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Soil loss tolerance (T value) is one of the criteria in determining the necessity of erosion control measures and ecological restoration strategy. However, the validity of this criterion in subtropical karst regions is strongly disputed. In this study, T value is calculated based on soil formation rate by using a digital distribution map of carbonate rock assemblage types. Results indicated a spatial heterogeneity and diversity in soil loss tolerance. Instead of only one criterion, a minimum of three criteria should be considered when investigating the carbonate areas of southern China because the one region, one T value concept may not be applicable to this region. T value is proportionate to the amount of argillaceous material, which determines the surface soil thickness of the formations in homogenous carbonate rock areas. Homogenous carbonate rock, carbonate rock intercalated with clastic rock areas and carbonate/clastic rock alternation areas have T values of 20, 50 and 100 t/(km2 a), and they are extremely, severely and moderately sensitive to soil erosion. Karst rocky desertification (KRD) is defined as extreme soil erosion and reflects the risks of erosion. Thus, the relationship between T value and erosion risk is determined using KRD as a parameter. The existence of KRD land is unrelated to the T value, although this parameter indicates erosion sensitivity. Erosion risk is strongly dependent on the relationship between real soil loss (RL) and T value rather than on either erosion intensity or the T value itself. If RL > > T, then the erosion risk is high despite of a low RL. Conversely, if T > > RL, then the soil is safe although RL is high. Overall, these findings may clarify the heterogeneity of T value and its effect on erosion risk in a karst environment.

This paper attempts to explain the theoretical reasons why local farmers have executed land mismanagement measures such as steep slope land cultivation, in order to reveal the mechanisms of karst rocky desertification (KRD, including light KRD, moderate KRD and severe KRD) through typical case studies. Firstly, this paper assumes that the low land capacity is the initial cause of KRD in peak-cluster depression areas. Furthermore, the ecological quality of the peak-cluster depression zone (a combination of clustered karst cones with a common base and depressions between cones) is influenced by the relationship between the area of depressions and the population of residential areas. Therefore, six typical peak-cluster depression areas of Guizhou province were selected to compare the distribution circumstances of cropland, the characteristics of settlements and the formation of KRD with the help of ALOS images in 2010 (with a resolution of 10 m × 10 m). The results show that there is a negative correlation between the percentage of the cultivated land and the percentage of KRD at peak-cluster depressions. The relationship could be concluded by three situations of the process of KRD, which are low, middle and upper carrying capacities of land. Severe KRD is only distributed in peak-cluster depression areas with less flatland, low land capacity and a high population. The harmonization between population pressure and bearing capacity of land will influence the ecological qualities in the peak-cluster depressions. The KRD phenomenon which occurred in six typical peak-cluster depression areas confirms that the hypothesis suggested by this paper is correct, and this result will contribute to understanding the natural mechanisms of KRD and guide the ecological restoration of KRD land.

Dominated by specific eco-hydrogeological backgrounds, a small watershed delineated by using the traditional method is always inauthentic in karst regions because it cannot accurately reflect the eco-hydrological process of the dual structure of the surface and subsurface. This study proposes a new method for the delineation of small watersheds based on digital elevation models (DEMs) and eco-hydrogeological principles in karst regions. This method is applied to one section of the tributary area (Sancha River) of the Yangtze River in China. By comparing the quantity, shape, superimposition, and characteristics of the internal hydrological process of a small watershed extracted by using the digital elevation model with that extracted by using the proposed method of this study, we conclude that the small karst watersheds extracted by the new method accurately reflect the hydrological process of the river basin. Furthermore, we propose that the minimum unit of the river basin in karst regions should be the watershed, whose exit is the corrosion and corrasion baselevel and a further division of watershed may cause a significant inconsistency with the true eco-hydrological process.