近100年喀斯特槽谷区洼地沉积速率与流域产沙强度

首次尝试通过沉积物定年反演喀斯特洼地流域单元近100年尺度的侵蚀产沙历史,这有助于认识人类活动对喀斯特石漠化演化过程的影响。以喀斯特槽谷区典型洼地—常家洼洼地为研究对象,应用137Cs、210Pbex定年法分析了近100年的流域产沙强度特征。结果表明:(1)洼地平均沉积速率为1.00cm/a(1917—1963年)和0.25 cm/a(1963—2017年),流域的平均产沙模数为609t/(km^2·a)(1917—1963年)和152t/(km^2·a)(1963—2017年);(2)1917—1963年期间流域产沙强度远高于1963年以后,这与该地区民国至新中国建国初期强烈的人类活动有密切关系,尤其是上世纪50年代末大规模伐木;(3)1963年以来产沙强度明显减小,这是由于此前发生过较强侵蚀导致土壤变少,局部基岩出露,加之此间植被恢复、人类扰动强度降低和水土保持工程实施;(4)常家洼流域产沙强度高于西南其他喀斯特地区,与流域岩性和人为扰动有关。喀斯特石漠化并非仅是近50年人类活动的结果,也与近100年乃至更长时间尺度的人类活动有关。

Deposition Rate of Karst Depression and Sediment Yield Intensity of the Watershed in Karst Trough-Valley Area in the Past 100 Years

This was the first attempt to investigate the sediment yields of karst environment at the time scale of 100 a, and expected to improve our understanding of the evolution karst rocky desertification impacted by human activity. Taking Changjiawa depression and its watershed in Karst trough-valley area as the research object, the ¹³⁷Cs and ²¹⁰Pb_ex techniques were applied to calculate sediment yield intensity over the past 100 a. The results indicated that:(1) The average sediment deposition rate in the depression was 1.00 cm/a (1917-1963) and 0.25 cm/a (1963-2017), the average specific sediment yield (SSY) in the basin was 609 t/(km²·a) (1917-1963) and 152 t/(km²·a) (1963-2017); (2) The high values during 1917-1963 were related to the intense human activities in the region from the Republic of China to the early period of New China, especially the large-scale deforestation in the 1950s; (3) The sharp decreased values of 1963-2017 were due to the fact that the previous erosion had led to less soil and exposed local bedrock, combined with the vegetation recovery, the decrease of human activity intensity, and conservation measurements; (4) The intensity of sediment yield in Changjiawa basin was larger than that in other karst areas in southwest China, which was mainly related to lithology and human disturbance. Karst rocky desertification was not only the result of human disturbances in the last 50 years, but also related to human activities with nearly 100 years and even longer.