Natural and man-made acids in the water dissolve many carbonates, which lead to Karst processes and features.
Carbonic acid is the largest player in the dissolution of bedrock.
This weak acid is formed when raindrops combine with carbon dioxide in the atmosphere. As this acidic rainwater seeps into the ground, it slowly dissolves the rock. This process leads to the creation of sinkholes, caves, springs, losing streams, and other Karst features. Missouri has some excellent examples of Karst. As for sinkholes, the area has both recent and ancient examples.