| Soil erosion is the main cause of deterioration of ecological environment and decline of land productivity,and it is the most harmful environmental problem.The quantitative research on soil erosion is of great significance to strengthening the construction of ecological civilization in China.The radionuclide tracer method can quickly analyze the spatial characteristics of long-term soil erosion and sedimentation on a slope and even in a watershed by measuring the difference in the distribution of nuclide content in the soil profile without changing the original topography.Compared with traditional methods?field survey method,runoff plot method,hydrology method,erosion needle method,model estimation method and remote sensing monitoring method?,the radionuclide tracer method has the advantages of simple operation,high precision of analysis and quantification,and rapid measurement.The superiority of low cost.This paper takes Yizhe Watershed in the northern part of Panlong District of Kunming as the research object,collects soil samples on the basis of field investigation,conducts indoor measurement and analysis,and uses 137Cs and 210Pbex dual-nuclear composite tracer technology to estimate the soil erosion rate.Combined with the analysis of soil macroelements,the effects of soil erosion on soil nutrients were discussed and the following conclusions were drawn:?1?This paper selects a hillside slope top?102°45'47''E,25°14'25''N?in the western part of the study area,and samples the plot as background value,where there is no disturbance and high vegetation coverage.The flat grassland has an area of 15 m2with a slope of less than 2°for grid sampling;in the range of 0.25 m2,12 background value samples are selected.The background value of 137Cs in this region was determined to be 644.95 Bq/m2,and the background value of 210Pbex was 21207.94Bq/m2.?2?The two types of nuclide content have different depth distribution and spatial distribution characteristics in different land types.The relationship between 137Cs content in the soil of farmland:corn field>cabbage field>green bean land,but the corn field is sedimentary profile,its 137Cs content is also greater than the background value of 137Cs;the relationship between 137Cs content in non-agricultural soil:primary mixed woodland>Grassland>Secondary forest land.The relationship between the content distribution of 210Pbex in the soil of agricultural land and non-agricultural land is consistent with 137Cs.In addition,there was a significant positive correlation between137Cs and 210Pbex in the soil profile at P<0.01.It indicates that the 210Pbex tracer method is applicable in the study area;therefore,in this study area,the 137Cs tracer method and the 210Pbex tracer method can be mutually corrected and compounded to trace soil erosion.?3?Select two non-agricultural soil profiles,such as C1-3 sampling points in grassland and L1-1 sampling points in native mixed forests,and compare the depth distribution of 210Pbex with the distribution of organic matter,total nitrogen,total phosphorus and total potassium.Analysis shows that 210Pbex is consistent with organic matter and total nitrogen in the soil profile of grassland,and the depth distribution of the three is the same,that is,the deeper the soil profile,the less its own content.In the soil profile of native mixed forest,210Pbex is roughly consistent with the trend of organic matter depth distribution.At the same time,from the correlation analysis,it was found that there was a significant positive correlation between 210Pbex and organic matter and total nitrogen content in the soil profile of the study area at P<0.01.Obviously,the soil organic matter and total nitrogen content in the vertical section of the soil have similar depth characteristics of nuclides(137Cs,210Pbex),that is,the undisturbed ground,which is exponentially decreasing from the surface layer of the soil.?4?In this study,the soil erosion rates obtained by the 137Cs method and the 210Pbexx method were combined to obtain the annual average soil erosion rate and the annual average soil loss thickness of different land types.Among them,the grassland soil erosion rate is 303.006 t/km2/a,the soil loss thickness is 0.225 mm/a;the Chinese cabbage soil erosion rate is 328.715 t/km2/a,and the soil loss thickness is 0.245 mm/a;The rate is 514.249 t/km2/a,the soil loss thickness is 0.420 mm/a;the corn field soil deposition rate is 87.560 t/km2/a;the native mixed forest erosion rate is 74.283 t/km2/a,and the soil loss thickness is 0.060 mm./a;The secondary forest erosion rate is 545.127t/km2/a,and the soil loss thickness is 0.380 mm/a.Overall,the vegetable erosion rate was 421.4482 t/km2/a and the soil loss was 0.222 mm/a.The non-agricultural erosion rate is 307.472 t/km2/a,and the soil loss thickness is 0.333 mm/a.According to the grading standards of soil erosion intensity,secondary forest land and green bean land are mildly eroded,and primary mixed forest land,grassland and pakchoi land are slightly eroded.?5?Find the loss of nutrient elements?TP,TN,SOM?in the study area:the amount of total phosphorus loss in the cabbage field is 0.39 t/km2/a,and the total nitrogen loss is 0.87 t/km2/a.It is 17.62 t/km2/a;in the green beans,the total phosphorus loss is 1.31t/km2/a,the total nitrogen loss is 2.31 t/km2/a,and the organic matter loss is 69.32t/km2/a;the original mixed wood In the woodland,the total phosphorus loss is 0.07t/km2/a,the total nitrogen loss is 0.22 t/km2/a,the organic matter loss is 8.18 t/km2/a,and the secondary forest land,the total phosphorus loss is 0.96 t/km2/a,total nitrogen loss is 2.76 t/km2/a,organic matter loss is 51.59 t/km2/a;grassland,total phosphorus loss is 1.01 t/km2/a,and total nitrogen loss is 1.97 t/km2/a The loss of organic matter is52.21 t/km2/a. |
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