青藏高原是全球独特的地域单元，其脆弱的生态环境具备土壤风蚀发生发展的环境条件和潜在因素，孕育着沙漠化的自然过程和人文过程。相对于中国北方干旱半干旱地区，青藏高原地区土壤风蚀与沙漠化的研究比较薄弱。青藏高原土壤风蚀的研究有助于认清青藏高原土壤风蚀与沙漠化发生过程、空间格局与演变规律，为土壤风蚀防治、生态安全屏障建设提供科学依据。土壤风蚀的定量评价是制定荒漠化防治、布设风沙防治工程的重要依据。但目前青藏高原实测土壤风蚀速率资料非常少，严重制约该区土壤风蚀定量评价，¹³⁷Cs示踪法是研究土壤风蚀的可靠方法。本文在青藏高原完成了222个¹³⁷Cs采样点的样品采集，通过样品测试分析、Walling背景值模型纬度分区细分为1°分区以及¹³⁷Cs转换模型的应用，在以下方面取得进展：

   （1）青藏高原¹³⁷Cs背景值分布

通过¹³⁷Cs层样分析确定了12个¹³⁷Cs背景值，青藏高原实测¹³⁷Cs背景值和纬度呈负相关；和经度、降雨量呈正相关。利用细分为1°分区的Walling背景值模型模拟值和实测值的函数关系，建立了青藏高原¹³⁷Cs背景值分布图。模型评估与对比分析表明模拟值与实测值大致吻合，且优于Walling¹³⁷Cs背景值模型。¹³⁷Cs背景值介于432-1403 Bq m^-2，平均值为784 Bq m^-2。青藏高原背景值整体呈现由东北向西南递减的空间分布特征。

（2）青藏高原各典型区、不同地表覆被类型¹³⁷Cs面积活度空间分布特征

青藏高原¹³⁷Cs面积活度介于低于仪器探测下限至1549 Bq m^-2之间，平均值为411 Bq m^-2。青藏高原¹³⁷Cs面积活度呈现自东向西递减，从江河湖源向南、向北递减的趋势。各典型区¹³⁷Cs平均面积活度大小顺序为江河湖源（893 Bq m^-2）>南亚通道（526 Bq m^-2）>北部盆地（342 Bq m^-2）>藏北高原（224 Bq m^-2）>雅江宽谷（198 Bq m^-2）；不同地表覆被类型¹³⁷Cs平均面积活度大小顺序为高寒草甸（761 Bq m^-2）>高寒草原（451 Bq m^-2）>农田（391 Bq m^-2）>荒漠草原（258 Bq m^-2）>荒漠（253 Bq m^-2）>灌丛（175 Bq m^-2）>戈壁（96 Bq m^-2）。¹³⁷Cs含量与年均降雨量、植被覆盖度、纬度呈显著正相关，与风速呈显著负相关。农田¹³⁷Cs含量很高的原因是由于灌溉带来了富含¹³⁷Cs泥沙沉积物以及农田防护林网内的沙尘沉降。

（3）基于¹³⁷Cs示踪法的青藏高原土壤风蚀速率

青藏高原土壤风蚀与风积并存，91%为风蚀样点，9%分为风积样点。风蚀样点的风蚀速率介于13-4462 t km^-2 a^-1之间，平均值为1362 t km^-2 a^-1，总体上呈现从东到西递增的趋势。风积样点的风积速率介于51-2954 t km^-2 a^-1之间，平均值为612 t km^-2 a^-1，主要发生在北部盆地和江河湖源。从不同典型区来看，北部盆地、江河湖源、南亚通道、藏北高原、雅江宽谷平均土壤风蚀速率分别为2585、210、471、1187、1670 t km^-2 a^-1。北部盆地平均土壤风蚀速率约为江河湖源的十倍、藏北高原的两倍、南亚通道的五倍。风积样点主要在江河湖源，其土壤风积速率为366 t km^-2 a^-1。从不同土地覆被类型来看，戈壁、农田、荒漠、荒漠草原、灌丛、高寒草原、高寒草甸样点的平均土壤风蚀速率分别3009、2615、2448、1560、888、554、302 t km^-2 a^-1。戈壁的平均土壤风蚀速率最大，农田次之，高寒草甸最小；戈壁的平均土壤风蚀速率约为高寒草甸的10倍。风积样点主要出现在高寒草原、高寒草甸，其风积速率分别为336、433 t km^-2 a^-1。

以¹³⁷Cs示踪法的非农田样点土壤风蚀速率校正RWEQ模型结果，校正后的RWEQ模型青藏高原土壤风蚀速率介于361-5908 t km^-2 a^-1之间，平均值为980 t km^-2 a^-1，基于¹³⁷Cs示踪法的非农田样点的平均土壤风蚀速率为1045 t km^-2 a^-1，二者较为一致。

