Estimation and Uncertainty of Recent Carbon Accumulation and Vertical Accretion in Drained and Undrained Forested Peatlands of the Southeastern USA

Abstract

The purpose of this study was to determine how drainage impacts carbon densities and recent rates (past 50 years) of vertical accretion and carbon accumulation in southeastern forested peatlands. We compared these parameters in drained maple‐gum (MAPL), Atlantic white cedar (CDR), and pocosin (POC) communities in the Great Dismal Swamp National Wildlife Refuge (GDS) of Virginia/North Carolina and in an intact (undrained) CDR swamp in the Alligator River National Wildlife Refuge (AR) of North Carolina. Peat cores were analyzed for bulk density, percent organic carbon, and 137Cs and 210Pb. An uncertainty analysis of both 137Cs and 210Pb approaches was used to constrain error at least partially related to mobility of both radioisotopes. GDS peats had lower porosities (89.6% (SD = 1.71) versus 95.3% (0.18)) and higher carbon densities (0.082 (0.021) versus 0.037 (0.009) g C cm−3) than AR. Vertical accretion rates (0.10–0.56 cm yr−1) were used to estimate a time period of ~84–362 years for reestablishment of peat lost during the 2011 Lateral West fire at the GDS. Carbon accumulation rates ranged from 51 to 389 g C m−2 yr−1 for all sites. In the drained (GDS) versus intact (AR) CDR sites, carbon accumulation rates were similar with 137Cs (87GDS versus 92AR g C m−2 yr−1) and somewhat less at the GDS than AR as determined with 210Pb (111GDS versus 159AR g C m−2 yr−1). Heightened productivity and high polyphenol content of peat may be responsible for similar rates of carbon accumulation in both drained and intact CDR peatlands.

Linking ecosystem function and hydrologic regime to inform restoration of a forested peatland

“…Hydrologic regime (mean and variation in water levels) exerts strong, long-term controls on peat accretion, with prolonged inundated or saturated conditions greatly reducing microbial decomposition. However, accretion rates are slow (0.3-6 mm/yr; Whitehead and Oaks, 1979;Craft and Richardson, 1993;Drexler et al, 2017), meaning current peat depths largely reflect historical rather than contemporary hydrologic regimes. Yet, reductions in contemporary water levels amplify both decomposition rates (Wosten et al, 1997;Wust-Galley et al, 2016) and fire vulnerability (Turetsky et al, 2015), and can lead to attendant losses of historical peat deposits and carbon storage (Reddy et al, 2015).…”

Carbon Chemistry of Intact Versus Chronically Drained Peatlands in the Southeastern USA

“…Furthermore, although dry peats are aerobic, which favors microbial decomposition and phenol oxidase activity, the principle enzyme that breaks down phenolic compounds (including lignin) has been shown to be restricted under low soil moisture conditions (Freeman et al, ; McLatchey & Reddy, ; Toberman et al, , ; Wang et al, ; Figure ). While we acknowledge that anaerobic microsites may be present under unsaturated conditions, southeastern peatlands have low‐BD soils (Drexler et al, ; Keiluweit et al, ). It is important to note that there were also some tangible differences between the surficial peat layers at AR relative to the GDS.…”

“…The minerotrophic peatlands in our study stand in contrast to short pocosins, which are also forested, but are entirely ombrotrophic (Richardson, ). In addition to streamflow, MPL2 and MPL3 sites at the GDS also receive consistent groundwater contributions (Drexler et al, ). The water table is near or at the surface at both AR and GDS during the winter season.…”

“…Climate in the AR is similar to that in the GDS. Cores were collected from three sites southeast of Sawyer Lake in an undrained stand of dense AWC, approximately 70 years old (Drexler et al, ). The sites also contained minor amounts of swamp tupelo ( Nyssa biflora Walter), pond pine, loblolly bay ( Gordonia lasianthus L.), and sweetbay ( Magnolia virginiana L.; DeBerry & Atkinson, ).…”

“…Generally, %OC consistently increased with depth at both sites, but this change was minor in AR peats, demonstrating enhanced stability of the carbon sink with depth (Table S5; Drexler et al, 2017). An increase in the relative content of OC with depth is expected as peats decompose (most notably via carbohydrate loss) and because inorganic materials are unavailable for dilution of soil organic matter in pocosin and AWC swamps, which receive most or all of their hydrologic inputs from precipitation (Leifeld et al, 2012;Tfaily et al, 2014).…”