The sources of dissolved inorganic carbon (DIC) and rock weathering processes were studied in the Houzhai catchment, a typical karstic catchment in the Changjiang River Basin, Southwest China.

The carbon isotopic compositions (δ¹³C_DIC) of DIC in the samples collected from the catchment vary from − 13.5‰ to − 6.9‰, with a mean value of − 9.8‰.  The DIC in the catchment is thereby considered to be mainly derived from soil CO₂ and weathering of carbonate rocks.  The DIC concentrations and the δ¹³C_DICvalues show pronounced seasonal variations, with the lowest values being observed during the high flow season (from May to October).  The logPCO2 values in the waters were positively correlated with the DIC contents and negatively correlated to the saturation index of calcite (SIc) and δ¹³C_DICvalues.

These observations indicate that CO₂ derived from organic matter oxidation plays an important role in the dissolution of carbonate for this typical karstic environment.  Based on a chemical mass balance, the weathering rate of carbonate rocks in the Houzhai catchment was estimated to be approximately 133 t/km2/year or 584 × 103 mol/km2/year in terms of CO₂ consumption rate, which is higher than the reported values for other rivers in Southwest China.

Publication name	Chemical Geology, Volume 277, Issues 3-4, 20 October 2010, Pages 301-309
Author(s)	LI SL , LIU CQ, LI J, LANG YC, DING H, LI LB
Corresponding author	LIU Congqiang liucongqiang@vip.skleg.cn　Chinese Acad Sci, Inst Geochem, State Key Lab Environm Geochem, Guiyang 550002, Guizhou Peoples R China

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