Assessment of underground soil loss via the tapering grikes on limestone hillslopes

Abstract

Determining the mechanism of rocky desertification by investigating the sediment transport process in carbonate aquifers with the great mixture of various karst conduit features presents severe difficulties. This study put its focus on the overlying soil entering the master small-scale surface karst negative (SSKN) feature, the tapering grike on limestone hillslopes. The objective is to assess the primary forms and the annual rates of underground soil loss relative to the crown cross-section of the grikes wall. The tapering grikes were differentiated into the fully and partially filled ones based on the current filling status of the soil. Through the analysis of the possible scenarios, the stable carbon isotope and 137Cs records of soil in the sample grikes in Southwest China, the underground soil loss form was mainly inferred as the downward creeping of overlying soil mass via the fully filled one, and the deposition of eroded overlying soils into the partially filled grike. The formula of inside space forming rate determined by the bedrock dissolution rate and the grike shape, was proposed for obtaining the current potential annual underground soil loss rate via the fully filled grike, the calculation result of which for the sample was 275.2 t km-2 y-1. The 137Cs identification method of the sediment deposition depth was used to estimate the average annual underground soil loss rate since 1963 via the partially filled grike, which was 3094.4 t km-2 y-1 for the sample. The calculations indicated that the underground soil loss via the tapering grikes contributed a lot to the overlying soil reduction in the process of karst rocky desertification. More attentions should be given to assess the underground soil loss via all the SSKN features on the whole hillslope scale and evaluate the impacts of human activities.