Organic Matter Accumulation and Community Change at the Peatland–Upland Interface: Inferences from 14C and 210Pb Dated Profiles.

Peatland-margin habitats with organic matter accumulation of 40–150 cm make up a significant but poorly quantified portion of Canada’s boreal forest region. Spanning the transition between non-wetland forest and fen proper, these ecosystems represent a zone of complex environmental and vegetation change, yet little is known about their ecological function or development. We here use vegetation and macrofossil analysis, traditional 14C, bomb-spike 14C, and 210Pb dating to investigate the development, organic matter accumulation, and recent vegetation history of peat margin communities at two sites in central Saskatchewan, Canada. Although similar in general shape, bomb-spike 14C and 210Pb chronologies show limited agreement in three of the four profiles examined, with 210Pb generally producing younger ages than 14C. Peat initiation and long-term organic matter accumulation at the Old Black Spruce (OBS) transect were probably driven mainly by the dynamics of Sphagnum, whereas at the Sandhill Fen (SF) transect, they were controlled by water level fluctuations in the neighboring fen. Bryophyte macrofossils suggest a recent drying of the vegetation surface at both sites, most likely triggered by regional drought in the late 1950s and 1960s. At OBS, the shift from Sphagnum- to feather moss-dominated communities continued in the 1990s, possibly reflecting effects of direct disturbance on local drainage patterns. Overall, our results suggest that community composition and C dynamics of peat-margin swamps respond dynamically to climatic and hydrologic fluctuations. However, uncertainties regarding the reliability of different chronologies limit our ability to link observed community changes to specific causal events. [ABSTRACT FROM AUTHOR]