| As a very important part of the global surface water cycles, river plays a crucial role on the biogeochemical cycles of the elements. The hydrological and geochemical features of river water are a signature of the extent of surface weathering and denudation. At the same time, the chemistry of river water reveals the characters of geology, geography, climate and entironment on a basin-wide scale. At present, many articles have reported the hydro-geochemical features in the basin waters but the small river basins are less selected to discuss than big river basins. In this paper, we take the upper reaches of Ganjiang River in the southern Jiangxi Province and Hongfeng Lake in the middle Guizhou Province as the research object, understand the key chemical weathering processes of the basin and discuss the influences of the different rock, atmospheric precipitation and human-activities using the major chemical constitutes of river water. We compute quantificationally the major sources of DIC using the δ13C, and work out the denudation flux of DOC according to the concentrations.The results are showed as follows:1. The chemical composition of the upper reaches of Ganjiang river is dominated by Na+, Ca2+, Cl- and HCO3-, at the same time, the concentration of Si is obvious high because of the dissolution of silicate rock. The biogeochemical character of the Hongfeng Lake river is dominated by dissolution of carbonate rock. The dominated ions are Ca2+, Mg2+, SO42- and HCO3-, which different from the character of the upper reaches of Ganjiang river. The TDS of Hongfeng Lake is higher than Ganjiang river and the mean value of the world rivers. The pH of groundwater is lower than surface water but EC is higher.2. According to the Gibbs graphs analysis, the upper reaches of Ganjiang river belongs to the intergrade of "precipitation controlling" and "rock weathering controlling" and the contribution rate of atmospheric precipitation is 11.31% that is higher than the mean value of the world. The Hongfeng Lake prone to "rock weathering controlling" and affected by artificial actions and acid sedimentation. The contribution rate of atmospheric precipitation is 14.18% that is close to the upper reaches of Ganjiang river. But the first is oceanic components and the later is terrestrial components. In addition, both of them are affected by artificial actions and the Guizhou province is more obvious.3. On the basis of the plots of the relationship among major ions and the principal composition analysis, the southern Jiangxi Province and the middle Guizhou Province indicatethe major chemical compositions in the river water of the area that is dominated by silicate rock and carbonate rock respectively. The evaporate and silicate rocks dissolution are the primary weathering processes and the weathering of carbonate take second place in the watersheds of the southern Jiangxi Province. At the same time, the carbonate rocks dissolution take the first place in the middle Guizhou Province.4. The DOC concentration in the water river of two drainage basins is lower than others, and the groundwater is lower than surface water. Based on the area of the catchments, the mean annual discharge and the DOC concentration, the denudation flux of DOC at the upper reaches of Ganjiang River is calculated to be 1.43x106gC·km-2·yr-1 and the 2.78x106gC·km<sup>-2·yr-1 in the Hongfeng Lake. The later is higher than that of Ganjiang river and the mean value of the world rivers. Both of them are lower than other drainage basins located in the same climate regions.5. The mean δ13C of DIC is measured to be -11.65‰ at the upper reaches of Ganjiang River and -8.72%o in the Hongfeng Lake. Based on the area of the catchments, the mean annual discharge and the HCO3- concentration, results of account indicate that the most DIC at the upper reaches of Ganjiang River are from soil CO2, a little is from the weathering of carbonate. The DIC in the Hongfeng Lake is half from soil CO2, the other come from rock self. |
