Spatio- temporal Variation of the Stable Isotopic Composition of River ine Dissolved Inorganic Carbon of the Xijiang Inner Estuary
西江河口段溶解无机碳稳定同位素组成的时空变化

For researching the spatio-temporal variation of the riverine dissolved inorganic carbon (DIC) isotopic characteristic, we carried out a survey throughout the hydrologic year which δ13CDIC of the surface water and its physiochemical parameter were examined along the Xijiang Inner Estuarine waterway from the autumn of September 2006 to the summer of June 2007. There were striking seasonal variations on the average δ13CDIC, as the average δ13CDIC in summer (-13.91‰) or in autumn (-13.09‰) was much less than that in spring (-11.71‰) or in winter (-12.26‰ ). The riverine δ13CDIC was controlled by decomposed condition of the riverine organic matter linking the seasonal variation of the physiochemical parameter in the surface water according to the correlation analysis which indicated notable relation between δ13CDIC and water temperature (p = 0.000; r = -0.569) or between δ13CDIC and oxide-reduction potential (p = 0.000; r = 0.646). The striking positive correlation between δ13CDIC and the sampling distance occurred in the summer high flow, while striking negative correlation occurred in the spring low flow, indicating that river-sea interaction influenced water physiochemical parameter and controlled riverine DIC property in the survey waterway. In view of the riverine δ13CDIC decreasing for the decomposition of the terrestrial organic matter in rainy season in summer and increasing for the briny invaded zone extending in dry season in spring along the waterway from the Makou gauge station to the Modaomen outlet, the δ13CDIC spatio-temporal variation was closely related to the geographical environment of the Xijiang basin.