How Will Riverine Carbon Emissions and Productivity Respond to Extreme Climate Events and Dam Regulations?

Climate change and anthropogenic activities have significantly altered the carbon (C) balance of rivers. However, the current understanding of how riverine C biogeochemistry responds to global climate change remains limited. Here we evaluate the spatiotemporal dynamics of carbon dioxide (CO2) flux and phytoplankton primary productivity (PP) in the main stem and tributaries of the Three Gorges Reservoir Region between 2010 and 2023. We found that the response of the CO2 flux and PP was evident in the extremely rainy months when, on average, the CO2 flux increased by 42.5% and PP decreased by 10.7%. Spatially, we also observed significant CO2 flux and PP differences between the backwater and upstream areas of the tributaries. CO2 flux at the upstream sites was 60-266% higher than at the backwater sites, while PP at the backwater sites was 4-13 times the amount of PP at the upstream sites. Differences in flow velocity and chlorophyll concentrations between the backwater and upstream sites, which primarily originate from the water level regulation operations of the dam, are believed to dominate spatial CO2 flux and PP gradients, respectively. This study reveals the response patterns and feedback mechanisms between riverine C biogeochemistry and global climate change factors in a large dammed river and associated tributaries.