Horizontal and vertical zoning of carbonate dissolution in China

Natural dissolution and denudation are the essential processes of karstification; however, their intensities depend on geographic and climatic conditions. Field dissolution tests of carbonate tablets were conducted in Hubei Province over a three years period to determine the impact of precipitation, lithology, altitude, vegetation and soil on carbonate dissolution. Results from the study show that carbonate dissolution rates vary from 1.23 to 2.86 mg cm−2 a−1. In addition, a comparative analysis of our results with those from 28 other sites reveal two lateral regional boundaries of karstification, one trending from South to North China, the other from North to Northwest China, with regional precipitation variations appearing to be the primary control factor. Comparison of the dissolution rate of carbonate tablets set up on the surface (150 cm above ground surface and on the ground surface) with those beneath the surface (20 cm and 50 cm beneath the ground surface) at different elevations reveal a vertical karstification boundary in the mountainous areas along the South-North karstification transition zone. The results also show that surface dissolution rates (1.50-2.18 mg cm−2 a−1) are higher than subsurface dissolution rates (0.53-1.61 mg cm−2 a−1) in high altitude areas. Conversely, in low altitude areas, the subsurface dissolution rate (3.94 mg cm−2 a−1) is much higher than surface dissolution rate (1.78 mg cm−2 a−1). Therefore, the horizontal and vertical karstification boundaries in China highlight the main karstification function based on local elevation as well as varying geographical conditions. It was also found that the magnitudes of carbonate dissolution are consistent with recent karstification degree, which is critical for modeling karst landform evolution in the near future.