PARENT SESSION
Oral Session # 54: Coastal Ecosystems: Salt Marshes.
Presiding: P Ringold
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 105.
Changes in Savannah River tidal marsh vegetation distributions following removal of a tidal flap gate.
Loftin, Cynthia1, McCloskey, Jon2, Kitchens, Wiley3, Dusek, Marsha4, 1 USGS-BRD Maine Cooperative Fish and Wildlife Research Unit, Orono, Maine, USA2 University of Maine, Orono, Maine, USA3 USGS-BRD Florida Cooperative Fish and Wildlife Research Unit, Gainesville, Florida, USA4 University of Florida, Gainesville, Florida, USA
ABSTRACT- We used remote sensing tools and field surveys to monitor changes in vegetation distributions in the Savannah River tidal marsh following the 1991 removal of a tidal flap gate. Landsat TM and SPOT multispectral imagery from October 1986, April 1987, May 1993, July 2000, October 2000, and April 2001 were compared using principle components analysis to identify areas of changed brightness and greenness. Vegetation maps were created from each image using classification procedures, and the maps were compared with principle components images to identify from-to change types. Predictions of a spatial vegetation succession model developed in earlier studies to estimate vegetation response to tide gate removal were compared with the vegetation maps to determine if tidal freshwater marsh had expanded as expected following tide gate removal. We identified changes in greenness and brightness indicating changes in biomass, vegetation types, and water levels in the area during the study period. Increased greenness was most extensive during 1987-1993. An increase in woody and freshwater species occurred by 1993 in nearly 1/3 of the region predicted to be dominated by freshwater vegetation 2 years following tide gate removal. Species found at sites with lowest salinity (<0.5ppt) before tide gate removal have since expanded into previously brackish regions of the marsh. By 2000 freshwater species had expanded to nearly 3/4 of the expected distribution of tidal freshwater marsh; Argyle Island and New Cut approximate the current southward extent of vegetation associations intolerant of salinity >3.0 ppt. Shifts in dominance of Scirpus validus and Zizaniopsis mileacea in mixtures with a variety of freshwater species have occurred within and between years in this region since the gate was removed, and extent of Z. mileacea has increased in this region since tide gate removal. Vegetation composition below Argyle Island has changed little in response to tide gate removal, and remains primarily a mixture of S. validus, S. robustus, and Spartina alterniflora.
Key words: tidal fresh marsh, restoration, Savannah River, remote sensing