Preliminary evaluation on soil erosion of alpine grassland fence project based on 137Cs and 210Pbex trace technique in the Northern Tibet

Studies on the soil erosion rate for aeolian grassland are crucial for accessing the effect of grassland restoration. Sandy land is widely distributed in the alpine grassland areas of Northern Tibet where the conflict between grass and livestock is severe. In order to effectively curb grassland degradation and reduce desertification, a series of protection projects have been implemented in that area. However, due to the lack of continuous observations in the field, the quantitative research on soil erosion process of alpine grassland has been relatively lagging behind, especially the impact of protection projects on soil erosion is difficult to evaluate. We compared soil erosion rates with and without fence protections through ¹³⁷Cs and ²¹⁰Pb_ex trace technique. We also combined soil erosion in sand source areas with vegetation and a near-source climbing dune to illustrate the effect of fence protection. The results showed that: (1) The area of fence protection reduced soil erosion, the soil erosion rates of ¹³⁷Cs and ²¹⁰Pb_ex in fenced protected area were 0.99 t·ha^-1·yr^-1 and -0.12 t·ha^-1·yr^-1, respectively, while those in free grazing areas were 3.68 t·ha^-1·yr^-1 and 0.46 t·ha^-1·yr^-1, respectively. (2) Fence protection significantly improved vegetation coverage, the average NDVI of fenced protected areas increased by 0.027 from 2011 to 2019, with a growth rate of 67.43%. The average NDVI in fenced protected areas in 2019 was 1.34 times that of free grazing areas. (3) After the implementation of the fence protection in the sand source area, the climbing dune had shown a development trend from mobile to semi-fixed dune from the foot of the climbing dune to the middle (about 100m distance). Therefore, our results highlighted that fence protection was the major reason for the mitigation of soil erosion in the alpine grasslands, which were the source of sand, and their climbing dunes. The results can be used as a reference for the evaluation of grassland restoration effectiveness on the Qinghai-Tibet Plateau.

Keywords: Soil erosion; Radionuclides; Fence protection; Alpine grassland; Climbing dune