Abiotic controls on permafrost C mineralization rates assessed based on incubating samples from 4 contrasting Arctic localities
Samuel Faucherre, PhD Student, CENPERM.
The vulnerability of the large carbon stocks stored in soils of the northern permafrost region is a key factor for understanding the potential warming climate feedback mechanism of greenhouse gas release to the atmosphere from thawing permafrost. It is widely accepted that the rate of carbon dioxide release is strongly related to soil temperature and water content, thus the overall environmental conditions given to microorganisms responsible for decomposing permafrost organic matter (Elberling et al., 2013). Here we assess the controls on permafrost terrain carbon lability based on 240 samples from more than 100 sites at four contrasting arctic localities and diverse landscapes. All samples were incubated for 1 year at field water content levels under similar temperature and oxygen condition. Selected replicates of the samples were wet thieved into 3 different grain size fractions separately incubated. While Kuhry et al. (in prep.) studied the dataset for landscape-level carbon lability classification, this study shows the importance of abiotic physical sediment parameters such as the initial organic carbon content, the C/N ratio, the carbon age and the substrate grain size. We demonstrate that the single most important parameter controlling mineralization is the total carbon content but including nitrogen content and sediment ages provide improved understanding of the observed variability. Results also show that grain size distribution, and particularly the finest grain sizes, can significantly influence the observed greenhouse gas production rates. We describe permafrost carbon mineralization rate over time using 5 rate measurements over a year for each sample and project mineralization rates for 10 years of incubation - around 50 field years - using three-pool C dynamics model (Schädel et al., 2013). We conclude that changes in observed rates decrease significantly over this time frame and need to be considered in future estimates of the permafrost carbon feedback to climate.
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