A FIELD-SCALE, NATURAL GRADIENT SOLUTE TRANSPORT EXPERIMENT IN PEAT AT A NEWFOUNDLAND BLANKET BOG

A field-scale, natural gradient solute transport experiment conducted at a Newfoundland blanket bog resulted in an asymmetrical plume owing to solute retardation in the dual-porosity matrix, An order of magnitude decrease in hydraulic conductivity 10-20 m downslope of the spill caused the transport rate to decrease and lateral dispersion to increase. Most transport occurred near the watertable and the transport rate increased as the watertable rose. Hydraulic conductivity between a depth of 0 and 0.2 m was 1.6 x 10(-2) m s(-1), whereas at a depth of 0.5 m it was 5-6 orders of magnitude lower owing to greater compaction and humification of the peat with depth. At a depth of 0.4-0.45 m diffusion may have become the dominant transport mechanism. In spite of the retardation process, the solute front's rate of movement was relatively high, about 2.3 m day(-1), owing to a combination of the high watertable during the study and a relatively steep hydraulic gradient of 0.055. Rain caused dilution and mixing of solute near the watertable, Evaporation did not have an appreciable effect on solute concentration, which is attributable to the high transport rate.