Hydrogeochemical characteristics in karst subterranean streams: a case history from Chongqing, China

Karst subterranean streams are important water resources and life-support systems in karst areas and hydrogeochemistry research is an indispensable tool for karst aquifer protection. There are approximately 380 known subterranean streams in the Chongqing area, which are a fundamental groundwater resource. Hydrogeochemical analysis of 84 karst subterranean streams in Chongqing indicated that the solutes mainly came from the dissolution of carbonate rock (using the Gibbs diagram) and most subterranean streams are influenced by the anthropogenic processes. Also, the hydrochemical characteristics showed clear regional effects in natural background chemistry and human impacts. The calcite content decreases and the dolomite content increase from Triassic to Cambrian carbonate rock (except in the Permian carbonate rock), so that subterranean streams that developed in the Cambrian carbonate rock have the highest Mg2+ concentration. Karst subterranean streams that developed in the Permian strata displayed the lowest Mg2+ concentration due to the lowest dolomite concentration in Permian strata. Under the same geological settings, major hydrochemical parameters of karst subterranean streams showed significant diversity across regions as a result of the varying intensity of human activities. Utilizing the Gibbs diagram, it is concluded the karst subterranean streams are deteriorating under the impact of industry activities, agriculture activities and city sewage.