Determination of soil redistribution-soil quality relationship and gully development using 137Cs- and 210Pbex techniques in West China

Determining a cause-effect relationship between soil quality and soil erosion is the key issue for selecting effective soil conservation measures. Understanding of past gully development is difficult in the areas without historical records of soil erosion and land use. We assumed that fallout radionuclides might have potentials for solve these two issues. Accordingly, our research work since Jakarta Meeting in October 2003, mainly focuses on: 1) Determination of the reference inventories of fallout 137Cs and 210Pb in study watersheds; 2) Assessment of spatial variations in soil quality affected by soil erosion on steep hill slope catchment; 3) Reconstruction of gully development using 137Cs and 210Pb dating and GPS survey. Our study areas are located Fangzhuang in Yanhe River Basin and Xichang in the Upper Yangtze River Basin. So far, we have completed the measurements of 400 soil samples collected, several papers were published in J. Soil and Water Conservation, and one paper was published in SSSAJ May 2004, and one book on gully erosion under global change was published in March 2004. Gully erosion is the major contributor to the overall sediment delivered to both the Yellow and Yangtze Rivers in the west China. Few studies have been conducted on the long-term impacts of the land use change on gully initiation and gully development. The target areas of our research are the dry-valleys located in the upper Yangtze River Basin, SW-China. Our objectives are: a) to obtain the environmental information on gully patterns and their development at different spatial and temporal scale in the upper Yangtze River Basin, b) to reconstruct the historical record of gully development and land use change over the past 200 years, and c) to quantify the processes and the effectiveness of land use structures on spatial patterns of gullies. The first investigations were carried out in the Anning Warm-Dry Valley of southern Sichuan in the territory of Xichang. Three gully systems were investigated in details). The size (length, average depth and width) and the volume of the gully system were measured in the field with RTK-GPS. 137Cs and unsupported 210Pb dating were used to distinguish the chronology of sediment profiles within the gully systems. Local culture and history records were analyzed, senior experts and farmers were interviewed for a detailed reconstruction of land use history. The temporal patterns of gully development processes at study gully catchments could be subdivided into five time periods. Gullies initiation occurred during 1920-1930, and maximum increase of gully development in the period from 1950 to 1970. Rapid decrease of gully development closely corresponded to increase in vegetation cover and reduction of intensive grazing intensity in the study area. A detailed analysis of land use impacts on gully development is under process