Evaluating the spatial heterogeneity of soil loss tolerance and its effects

Soil loss tolerance (T value) is the ultimate criterion to determine the necessity of erosion control 14 measures and ecological restoration strategy. However, the validity of this criterion in subtropical karst regions is 15 strongly disputed. In this study, T value is computed based on soil formation rate by using a digital distribution map 16 of carbonate rock assemblage types. Results indicated spatial heterogeneity and diversity in such values; moreover, 17 a minimum of three criteria should be considered instead of only one criterion when investigating the carbonate 18 areas of South China given that the “one region, one T value” concept may not apply to this region. T value is 19 proportionate to the amount of argillaceous material in formations that determine surface soil thickness in 20 homogenous carbonate rock areas; such values are 20 and 50 t/(km2·a) in carbonate rock intercalated with clastic 21 rock areas and 100t/(km2·a) in carbonate/clastic rock alternation areas. These three areas are each extremely, 22 severely, and moderately sensitive to soil erosion. This erosion is extreme in karst rocky desertification (KRD) land 23 and reflects the degree of erosion risk. Thus, the relationship between T value and erosion risk is determined with 24 KRD as a parameter. The existence of KRD land is unrelated to T value, although this parameter indicates erosion 25 sensitivity. In fact, erosion risk is strongly dependent on the relationship between real soil loss (RL) and T value 26 rather than on either erosion intensity or the T value itself. If RL >> T, then erosion risk is high despite a low RL. 27 Conversely, if T >> RL, the soil is safe although RL is high. Overall, these findings may clarify T value 28 heterogeneity and its effect on erosion risk in a karst eco-environment; hence, innovative technological assessment 29 solutions need not be invented. 30