末次间冰期以来黄河中游黄土高原沟谷侵蚀-堆积过程初探

Processes of Gully Erosion and Accumulation in the Central Loess Plateau of China Since the Last Interglacial

以陕西洛川北汉寨小流域为基础 ,建立末次间冰期以来黄河中游黄土高原的沟谷侵蚀 -堆积模式 ,并定量计算该流域不同时期侵蚀模数或堆积速率 ,初步恢复了末次间冰期以来黄土高原中部地区的沟谷侵蚀 -堆积过程。计算结果表明 ,末次间冰期以来 ,黄土高原中部地区的自然侵蚀作用可能在逐渐加剧。侵蚀 -堆积是黄土区沟谷发育的基本过程 ,并与气候变化密切相关。侵蚀期相当于湿润期 ,也就是降雨量大的时期 ;沉积黄土层的时期沟谷发育大大减缓甚至停止 ,并且在原来的谷底、谷坡上还可堆积黄土。

A model was proposed for illustrating gully erosion accumulation processes since the last interglacial. According to this model, the erosion modules and accumulation rates of several erosion and/or accumulation stages for a typical small watershed in the central Loess Plateau of China were quantitatively calculated. Our calculations show that the erosion modules in the selected small watershed have values of 2 126 t/km 2·a during the marine isotope stage 5 (MIS5, 127~73 ka BP) and 972 t/km 2·a during MIS3 (62~26 ka BP), respectively, which are much less than modern erosion module with a value of about 5 000 t/km 2·a in the studied area. The increase of modern erosion module seems to suggest that loess erosion in the central Loess Plateau of China tends to be accelerated presently. Furthermore, gully erosion mainly occurred in the warm and humid interglacial periods, being dominant contributions to the total erosion. During the cold and dry glacial periods, gully development became evidently slowed down or was suspended, and loess deposits accumulated on the gully slope. Our results also demonstrate that gully evolution in the Chinese Loess Plateau is closely linked to paleoclimatic variations, and further indicate that abundant rainfall in the region of the plateau may give rise to occurrence of sediment hazards in the lower Huanghe River.