Tracing anthropogenic DIC in urban streams based on isotopic and geochemical tracers

To elucidate the type and extent of anthropogenic DIC (dissolved inorganic carbon), carbon isotopic composition of DIC and dissolved ion concentration were determined in three streams (Gap, Yudeung and Daejeon) draining populated Daejeon metropolitan area, South Korea. Seasonal variations in water chemistry and carbon isotopic composition of DIC (delta(13) C-DIC) reflected changing contribution from two main DIC sources, i.e., soil weathering and sewages. DIC input from the soil weathering was characterized by delta C-13(DIC) values ranging from -16.7 to -16.0 % and higher during Jun-Nov. The sewage-derived DIC became dominant during Dec-May with delta(13) C-DIC values ranging from -11.4 to -7.4 %. Si and Cl served as indicators of DIC inputs from soil weathering and sewages, respectively. The higher delta(13) C-DIC values of sewages in the study area indicated that detergents (delta(13) C-DIC of -12.0 to -6.5 %) carried by the urban sewages were the main anthropogenic DIC component. The extent of anthropogenic DIC relative to soil-derived DIC in stream waters increased when the precipitation was low and discharge decreased. The results of this study provide a method to quantify anthropogenic DIC, which can help manage water quality in urban stream waters.