THE CARBON CYCLE AND CARBON INTERACTIONS IN KARST DYNAMIC SYSTEMS

The functions of karst dynamic systems are principally associated with carbonate rock formation, dissolution and weathering. The formation of the earth's carbonate rocks created a large atmospheric CO₂ sink in the geological past, and as a result the atmospheric concentration of CO₂ was reduced from over 25% in the primitive atmosphere to only 0.03-0.04% in modern atmosphere. Carbon stored as carbonate minerals in the lithosphere, which amounts to 61×10¹⁵t, is the largest carbon pool on the modern earth. In modern karst dynamic systems, carbonate rock dissolution and weathering actively particpate in the global carbon cycle, although the overal impact when balanced with carbonate mineral precipitation in the oceans is not clear, in part becuase these processes are sensitive to climatic and other environmental changes. Current estimates of the the annual carbon sink flux from the continents to the oceans derived from carbonate rock dissolution amounts to 0.36-0.44 PgC/a, which is equal to about 33-40% of the global forest carbon sink of 1.1 PgC/a from 1990 to 2007. This figure equals 45-55% of the net carbon flux for the global soil organic carbon pool under appropriate management. This paper provides a conceptual model of the karst carbon cycle at the watershed scale, consisting of three parts: carbonate rock dissolution transfering atmospheric/soil CO₂ to water to produce dissolved inorganic carbon; dissolved inorganic carbon transport along with water flow; and interaction between inorganic carbon and organic carbon with aquatic plants through photosynthesis, with some of the organic carbon being deposited on river/lake/reservoir beds and mixing with sediments.