Investigating the role of the critical zone structure and lithology on the hydrology and carbon dynamics of boreal peatlands in Maine

Northern peatlands are a critical component of the global carbon cycle with recent studies estimating a carbon pool of 1.1 trillion tons when considering differences in accumulation rates around the world, and representing more than twice previous estimates of stored carbon in boreal systems. We hypothesize that geologic features beneath the peat influence hydrological and biogeochemical process that affect carbon cycling within peat deposits. This linkage will likely impact greenhouse gas (e.g. CO2 and CH4) production and release from peatlands. Geology may also impact peatland development (accumulation rates) influencing the capacity of these systems to sequester and store carbon. However, the effect of lithology on the accumulation and evolution of peat has not been systematically investigated. In this work we initiate a project to expand on previous investigations in Caribou Bog (Maine) to explore how differences in mineral soil lithology may influence surface hydrology (like the presence of open water pools) and carbon fluxes across previously unexplored peatlands in Maine. The project combines an array of ground-based near-surface geophysical and hydrological methods with airborne lidar datasets to highlight the connection between surface and subsurface information acquired at different scales of measurement over each peatland. The selected peatlands are characterized by: 1) the presence (or absence) of glacial esker deposits surrounding peatland boundaries as identified from DEM images and potentially lying underneath the peat deposits; and 2) the proximity to the inland marine limit reached by the sea during the ice retreat following the last glacial period and its influence on critical zone structure and lithology. Preliminary ground-penetrating radar (GPR) results show that while some peatlands show a strong correspondence between surface pool patterning and presence of buried permeable esker deposits, other similar systems lack such correspondence. While these results may show that our initial hypothesis is oversimplified and not applicable to every peatland investigated, these inconsistencies may simply reflect the potential limitations of GPR to image the mineral soil structure beneath these peatlands. Additional geophysical data acquisition is planned to address this potential limitation.