The isotopic composition of dissolved inorganic carbon (DIC) in estuarine environments has been studied for its significant role in determining the isotopic composition of inorganic/organic matter and its applications to the study of various natural processes. In this paper, based on the stable isotope geochemical characteristics of dissolved inorganic carbon in the Jiulong River Estuary, the following conclusions are drawn: (1) δC values are mainly controlled by the mixing ratio of fresh water and sea water; (2) δC values are linearly related to the δC values; (3) δC values for the Jiulong River Estuary are affected by anthropogenic pollution significantly; and (4) the comprehensive analysis of δC, δC and δC shows that along with increasing salinity, the proportion of POM derived from the degradation of phytoplanktons gradually increases. [ABSTRACT FROM AUTHOR]