Effect of human activity on carbon balance in meadows in a thermokarst depression in Siberia [Russian Federation]

There are around 16,000 thermokarst depressions, also known as 'Alas', located in Central Yakutia lowland within the boreal forest region with a total area of 440,000 ha. The Alas covers 17% of the total land area of Central Yakutia, Russia. Steppe grasses are widely distributed on these formations replacing boreal forests during the Alas development. Alas soils are formed with the combination of buried and superficial horizons of lake-marsh genesis and with high carbon (C) stock in the stage of thermokarst formation during the early Holocene. During the xeromorphic stage, meadows developed with the fluctuation of Alas lake. We studied the carbon budget in an Alas near Yakutsk, Russia during the snow free period (86 days) in 2006. Soil C storage in 0-40cm top layer amounted to 49.7 Mg C/ha in the forest surrounding the Alas. On the other hand, the soil C storage in the middle grassland of Alas was 4.3 times larger than in the forest, but the dry grassland reduced soil C storage to 19.1% of the forest. The cumulative microbial respiration (Mg C/ha/period) was estimated as 1.81 in dry grassland and 1.89 in middle grassland, which were smaller than that in forest (2.86). The net ecosystem production (NEP) and the net biome production (NBP=NEP-harvest) were positive in dry grassland (0.420 and 0.162 Mg C/ha, respectively), while being negative in middle grassland (-0.581 and -1.21 Mg C/ha, respectively) indicating that the larger soil C storage area reduced more C. The hay harvest as well as the microbial respiration could be strong factors in reducing C budget of grasslands in thermokarst depression of boreal forest region.