The effects of water table draw-down (as a surrogate for climate change) on the hydrology of a fen peatland, Canada

Abstract

Hydrological response to climate change may alter the biogeochemical role that peatlands play in the global climate system, so an understanding of the nature and magnitude of this response is important. In 2002, the water table in a fen peatland near Quebec City was lowered by ∼20 cm (Experimental site), and hydrological response was measured compared to Control (no manipulation) and Drained (previously drained c. 1994) sites. Because of the draw-down, the surface in the Experimental pool decreased 5, 15 and 20 cm in the ridge, lawn and mat, respectively, increasing bulk density by ∼60% in the Experimental lawn. Hydraulic conductivity (K) generally decreased with depth and from Control (25–125 cm) 10⁻¹ to 10⁻⁵ cm s⁻¹ to Experimental (25–125 cm) 10⁻² to 10⁻⁷ cm s⁻¹ and to Drained (25–75 cm) 10⁻² to 10⁻⁶ cm s⁻¹. In similar topographic locations (ridge, lawn, mat), K trended Control > Experimental > Drained, usually by an order of magnitude at similar depths in similar topographic locations. Water table fluctuations in the Drained site averaged twice those of the Control site. The water table in the Control lawn remained at a stable depth relative to the surface (∼− 1 cm) because the lawn peat floats with changes in water table position. However, the Drained lawn peat was more rigid because of the denser degraded peat, forcing the water to fluctuate relative to the surface and further enhancing peat decay and densification. This provides a positive feedback loop that could intensify further peat degradation, changing the carbon cycling dynamics. Copyright © 2006 John Wiley & Sons, Ltd.