Anthropogenic flooded lands and atmospheric methane

The secular increase of the atmospheric methane has been attributed to fossil fuels, biomass burning, waste deposition, rice paddies, and beef production. In this article we reinforce that a neglected methane source are the anthropogenic flooded lands (AFL). The reasons rely on the drop-pressure effect, where dam turbine/spillway may annually release larger amounts of methane than the flooded surface itself. Based on current available information, the methane emissions through global AFL surfaces are estimated as nearly 12Tg CH4 for a total AFL area of 1.5 106km2. The global AFL annual emissions through spillways and turbines in 2005 are respectively 10 and 70Tg CH4, for low (S1) and high (S2) dissolved methane concentration scenarios. A 5-year time step series between 1880 and 2004 of the global atmospheric methane (Antarctic ice core and ground station) exhibits good agreement to AFL emissions, especially for the S2 scenario. Remote sensing flux estimation and ecohydrology solutions to mitigate emission and recover AFL methane for energy production are also briefly discussed. By this approach, about 80Tg CH4 could be annually recovered for energy production in the world, 30% of which in Brazil.