Response of dissolved inorganic carbon (DIC) and δ13CDIC to changes in climate and land cover in SW China karst catchments

Monthly hydrochemical data and delta C-13 of dissolved inorganic carbon (DIC) in karst water samples from September 2007 to October 2012 were obtained to reveal the controlling mechanisms on DIC geochemistry and delta C-13(DIC) under different conditions of climate and land cover in three karst catchments: Banzhai, Dengzhanhe and Chenqi, in Guizhou Province, SW China. DIC of karst water at the Banzhai site comes mainly from carbonate dissolution under open system conditions with soil CO2 produced by root respiration and organic carbon decomposition with lowest delta C-13 values under its dense virgin forest coverage. Weaker carbonate bedrock dissolution due to sparse and thin soil cover results in lower delta C-13(DIC), pCO(2), DIC and EC, and lower cation and anion concentrations. At the Chenqi site, larger soil CO2 input from a thick layer of soil results in high pCO(2) and DIC, and low pH, SIc and delta C-13(DIC) in the karst water. At the Dengzhanhe site, a lesser soil CO2 input due to stronger karst rock desertification and strong gypsum dissolution contribute to higher delta C-13(DIC), high EC and high cation and anion concentrations. Soil CO2 inputs, controlled by biological activity and available soil moisture, carbonate bedrock dissolution, dilution and degassing effects, vary seasonally following rainfall and temperature changes. Consequently, there are seasonal cycles in hydrochemistry and delta C-13(DIC) of the karst water, with high pCO(2) and low pH, EC, SIc, and delta C-13(DIC) values in the warm and rainy seasons, and vice versa during the cold and dry seasons. A strongly positive shift (>3 parts per thousand) in delta C-13(DIC) occurred in the drought year, 2011, indicating that delta C-13(DIC) in groundwater systems can be an effective indicator of environmental and/or climate changes. (C) 2015 Elsevier Ltd. All rights reserved.