The Influence of Thermokarst on Potential Decomposability of Soil Organic Matter in a Taiga and Tundra setting in NE Russia

Abstract:

Permafrost regions play a key role in global carbon budgets because of the size and vulnerability of their soil organic carbon (SOC) stock. Climate change is expected to raise soil temperatures resulting in an increased soil organic matter (SOM) source available for decomposition. Mineralized in the form of greenhouse gasses (GHG), this carbon can cause a positive feedback for further climate change.

Thermokarst lake formation show a cyclic behaviour starting with ice melt, lowering of the permafrost table, ground surface subsidence, the formation of wetlands and eventually thermokarst lakes. In time, these lakes often drain either by proceeding permafrost degradation and talik formation, or by being cut into by another water body or drainage channel.

The potential decomposition (quality) of SOM is of great importance to predict potential GHG release from permafrost regions and model global climate scenarios. Thermokarst development is often considered an important factor in permafrost degradation and increasing availability of SOM for decomposition.

However, the influence of past thermokarst events and thus episodes of increased decomposition, is less understood. What is the difference in SOM between sites that have undergone former thermokarst cycles and sites that have not? Will there be a different response in decomposition upon climate change for these different land surface types?

Two Siberian field sites, Spasskaya Pad (boreal forest) and Kytalyk (tundra), both with extensive active and relict thermokarst features, have been sampled. Simple geochemical characteristics that might be indicative of potential decomposition have been determined for all groups and will be compared. A comparison of results from permafrost affected and intact areas are presented and discussed.