『Abstract
　A detailed investigation of the fluvial geochemistry of the Han River system allows to estimate the rates of chemical weathering and the consumption of CO2. The Han River drains approximately 26,000 km² and is the largest river system in South Korea in terms of both water discharge and total river length. It consists of two major tributaries: the North Han River (NHR) and the South Habn River (SHR). Distinct differences in basin lithology (silicate vs. carbonate) between the NHR and SHR provide a good natural laboratory in which to examine weathering processes and the influence of basin geology on water quality. The concentrations of major elements and the Sr isotopic compositions were obtained from 58 samples collected in both summer and winter along the Han River system in both 2000 and 2006. The concentrations of dissolved loads differed considerably between the NHR and SHR; compared with the SHR, the NHR had much lower total dissolved loads (TDS), Sr and major ion concentrations but a higher Si concentration and ⁸⁷Sr/⁸⁶Sr ratio. A forward model showed that the dissolved loads in the NHR came primarily from silicate weathering (55±11％), with a relatively small portion from carbonates (30±14％), whereas the main contribution to the dissolved loads in the SHR was carbonate weathering (82±3％), with only 11±4％ from silicates. These results are consistent with the different lithologies of the two drainage basins: silicate rocks in the NHR versus carbonate rocks in the SHR. Sulfuric acid derived from sulfide dissolution in coal-containing sedimentary strata has played an important role in carbonate weathering in the SHR basin, unlike in the NHR basin. The silicate weathering rate (SWR) was similar between the HR and SHR basins, but the rate of CO2 consumption in the SHR basin was lower than in the NHR basin due to an important role of sulfuric acid derived from pyrite oxidation.

Keywords: Chemical weathering; Silicate; Carbonate; CO2 consumption rate; Sulfuric acid; Han River』

1. Introduction
2. Study area
　2.1. Geography and climate
　2.2. Geology
3. Methods
4. Results and discussion
　4.1. Hydrogeochemistry and chemical weathering
　　4.1.1. Major elements and Sr isotopes
　　4.1.2. Atmospheric inputs
　　4.1.3. Sulfide oxidation
　　4.1.4. Carbonate weathering
　　4.1.5. Silicate weathering
　4.2. Model calculation
　　4.2.1. The model
　　4.2.2. Model results
　　4.2.3. Flux calculations
5. Conclusions
Acknowledgements
References