Holocene development of a peatland (southern Quebec): a spatio-temporal reconstruction based on pachymetry, sedimentology, microfossils and macrofossils

This study examines the relationships between allogenic and autogenic processes during the Holocene development of a southern Quebec bog. Local vegetation, surface moisture and peat accumulation were independently reconstructed from palaeoecological data (microfossils, macrofossils, loss-on-ignition and radiocarbon dating) and sedimentological analyses conducted on seven profiles. The observed successional stages, from pond to marsh, rich fen, poor fen then bog, represents a typical hydrosere. The early wetland development provides an obvious illustration of the facilitation model: each community modified the hydrological conditions by means of peat accumulation which then favoured the onset of the succeeding stage. No direct link is evidenced between vegetation, moisture and peat accumulation, while all of them clearly reveal the initial influence of minerotrophic groundwater supply. Notably, the decrease in this allogenic influence is reflected by the increasing asynchrony of local vegetation change. The comparison of the seven profiles also shows several asynchronous moisture fluctuations at the peatland scale but none seems to be related to climate. In contrast, net peat accumulation shows similar trends in all marginal profiles and at the peatland scale. As a consequence of the initial minerotrophic supply, peat-accumulation rates were high during the early Holocene and low during the mid- and late Holocene. Our results, which show the major influence of groundwater and autogenic processes on peat accumulation, strongly contrast with the general climatic control recognized for European peatlands.