Sources and concentration of DOC, DIC, and POC in the Lianjiang River: A representative karst tributary of the Beijiang River

Isotopic compositions of δ 13 C DIC , sources and abundance of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate organic carbon (POC), and their response to hydrologic regimes were examined from Lianjiang River stream in rainy (DIC and DOC) and dry seasons (DOC and POC). Lianjiang River was recharged by groundwater in dry season, the abundance of DIC was higher than DOC. Apart from DIC concentrations in dry season, DIC and DOC concentrations, and δ 13 C DIC showed on spatial variation from upstream to downstream. DIC concentrations in rainy season was higher than those in dry season, while δ 13 C DIC in dry season was higher than those in rainy season because of increasing contributions from karst groundwater. Carbonate-sourced DIC contributed from 37.1% to 47.8% with an average of 42.6% of the riverine DIC in rainy season, and contributed from 44.6% to 54.5% with an average of 49.9% of the riverine DIC in dry season. Similar carbonate-sourced and soil CO 2 sourced DIC to Lianjiang River in dry season also indicates that Lianjiang River was recharged by groundwater in dry season. Total n-alkanes concentrations in POM were higher than those in DOM, and anthropogenic n-alkanes concentrations were higher than those in biogenic n-alkanes concentrations. Algae and floating/submerged aquatic plants were the major biogenic sources POM and DOM, but part sampling sites with DOM source from terrestrial plants, aquatic macrophytes sources. Light petroleum input and incomplete fossil fuel burning at high temperature and heavy oil emission were the major source of DOM and POM in Lianjiang River, but the contribution of incomplete fossil fuel burning or heavy oil emission in POM was higher than those in DOM. The results shed light on the characteristics and dynamics of different carbons in typical karstic river.