Role and character of seasonal peat soil deformation on the hydrology of undisturbed and cutover peatlands

Abstract

This paper describes the nature and magnitude of peat soil volume changes and its relation to seasonal changes in water table at an undisturbed bog peatland and on two cutover sections of the same peatland and its effect on hydraulic conductivity. In the latter two sites, operations had ceased 2 and 7 years prior to this study, respectively. The water table dropped to a maximum depth of 40, 50, and 68 cm, respectively, at the undisturbed, 2-year, and 7-year abandoned sites and a resulted in subsidence of 0.96, 3.84, and 2.65 cm m-1, respectively. At the undisturbed site, surface elevation changes did not always correspond to water table changes, but peat underwent a period of swelling even as the water table fell, probably due to the accumulation of methane in soil pores. At all sites most volume change occurred in the upper 50 cm layer, with maximum strain of 5, 15, and 5% at the undisturbed, 2-year, and 7-year abandoned sites, respectively, and was strongly related to water table decline. A model of peat deformation in the zone of saturation (100 cm depth), based on changes in saturated soil moisture (6%), grossly overestimated strain (1%) in the saturated zone, and again methane accumulation was the suspected cause of the soil moisture decrease. Peat compression (and perhaps methane accumulation) caused hydraulic conductivity to decrease over two orders of magnitude at 75, 125, and 170 cm depth. The decrease in hydraulic conductivity as a peatland dries may be an important self-preservation mechanism (i.e., against further water loss).