Semester of Graduation

Spring 2024


Master of Science (MS)


The Department of Renewable Natural Resources

Document Type



The Mississippi-Atchafalaya River system contributes significantly to both dissolved carbon transportation to the northern Gulf of Mexico and vertical CO2 flux. Several factors, particularly flow velocity and wind speed, can influence aquatic CO2 emissions, which are often calculated (rather than measured) using a gas exchange balance. These factors have an impact on a critical parameter in the balancing approach, the gas exchange coefficient KT. On the other hand, river floodplains influence these fluvial carbon processes. Two connected investigations in this thesis aim to discover environmental factors affecting river carbon dynamics. This research used water samples and in situ measurements of pCO2 and ambient water characteristics from the Lower Mississippi River in Baton Rouge and the Atchafalaya River in Morgan City, Louisiana, USA. Additional meteorological and hydrological data were obtained from public sources. During the three-year investigation, fluctuating flow velocity and wind speed caused significant changes in gas exchange coefficients (KT). The velocity-based KT method had an average CO2 emission of 44.36 mmol m−2 h−1, while the wind-based and constant KT methods had averages of 10.05 mmol m−2 h−1 and 11.64 mmol m−2 h−1, respectively. These results understate the effect of conditions of flow on CO2 outgassing, showing significant uncertainty in global river CO2 emission estimates. The study found an average CO2 emission rate of 12.70 mmol m-2 hr-1 in the Atchafalaya River with pCO2 levels varying from 850 to 5422 μatm over the 24-month study period. The higher DIC content (27 ± 6 mg L-1) than DOC (9.10 ± 4.6 mg L-1) in the Atchafalaya indicates faster DOC mineralization. The mass transfer of DIC and DOC from the Atchafalaya into the Gulf of Mexico was 4.21 Tg C yr-1 and 1.78 Tg C yr-1. The higher CO2 degassing rate in the Atchafalaya River than the Mississippi River indicates the rapid carbon transport and transformation compared to the levee-confined river.



Committee Chair

Xu, Yi-jun

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