TEMPORAL CHANGES IN GROUND-WATER HYDROLOGY AND SOLUTE TRANSPORT IN CARIBOU BOG, MAINE

Piezometers installed in Caribou Bog, a 2200 hectare peatland located in central Maine, have been monitored over the past five years to evaluate temporal patterns in ground-water flow within this peatland. A saline tracer experiment, monitored using geophysical and direct sampling methods, was initiated in June 2001 to assess solute transport processes within peat. This past year, a boardwalk was constructed to allow public access to the peatland, and we were concerned that the boardwalk would alter flow patterns and effect the tracer experiment.

To assess the impact of the boardwalk, water-level data collected from piezometer clusters during and after boardwalk construction were compared to previously collected water-level data. Two possible outcomes were hypothesized: 1) trenching for the boardwalk would act as drainage ditches or 2) permeability reduction by peat compressing under the weight of the boardwalk would slow and divert flow. Preliminary analysis of water table maps suggest that the boardwalk has had little impact on flow patterns in Caribou Bog.

The NaBr Tracer injected into the peatland in June 2001 has moved little over the past two years. Solute transport modeling of the saline tracer indicate that matrix diffusion is slowing the migration of the tracer. Numerical simulations that incorporate matrix diffusion indicate an inflection point will be present when plotting concentration of tracer in the injection well against time and this pattern is present in our specific conductance measurements. We continue to monitor the migration of the tracer.