Effect of inundation, oxygen and temperature on carbon mineralization in boreal ecosystems

•We measured CO2 and CH4 production from boreal forest and peat litter and soils.•Flooding led to a 24% decrease in CO2 production and a 32% increase in CH4 production.•Higher temperatures resulted in more CO2 and CH4 production under both flooded and non-flooded conditions.•C release was generally litters > soils, but varied with treatment conditions.

The inundation of boreal forests and peatlands through the construction of hydroelectric reservoirs can increase carbon dioxide (CO2) and methane (CH4) emission. To establish controls on emission rates, we incubated samples of forest and peat soils, spruce litter, forest litter and peatland litter collected from boreal ecosystems in northern Quebec for 16 weeks and measured CO2 and CH4 production rates under flooded or non-flooded conditions and varying oxygen concentration and temperature. CO2 production under flooded conditions was less than under non-flooded conditions (5-71 vs. 5-85 mg C g− 1 C), but CH4 production under flooded conditions was larger than under non-flooded conditions (1-8158 vs. 0-86 μg C g− 1 C). The average CO2 and CH4 production rate factor for flooded:non-flooded conditions was 0.76 and 1.32, respectively. Under flooded conditions, high oxygen concentrations increased CO2 production in peat soils but decreased CH4 production in forest and peat soils and spruce litter. Warmer temperatures (from 4 to 22 °C) raised both CO2 production in peat soils and peatland litter, and CH4 production in peat soils and spruce litter. This study shows that the direction and/or strength of CO2 and CH4 fluxes change once boreal forests and peatlands are inundated.