Variation in soil total salt and base ions content of tidal-flat reclamation with different years

Abstract: China has an extensive coastline and a large area of intertidal zone, which is one of the important reserved land resources. Jiangsu province has the most abundant resources of intertidal land in China, accounting for 1/4 of the total intertidal land in China. However, salinization of the low beaches along the North of Jiangsu province is one of the main obstacles that restrict the development and utilization of intertidal land. Therefore, it is great significance to find out the current status of the saline alkali and the composition of the salt base ions in the reclamation area. The tidal flats and reclaimed area in the eastern of Dafeng city was chosen as the study area of this work. The study area was divided into five zones according to historical maps and interpretation results of remote sensing. The areas that had been reclaimed for 90 years , 60 years, 30 years and 10 years were designated as zone V, zone Ⅳ, zone Ⅲ, and zone Ⅱ, respectively. The tidal flat was zone I. The total area of the five zones is about 1600 km2, with a length of 56 km in north-south direction and a width of 19 to 38 km in latitudinal direction. 241 samples (0~20 cm) were collected from the surface of the five zones, 60 of which were from the tidal flat sediments. Sample sites were chosen uniformly from the five zones, and any zone has no less than 40 samples. The samples included farmland soil, fish farm sediment, tidal flat sediment and wasteland soil. We adopt quantity statistics, correlation analysis, factor analysis and other methods to understand the salinity of surface soil, the change rule and influencing factors of their salt base ions in coastal reclamation area of Jiangsu for the recent 100 years. The research ascertained the soil salinity, the content change and correlation of Cl-, SO42-, HCO3-, Na+, K+, Ca2+ and Mg2+, salinization characteristics and soil physical and chemical properties on desalination, indicating that, with increase of reclamation duration, the content of soil salinity and base ion reduced. The average soil salinity in the reclamation area was lower than 1 g/kg in 1960s, meaning that the desalination process was almost finished and the major salinization changed from type chloride into type sulfate. With the processing of desalination, the correlation between base ions and combination features changed dramatically. The main control factors, such as Cl- and Na+, at the beginning were replaced with SO42-, Ca2 + by the late period of reclamation. During the reclamation process, the variation of soil physicochemical properties has influenc on the changes of inorganic salt and salt base ions. The desalination was accelerated with the increase of soil organic matter and silt proportion, as well as the decease of sand and clay grains. The lands with different types of utilization have different desalination speed. Farm land and fish pond, which need fertilization, cultivation and irrigation, have higher speed of the desalination process. In the reclamation process, the salt base ions keep a close relationship with the soil pH, and the variation is a driving factor to change the soil pH value. Soil conductivity is related with salt content and salt base ions, so that the soil salinity can be estimated by measuring the soil conductivity of the coastal areas.