Geophysical surveys and chemical analyses on cores were carried out in three Ontario peatlands, from which we have gained a better understanding of the peat properties that control the geophysical responses. The electrical conductivity depends linearly on the concentration of total dissolved solids in the peat pore waters and the pore waters in turn bear the ionic signatures of the underlying mineral sediments. The ionic concentration, and thus the electrical conductivity, increase linearly from the surface to basement. The average bulk electrical conductivity of peatlands at Ellice Marsh, near Stratford, and at Wally Creek Area Forest Drainage Project, near Cochrane, are of the order of 25 mS/m. The Mer Bleue peatland, near Ottawa, has extremely high electrical conductivity, reaching levels of up to 380 mS/m near the base of the peat. The Mer Bleue peatland water has correspondingly high values of total dissolved solids, which originate from the underlying Champlain Sea glaciomarine clays. The dielectric permittivity in peats is largely controlled by the bulk water content. Ground penetrating radar can detect changes in water content greater than 3%, occurring within a depth interval less than 15 cm. The principal peatland interfaces detected are the near-surface aerobic to anaerobic transition and the peat to mineral basement contact. The potential for the successful detection of the basement contact using the radar can be predicted using the radar instrument specifications, estimates of the peatland depth, and either the bulk peat or the peat pore water electrical conductivities. Predicted depths of penetration of up to 10 m for Ellice Marsh and Wally Creek exceed the observed depths of 1 to 2 m. At Mer Bleue, on the other hand, we observe that, as predicted, a 100 MHz signal will penetrate to the base of a 2 m thick peat but a 200 MHz signal will not. In trod uct ionA variety of geophysical methods have been used on pe penetrating radar (GPR), resistivity, and electrom veying. The full potential of these techniques remains because our understanding of the physical factors that control the instrument response in peatlands is incomplete. The water table is normally at, or slightly below, the ground surface; the peat thickness can range from 40 cm to 10 m (e.g. Remotec 1982; Welsby 1988). In bulk, peat is mostly water, with a supporting matrix made of purely organic materials. The organic materials are t decomposed remains of plants, which can take millennia to accumulate of peat. Internal stratigraphic features and thicknesses of peatlands can vary dramatically with little predictability on the basis of surface vegetation.We discuss the use of geophysics, alone and as a supplement to conventional coring programs. We have investigated three peatland sites (Figs 1 4 , and have carried out comparisons of the electrical property variations and of the haat p h p ical properties that may be detected by geophysical method$, from sit$ rn iiim within individual pearlands. We also suggest a systematic protocol for ths ge...

Ground penetrating radar (GPR) has been applied to the mapping of stratigraphy and peat thickness of a large bog in southwestern Ontario. The GPR survey was undertaken in conjunction with a conventional coring survey and measurement of peat physical properties. The results indicate that GPR responds to peat moisture content and bulk density, which vary with stratigraphic changes. In particular, the acrotelm–catotelm boundary and the basal clay are GPR reflectors. The presence of gyttja above the clay is indicated by complex basal reflections. Ground penetrating radar is a viable alternative to an intensive coring survey for evaluating peat depth and extent.