Hydrogeochemistry and dissolved inorganic carbon isotopic composition on karst groundwater in Maolan, southwest China

摘要

The forest ecosystem in the Maolan karst forest, southwest China is the only concentrated, intact, and relatively stable karst forest ecosystem which has survived in the area at the same latitude in the world, and is a valuable karst forest plant resource as well. Groundwater samples from Maolan karst forest were collected from wells and springs during summer; and concentrations of major ions and dissolved inorganic carbon (DIC) isotopic compositions were measured. The pH values range from 7.2 to 8.3 results from the dissolution of carbonate, HCO_3~-is the dominant species of DIC in groundwater. Calcium and HCO_3~-, followed by Mg~(2+) and SO_4~(2-) dominate the chemical composition of major ions in the groundwaters. Groundwater samples have δ~(13)C values in the range from -8.1%o to - 16.6‰, which are lower than that of the other karst city groundwaters in the southwest China. Combining δ~(13)C_(dic) ratios with measurements of HCO_3~- and pH clearly distinguishes the principal processes underlying the geochemical evolution of groundwater in Carboniferous carbonate aquifers, where processes can be both degradation of organic matters in the soil and the carbonate dissolution.