Abstract
Abstract. Peatlands in discontinuous permafrost regions occur as a mosaic of wetland types, each with variable sensitivity to climate change. Permafrost thaw further increases the spatial heterogeneity in ecosystem structure and function in peatlands. Carbon (C) fluxes are well characterized in end-member thaw stages such as fully intact or fully thawed permafrost but remain unconstrained for transitional stages that cover a significant area of thawing peatlands. Furthermore, changes in the environmental correlates of C fluxes, due to thaw, are not well described – a requirement for modeling future changes to C storage of permafrost peatlands. We investigated C fluxes and their correlates in end-member and a number of transitional thaw stages in a sub-arctic peatland. Across peatland-lumped CH4 and CO2 flux data had significant correlations with expected correlates such as water table depth, thaw depth, temperature, photosynthetically active radiation and vascular green area. Within individual thaw states, bivariate correlations as well as multiple regressions between C flux and environmental factors changed variably with increasing thaw. The variability in directions and magnitudes of correlates reflects the range of structural conditions that could be present along a thaw gradient. These structural changes correspond to changes in C flux controls, such as temperature and moisture, and their interactions. Temperature sensitivity of CH4 increased with increasing thaw in bivariate analyses, but lack of this trend in multiple regression analyses suggested cofounding effects of substrate or water limitation on the apparent temperature sensitivity. Our results emphasize the importance of incorporating transitional stages of thaw in landscape level C budgets and highlight that end-member or adjacent thaw stages do not adequately describe the variability in structure-function relationships present along a thaw gradient.
Highlights
Northern permafrost regions contain approximately 50 % (1672 Pg) of the world’s soil carbon (C) pool and peatlands store 277 Pg of this C (Schuur et al, 2008; Tarnocai et al, 2009)
We identified the major abiotic and biotic correlates of the ecosystem – atmospheric exchanges of CO2 and CH4 across Stordalen mire and found that, as per our expectation, these environment-function relationships changed variably across the thaw gradient, suggesting that correlates of CO2 and CH4 fluxes in transitional stages are not necessarily represented well by correlates of the end-member or adjacent thaw stages
Strongest environmental factors associated with the CH4 flux across all sampled collars were- elevation, water table depth, pH, vascular green area (VGA), thaw depth and surface water C : N
Summary
Northern permafrost regions contain approximately 50 % (1672 Pg) of the world’s soil carbon (C) pool and peatlands store 277 Pg of this C (Schuur et al, 2008; Tarnocai et al, 2009). Peatlands in the permafrost regions are currently experiencing increased rates of thaw and related changes to abiotic and biotic components (structure) and elemental cycling (function; Camill, 2005; Osterkamp, 2005). Thawing peatlands are a mosaic of different wetland types, ranging from permanently frozen (e.g., palsa) to permafrost-free and minerotrophic fens (Luoto et al, 2004). Each component of these heterogeneous landscapes has distinct C function, contributing to uncertainties in estimating landscape level C budgets. Constraining the spatial variability in peatland C fluxes and related abiotic and biotic factors, is an essential step toward estimating the positive feedback potential of thawing permafrost on climate change
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