. The depth of salt accumulation layer is about 20-30 cm from the surface. In most of layers, the total salt content has strong correlation with sulfate ion, summation of potassium ion and sodium ion, chlorideion and magnesium ion, as well sulfate ion and chloride ion has strong correlation with summation of potassium and sodium ions, whereas on layer of 90-100 cm, each type of correlation attenuated. On the vertical soil profile, the layer with fine particles has higher salt content and the layer with coarse particles has lower salt content. Furthermore, the layers with coarse particles are thicker, the surface salinization is less intense, and the layers with fine particles are thicker, the surface salinization is more intense. 

Key words: middle reach of Heihe River, salt content of soil, soil profile, groundwater