Long-Term Carbon Accumulation in Temperate Swamp Soils: A Case Study from Greenock Swamp, Ontario, Canada
Abstract Wetlands that develop peat are a globally significant pool of soil carbon. While some wetland types such as bogs and fens are well characterized by the consistent development of carbon-rich peat, swamps soils are more variable both in terms of their carbon densities and accretion rates. Subcategorizing swamps by forest type may be a useful way of understanding this variability. Here we provide a case study of carbon accumulation in two distinct forest stands of Greenock Swamp located in the Great Lakes – St Lawrence mixed forest region in Bruce County, Ontario, Canada: an Acer - Fraxinus (maple-ash) dominant stand (i.e., broad-leaved swamp) and a Thuja occidentalis (cedar) dominant stand (i.e., needle-leaved swamp). Organic matter and organic carbon contents were analyzed among seven Acer - Fraxinus soil cores and one Thuja occidentalis core collected from Greenock Swamp. The Acer - Fraxinus cores had peat depths ranging from 18-60 cm with a mean organic matter content of 54% and an organic carbon content of 34% of dry mass. The Thuja occidentalis swamp core had at least 4 m of almost homogeneous peat with a mean organic matter content of 89%. Radiocarbon dating indicates that the Acer - Fraxinus swamp accumulates peat episodically whereas the Thuja occidentalis swamp showed continuous peat accumulation since the Middle Holocene. Overall, both broad-leaved and needle-leaved swamps have important soil carbon stocks, and are prevalent wetland types in middle latitudes. Both need to be considered to fully represent the carbon pools and potential sink of temperate wetlands.