Hydraulic conductivity of peat at Ellergower Moss, Scotland

Abstract

AbstractFalling head (and a few rising head) measurements were made of hydraulic conductivity k in a profile of a 7 m deep, small raised bog in southwest Scotland. The seven piezometer pipes were 39 mm diameter, and most of the measurements were made with attached tubes of 2·5 mm diameter, so that only 2–3 mm of water crossed the peat interface during a run. There were no consistent effects of pre‐flushing, direction of flow (falling, rising), or measuring‐tube size. Variability of 10–20% in k did not obscure an exponential decrease with depth from 5 × 10−6 cm s−1 at 100 cm to 0·7 × 10−6 cm s−1 at 500 cm. This decrease was uncorrelated with dry bulk density or peat stiffness, and only loosely so with a measure of humification. Calculated mean bulk velocity of pore water may be as low as 1 mm year−1. Pressure in the silty sand below the peat was 180 mbar less than expected, suggesting a thin highly impermeable layer (‘pan’?) at the peat base. The substratum may have hydrological connection with an adjacent lake. The hydraulic properties of this raised bog contrast strongly with those of a raised bog in Minnesota, and do not fit the assumptions made for Ingram's simple groundwater mound model of raised bog shape. Copyright © 2004 John Wiley & Sons, Ltd.