Hydrogeophysics reveals evidence for groundwater inputs influencing the hydrology and ecology of northern raised bogs

Northern raised peat bogs are usually assumed to be entirely precipitation-fed, implying that they lack groundwater inputs from underlying sediments. The development and persistence of patterned pools in raised bogs have historically been attributed to both surficial flow filling depressions along the peat surface, and subtle differences in peat pore water chemistry. In contrast, we find hydrogeophysical evidence that patterned pools in three northern peat bogs of Maine (USA) are partially fed by localized upwelling of minerogenous groundwater from underlying glacial sediments imaged using ground-penetrating radar. Paired point measurements of temperature and specific conductance (SpC) around numerous pools across the three raised bogs showed statistically significant relationships diagnostic of focused groundwater upwelling, despite hydraulic heads measured using nests of piezometers generally suggesting downward flow around pools. Drone-based thermal infrared (TIR) mapping, augmented by handheld TIR imaging, further indicated groundwater inputs into pools during cold and warm seasons. Surface water samples from upwelling zones showed elevated iron and manganese concentrations indicative of glacial aquifer sources.   Vegetation samples taken around two pools with contrasting groundwater inputs indicate that the composition of plant communities is associated with contrasting water chemistry. This supports the hypothesis that these inputs influence the vegetation within the raised bog ecosystem. Visual observations and information from shallow geophysics suggest that macropore, ‘peat pipe’ features might enhance vertical connectivity between groundwater and pools, and horizontal connectivity by connecting pools across the landscape.