河道型水库溶解无机碳同位素组成特征与来源--以万安水库为例

Characters and sources of dissolved inorganic carbon isotope in channel reservoir:A case of Wanan Reservoir

以江西万安水库为研究对象,于2014年9月至2015年6月进行4次季节性采样,对该区域9处采样点的溶解无机碳(DIC)及其同位素(δ13CDIC)进行分析。结果表明:夏、秋季DIC含量较春、冬低;δ13CDIC也较冬、春季偏负。DIC含量从上游到下游呈下降趋势,碳同位素值则趋于偏正。光合作用与有机质分解是影响库区表层水体δ13CDIC值变化的主要因素。垂直剖面上,表、底层水温等参数差异不显著,上下水体混合较为均匀。DIC含量基本上随深度的增加而增大,δ13CDIC值趋于偏负。利用质量平衡计算得出:入库水体中DIC约57%来自于土壤CO2,而坝下水体中DIC约49%来自土壤CO2,万安水库拦截对河流地球化学过程信息有一定的改造作用。

In this study, Wanan Reservoir was investigated with four seasonal samplings from September 2014 to June 2015, to understand the characters and sources of dissolved inorganic carbon （DIC） and its carbon isotope （δ13CDIC）. Nine sampling sites covering the reservoir were included in the field survey. Results showed that the concentration of DIC in water was lower in summer and autumn than that in other seasons. The value of δ13 CDIC was more positive in winter and spring. From upstream to downstream, DIC concentration showed a decrease trend, while δ13CDIC become more positive gradually. Photosynthesis and organic matter decomposition played important roles in controlling the variation of δ13 CDIC in the surface water. Along the water column in the central reservoir, in situ parameters such as water temperature had no significant differ- ence, indicating a weak thermal stratification in reservoir. However, DIC concentrations had an increase trend downwardly, while δ13 CDIC gradually become more negative from surface water to deep water. Based on mass-balance calculation, about 57% of DIC derived from soil CO2 at the reservoir entrance, while this value was 49% at the site of reservoir discharge. This result means that river damming could change the weathering information contained in the chemical composition of river water.