Pool patterning in a northern peatland: Geophysical evidence for the role of postglacial landforms

SummaryA hydrogeophysical study conducted in a 2200-ha peatland in central Maine shows evidence that a laterally continuous esker deposit extends below the peat soil following the direction of glacier retreat and coinciding with the presence of a pool system. Ground penetrating radar (GPR), electrical resistivity (ER) imaging and terrain conductivity measurements were constrained with limited hydrological measurements, direct sampling of inorganic sediments and radiocarbon dating of peat soils to develop a conceptual model for pool formation that could explain the unique pool patterning observed in other northern peatlands. GPR profiles revealed three-dimensional images of two esker crests below the easternmost edge of the pool area. GPR data was supported by ER imaging and terrain conductivity data and allowed for facies differentiation to infer processes related to esker formation during the glacier front retreat. Hydrologic data showed preferential flow of groundwater towards the esker, suggesting that pools may persist as a result of enhanced peat decomposition and carbon loss due to oxygenation and/or upward supply of alternative electron acceptors from the mineral soil along narrow, permeable inorganic esker crests. Variations in pool depths and radiocarbon dating of peat samples from the pool bottom support a model whereby pools originate at a focus centered along the two esker crests and subsequently spread laterally outwards.

Research highlights
► Sedimentary structures underlying a peatland are characterized using near surface geophysics.
► Hydrologic measurements suggest a link between the groundwater flow and pool persistence.
► The role of an esker underlying a peatland on pool development is evaluated.
► We propose a conceptual pool formation model for large peatlands underlain by permeable units.