The Qinghai-Tibet Plateau is a unique regional unit in the world, and its fragile ecological environment has the environmental conditions and potential factors for the occurrence and development of soil wind erosion, which breeds the natural process and human process of desertification. Compared with the arid and semi-arid areas in northern China, the study of soil wind erosion and desertification in the Qinghai-Tibet Plateau is relatively weak. The study of soil wind erosion on the Qinghai-Tibet Plateau is helpful to understand the occurrence process, spatial pattern and evolution law of soil wind erosion and desertification on the Qinghai-Tibet Plateau, and provide scientific basis for soil wind erosion prevention and ecological security barrier construction. Quantitative evaluation of soil wind erosion is an important basis for the establishment of desertification control and sand control projects. However, the measured soil erosion rate data in the Qinghai-Tibet Plateau are very few, which seriously restricts the quantitative evaluation of soil erosion in this region. ¹³⁷Cs tracer method is a reliable method to study soil wind erosion. This paper completed sample collection of 222 ¹³⁷Cs sampling points on the Qinghai-Tibet Plateau. Through sample test analysis, subdivision of latitude partition of Walling background value model into 1° partition, and application of ¹³⁷Cs conversion model, progress has been made in the following aspects:

Distribution of ¹³⁷Cs background values over the Qinghai-Tibet Plateau

Twelve ¹³⁷Cs background values were determined through the analysis of ¹³⁷Cs samples. The measured ¹³⁷Cs background values were negatively correlated with latitude and positively correlated with longitude and rainfall over the Qinghai-Tibet Plateau. Based on the functional relationship between the simulated values and the measured values of the Walling background value model modified to 1° partition, the ¹³⁷Cs background value distribution map of the Tibetan Plateau was established. Model evaluation and comparative analysis show that the simulated values are roughly consistent with the measured values, and better than the Walling ¹³⁷Cs background value model. The simulated background values of ¹³⁷Cs range from 432-1403 Bq m^-2, with an average of 784 Bq m^-2. The simulated background values of the Tibetan Plateau showed a decreasing spatial distribution from northeast to southwest.

Spatial distribution characteristics of areal activity of ¹³⁷Cs in different typical areas and land cover types on the Tibetan Plateau

The area activity of ¹³⁷Cs over the Tibetan Plateau ranges from lower than the lower limit to 1549 Bq m^-2, with an average value of 411 Bq m^-2. The area activity of ¹³⁷Cs on the Qinghai-Tibet Plateau decreased from east to west, and from the source of rivers and lakes to south and north. The order of area activity of ¹³⁷Cs in each typical area was river and lake source (893 Bq m^-2) > South Asian Channel (526 Bq m^-2) > Northern Basin (342 Bq m^-2) > Northern Tibet Plateau (224 Bq m^-2) > Yajiang Wide Valley (198 Bq m^-2). The different land cover types were Alpine meadow (761 Bq m^-2) > Alpine steppe (451 Bq m^-2) > Farmland (391 Bq m^-2) > Desert steppe (258 Bq m^-2) > Desert (253 Bq m^-2) > Scrub (175 Bq m^-2) > Gobi (96 Bq m^-2). The content of ¹³⁷Cs was significantly positively correlated with the average annual rainfall, vegetation coverage and latitude, and negatively correlated with wind speed. The reason for the high content of ¹³⁷Cs in farmland is due to the ¹³⁷Cs-rich sediment brought by irrigation and the dust deposition in the farmland protective forest network.

(3) Soil wind erosion intensity over the Qinghai-Tibet Plateau based on ¹³⁷Cs tracer technology

Wind erosion and deposition coexist in the Qinghai-Tibet Plateau soil, 91% are wind erosion sample points, 9% are wind deposition sample points. The soil wind erosion rate in the Qinghai-Tibet Plateau ranges from 13-4462 t km^-2a^-1, with an average value of 1362 t km^-2a^-1, showing an increasing trend from east to west. The aeolian velocity ranges from 51 to 2954 t km^-2a^-1, with an average of 612 t km^-2a^-1, mainly in the northern basin and the source of rivers and lakes. From the perspective of different typical areas, the average soil wind erosion rates of the northern basin, the source of rivers and lakes, the South Asia Channel, the northern Tibet Plateau and the Yajiang Wide Valley are 2585, 210, 471, 1187 and 1670 t km^-2a^-1, respectively. The average soil wind erosion rate in the northern basin is about ten times that of the river and lake source, twice that of the northern Tibetan Plateau, and five times that of the South Asian channel. The average soil wind erosion rates of Gobi, farmland, desert, desert steppe, shrub, alpine steppe and alpine meadow were 3009, 2615, 2448, 1560, 888, 554 and 302 t km^-2a^-1, respectively. The average soil wind erosion rate of Gobi was the highest, followed by farmland and the lowest in alpine meadow. The average soil wind erosion rate of the Gobi is about 10 times that of the alpine meadow. The aeolian samples were mainly found in alpine steppe and alpine meadow, and the aeolian deposition rates were 336 t km^-2a^-1 and 433 t km^-2a^-1, respectively.

The results of the RWEQ model were corrected using the ¹³⁷Cs tracer method for non-farmland soil wind erosion rate. The corrected RWEQ model for the Tibetan Plateau soil wind erosion rate ranged from 361-5901 t km^-2a^-1, with an average value of 980 t km^-2a^-1. The average soil wind erosion rate of non-farmland samples based on ¹³⁷Cs tracer method is 1045 t km^-2a^-1, and the two are consistent.