HYDROLOGY AND MICROCLIMATE OF A PARTLY RESTORED CUTOVER BOG, QUÉBEC

Abstract

Peatlands do not readily return to functional wetland ecosystems after harvesting (cutting), because the harsh hydrological and microclimatic conditions are unsuitable for Sphagnum regeneration. In this study, drainage ditches blocked after harvesting restored the water balance to a condition similar to a nearby natural bog. Evaporation averaged 2.9 and 2.7 mm day -1 on the cutover and natural bog, respectively. Evaporation consumed most of the rainfall input (86 and 80%, respectively), whereas runoff was minor at both sites (6 and 4%, respectively). However, the water table position was markedly different at these sites. Median water table depth was 0.05m below the surface in the natural bog, compared with 0.44m in the cutover bog (ditches blocked). Changes to the peak soil matrix owing to drainage and cutting reduced the specific yield (Sy) of the peat to 0.04-0.06 from 0.35-0.55, causing exaggerated water table changes in the cutover site. Nevertheless, volumetric soil moisture in the cutover site (0.67 ±.08) had low variability, and was maintained above moisture contents found in Sphagnum hummocks in the natural bog (0.48 ±.10), although less than on Sphagnum lawn (0.84 ±.11). Poor Sphagnum regeneration on cutover surfaces can therefore be attributed to its inability to extract water from the underlying peat, which retains water at matric suction greater than the non-vascular Sphagnum can generate. The corrupted iron pan under main ditches has permitted partial recharge of the underlying aquifer, reducing local hydraulic gradients, thereby decreasing vertical seepage loss.