Seasonal variation of organic carbon fluxes in the Yangtze River and influence of Three-Gorges engineering

The water samples of the surface layer sampled in the lower Yangtze River from June 2003 to July 2005 were used for determination of dissolved organic carbon (DOC) and particulate organic carbon (POC). The concentrations of DOC and POC during the observation were 1.59 ± 0.21 and 0.91 ± 0.42 mg/L, respectively, in which DOC in dry season was higher than that in flood; while POC showed the opposite tendency. POC concentration and total suspended matter (TSM) in waters had marked positive correlation, the POC% in TSM decreased with the increasing of TSM concentration. The DOC fluxes of Yangtze River in 2003, 2004 years were 1.32 × 10⁶t and 1.20 × 10⁶t respectively, the POC fluxes were 2.69 × 10⁶t and 1.63 × 10⁶t, and about 76% of the total organic carbon was transported into sea in flood season with its composition being mainly particular phase. In 2003-2004 years POC fluxes decreased rapidly. The ratio value of DOC and POC fluxes increased rapidly, related possibly with retaining, reforming and eutrophication.