DILLERVILLE SWAMP: A MAJOR WETLAND IN SE PENNSYLVANIA?

Wetlands are excellent locations for the accumulation and preservation of sedimentary records of past climates and changes in the landscape. Numerous studies have addressed the Quaternary and Holocene climate of the eastern US however few studies have focused on SE Pennsylvania. This is partly due to land use changes over the last 300 years that have destroyed most of the wetlands in this area.

Anecdotal evidence suggests that a large (ca. 325 ha) wetland called 'Dillerville Swamp' existed to the north of Lancaster City in an area that is now commercially developed. This area is a broad valley located on Conestoga limestone bedrock surrounded by low hills and could potentially preserve a thick sequence of wetland sediment. Most of the area was infilled and developed in the 1930's to 1950's and modified to the extent that very little of the original morphology is preserved. Remnants of the supposed extensive swamp occur adjacent to the Red Rose Commons development and in other isolated locations.

A previous unpublished study of sediments cored from this remnant swamp contained inorganic deposits overlain by thin pre-colonial organic-rich wetland deposits (King 1975). The inorganic deposits were interpreted as fluvial deposits from a meandering stream in the marsh. Post-colonial deposition showed a steady increase in inorganic sediment resulting from deforestation and agricultural land-use.

GIS analysis of historical maps and aerial photos identified potential areas of pre-colonial swamp. These areas were augered and cored. Analyses of grain size, magnetic susceptibility, LOI and pollen were completed on selected cores. The results confirmed King's general stratigraphy but failed to identify a long-lived and extensive wetlands area. In most areas the organic rich sediments were less than 50cm thick. Pollen analysis seems to confirm that the lower parts of the organic-rich layer is pre-colonial but there is little evidence for widespread and persistent wetlands. It is likely that the pre-colonial wetland areas were restricted to floodplains and isolated marshes adjacent to local streams. The construction of the Lancaster-Harrisburg railroad in the early 1800's probably altered the hydrology of the area and increased the aerial extent of the wetlands, hence the anecdotal evidence for a large swamp in the area.