Carbon footprint of reservoirs – lessons learned from tropical systems

Raquel Mendonça

Reservoirs play key social and economic roles as source of water and hydropower. There are currently about 38,000 dams around the world and many new ones are planned especially in the tropics, affecting landscape-scale greenhouse gas emissions and the carbon cycle. Particularly methane emission is of major concern, since the transformation of previously fixed atmospheric carbon dioxide to methane implies a 34-fold amplification in global warming potential.

However, reservoirs also trap large amounts of fluvial sediments containing organic carbon in a burial-prone environment, thereby enhancing basin-scale organic carbon sequestration. In my talk, I will discuss some of the latest advances towards quantifying the carbon footprint of reservoirs, showing the research that my group has developed over the past years. We have demonstrated, for example, that reservoirs sequester terrestrial organic carbon with higher efficiency than other depositional environments. We also confirmed that methane emission through bubbles, an emission pathway largely overlooked, can account for most of a reservoir greenhouse gas emission. It is clear that the ultimate carbon footprint of a reservoir is strongly dependent on the characteristics of its project and on the properties of its catchment. Based on this, I will also discuss ideas of how strategic dam planning can reduce greenhouse gas emission.