The impact of peat harvesting and natural regeneration on the water balance of an abandoned cutover bog, Quebec

Abstract

Abstract:Harvested sites rarely return to functional ecosystems after abandonment because drainage and peat extraction lower the water table and expose relatively decomposed peat, which is hydrologically unsuitable for Sphagnum moss reestablishment. Some natural regeneration of Sphagnum has occurred in isolated pockets on traditionally harvested (block-cut) sites, for reasons that are poorly understood, but are related to natural functions that regulate runoff and evaporation. This study evaluates the water balance of a naturally regenerated cutover bog and compares it with a nearby natural bog of similar size and origin, near Riviere du Loup, Quebec. Water balance results indicated that evapotranspiration was the major water loss from the harvested bog, comprising 92 and 84% of total outputs (2Ð9 mm day 1 ) during the 1997 and 1998 seasons, respectively. Despite denser tree cover at the harvested site, evapotranspiration from the natural bog was similar, although less spatially variable. At the harvested site, evaporative losses ranged from 1Ð9 mm day 1 on raised baulks and roads to 3Ð6 mm day 1 from moist surfaces with Sphagnum. Although about half of the ditches were inactive or operating at only a fraction of their original efficiency, runoff was still significant at 12 and 24% of precipitation during the 1997 and 1998 study seasons, respectively. This compares with negligible rates of runoff at the natural bog. Thus the cutover bog, although abandoned over 25 years ago, has not regained its hydrological function. This is both a cause and effect of its inability to support renewed Sphagnum regeneration. Without suitable management (e.g. blocking ditches), this site is not likely to improve for a very long time.

A water-table dependent reservoir model to investigate the effect of drought and vascular plant invasion on peatland hydrology

“…Thus the averaged percolation rate was about < 60mm/year and be considered negligible for the observation wells located in the closed areas with vascular plants. This is close to Van Seters and Price (2001), who omitted percolation in their water balance of Quebec peatlands. The runoff coefficient changes with the WT depth (equation 9).…”

“…where db is the change in peat thickness, measured as a change in surface elevation (Van Seters and Price, 2001). Surface elevation changes (db) were monitored at the four well locations with different peat depths by measuring the distance between the Sphagnum capitulum elevation and the top of the wells.…”

“…Frequent WT drawdowns creating a deeper and thicker acrotelm than is observed in intact peatlands may lead to further degradation and to a reinforcement of the runoff generation by erosion phenomena, change the water quality (Daniels et al, 2008) and modify evapotranspiration (Restrepo et al, 1998). This is also evidenced in harvested sites where drainage and peat extraction lower the WT, expose relatively decomposed peat and increase the runoff (Van Seters and Price, 2001), whereas creating artificial drain blocking increases the WT, modifies the runoff and the water quality (Worrall et al, 2007).…”

Moisture dynamics and hydrophysical properties of a transplanted acrotelm on a cutover peatland

“…In contrast, the natural site demonstrated a diurnal change in VMC of three times lower at ¾10%. Studies have shown that evaporation can range from 2Ð7-2Ð9 mm d 1 at natural peatlands, 2Ð9-3Ð1 mm d 1 at bare/harvested peatlands and 2Ð6-2Ð9 mm d 1 at partially restored peatlands (mulch covered) (Price, 1996;Price et al, 1998;Van Seters and Price, 2001). However, the daily  c changes at the experimental site capitula represent a daily loss of ¾10 mm, over three times greater than the studied natural and standard restored sites.…”

“…In areas such as the St Lawrence lowlands in Québec, loss of peatlands for peat extraction exceed 70% (Van Seters and Price, 2001). Block-cutting and vacuum extraction (dry harvest) techniques have been used primarily for the peat horticulture industry in Canada.…”