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

- An annual study on CH4 and N2O based on monthly campaigns is proposed.
- This study will contribute to fill the gap of GHG data for temperate reservoirs.
- CH4 and N2O emissions were dominated by the diffusion a the reservoir surface.
- Expressed in CO2equivalent, CH4 emissions were about 3 times those of N2O.
- The emission ratio of the reservoir is in the lower range of values for hydropower.

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.

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