Spatiotemporal Distribution of DOC and DIC in the Atchafalaya River, the Largest Distributary of the Mississippi River

Carbon transport in large river systems is an important component of global carbon cycling. This is especially true when considering the transport of dissolved carbon, which has been found to experience rapid change in mixing zones where freshwater and saltwater meet. Although transport of organic carbon from the Mississippi River (MR) and its distributary, the Atchafalaya River (AR), to the Gulf of Mexico has been investigated extensively, knowledge of dissolved carbon dynamics in the large river system is limited. This study aims to assess spatial and temporal distribution of dissolved organic and dissolved inorganic carbon along this 200-km long Atchafalaya River, which receives about 25% of the Mississippi River’s flow as well as the entire flow of the Red River. Since March of 2014, we have been conducting monthly sampling at four sites along the Atchafalaya River. In addition, we also have collected water samples in the Red River and the Mississippi River main channel to better understand factors influencing the processing and transport of dissolved carbon. Water samples are analyzed for concentrations of dissolved organic carbon, dissolved inorganic carbon, total organic carbon, and total inorganic carbon. Field measurements taken at each site include parameters such as water temperature, pH, dissolved oxygen, and salinity. Preliminary results indicate that the MR and AR system is transporting a large quantity of dissolved carbon into the northern Gulf of Mexico, and that the input of dissolved inorganic carbon is much higher than that of dissolved organic carbon. This paper will present major findings from the 2-year intensive monitoring effort and discuss their potential role in near-shore carbon dynamics in the world’s second largest hypoxic zone.