Factors controlling carbon isotope ratios of dissolved inorganic carbon in two major tributaries of the Han River, Korea

Understanding the carbon cycle of the Han River system in Korea is of prime interest in managing and preserving this valuable water resource for more than 20 million residents in the area. As a part of a comprehensive carbon cycling study for the Han River system, this report focuses on the carbon isotope compositions of dissolved inorganic carbon (DIC) in its two major tributaries, the North and the South Han Rivers. The major difference in carbonate chemistry of the tributaries originates primarily from the lithology of the catchment areas. The South Han River, draining a carbonate-dominant terrain, has much higher alkalinities and DIC concentrations, whereas the lower concentrations in the North Han River indicate little influence of carbonate weathering. Likewise, delta C-13(DIC) values in the South Han River indicate that the DIC input from the carbonate rocks is important in controlling carbon isotope ratios of DIC. For the North Han River, the oxidation of organic material influences the amount of riverine DIC and delta 13C(DIC) values to a greater extent. Overall, remarkable seasonal and spatial variations of river chemistry and carbon isotope compositions of DIC reflect the variability in geo-hydrologic characteristics, in the water regime, and in metabolic activities in the river water and/or the drainage areas. Copyright (c) 2006 John Wiley & Sons, Ltd.