Methane and nitrous oxide annual emissions from an old eutrophic temperate reservoir

Two greenhouse gases -methane (CH₄) and nitrous oxide (N₂O) - were monitored monthly during one year (2011) at the Eguzon Reservoir in France. The objective of the study was to quantify for the first time in a temperate area the total emissions of these gases through the main emission pathways (diffusion and bubbling from the reservoir, degassing and downstream diffusion). The reservoir was impounded in 1926 and had, in 2011, a eutrophic status promoting high organic matter degradation and nitrification-denitrification, all favouring CH₄ and N₂O production. CH₄ and N₂O emissions were dominated by diffusion from the reservoir surface (respectively 78.0% and 92.3%). Ebullition was only observed for CH₄ and accounted for 14.0% of total CH₄ emissions. Downstream degassing and diffusion represented 8.1% of the total CH₄ emissions and 7.7% of the total N₂O emissions.