Dissolved Inorganic Carbon in the Atchafalaya River: Fluxes, Sources, and Trends

Emily DelDuco: School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, 70803, edelduco19@lsu.edu; Yijun Xu School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, 70803, yjxu@lsu.edu, Songjie He, School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, 70803, she5@lsu.edu; and Kaci Fisher, School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, 70803, kaci.fisher@gmail.com

Large rivers play an important role in global carbon cycling, transporting terrestrially derived carbon to ocean systems and experiencing many carbon transformations and exchanges along the way. The Atchafalaya River (AR) discharges approximately 200 km3 of water each year into the Gulf of Mexico, representing a significant portion of the total water discharged annually from the continental US. Although transport of organic carbon from the Mississippi-Atchafalaya River System to the Gulf of Mexico has been investigated extensively, knowledge of dissolved inorganic carbon (DIC) dynamics within the AR is still limited. This study aims to 1) assess spatial and temporal distribution of DIC along this 200-km river and to 2) determine sources of riverine DIC through δ13C analysis. Since March of 2014, we have been conducting monthly sampling at four sites along the Atchafalaya River. Additionally, water samples have been collected in the Red River and the Mississippi River main channel in order to evaluate how the separate inputs of these rivers into the AR impact the processing and transport of DIC in the AR, as well as its isotopic ratios. Water samples are analyzed for concentrations of dissolved organic carbon, dissolved inorganic carbon, total organic carbon, and total inorganic carbon. In May of 2015 we also began analyzing samples for DIC δ13C signature. Standard in situ water quality measurements are recorded monthly at each site. This long-term intensive analysis of dissolved carbon concentrations and fluxes in the AR has revealed that large quantities of DIC are being discharged into the Gulf of Mexico, with increasing concentrations from inlet to outlet. This paper presents these findings, as well as preliminary findings in seasonal and spatial variations of DIC isotopic ratios.