Seasonal and spatial variation in 13C signature of emitted methane and pore water methane in northern mires

Methane emission from northern mires shows typically strong spatial and seasonal variations. These variations have been assigned to e.g. differences in methane production due to variation in substrate input, transport pathways, methane oxidation in aerobic peat layers, and temperature variations. Stable isotope signatures of the emitted methane and methane in pore water can help us to constrain our hypotheses of these variations.

We have measured δ¹³C of methane emission in Mycklemossen mire in Sweden by automated chamber system for two years. We also have measured δ¹³C of methane in pore water in three depths in Siikaneva mire in Finland by an automated diffusion tube system for one seasonal cycle. At both sites ecosystem scale δ¹³C of emitted methane was measured using nocturnal boundary layer accumulation (NBLA) approach.

We observed systematic spatial variation in δ¹³C of emitted methane at Mycklemossen site, which mostly indicated the importance of substrate availability in explaining the spatial variability. At Siikaneva we observe systematic differences in the depth distribution of δ¹³C of pore water methane. Interestingly, this distribution is different in summer and winter.  The ecosystem scale δ¹³C of emitted methane derived by chambers and NBLA approach very close to each other. We will discuss the observations, their implications, and future integration of the data and new measurement.