Annual carbon sequestration and loss rates under altered hydrology and fire regimes in southeastern USA pocosin peatlands.

Abstract

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 21.2Mg CO2 ha-1 year-1 (1Mg=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 2Mg CO2 ha-1 year-1 , a 94% reduction. If the WTD was 20 cm, the peatlands became a net carbon sink (-3.3Mg CO2 ha-1 year-1 ). Hence, net C reductions could reach 24.5Mg 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 0.75million ha of southeastern STWPs, between 450 and 770 km2 could be rewet, reducing annual GHG emissions by 0.96-1.6Tg (1Tg=1012 g) of CO2 , through suppressed microbial decomposition and 1.7-2.8Tg 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 (1Pg=1015 g). Suggesting pocosin restoration can contribute disproportionately to the US goal of achieving net-zero emission by 2050.