The karst in southwest China is one of the largest, continuous exposed karst regions in the world, covering large parts of Guizhou, Guangxi, Sichuan and Yunnan provinces. Resulting from the shallow depth and slow formation rate of soil, soil erosion in karst areas of southwest China has been considered to be more serious also due to its lower soil loss tolerance (0.3~0.68 Mg ha^-1 y^-1). Additionally, land uses including logging, overgrazing and agriculture have accelerated soil erosion and resulted in rock desertification where soil is seriously or thoroughly eroded and basement rocks are extensively exposed.

However, karsts develop mainly on soluble carbonate rocks where the epikarst and double-layer hydrological structure are well developed. They are characterized by a specific type of hydrological situation with rapid transport of surface water to groundwater within the time scale of rainfall events. Erosion models have not been designed for karst landscapes as an efficient method to yield quantitative predictions of soil erosion rates.

In a paper in Geomorphology, researchers in the Institute of Subtropical Agriculture of the Chinese Academy of Sciences (ISA) revised Universal Soil Loss Equation (RUSLE) to estimate the annual soil erosion rates on hillslopes and compared them with 137Cs budget in the depressions at two typical karst peak-cluster depression basins (named GZ1 and GZ2 basin).

The team found that the peak-cluster depression basins in a karst area of southwestern China provided an opportunity to study soil erosion on the surrounding karst hillslopes and compare it with the deposition records in the central depressions. The accuracy of the RUSLE model was greatly affected by the slope or flow length because of the discontinuous nature of the overland flow due to rapid and significant underground seepage on karst hillslopes.

The average annual soil erosion rate on the surrounding hillslopes was 0.22 Mg ha^-1 y^-1 in the partially cultivated GZ1 basin and 0.10 Mg ha^-1 y^-1 in the undisturbed GZ2 basin during 2006-2011.

This research was supported by grants from the National Key Basic Research Program of China (2015CB452703), the Action Plan for the Development of Western China of Chinese Academy of Sciences (KZCX2-XB3-10), and the National Natural Science Foundation of China (51379205).

The study entitled "Soil erosion rates in two karst peak-cluster depression basins of northwest Guangxi, China: comparison of the RUSLE model with ¹³⁷Cs measurements" has been published in the 253 issue of Geomorphology, 2016; details could be found at http://www.sciencedirect.com/science/article/pii/S0169555X15301781. 

Photos of the runoff plots (a) and the hillslopes of the GZ1 (b) and GZ2 (c) basins. (Image by FENG Teng)