24-11 Reconstructing Carbon Accumulation and Vegetation Development in Pennsylvania Freshwater Fens

Session: Lake Sedimentary Records of Past Climate and Environment (Posters)

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Abstract:

Carbon accumulated and stored in wetlands is a major sink of atmospheric carbon dioxide. However, accumulation rates and total carbon stocks of freshwater, non-tidal marshes, and fens in temperate climates such as Pennsylvania are poorly characterized. The study features two large headwater fens in southeastern PA, Great Marsh and Pine Swamp in Chester and Berks Counties, respectively, which are among few surviving examples of natural valley-bottom wetlands formed within the Mid-Atlantic post-periglacial environment during the Holocene. To investigate the development of these wetlands during the Pleistocene to Holocene climate transition,  multi-proxy data are presented, including loss-on-ignition (LOI) organic matter content, carbon and nitrogen (C:N) ratios, bulk soil organic δ13C, plant macrofossils, and sedimentary charcoal. This multi-proxy dataset serves to reconstruct the Holocene history of carbon accumulation and paleoecology from freshwater wetlands in the Piedmont province of southern Pennsylvania. Additionally, subsurface sediments were sampled from buried wetland soils at Millbrook Marsh, Hellertown Marsh, and Little Conestoga Creek as a regional reference database for the two main freshwater wetlands surveyed. At Great Marsh, organic matter first accumulated between ~11,000 - 8,200 years ago, with LOI values up to 80% and a substantial amount of woody debris incorporated into the organic-rich sediments. Organic accumulation ceased or was later oxidized during the mid and late Holocene (possibly historically) as 8,000-year-old organic sediments are unconformably capped by a ~40 cm modern organic horizon. At French Creek, the LOI values peaked at ~90%, and radiocarbon dating ages the basal peat layer at the site at ~ 7,000 cal yr BP. Soil coring revealed prominent Spruce/Tamarack debris, suggesting the site was ecologically similar to a peatland during the early Holocene. The dataset from this work will allow for an evaluation of long-term trajectories of carbon accumulation, vegetation composition, and local fire regimes and provide an opportunity to better understand relations among resource availability, climate, disturbance, and landscape change.

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