西江河口段溶解无机碳稳定同位素组成的时空变化

Spatio-temporal Variation of the Stable Isotopic Composition of Riverine Dissolved Inorganic Carbon of the Xijiang Inner Estuary

从2006年9月至2007年6月间对西江河口段溶解无机碳稳定同位素组成(!13CDIC)及其相关的水体理化参数进行了一个水文年的季节性采样调查。夏、秋两季"13CDIC平均值(-13.91‰、-13.09‰)小于春、冬季节(-11.71‰、-12.26‰),呈现出明显的季节性。#13CDIC与温度呈负相关(p=0.000;r=-0.646),而与氧化还原电位正相关(p=0.000;r=0.569),表明河段表层水体$13CDIC受到季节性变化的水体理化性质等河道有机质氧化分解条件的控制;夏季洪水期%13CDIC与航测距离呈正相关,而春季枯水期的&13CDIC与航测距离负相关。’13CDIC的这种时空变异证明了研究河段河-海作用过程影响了水体的理化性状进而控制了河道表层水体DIC的性质。研究河段(13CDIC的上述时空分布规律与流域所处的地理环境关系密切,汛期的夏季受陆源有机质的强烈分解作用的影响,DIC的同位素组成向海洋方向变轻;枯期的春季因海洋作用加强以及咸潮的入侵,河道DIC的同位素组成向海洋方向变重。

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 δ^13CDIC 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 δ^13CDIC, as the average δ^13CDIC 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 δ^13CDIC 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 δ^13CDIC and water temperature （p = 0.000; r = -0.569） or between δ^13CDIC and oxide-reduction potential （p = 0.000; r = 0.646）. The striking positive correlation between δ^13CDIC 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 δ^13CDIC 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 δ^13CDIC spatio-temporal variation was closely related to the geographical environment of the Xijiang basin.