Annual carbon sequestration and loss rates under altered hydrology and fire regimes in southeastern USA pocosin peatlands
2022
Peatlands drained for agriculture or forestry are susceptible to the rapid release of greenhouse gases (GHGs) through enhanced microbial decomposition and increased frequency of deep peat fires. We present evidence that rewetting drained subtropical wooded peatlands (STWPs) along the southeastern USA coast, primarily pocosin bogs, could prevent significant carbon (C) losses. To quantify GHG emissions and storage from drained and rewetted pocosin we used eddy covariance techniques, the first such estimates that have been applied to this major bog type, on a private drained (PD) site supplemented by static chamber measurements at PD and Pocosin Lakes National Wildlife Refuge. Net ecosystem exchange measurements showed that the loss was 21.2 Mg CO₂ ha⁻¹ year⁻¹ (1 Mg = 10⁶ g) in the drained pocosin. Under a rewetted scenario, where the annual mean water table depth (WTD) decreased from 60 to 30 cm, the C loss was projected to fall to 2 Mg CO₂ ha⁻¹ year⁻¹, a 94% reduction. If the WTD was 20 cm, the peatlands became a net carbon sink (−3.3 Mg CO₂ ha⁻¹ year⁻¹). Hence, net C reductions could reach 24.5 Mg CO₂ ha⁻¹ year⁻¹, and when scaled up to the 4000 ha PD site nearly 100,000 Mg CO₂ year⁻¹ of creditable C could be amassed. We conservatively estimate among the 0.75 million ha of southeastern STWPs, between 450 and 770 km² could be rewet, reducing annual GHG emissions by 0.96–1.6 Tg (1 Tg = 10¹² g) of CO₂, through suppressed microbial decomposition and 1.7–2.8 Tg via fire prevention, respectively. Despite covering <0.01% of US land area, rewetting drained pocosin can potentially provide 2.4% of the annual CO₂ nationwide reduction target of 0.18 Pg (1 Pg = 10¹⁵ g). Suggesting pocosin restoration can contribute disproportionately to the US goal of achieving net‐zero emission by 2050.
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