| At present, tracing technique using environmental radionuclides has been widely applied in the research of soil erosion and environmental evolution; it has been the major component of the research of catchments and environmental systems. In particular, the quantitative research of high-resolution nuclear technology has been the key means to overcome the limitations of the method of traditional soil erosion research, to broaden the means to study soil erosion, to deeply study the rule of soil erosion.From the point of view of nuclear tracing method, technique and application, the paper research the comparison between in-situ measurement of environmental radionuclides and traditional laboratory measurement, discuss the uncertainty of environmental radionuclides measurement by the proficiency test and intercomprision of environmental radionuclides measurement, study the soil erosion in Tibet Plateau of China using tracing technique of environmental radionuclides. From this dissertation, the following conclusion can be drawn:1. The in-situ measurement of environmental radionuclides using ISOCS portableγspectrometry system is an effective tracing technique that can rapidly and accurately assess the soil erosion and spatial redistribution of soil. It can resolve the problem that difficult to determine the reference site of environmental radionuclides in wind erosion area. The distribution of environmental radionuclides in soil profile and the detection area of detector are the important factors that influence the activity of environmental radionuclides by in-situ measurement. The optimum measurement condition that can achieve the accurate results is the detector is 1m distance above the ground, the angle of collimator is 90°, the detection area of detector is 2.91m2. Using the in-situ measurement technique to tracing the wind erosion, the wind erosion rate calculated by conversion model in Inner-mongolia Xilinhot grassland is 0.8 t·ha-1·yr-1.2. The results of proficiency test and international intercomparision indicated: 137Cs is man-made radionuclide, the results measured byγspectrometry have no influence of background of lead shield, and the combine uncertainty is low, short measurement time of can achieve the accuracy expected. 210Pb is natural radionuclide existed in nature, it require higher measurement condition usingγspectrometry. We should take the source of uncertainty from soil matrix, background of lead shield, the shape and material of sample container into consideration; make the accurate non-source efficiency calibration. It needs long measurement time for good precision expected. Achieving the accuracy and precision is the key issue that applies the environmental radionuclides to trace the soil erosion.3. The activity of radionuclides of soil reference materials sampling from natural matrix is very low, the uncertainty of measurement is large. It is important for making the reference material to select the sampling site with high activity radionuclides and no erosion. We select Shouyang in loess plateau as the sampling site, to collect soil sample to be the matrix of reference material. The results of measurement indicate: the activity of 137Cs is 4.23Bq/kg; the activity of 210Pb is 80.43Bq/kg. The standard deviation of 137Cs and 210Pb activity is 0.22Bq/kg, 2.10 Bq/kg. The results using one-way ANOVA analysis indicate that the activity of 137Cs and 210Pbex between PT samples of 3 groups have no distinct differences, the homogeneity is good. The PT samples can be provided to make the proper quality control measurement and assessment of measurement procedure for the environmental radionuclides analysis laboratory, also can be provided to do the proficiency and intercomparision in environmental radionuclides measurement.4. Using the tracing technique of environmental radionuclides, the distribution pattern of soil erosion and the relationship with human being activity from west to east in Qing-Tibet Plateau were assessed. The results indicated that: (1) From west to east region in Qing-Tibet plateau, the background value of 137Cs is in the range from 452.7 Bq/m2 to 1714.1Bq/m2, the distribution characteristic is the background value of 137Cs is increasing from west to east region with the elevation decreasing. 210Pb background value from west to east region in Qing-Tibet plateau is in the range from 2612 Bq/m2 to 7377Bq/m2. The distribution characteristic of 210Pb is same as 137Cs. The regional distribution of 137Cs and 210Pbex shows significant correlation, the equation of correlation is 210Pbex =3.6×137Cs +1466.2,R2=0.9519;(2) In Tuotuo River of Changjiang headstream, the migration pattern of 137Cs and 210Pbex in typical slope has no difference. The distribution characteristic of 137Cs is that the topsoil in the soil profile is eroded, 137Cs activity in topsoil is low, and the distribution depth is shallow. It is typical soil profile with wind erosion. The distribution of 210Pbex reaches in the 60cm depth in soil profile. The maximum of 210Pbex is in the 0-2mm of surface soil. Tuotuo River of Changjiang headstream is a typical wind erosion area, soil erosion rate is 2.5t·ha-1·yr-1. This area is one of the important sources of dust storms of Tibet plateau; (3)In Maduo county of Yellow River headstream region, 137Cs significantly deposit in the upper slope, and decrease in middle slope and lower slope. The inventory of 210Pbex from upper slope to lower slope showed increasing trend, it is caused under water erosion along the downward slope of the migration. From the surface to the bottom in Maduo soil profile, 210Pbex showed exponential decreasing trend. In the soil profile, there is a blank area of 210Pbex in the 80-100mm; the depth of the blank area is same as the depth of 137Cs. This is caused by heavy rain in the extreme events from the 1950s to 1960s in the 20th century. The last 40 years, animal husbandry activities in Maduo have more disturbances to soil than the impact of the natural factors. The soil deposition rate is 0.3 t·ha-1·yr-1;(4)The results showed that: in Dongqinggou of Maqin, in the 0-20mm of surface soil is enriched layer of 137Cs, in the 20-40 mm is low activity. Because of more rainfall in the region, 137Cs deposite to the surface soil with the rainfall, the thin layer of soil and less physical clay content, 137Cs concentrate in the soil surface, no leaching downward migration. The distribution characteristic of 210Pbex is same as 137Cs. Soil deposition rate is 4.2 t·ha-1·yr-1;In Jun pasture, 137Cs enrich in the 0-20mm of surface soil, decrease in the 20-40 mm depth. The distribution characteristic of 210Pbex is same as 137Cs. Dongqinggou and Jun pasture of Maqin is the core area of Sanjiangyuan ecological protection reserve, the alpine meadow and shrub vegetation have better effectiveness of soil and water conservation, soil erosion is not serious;(5)In the Jungongzhen of Maqin, the result of serious water erosion site shows that 137Cs enrich in the 8-10cm of soil profile, from surface soil to 10cm, 137Cs shows exponential increasing trend with depth of soil profile, from 10cm to 16cm, 137Cs shows exponential decreasing trend with depth of soil profile. There is blank area of 137Cs in the 16-22cm of soil profile. There are blank area of 210Pbex in the 6-8cm, 14-16cm and 20-24cm of soil profile. The blank area of 137Cs and 210Pbex was caused by heavy rain in the extreme events in the region from 50 to 60 years in the 20th century. The water erosion caused by vegetation destroy in Jungongzhen of Maqin is serious; the soil erosion rate is 8t·ha-1·yr-1;(6) In the past 40 years, in Sanjiangyuan region of Tibet Plateau, human activity and climate events have accelerated the occurrence and development of soil erosion. |
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