Quantifying Hydrological and Dissolved Organic Carbon (DOC) Dynamics in an Eastern Quebec Peatland Managed with the ACrotelm Harvesting Method (ACM)

Abstract

Horticultural peat extraction in Canada requires removal of vegetation and partial drainage of the peatland, resulting in altered ecohydrological conditions, changes to dissolved organic carbon (DOC) chemistry and the peatland becoming a net carbon emitter. This study explores the impacts of a new “ACrotelm Harvesting Method” (ACM) on the hydrological and DOC dynamics on an ombrotrophic bog near Pointe-Lebel, Quebec (49º8’N, 68º13’W). The ACM represents a less invasive method in contrast to vacuum-harvesting, and harvests 10 cm of acrotelm peat by lifting and replacing surface vegetation. This study utilized paired well and piezometer nests (35, 60 and 85 cm depth) to measure water table depth, specific yield, saturated hydraulic conductivity, DOC concentration and quality across four peatland sections each harvested in a different year (2021 to 2024) using ACM, and compared these results to two unharvested control sections within the study area. Measurements were obtained pre- and post-harvest from the section harvested in 2024, which was used as a case study. Post-harvest measurements indicated that the surface was 15 cm closer to the water table, as a function of harvesting acrotelm peat and compression caused by the ACM machinery, resulting in a vertical shift of the ground surface into deeper peat. The lower specific yield and transposition of saturated hydraulic conductivity values observed at deeper depths pre-harvest to shallower depths post-harvest provided further evidence for this vertical shift. This shift resulted in leaching of organic matter below the harvested layer, which increases microbial activity (as indicated in by DOC quality metrics) and the DOC concentration, with the largest increase observed in the top 60 cm of the peat profile. A chrono-sequence of the harvested sections indicated a continuous increase of DOC concentration following the initial increase post-harvest, and a shift towards a higher degree of humification with time since harvest. The magnitude of changes in the peat hydrophysical properties and DOC dynamics observed at the ACM-harvested sections are lower than those observed in vacuum-harvested sites, suggesting a smaller impact of ACM. Further, effects of ACM on hydrophysical properties and DOC dynamics are relatively short-lived.