Hydrology-mediated differential response of carbon accumulation to late Holocene climate change at two peatlands in Southcentral Alaska

Abstract

Peatlands are among the largest reservoirs of terrestrial carbon in the northern hemisphere. Understanding how this reservoir will respond to climate changes is critical to assessing potential climate feedbacks. Peatland carbon accumulation rates (PCAR) are controlled by the difference between production and decomposition, which is affected by local and climatic factors including hydrology and temperature. To better understand how local controls can influence the response of PCAR to climate change, we investigated modern hydrology, paleohydrology, and PCAR at two nearby Sphagnum-dominated peatlands with different surficial geology (lowland and moraine settings) in Southcentral Alaska. Modern hydrological data indicated a higher rate of subsurface drainage at the lowland site, suggesting greater hydrologic sensitivity to prolonged dry periods of the past. We investigated past responses of these peatlands to well-documented climatic changes, like the Medieval Climate Anomaly (MCA) at ∼1000–600 cal yr BP and Little Ice Age (LIA) at ∼600–200 cal yr BP, using water-table depth (WTD) inferred from testate amoebae and PCAR calculated from loss-on-ignition and 14C-dating analyses. Our results indicate that WTD and PCAR remained relatively stable at the moraine site throughout the last 1100 years, including the MCA and LIA. However, the lowland site experienced relatively stable WTD and higher PCAR during the MCA, but highly variable WTD and lower PCAR during the LIA. These differences suggest that hydrology and likely decomposition were the primary control on PCAR at these peatlands. Our results highlight the importance of local-scale controls, like surficial geology, in mediating the response of peatland hydrology and carbon accumulation to climate change.