Aug 10th, 2012
From International Rivers
Typically, at moderate sizes, power generated by dams and reservoirs is considered “green.” However, a new study from Washington State University has found that during times of drawdown — a period in which the water level behind a dam is rapidly lowered — temperate reservoirs can produce up 20 times more methane than normal.
Methane is a greenhouse gas 25 times moreeffective than CO2 at trapping heat in the atmosphere over 100-year period, and is a hundred times more potent over 20 years. It is produced naturally in reservoirs thanks to biological activity.
“Bridget Deemer, a doctoral student at Washington State University-Vancouver, measured dissolved gases in the water column of Lacamas Lake in Clark County and found methane emissions jumped 20-fold when the water level was drawn down. A fellow WSU-Vancouver student, Maria Glavin, sampled bubbles rising from the lake mud and measured a 36-fold increase in methane during a drawdown.”
Though researchers have long known that methane levels spike in reservoirs during drawdown, this study was the first to show the relationship and put a number on the actual methane emissions.