[Dissolved inorganic carbon and its carbon isotope composition in cascade reservoir of the Maotiao River during summer and autumn].

Water samples along water column in the front of dams and samples at 0.5 m below surface water from tributary rivers were collected in July and October, 2007. The water chemistry, concentrations of dissolve inorganic carbon and its carbon isotopic compositions were determined, in order to investigate the geochemical behavior of carbon in the Maotiao River. This study aimed to understand the variations of the concentrations of dissolved inorganic carbon (DIC) and delta13 C(DIC) during its transport along the cascade reservoirs and river system. The results showed that DIC concentrations in summer were lower than that in autumn. In summer, the DIC concentrations were 1.35-2.84 mmol/L, with an average value of 2.12 mmol/L; and in autumn they fell into 2.03-3.98 mmol/L, with an average value of 2.67 mmol/L. The delta13 CD1 in surface water along Maotiao River ranged from -10.3% per hundred to -5.1% per hundred in summer, with a value of -8.6% per hundred in average, and in autumn, delta3 C(DIC) became more negative, and had a range from -13.0% per hundred to -6.9% per hundred, with an average value of -9.0% per hundred. Generally, DIC in surface water showed a trend to decrease from the upper reaches to lower reaches along Maotiao River, and t3 Cc1 gradually becam me more negative downstream. On the water column, DIC concentrations were higher in hypolimnion, while a delta13 C(DIC) had a reverse trend with higher values occurred in epilimnion. The results indicated that the hydrochemistry of river could be significantly changed by river damming processes. As for carbon, reservoir should be an important place for the transformation among the different carbon species.