Grading Standard for Determining Underground Soil Leakage in a Mountain with Karst Topography in the North of Guangdong Province

Soil transfer and loss on the surface of terrain with karst topography due to fissures or caves in carbonate rocks, together with rainwater infiltration is a universal phenomenon. The degree of soil loss increases with increases in combined geological conformation movement, physical and chemical weathering, and corrosion. The combined action of underground soil leakage and surface erosion can lead to changes in the karst ecosystem and degeneration of soil and vegetation. Establishment of a grading standard for underground soil leakage is essential for assessing and analyzing degradation of karst ecosystems. For this purpose, a field study was conducted in Karst Mountain located in Liannan County, covering eight surfaces fractured by mining and road building, over 40 quadrats in Karst Hill, and the needle area of Yanbei town, Jiulong town, and Yingde city, north of Guangdong province. Based on field survey, we had got basic data, including data on 56 fissures, 40 doline funnels, and some karst caves in fractured surfaces, in addition,together with research results and survey data collected over 10 years in the Karst Mountains, hill, and needle Karst landscape, a grading standard for underground soil leakage, and a reference index for landscape characteristics of Karst mountain surfaces were set and discussed. (1) Three primary indices (fissure, karst cave, and doline funnel) and nine secondary indicators (connecting fissures between Karst caves, area ratio of fissures to fracture surfaces, fissure density, type of Karst cave, quantity of Karst caves, Karst cave location, doline funnel depth to width ratio, doline funnel shape, and fissure development surrounding a doline funnel) were selected. Underground leakage was stratified into four levels: no soil leakage, light soil leakage, moderate soil leakage, and serious soil leakage. The pathway of soil leakage, stage, relevance among all indicators, survey data from all fracture surfaces, and easily obtained index data were fully considered before selecting indices and standard data. Indicators were quantized to the extent possible, but were also combined with some qualitative indices to ensure practical grading of underground leakage. (2) Key features of karst landscape and data, including rock type, geomorphic features, landform, extent of uncovered rock, vegetation form, vegetation structure, vegetation coverage, and soil depth were selected to construct a reference index for determining landscape characteristics of the Karst mountain surface as an auxiliary index to the grading standard for underground leakage. A combination of these two sets of evaluation criteria will contribute to the development of an intact karst ecosystem evaluation method that is fully integrated with the assessment systems for rocky desertification. (3) This new evaluation criterion system for underground soil leakage will contribute to the overall assessment of karst ecosystems, especially for assessments of water and soil loss in road building, mining, and ecological environment construction, and can help us to draft a scientifically sound environmental governance policy for karst ecosystem resource utilization. These results will support further studies on karst ecosystems and more comprehensive evaluation of degraded karst environments