Unexpected Consequences of River Engineering on the Carbon Cycle

Abstract

Rivers around the world have been heavily engineered, and these man‐made changes are affecting important biogeochemical cycles. Rivers play a key role in the global carbon cycle, by mobilizing organic carbon from land and delivering it to the oceans. River engineering techniques, like levees that prevent flooding, change the way carbon is cycled through rivers, but it is difficult to identify and quantify these changes. Shen et al. (2021) were able to quantify changes in river organic carbon fluxes induced by bank stabilization in the Mississippi River. The authors compared the age distribution of organic carbon in modern river sediment and old river sediment deposited before the construction of extensive levee systems. They found that bank stabilization significantly reduces the amount of time organic carbon spends in the river system before being exported to the Gulf of Mexico. As a result, less organic carbon is oxidized to CO 2 and more organic carbon is exported to the ocean, ultimately reducing atmospheric CO 2 . This study highlights an important effect of anthropogenic activity on river carbon fluxes that should be considered in global carbon cycle models. River engineering practices, like artificial levees, prevent rivers from depositing organic carbon on their floodplains Bypassing floodplain storage limits the release of CO 2 to the atmosphere and increases the flux of organic carbon to the oceans