Stable Carbon and Sulfur Isotope Characteristics of Stream Water in a Typical Karst Small Catchment, Southwest China

Surface water samples from the Maolan National Natural Reserved Park (MNNRP) were analyzed from Sept. 2013 to June 2014, for major ion concentrations (K+, Na+, Ca2+, Mg2+, Cl-, SO42-, HCO3-), delta C-13-DIC and delta S-34-SO4(2-) to quantify the sources of solutes and chemical weathering. The results show that HCO3- and SO42- are the main anions in Banzhai watershed, which account for 86.2 and 10.4% of the total anion equivalent, respectively. While Ca2+ and Mg2+ account for 76.9 and 20.5%, respectively. Considerable Mg2+ in stream water indicates that it may be affected by dolomite weathering. stream water samples present the delta C-13-DIC values in the range of -16.9 parts per thousand similar to-10.8 parts per thousand (mean value was -13.9 parts per thousand), which were lower than that of the groundwater. The delta S-34-SO42- values ranged from -15.2 parts per thousand to 1.7 parts per thousand (mean value was -4.4 parts per thousand). There was a negative correlation between HCO3- content and delta C-13 value, implying the result of the interaction of temperature and precipitation intensity in different seasons. The significant positive correlation between SO42- content and delta C-13-DIC indicates that H2SO4 may be involved in the weathering process of carbonate rocks in small watershed scale. The content of SO42- in a school sample site was much higher than that of other sample sites for the interference from human sources. The delta S-34 values show that the average delta S-34-SO42- in most sites is close to the delta S-34 isotopic values of Guizhou coal and rain, indicating that they may be affected by local coal.

Automated summary

Surface water samples from Maolan National Natural Reserved Park were analyzed for major ions and carbon, sulfur isotopes from September 2013 to June 2014. The results suggest that bicarbonate and sulfate are the main anions in the watershed, indicating an influence of rock weathering on water chemistry. Additionally, human activities have led to higher sulfate content in some sample sites.