Incorporating spatial variation to estimate carbon fluxes in a tundra landscape undergoing permafrost thaw

Background/Question/Methods and Results/Conclusions

  The future carbon (C) balance of high latitude ecosystems is dependent on the sensitivity of biological processes (photosynthesis and respiration) to the physical changes occurring with permafrost thaw. But predicting C exchange in these ecosystems is difficult because the thawing of permafrost is not a uniform and homogeneous process. We measured net ecosystem exchange (NEE) of C using eddy covariance (EC), in a tundra landscape visibly undergoing thaw, during two 6-month campaigns in 2008 and 2009. We developed a spatially explicit quantitative metric of permafrost thaw based on variations in microtopography and incorporated it into an EC carbon flux estimate using a generalized additive model (GAM). This model allowed us to make predictions about C exchange for the landscape as a whole, and for specific landscape patches throughout the continuum of permafrost thaw and ground subsidence. Our objective was to estimate the C balance of a heterogeneous landscape and more accurately determine the collective effect of permafrost thaw on ecosystem C balance. During June through November of 2008, the GAM predicted the landscape on average took up 337.1 gCm^-2 and released 289.5 gCm^-2, resulting in a net C gain of 47.5 gCm^-2. During April through October of 2009, the landscape on average took up 498.7 gCm^-2 and released 410.3 gCm^-2, resulting in a net C gain of 87.8 gCm^-2. On average between the years, areas with the highest permafrost thaw took up 17.7% more and respired 3.3% more C than the average landscape. Areas with the least thaw took up 15% less and respired 5.1% less than the landscape on average. By incorporating spatial variation into the EC C estimate, we were able to determine how thaw affect C flux. Overall, permafrost thaw increases the amplitude of the C cycle by stimulating both C release and sequestration.