Prediction of GHG Emissions from a New Reservoir

Abstract

Not until the 1990s was the significance of carbon emissions from reservoirs to greenhouse gas (GHG) accumulation in the atmosphere realized. Currently, hydroelectric projects proposed for World Bank funding must estimate their net GHG footprint, which in most cases has been estimated based on field measurements from similar reservoirs. Here we describe the development and application of CE-QUAL-W2 for prediction of future water quality and net GHG emissions from the proposed Amaila reservoir and downstream Kuribrong River in Guyana, South America. Sediment diagenesis was simulated, and the model enhanced to include the decomposition of a submerged tropical forest. The project site is located upstream of Amaila Falls in the remote highlands of the Guiana Shield. The water quality of the upper Kuribrong River exhibits low pH, low alkalinity, and somewhat high organic carbon concentrations, which is very different from reservoirs in the lowlands of French Guiana and Brazil where GHG fluxes have been measured. High CO 2 concentrations in the reservoir were caused primarily by the low pH and high CO 2 concentrations in the river inflows. Much of this CO 2 was emitted to the atmosphere within the reservoir, and most of the rest was passed through the dam. Net CO 2 emissions for the average flow year with vegetation harvested or burned were 30,799 T/yr. Net emissions for the no removal of vegetation were 71,824 T/yr. Methane concentrations in the dam outflow were less than 0.8 mg/L after the first year and 0.4 mg/l after 5 years.