Spatial patterns of 137Cs inventories and soil erosion from earth-banked terraces in the Yimeng Mountains, China

The Yimeng Mountains is one of China's most susceptible regions to soil erosion. In this region, slopes are composed of granite- or gneiss-derived soils that are commonly cultivated using earth-banked terraces. Based on the 137Cs measurement for nine reference cores, the present study analysed the spatial patterns of 137Cs inventory and soil erosion using 105 sampling points in a seven-level earth-banked terrace system. The mean 137Cs inventory, standard deviation, coefficient of variation, and allowable error for the nine reference cores were 987 Bq m−2, 71 Bq m−2, 7%, and 6%, respectively, values that may reflect the heterogeneity of the initial 137Cs fallout deposit. Within each terrace, the 137Cs inventory generally increases from the rear edge to the front edge, accompanied by a decrease in the erosion rate. This results from planation by tillage and rainfall runoff during the development of the earth-banked terraces. Across the entire seven-level terrace system, 137Cs inventories decrease from the highest terrace downwards, but increase in the lower terraces, whereas erosion rate displays the opposite trend. These trends are the result of the combined effects of the earth-bank segmented hillslope, the limited protection of the earth banks, and rainfall runoff in combination with tillage. The high coefficients of variation of 137Cs inventories for the 21 sampling rows, with a mean value of 44%, demonstrate the combined effects of variations in original microtopography, anthropogenic disturbance, the incohesive soils weathered from underlying granite, and the warm climate. Although earth-banked terraces can reduce soil erosion to some extent, the estimated erosion rates for the study area are still very high.