A conceptual model of volume-change controls on the hydrology of cutover peats

Abstract

Modeling hydrological processes in certain peats requires a detailed understanding of short-term changes in soil volume and it's influence on the system's hydraulic properties. A study of cutover sites abandoned for 7-years (H92) and 2-years (H97), and an undisturbed section of the Lac Saint-Jean (LSJ) cutover bog was conducted to characterize peat volume changes and its associated hydrological behaviour. Shrinkage and compression accounted for 96–97% of seasonal volume change. Saturated hydraulic conductivity ( K S) varied linearly with peat compression; a 1 cm decrease in peat thickness causing a 5.2 cm d −1 decrease in K S at H92, and a 1.4 cm d −1 decrease in K S at H97. A 2–6% seasonal decrease in saturated volumetric moisture content ( θ S) at the cutover sites was partly due to soil compression, although the development of CH 4 bubbles possibly affected moisture content. In the unsaturated zone moisture retentivity ( θ– Ψ) was seasonally transient due to the shifting soil structure. The greater volumetric response to a change in water storage of the more porous and less decomposed peat at H97 indicates a long-term decreasing trend in peat compressibility due to irreversible losses in pore volume. Deterioration of high water storage and low water retention properties at H92 suggests that cutover sites abandoned for longer periods will become increasingly hostile to Sphagnum recolonization despite the blockage of drainage ditches.