Examining the role of allogenous and autogenous factors in the long-term dynamics of a temperate headwater peatland (southern Québec, Canada)

Plant macrofossil and testate amoebae analyses were conducted on a sedimentary core taken from a headwater peatland located near the summit of a hill at the northern extension of the Adirondack Mountains (Québec, Canada). The aims were to reconstruct the developmental stages of the peatland and to examine the allogenous and autogenous factors associated with its long-term dynamics. Results were compared with a quantitative paleoclimatic reconstruction based on the modern analog technique using pollen data from the same core. The long-term development of the peatland (pond-rich fen-intermediate fen-poor fen-bog) mainly reflects an autogenous hydroseral succession. Active peat accumulation under the relatively dry climate of the Early Holocene suggests that summer temperature was a critical factor in peat accumulation through enhanced biomass production. A major long-term decrease in net peat accumulation rates and a progressive decline of mean water-table depth occurred during the Mid- to Late-Holocene (7900-500 cal yr BP), even though annual precipitation was abundant at the time. The high summer temperature associated to the highest evapotranspiration rates maintained a low water table which in turn led to strong humification of the peat. A similar, synchronous pattern in vertical peat accumulation dynamics characterized another nearby peatland. Based on these results, we suggest that small peatlands situated atop a watershed and/or within a small watershed are ecosystems sensitive to changes in precipitation and/or evapotranspiration, due to their limited water supply.