The effects of hydrologic restoration on carbon budgets and GHG fluxes in southeastern US coastal shrub bogs

Abstract

The southeastern US coastal plain was originally home to over one million ha of evergreen shrub bogs, locally known as pocosin. More than 70% have been drained for agriculture and forestry. These drained peatlands release GHGs to the atmosphere, mainly as CO2, which has resulted in significant concerns about their impact on climate change. Our long-term study at Pocosin Lakes National Wildlife Refuge (PLNWR) and adjacent private peatlands in North Carolina investigates the effect of drainage, and hydrologic restoration on carbon (C) budgets, including GHG losses, C sequestration rates, soil C respiration, and net ecosystem exchange (NEE). Soil CH4 and N2O emissions were negligible as CO2 emissions made up 99% of their GHG contributions. Carbon budgets indicate that the vast majority of C (>97%) is stored in the peat soil with the drained site having only about 53% of the peat mass found at the restored site. The reference site with the highest biomass produced the highest annual soil GHG loss of 11.3 Mg C ha−1 yr−1 followed by the drained site at 6.8 Mg C ha−1 yr−1 with the restored site having the lowest annual losses at 5.2 Mg C ha−1 yr−1. The drained site exported 0.39 Mg ha−1 yr−1 of TOC through hydraulic transport, a value 15% higher than either the restored or reference site annual mean. Eddy-covariance analyses revealed that restoring peatlands by raising water tables by 30 cm, i.e., by decreasing water table depth (WTD) from −60 to −30 cm, reduces CO2 losses to the atmosphere by >90%. When annual mean WTDs are deeper than a threshold of -30 cm, the drier peatlands generate an annual C loss and if WTDs are shallower (-20 cm) and wetter the peatlands show annual C gains, thus providing restoration guidelines.