[Temporal and Spatial Variations of Dissolved Inorganic Carbon and Its Stable Isotopic Composition in the Surface Stream of Karst Groundwater Recharge].

Stable carbon isotope of dissolved inorganic carbon (δC), which is mainly constituted by HCO in karst water, is widely used to trace the different sources and influential factors of dissolved inorganic carbon (DIC). In order to understand the distribution of DIC and δC in subtropical karst area, this paper researched the water chemistry and δC in a karst surface stream in detail, which is fed by Guancun subterranean stream in Liuzhou City, Guangxi Province, in the southwest of China. The results showed that the contents of DIC in subterranean stream outlet (G1 site) ranged from 4.60 to 4.90 mmol·L with an average of 4.73 mmol·L in dry season, and from 2.80 to 4.70 mmol·L with an average of 4.23 mmol·L in rainy season. The contents of DIC in 1.35 km downstream site (G2 site) ranged from 4.30 to 4.90 mmol·L with an average of 4.56 mmol·L in dry season, and from 3.00 to 4.70 mmol·L with an average of 4.20 mmol·L in rainy season. The δC of subterranean stream outlet (G1 site) varied from -12.8‰ to -11.53‰ with an average of -12.22‰ in dry season, and from -13.12‰ to -11.01‰ with an average of -12.28‰ in rainy season. The δC of stream downstream site (G2 site) ranged from -11.71‰ to -9.55‰ with an average of -10.73‰ in dry season, and ranged from -12.18‰ to -9.85‰ with an average of -11.10‰ in rainy season. The contents of DIC of G1 site were higher than those of G2 site. The DIC contents in dry season in both G1 and G2 site were higher than those in rainy season. The values of δCof G1 and G2 site in dry season were more positive than those in rainy season. The δCvalue of G1 site was more negative than that of G2 site. The main sources of DIC in underground river and surface stream were soil COand carbonate dissolution. However, the differences of DIC and δCbetween G1 and G2 site showed that COdegassing and photosynthesis of aquatic plants had significant influence on water DIC and δC value. This study is helpful to understand the dynamic change and distribution of DIC and δC in karst surface stream.