Improving Understanding Of Peatland Hydrogeology Using Electrical Geophysics

A geophysical survey was completed in Caribou Bog, a large peatland in Maine, to evaluate<br>peatland stratigraphy and hydrology. Geophysical measurements were integrated with direct<br>measurements of peat stratigraphy from probing and with measurements of fluid chemistry. Consistent<br>with previous field studies, GPR was an excellent method for delineating peatland stratigraphy.<br>Prominent reflectors from the peat-lake sediment and lake sediment-mineral soil contacts were precisely<br>recorded up to 8 m deep. However, GPR provided no information below the mineral soil contact. 2D<br>resistivity and induced polarization (IP) imaging was used to further investigate the stratigraphy of this<br>peat basin. We observe that the peat is chargeable and that IP imaging is an alternative method for<br>defining peat thickness. This chargeability is attributed to the high surface charge density on partially<br>decomposed organic matter. The conductivity imaging resolved glaciomarine sediment thickness and its<br>variability across the basin. Terrain conductivity measured with a Geonics EM31 correlated with<br>glaciomarine sediment thickness and was effective in characterizing variability in layer thickness over<br>approximately 18 km2. The electrical imaging indicates that variations in glaciomarine sediment<br>thickness may exert a key control on the hydrogeology and vegetation distribution within this peatland.