PARENT SESSION
Oral Session # 2: Paleoecology.
Presiding: B Lynch
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.
Long-term geomorphic and vegetation change on the Roanoke River floodplain, North Carolina.
Townsend, Philip*,1, Brown, Roger1, Willard, Debra2, 1 University of Maryland Center for Environmental Science, Frostburg, Maryland2 U.S. Geological Survey, Reston, Virginia
ABSTRACT- We established a series of 50 transects across a 200-km extent of the lower Roanoke River floodplain in North Carolina. Along these transects, we collected sediment cores at regular intervals to conduct paleoecological reconstructions of sedimentation history and vegetation change. Analyses of ragweed pollen concentration from the cores indicate up to 5 m of sediment deposition on the floodplain during the 300 years since European settlement. Moreover, deep cores from the early Holocene suggest that total amounts of sedimentation during recent centuries exceed total accumulations from the previous 10,000 years. We compared sediment characteristics and pollen assemblages from the pre-colonial landscape to surface pollen samples and a recent vegetation survey along the established transects. We found that floodplain soils underwent a transition from a largely organic substrate prior to European settlement to mineral soils during the period of rapid sedimentation, and that the soils are showing signs of increasing organic matter content in recent decades as the river has become sediment-starved due to dam construction. Paleoecological evidence suggests the development of less flood tolerant forest assemblages across large areas of the floodplain that experienced deep sedimentation. Deepwater swamp habitats remain dominated by species of Taxodium and Nyssa, although selective logging of bald cypress in recent centuries has led to switch in dominance from Taxodium distichum to Nyssa aquatica. In addition, a rich fern flora that was previously associated with Taxodium-Nyssa swamps appears to have disappeared from the modern landscape, possibly due changes in soil characteristics and flooding regimes. In a long-term context, the sedimentation that resulted from the clearing of uplands during the period of European settlement appears to have led to substantial changes in floodplain forests.
Key words: sedimentation history, paleoecology, forested wetlands, vegetation change