Variability in methane emissions from West Siberia's shallow boreal lakes.

Small lakes represent an important source of atmospheric CH₄ from northern wetlands. However, spatio-temporal variations in flux magnitudes and the lack of knowledge about their main environmental controls contribute large uncertainty into the global CH₄ budget. In this study, we measured methane fluxes from small lakes using chambers and bubble traps. Field investigations were carried out in July-August 2014 within the West Siberian middle and south taiga zones. The average and median of measured methane chamber fluxes were 0.32 and 0.30 mgCH₄ m^-2 h^-1 for middle taiga lakes and 8.6 and 4.1 mgCH₄ m^-2 h^-1 for south taiga lakes, respectively. Pronounced flux variability was found during measurements on individual lakes, between individual lakes and between zones. To analyze these differences and the influences of environmental controls we developed a new dynamic process-based model. It shows good performance with emission rates from the south taiga lakes and poor performance for individual lakes in the middle taiga region. The model shows that, besides well-known controls such as temperature, pH and lake depth, there are significant variations in the maximal methane production potential between these climatic zones. In addition, the model shows that variations of gas-filled pore space in lake sediments are capable to control the total methane emissions from individual lakes. The CH₄ emissions exhibited distinct zonal differences not only in absolute values but also in their probability density functions: the middle taiga lake fluxes were best described by a lognormal distribution while the south taiga lakes followed a power law distribution. The latter suggests applicability of self-organized criticality theory for methane emissions from the south taiga zone, which could help to explain the strong variability within individual lakes. [ABSTRACT FROM AUTHOR]