Field-scale compression of Sphagnum moss to improve water retention in a restored bog

Abstract

The restoration and subsequent regeneration of Sphagnum moss on harvested peatlands can result in poor hydrological connectivity between the regenerated Sphagnum moss and the remnant cutover peat due to the formation of a capillary barrier that favours retention of water in the underlying cutover peat. In a restored cutover peatland in Québec, Canada, this resulted in a lower soil water content of the regenerated Sphagnum moss compared to a natural analogue, which may limit carbon sequestration potential. Previous work has shown it may take > 40 years for the regenerated moss layer to overcome this capillary barrier effect, however mechanical compression may provide a novel restoration technique to weaken the capillary barrier in restored peatlands. This study evaluated the effectiveness of field-based mechanical compression to ameliorate the capillary barrier effect and increase the moisture content in a restored cutover peatland. A section of restored Bois-des-Bel peatland was compressed using a John Deere 6430 series tractor in January 2016, followed by hydrological monitoring May-August. The Compressed site was compared to a nearby Uncompressed site, and a natural peatland ∼ 2 km away, to determine relative success of mechanical compression. The compression reduced moss height by 48%, increasing bulk density by 37% and reducing the proportion of macropores by 15% throughout the moss layer. Consequently, compression increased soil water retention and average soil moisture content at the Compressed site was consistently higher throughout the moss profile than in the Uncompressed site. This increased the resilience of the moss to drying, though the degree of increased resilience is unknown. Despite not having the same hydrophysical properties of the Natural site, the Compressed site was wetter than the Uncompressed site due to the lessening of the capillary barrier effect and moving the surface closer to the water table, thus decreasing the water stress of the regenerated Sphagnum carpet.