Abstract
During August-September 2012, we sampled six hydropower reservoirs in southeastern United States. for CO2 and CH4 emissions via three pathways: diffusive emissions from water surface; ebullition in the water column; and losses from dam tailwaters during power generation. Average total emission rates of CO2 for the six reservoirs ranged from 1,127 to 2,051 mg m-2 d-1, which is low to moderate compared to CO2 emissions rates reported for tropical hydropower reservoirs and boreal ponds and lakes, and similar to rates reported for other temperate reservoirs. Similar average rates for CH4 were also relatively low, ranging from 5 to 83 mg m-2 d-1. On a whole-reservoir basis, total emissions of CO2 ranged nearly 10-fold, from ~51,000 kg per day for Fontana to ~486,000 kg per day for Guntersville, and total emissions of CH4 ranged nearly 20-fold, from ~5 kg per day for Fontana to ~83 kg per day for Allatoona. Emissions through the tailwater pathway varied among reservoirs, comprising from 20 to 50% of total CO2 emissions and 0 to 90% of CH4 emissions, depending on the reservoir. Several explanatory factors related to reservoir morphology and water quality were considered for observed differences among reservoirs.
