Page 146 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 6. Roles of thermokarst lakes in a warming world
The future of thermokarst lakes
Thermokarst lake dynamics are highly complex and less cyclic than often assumed (Jorgenson and Shur 2007). For Siberia, it has been reported that thaw leads to initial lake formation and lake area expansion, which is followed by rapid drainage and lake disappearance (Smith et al. 2005). Rapid lake drainage can also be observed in Alaska and the western Canadian Arctic (Hinkel et al. 2003; Plug, Walls and Scott 2008). Due to these dynamic processes, thermokarst is often considered to have a major impact in the short term (Brouchkov et al. 2004). However, its dynamic nature hampers accurate quantification of future thermokarst lake development, which stresses the need for field data (Smith et al. 2005; Davidson and Janssens 2006). Data on microbial CH4 dynamics in thermokarst lakes are essential to better estimate CO2 to CH4 emission ratios. These ratios are a main input for current permafrost climate feedback models.
Major changes in water chemistry and microbiology occur when permafrost thaw results in small thermokarst water bodies (0.001-0.01 ha). These small lakes are often not included in global models but they have a significant contribution to the hydrology and GHG emissions of the ecosystem (Downing et al. 2006; Negandhi et al. 2013; Shirokova et al. 2013). Future GHG emission models should therefore aim to include these small water bodies.
Concluding remarks and future perspectives
Due to its large total wetland area the Arctic is a significant source of atmospheric CH4 (32-112 Tg CH4 yr-1) (McGuire et al. 2009). The total permafrost carbon feedback could contribute up to 0.39°C to the rise of surface air temperature by 2300 (Schneider von Deimling et al. 2015b). Although the modeled CH4 emission from permafrost ecosystems is relatively low within the total GHG budget (2.3% of GHG release) it contributes up to half of the expected climate forcing when taking the global warming potential (GWP) into account (34 times the GWP of CO2 for 100 years) (Myhre et al. 2013; Schuur et al. 2013). Increases in thermokarst features are an early indicator of enhanced permafrost loss which is linked to enhanced GHG emissions (Bowden 2010). The balance in GHG emissions is determined by methanogenic and methanotrophic activity. Whereas methanogenesis and aerobic methanotrophy are included in most studies, there is limited knowledge of the potential of AOM to function as a CH4 filter, especially for marine-influenced thermokarst environments. Since AOM can function as
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