^(137)Cs和^(210)Pb_(ex)双核素示踪“三北”防护林区退耕前后坡地土壤侵蚀变化  

^(137)Cs and ^(210)Pb_(ex) tracing of soil erosions on cultivated and reforested slope lands in Three North-Shelter Forest Region

作　　者：王俊杰 苏正安[1] 周涛 王丽娟 王晓艺 刘翊涵 伍佐 Wang Junjie;Su Zhengan;Zhou Tao;Wang Lijuan;Wang Xiaoyi;Liu Yihan;Wu Zuo(Key Laboratory of Mountain Hazards and Earth Surface Processes,Institute of Mountain Hazards and Environment,Chinese Academy of Sciences,Chengdu 610041,China;University of Chinese Academy of Sciences,Beijing 100049,China;College of Water Conservancy and Hydropower Engineering,Sichuan Agricultural University,Ya’an 625014,China;College of Geography and Resources Science,Sichuan Normal University,Chengdu 610101,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,中国科学院山地灾害与地表过程重点实验室,成都610041 [2]中国科学院大学,北京100049 [3]四川农业大学水利水电学院,雅安625014 [4]四川师范大学地理与资源科学学院,成都610101

出　　处：《农业工程学报》2020年第24期64-72,共9页Transactions of the Chinese Society of Agricultural Engineering

基　　金：水体污染控制与治理科技重大专项(2017ZX07101-001);国家自然科学基金(41401313)联合资助。

摘　　要：为查明"三北"防护林建设前后农耕地和退耕地土壤保持效益变化,该研究利用^(137)Cs和^(210)Pb_(ex)双核素示踪技术,选择了防护林建设较为成功的张家口坝上地区(风力侵蚀区)作为典型区,研究了农耕地以及退耕地土壤^(137)Cs和^(210)Pb_(ex)的剖面变化规律及其示踪的土壤侵蚀变化。结果表明:1)由于耕作的混匀作用,农耕地土壤剖面中^(137)Cs和^(210)Pb_(ex)均呈均匀态分布;退耕地土壤剖面中^(137)Cs和^(210)Pb_(ex)则表现为表层(0~5cm)比活度最高、下层(5~25cm)均相对较低且分布相对均匀的形态,这表明退耕后坡地土壤^(137)Cs和^(210)Pb_(ex)剖面形态均会发生一定变化,退耕驱动土壤^(137)Cs和^(210)Pb_(ex)剖面变化导致运用土壤核素估算侵蚀模型在该区域难以适用;2)基于土壤^(137)Cs和^(210)Pb_(ex)剖面变化规律,利用^(210)Pb_(ex)质量平衡方程,提出了退耕地土壤^(210)Pb_(ex)土壤侵蚀估算模型;3)利用^(137)Cs比例模型估算退耕地土壤侵蚀速率为(27.94±11.92)t/(hm^2·a),农耕地侵蚀速率为(29.11±14.42)t/(hm^2·a),而利用修正后的210Pbex转换模型估算得到"三北"防护林区退耕地造林前平均侵蚀速率为(82.16±14.36)t/(hm^2·a),造林后平均侵蚀速率为(-41.28±33.91)t/(hm^2·a);农耕地造林前平均侵蚀速率为(68.55±22.11)t/(hm^2·a),造林后平均侵蚀速率(-8.52±47.32)t/(hm^2·a)。这表明137Cs示踪技术主要表征了1963年以来该区坡地土壤侵蚀和沉积的平均结果,而^(210)Pb_(ex)示踪技术则可以较好地示踪防护林建成前后的土壤侵蚀变化。此外,研究结果也表明,相比于"三北"防护林建成之前,建成之后该区农耕地和退耕地的土壤侵蚀速率均呈显著下降趋势,且均由前期的风沙侵蚀转变成了风沙沉积。^(210)Pb_(ex) and ^(137)Cs measurements were carried out to trace the variations in soil depth and erosion rates in the cultivated and reforested land,aiming to explore the changes of soil retention due to the construction of the"Three North"shelterbelt program in the north of China.A typical shelterbelt and wind dominant region was selected,particularly on the Bashang Region of Zhangjiakou City,Hebei province,China.The results showed that in the cultivated land,both ^(137)Cs and ^(210)Pb_(ex) in the soil profile were uniformly distributed,due mainly to the mixing effect of tillage.In the reforested land,the ^(137)Cs and ^(210)Pb_(ex) concentrations in the 0-0.05 m soil layers were obviously higher than those in the other depth soil layers.There were roughly uniform concentrations of ^(137)Cs and ^(210)Pb_(ex) from 0.05 m to 0.15 m of the upper 0.15 m soil layer.It infers that the ^(137)Cs and ^(210)Pb_(ex) profile of soil can be changed after reforestation,thereby posing a great challenge on the use of ^(137)Cs and ^(210)Pb_(ex) to estimate the variation in soil erosion rates under the conditions of reforestation.A revised ^(210)Pb_(ex) model of soil erosion in the reforested land was proposed using the ^(210)Pb_(ex) mass balance equation in the temporal change trends of ^(137)Cs and ^(210)Pb_(ex) profiles.In the ^(137)Cs proportional model,the mean soil erosion rates of reforested and cultivated land were 27.94±11.92 t/(hm^(2)·a)and 29.11±14.42 t/(hm^(2)·a).In the revised ^(210)Pb_(ex) conversion model,the soil erosion rates of reforested and cultivated land were 82.16±14.36 t/(hm^(2)·a)and 68.55±22.11 t/(hm^(2)·a)before the construction of Three-North shelter forest,whereas,those were-41.28±33.91 t/(hm^(2)·a)and-8.52±47.32 t/(hm^(2)·a)after the constructed.It indicates that the 137Cs tracing can be used to characterize the average soil erosion rates and deposition rates on the slopes since 1963.Nevertheless,the ^(210)Pb_(ex) tracer technology can be used to trace the variations in soil erosion rate

关 键 词：土壤 侵蚀 模型 ^(210)Pb_(ex) ^(137)Cs 防护林 退耕还林 

分 类 号：S157.1[农业科学—土壤学]