SHI Zhonglin1, WEN Anbang1, YAN Dongchun1, CHEN Jiacun1, 2, LONG Yi1, ZHOU Ping1
(1. Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041;
2. University of Chinese Academy of Sciences, Beijing 100049)
Abstract: 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 and quantitatively by combining magnetic susceptibility χlf and fallout radionuclide 210Pbex signatures. Results showed that the average concentrations of χlf and 210Pbex for the three potential sediment sources were (21.81 ± 9.43) ×10-8 m3/kg and 40.53 ± 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 χlf and 210Pbex 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 soil and water conservation strategies in this area may direct particular attention to the incised and eroding channels to reduce the risks of sediment disaster such as debris flow.
Key words: sediment source; fingerprinting technique; catchment management; magnetic susceptibility; 210Pbex; lower Jinsha River
EARTH AND ENVIRONMENT Vol.49, No.2, Tot No.340, 2021, Page 125-133
