Isotope Distribution And Migration Of Weathering Crust (Soil) In East Dianchi Lake

It’s always a difficult problem to research the weathering crust (soil) erosion in a quantitative approach for along time. Now the technique of radioisotope tracer is a new method to research the weathering crust (soil) erosion. This is a effective way to research the basin. The method is not only high reliability, but also saving time and labor. In this paper, the dating principle about 137Cs is applied, and combining with the test data about the content of organic carbon, total nitrogen and total phosphorus. In this study, the weathering crust (soil) was in Baoxianghe small drainage area and Songmao reservoir area where the east bank of Dianchi basin to be researched. This article draws the following results:1. The content of the radioactive isotope 137Cs is related to the types of the weathering crust (soil). The average content of 137Cs in different soil types about Songmao reservoir is in increasing sequence:abandoned land 6.73 bq/m2< woodland 83.38 bq/m2< flood land 290.40 bq/m2< grassland 332.99 bq/m2. The least average content of 137Cs is abandoned land, the most one is grassland. The average content of 137Cs in different soil types about Baoxianghe small drainage area is in increasing sequence:shrub land 70.46 bq/m2< woodland 77.86bq/m2< grassland 84.17 bq/m2. The least average content of 137Cs is shrub land, the most one is grassland.The content of organic carbon (TOC) total nitrogen (TN) and total phosphorus (TP) also bear on the weathering crust (soil) type. The rate of soil erosion affects the loss of the TOC, TN and TP.Songmao reservoir: TOC:abandoned land 5.44%< grassland 8.955%< flood land 13.73%< woodland 14.71%; TN:abandoned land 2.03%< woodland 2.07%< grassland 2.13%< flood land 3.16%: TP:woodland 0.85%< abandoned land 0.87%< flood land 1.42%< grassland 1.58%。Baoxianghe small drainage area: TOC:shrub land 8.48%< woodland 9.8%< grassland 12.1%; TN:woodland 0.88%< shrub land 1.16%< grassland 1.48%; TP:woodland 0.26%< shrub land 0.33%< grassland 0.37%.The lowest content of TOC and TN is abandoned land in Songmao reservoir. The highest one is grassland and the lowest one is woodland about TP. The lowest content of TOC and TN is shrub land; and the highest one is grassland in Baoxianghe small drainage area. The highest one is grassland and the lowest one is woodland about TP.2. The content of the radioactive isotope 137Cs related to the depth of the weathering crust (soil):with the increasing of depth, the content of 137Cs decreased constantly.At the same time, the soil erosion all occurred in Songmao reservoir area and Baoxianghe small drainage area. The reference of 137Cs is 906bq/m2 in Dianchi basin. The content of 137Cs which are kind of soil were less than the reference whatever Songmao reservoir area or Baoxianghe small drainage area. They all have undergone the soil erosion.3. The rate of weathering crust (soil) erosion bears on soil types. The formula "Ah=Aref(1-eλh)" was used to count the rate of soil erosion in each small drainage areas. The average rate of soil erosion were 19.892 cm/a and 19.962 cm/a in Songmao reservoir area and Baoxianghe small drainage area. The soil erosion is more serious in Baoxianghe small drainage area.The rate of soil erosion in Songmao reservoir area is in increasing sequence: grassland 19.787 cm/a< flood land 19.836 cm/a< woodland 19.948 cm/a< abandoned land 19.997 cm/a. The rate of soil erosion in Baoxianghe small drainage area is in increasing sequence:grassland 19.958 cm/a< woodland 19.961 cm/a< shrub land 19.966 cm/a.4. It was positively related that the rate of soil erosion with the content of organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in weathering crust (soil). The faster the rate of soil erosion is, the less the content of TOC, TN and TP.