HOLOCENE CARBON ACCUMULATION AND PALEOCLIMATE HISTORY OF FRESHWATER RIVER-WETLAND CORRIDORS IN SOUTHEASTERN PENNSYLVANIA

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. In the pre-Colonial era, these river-wetlands corridors may have been an underappreciated carbon sink, one now severely degraded by the legacy of colonial mill damming. Here, we present loss-on-ignition (LOI), carbon and nitrogen (C:N) ratios, and bulk organic δ13C data to reconstruct the Holocene history of carbon accumulation and paleoclimate from a freshwater wetland in the Piedmont province of southern Pennsylvania. Great Marsh in Chester County, PA (~150 m asl) serves as a surviving example of a natural valley-bottom marsh formed within the Mid-Atlantic periglacial environment. We paired our proxy data with 210Pb and 137Cs chronologies and radiocarbon dating to calculate rates of both short-term (~100 years) and long-term (multi-millennial) carbon accumulation. At Great Marsh, organic matter 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 as 8,000 year old organic sediments are unconformably capped by a ~40 cm modern organic horizon. We will use C:N ratios and bulk organic δ13C values to understand the decomposition and potential sources of organic carbon during the early Holocene and modern era. Together, our analysis of carbon cycling in a surviving Piedmont wetland will help to better understand carbon cycling in analog systems for the ongoing restoration of river-wetland corridors in southeastern PA.