HYDROELECTRIC DAMS AS “METHANE FACTORIES”: THE ROLE OF RESERVOIRS IN TROPICAL FORE ST AREAS AS SOURCES OF GREENHOUSE GASES

Abstract

Estimates of greenhouse gas emissions of hydroelectric dams are relevant when allocating public resources among the various methods for generating and conservation of electricity. Dams in tropical forest areas like the Amazon often have large drawdown zones in which of easily composed herbaceous plants can grow quickly when the water level of the reservoir falls. These plants decompose at the bottom of the reservoir when the water level rises again, thus producing methane gas. This source of methane (a greenhouse gas) is permanent, unlike the large initial emission peak from the decomposition of carbon from the soil, vegetation, and litter of the original forest that takes place after the forested area is fl ooded. Turbines and spillways in dams draw water from under the reservoir's thermocline, releasing large amounts of dissolved methane gas to the atmosphere. Carbon dioxide from the decomposition of exposed tree tops in the fl ooded forest represents another signifi cant source of greenhouse gas emissions during the early years of the reservoir implantation.