基于磁化率和^(210)Pb_(ex)的金沙江下游小流域泥沙来源研究  

Fingerprinting Sediment Sources in a Small Catchment in the Lower Jinsha River Basin Using Magnetic Susceptibility and Pb Signatures

作　　者：史忠林[1] 文安邦[1] 严冬春[1] 陈佳村 龙翼[1] 周萍[1] SHI Zhonglin;WEN Anbang;YAN Dongchu;CHEN Jiacun;LONG Yi;ZHOU Ping(Institute of Mountain Hazards and Environment,Chinese Academy of Sciences,Chengdu 610041,China;University of Chinese Aeademy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院、水利部成都山地灾害与环境研究所,成都610041 [2]中国科学院大学,北京100049

出　　处：《地球与环境》2021年第2期125-133,共9页Earth and Environment

基　　金：国家重点基础研究发展计划项目(2015CB452704)。

摘　　要：金沙江下游地区侵蚀泥沙研究基础薄弱,实测资料较少,可靠的泥沙来源信息尤其是一系列国家重点水土保持工程如"长治"工程实施后流域泥沙的主要来源及贡献,对该区未来水土保持和生态环境建设以及不同治理措施效益评价具有重要意义。利用低频磁化率χlf和放射性核素^(210)Pb_(ex)双指纹因子,开展了金沙江下游一"长治"工程治理小流域(元谋县凉山乡小流域)泥沙来源研究。结果表明,坡耕地表土、林地表土和沟谷堆积物三种物源的χlf和^(210)Pb_(ex)平均含量分别为(21.81±9.43)×10^(-8)m^(3)/kg和40.53±9.49 Bq/kg、(24.06±9.61)×10^(-8)m^(3)/kg和119.35±22.81 Bq/kg、(16.60±5.27)×10^(-8)m^(3)/kg和30.62±12.69 Bq/kg。流域出口泥沙的χlf和^(210)Pb_(ex)平均含量分别为(17.69±2.87)×10^(-8)m^(3)/kg和33.63±6.17 Bq/kg。混合模型计算结果表明凉山乡小流域泥沙主要来源于沟谷堆积物,相对贡献率为79.6%;未经治理的陡坡耕地产沙贡献率为19.1%;林地面积占比最大但泥沙贡献极微,仅1.3%。基于χlf和^(210)Pb_(ex)的双指纹泥沙来源判别结果与利用地球化学元素复合指纹分析结果一致。受地质地貌等自然因素主控,沟谷侵蚀是金沙江下游河流泥沙的主要来源;以坡改梯和植被恢复为主的小流域治理工程对坡面侵蚀泥沙减控具有积极作用。该区未来水土保持工作应重点加强流域沟谷治理,降低泥石流等泥沙灾害风险。Reliable sediment source information is important for both soil and water conservation and ecological environment construction,as well as the evaluation of different conservation measures in the lower reaches of Jinsha River,especially where a series of national conservation programmes have been carried out such as the‘State Key Soil and Water Conservation Project in the Upper Yangtze River Basin’. Suspended sediment sources in a heavily managed small catchment,the Liangshan catchment,in the lower Jinsha River basin were differentiated qualitatively by combining magnetic susceptibility χlfand fallout radionuclide^(210)Pb_(ex)signatures. Results showed that the average concentrations of χlf and^(210)Pb_(ex)for the three potential sediment sources were( 21. 81±9. 43) ×10-8 m3/kg and40. 53±9. 49 Bq/kg( cropland topsoil),( 24. 06±9. 61) ×10-8 m3/kg and 119. 35±22. 81 Bq/kg( woodland topsoil),and( 16. 60±5. 27) ×10-8 m3/kg and 30. 62±12. 69 Bq/kg( channel deposits). Mean values of χlfand^(210)Pb_(ex)for sediment samples collected at the catchment outlet were( 17. 69±2. 87) ×10-8 m3/kg and 33. 63±6. 17 Bq/kg,respectively. Source apportionment results indicated that materials originating from incised and actively eroding channels represent the most important source of sediment,which contributed 79. 6% of sediment to the catchment outlet. Sediment contributions from unmanaged steep-slope cultivated land were estimated to be 19. 1%. The woodland area contributed 1. 3% of sediment,although this land use takes the largest proportion in area. This result is consistent with that from geochemical fingerprinting. The findings of this study demonstrate that sediment eroded from channel bank and bed is the main sediment source in the lower Jinsha River basin,which are predominantly controlled by natural factors such as geology and geomorphology. The catchment management practices including terracing and reforestation also have positive effects on the slope erosion control and thus sediment mitigation. Future so

关 键 词：泥沙来源 指纹技术 小流域治理 磁化率 ^(210)Pb_(ex) 金沙江下游 

分 类 号：S157.1[农业科学—土壤学]