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SOC stability is represented by turnover time τ, indicating soil organic carbon activity based on carbon inputs and outputs. The most straightforward and effective way to calculate τ is by assuming a steady-state system with constant SOC stock, irrespective of pool differentiation, and equal inputs and losses. Using these assumptions, τ for various SOC pools in lumped ecosystems (representing average ecosystems in a given area) has been estimated to range between 10-2 and 103 years. Nevertheless, wetlands show a higher degree of complexity in comparison to upland ecosystems due to seasonal variations in inundation, leading to changes in redox conditions, microbial activity, and plant processes These factors indicate that τ of SOC in wetlands may seasonally change.
In this project, we studied the turnover time of the different pools (dissolved organic carbon, particulate organic carbon and mineral associated organic carbon) using the output from BRTSim-BAMS4 (Biotic and Abiotic Model for SOM version 4, Pasut et al., 2021) and compute τ at near-steady state at a monthly steps. The study covers all global wetlands at 0.5° resolution from 2000 to 2017.
On a global scale, the turnover time of soil organic carbon ranges from 1 to 1,000 years. Anaerobic respiration controls τ in approximately 78% of global wetlands, while aerobic respiration plays a role in 15% of wetland areas, and abiotic destabilization from soil minerals contributes to 5%. Notably, τ can vary significantly in temperate, continental, and polar regions, with up to a tenfold difference, due to seasonal temperature changes. This variation can lead to a shift from aerobic to anaerobic control of SOC turnover. The observed seasonal variability in SOC turnover highlights the vulnerability of wetlands to climate-induced changes in seasonality. To accurately estimate carbon exchanges between land and the atmosphere, it is crucial to account for these seasonal fluctuations at geographic scales.
More details in PUBLICATIONS.
Figure 1. Long-term average turnover times τ.
Figure 2. Geographic distribution of the dominant processes controlling τ of SOC.
Figure 3. Long-term monthly average C fluxes and soil organic carbon turnover time τ.
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