Examining the Distribution and Variation of Dissolved Carbon Species and Seasonal Carbon Exports within the Jiulongjiang River Basin (Southeast China)

The water chemistry, including major ions and dissolved carbon of Jiulongjiang River in SE China, were determined to examine the distributions and variations of dissolved carbon species. Dissolved inorganic carbon (DIC) concentrations in the river water were within the range of 7.50 to 49.04 mg/L (averaged 22.12 mg/L) in the wet season and from 8.83 to 84.91 mg/L (averaged 41.17 mg/L) in the dry season. Dissolved organic carbon (DOC) varied from 0.54 to 2.89 mg/L (averaged 1.04 mg/L) in the wet season and from 1.34 to 3.56 mg/L (averaged 2.34 mg/L) in the dry season. The concentrations of DIC were comparable among the three tributaries, whereas the DOC was significantly higher in the Xixi River and Nanxi River than the Beixi River. The calculations employing the mass balance method indicated that weathering process and anthropogenic inputs played an important role in the dissolved carbon production in the Jiulongjiang watershed. The DOC exhibited significant correlations with the rural area whereas the DIC did not show any significant correlations with land-use types, indicating that the DOC was closely related to agricultural activities. The carbon export fluxes from the Jiulongjiang River were calculated based on the discharge data. The DIC-C export reached to 1.2 x 10(5)t/y, whereas the DOC-C export was nearly 3.2 x 10(4)t/y. In addition, seasonal variation of carbon exports had been observed; because of the large water discharge in the wet season, more DIC and DOC were transported from the Jiulongjiang River in the wet season than in the dry season. The source analysis demonstrated natural processes account for the majority of carbon exports.