Climatic and anthropogenic impacts on soil formation in the semiarid loess tablelands in the middle reaches of the Yellow River, China

Research into human interactions in past global changes at a landscape scale offers a common unit for integrating diverse evidence and allows the changes to be traced through time. Holocene pedogenic change and climatic and anthropogenic factors on a loess tableland in the semi-arid region of the middle reaches of the Yellow River drainage basin were investigated. Several Holocene loess-soil profiles were sampled and analysed. The results show that on the gentle loess ground with a surface gradient changing from 3°30′ to ca. 1°, natural sheet erosion and redeposition occurred in responding to climatic amelioration and, especially, to increased precipitation in the early Holocene. There was no obvious sheet erosion and redeposition recorded during the formation of Ustic Luvisols in the mid-Holocene Climatic Optimum. When the pre-historical people of the Taosi Culture occupied the loess tableland and cleared land for settlement and arable cultivation between 4400 and 3900 a B.P., a global event of rapid climatic change (4200-3800 a B.P.) hit the area. Both climatic instability and human disturbance has resulted in strong overland flows causing intensive sheet erosion on the upper part of the slope, redeposition and episodic flooding on the lower part of the slope and bottomland. The climatic instability, human disturbance, erosion and redeposition have resulted in a pedogenic regression over the tableland. On the ground outside the settlement, Ustic Luvisol formation was interrupted temporarily. Dust accumulation and pedogenic modification to it resumed soon when the settlement was deserted at ca. 3900 a B.P. On the ground within the extent of the settlement, the mid-Holocene Ustic Luvisol has been truncated permanently because of human occupation. In the late Holocene from 3100 onward, erosion and redeposition accelerated clearly due to the increasingly intensified arable cultivation, widespread and dense settlement and climatic decline. The construction of settlement, road system, terraced fields from the pre-historical time has redirected the runoff and resulted in gully erosion which has the loess tableland dissected.