^137Cs tracing dynamics of soil erosion,organic carbon,and total nitrogen in terraced fields and forestland in the Middle Mountains of Nepal  

作　　者：SU Zheng-an XIONG Dong-hong DENG Wei DONG Yi-fan MA Jing PADMA C Poudel GURUNG B Sher 

机构地区：[1]Key Laboratory of Mountain Hazards and Earth Surface Processes,Institute of Mountain Hazards and Environment,Chinese Academy of Sciences,Chengdu 610041,China [2]University of Chinese Academy of Science,Belting 100049,China [3]College of Water Conservancy and Hydropower Engineering,Sichuan Agricultural University,Ya'an 625014,China [4]Central Department of Geography,University Campus,Tribhuvan University,Kirtipur 8212,Nepal

出　　处：《Journal of Mountain Science》2016年第10期1829-1839,共11页山地科学学报（英文）

基　　金：Financial support for this study was provided by the Aid project on Science and Technology for developing countries from Ministry of Science and Technology of China(2013);the National Natural Science Foundation of China(No.41401313)

摘　　要：The Middle Mountains is one of the regions of Nepal most vulnerable to water erosion, where fragile geology, steep topography, anomalous climatic conditions, and intensive human activity have resulted in serious soil erosion and enhanced land degradation. Based on the 137 Cs tracing method, spatial variations in soil erosion, organic carbon, and total nitrogen(TN) in terraced fields lacking field banks and forestland were determined. Soil samples were collected at approximately 5 m and 20 m intervals along terraced field series and forestland transects respectively. Mean 137 Cs inventories of the four soil cores from the reference site was estimated at 574.33 ± 126.22 Bq m-2(1 Bq(i.e., one Becquerel) is equal to 1 disintegration per second(1 dps)). For each terrace, the 137 Cs inventory generally increased fromupper to lower slope positions, accompanied by a decrease in the soil erosion rate. Along the entire terraced toposequence, 137 Cs data showed that abrupt changes in soil erosion rates could occur between the lower part of the upper terrace and the upper part of the immediate terrace within a small distance. This result indicated that tillage erosion is also a dominant erosion type in the sloping farmland of this area. At the same time, we observed a fluctuant decrease in soil erosion rates for the whole terraced toposequence as well as a net deposition at the toe terrace. Although steep terraces(lacking banks and hedgerows) to some extent could act to limit soil sediment accumulation in catchments, soil erosion in the terraced field was determined to be serious. For forestland, with the exception of serious soil erosion that had taken place at the top of slopes due to concentrated flows from a country road situated above the forestland site, spatialvariation in soil erosion was similar to the "standard" water erosion model. Soil organic carbon(SOC) and TN inventories showed similar spatial patterns to the 137 Cs inventory for both toposequences investigated. However, due to the different dominant erosion The Middle Mountains is one of the regions of Nepal most vulnerable to water erosion, where fragile geology, steep topography, anomalous climatic conditions, and intensive human activity have resulted in serious soil erosion and enhanced land degradation. Based on the ^137 Cs tracing method, spatial variations in soil erosion, organic carbon, and total nitrogen（TN） in terraced fields lacking field banks and forestland were determined. Soil samples were collected at approximately 5 m and 20 m intervals along terraced field series and forestland transects respectively. Mean ^137 Cs inventories of the four soil cores from the reference site was estimated at 574.33 ± 126.22 Bq m^-2（1 Bq（i.e., one Becquerel） is equal to 1 disintegration per second（1 dps））. For each terrace, the ^137 Cs inventory generally increased fromupper to lower slope positions, accompanied by a decrease in the soil erosion rate. Along the entire terraced toposequence, ^137 Cs data showed that abrupt changes in soil erosion rates could occur between the lower part of the upper terrace and the upper part of the immediate terrace within a small distance. This result indicated that tillage erosion is also a dominant erosion type in the sloping farmland of this area. At the same time, we observed a fluctuant decrease in soil erosion rates for the whole terraced toposequence as well as a net deposition at the toe terrace. Although steep terraces（lacking banks and hedgerows） to some extent could act to limit soil sediment accumulation in catchments, soil erosion in the terraced field was determined to be serious. For forestland, with the exception of serious soil erosion that had taken place at the top of slopes due to concentrated flows from a country road situated above the forestland site, spatialvariation in soil erosion was similar to the ＂standard＂ water erosion model. Soil organic carbon（SOC） and TN inventories showed similar spatial patterns to the ^137 Cs inventory for both toposequences investigated. However, due

关 键 词：Nepal 137Cs inventory Soil erosion/deposition Soil organic carbon Total nitrogen 

分 类 号：S157.1[农业科学—土壤学]