Pollen-Derived Paleovegetation Reconstruction and Long-Term Carbon Accumulation at a Fen Site in the Attawapiskat River Watershed, Hudson Bay Lowlands, Canada

Abstract

The Hudson Bay Lowlands (HBL) constitute a globally significant carbon pool; the paleoecological record provides an opportunity to investigate long-term drivers of change in carbon accumulation and related changes in vegetation. We present a Holocene record from the Victor Fen site (VM-3-3) in Ontario’s HBL to reconstruct vegetation history, quantify rates of carbon accumulation, and determine the role of paleoclimatic drivers. Pollen analysis indicates initiation of peat accumulation over a mineral substrate, accompanied by relatively rapid rates of carbon accumulation, following emergence from the Tyrrell Sea ∼6900 yrs BP. The earliest vegetation assemblage consisted of a tidal marsh, quickly succeeding to a Typha marsh, then a poor fen dominated by Sphagnum and Cyperaceae by 6400 yrs BP. Rapid rates of isostatic uplift at the time likely contributed to these changes. Once established, this fen community persisted without major vegetation change until the most recent century, when the abundance of shrub and Cyperaceae pollen increased, suggesting increasingly minerotrophic conditions. Average rate of long-term carbon accumulation (LORCA) for the whole record (mean = 22.8 g C m-2 yr-1) is similar to other northern peatlands, and higher than the Holocene average for an adjacent bog. Increased precipitation after ∼2400 yrs BP may have contributed to the higher LORCA reconstructed for the late Holocene, but the increased precipitation did not coincide with any apparent changes in vegetation as inferred from pollen assemblages.