CH₄flux in an alas ecosystem formed by forest disturbance near Yakutsk, Eastern Siberia, Russia

Alas is a round area of grassland with a pond at the center, formed by subsidence associated with permafrost thawing in Taiga forests in eastern Siberia. Some Alases have a Pingo, which is a round mound formed by the refreezing of the Alas pond. To characterize the relationship between the CH4 dynamics and soil properties in a forest-Alas ecosystem, we investigated 2 line transects in an Alas near Yakutsk: one transect from the forest to the pond (300 m), and the other from the top of the Pingo to the pond (26 m). Both soil pH and EC in the topsoil were higher in the grassland and the Pingo (5.8–7.1 for pH and 7–141 mS m−1 for EC) than in the forest (4.3 for pH and 1–17 mS m−1 for EC). The organic carbon contents of the soils were also higher in the grassland and the Pingo than in the forest. CH4 uptake in the forest soils ranged from −13 to −17 µg C m−2 h−1. On the other hand, CH4 emission in the grassland increased from −8 to 3.8 × 103 µg C m−2 h−1 with the approach to the pond. Large CH4 emissions of 0.6 to 7.0 × 103 µg C m−2 h−1 were observed at the edge of the pond. The values of the CH4 fluxes were similar to those previously reported −25 to −5 µg C m−2 h−1 for forests and 0.1 to 5.2 × 103 µg C m−2 h−1 for wetlands in Alaska and northern Europe. CH4 fluxes were strongly correlated with the soil moisture content, but not with the soil temperature. No CH4 flux was observed in the Pingo soils, probably due to the large accumulation of salts. These results suggest that Alas formation with forest disturbance increases CH4 production and decreases CH4 consumption due to the accumulation of salts and the increase in the soil moisture and organic carbon content in the Alas soil.