The role of sub-peatland critical zone structure on the hydrology of northern peatlands

The hydrology of northern peatlands is increasingly recognized to be influenced by groundwater flow between peat and underlying mineral sediments. These hydrologic fluxes have been measured in peatlands of central and northern Maine where peatlands formed in depressions within the complex landscape left after the last glacial ice retreat. Although most of these peatlands formed on top of a low permeability confining glaciomarine clay, surface digital elevation maps and subsurface geophysical datasets (ground penetrating radar, electromagnetic and resistivity imaging) indicate that, in places, they are often in hydrogeological contact with eskers (glacial outwash deposits) and possibly even directly in contact with bedrock. Hydrogeological datasets, including direct hydraulic head observations and indirect observations of seepage fluxes, support the case that these points of hydrogeological contact exert a profound influence on the surface hydrology, including pool formation, and ecology of these peatland systems. The unique properties of peat, including the formation of pipe structures, result in highly focused discharges of mineralized water as evidenced from temperature sensing and aqueous geochemistry data (specific conductance, dissolved iron, dissolved manganese). These pipe networks may exert a control on carbon cycling in peatlands via the delivery of nutrients, or possibly by serving as conduits for the release of free phase gas stored in the deep peat. Preliminary observations using gas traps lend support to this hypothesis.