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Linking Shifts in Historic Vegetation to Salinity Changes using a GIS


Authors: Carrie Smith, Merryl Alber, and Alice Chalmers (Dept of Marine Sciences, Univ of Georgia, Athens, GA, USA)

Citation: Proceedings of the 2001 Georgia Water Resources Conference, Athens, GA (K.J. Hatcher, editor) The Institute of Ecology, Univ. of Georgia, pp.615-618.

PDF: The full paper is available (opens in new window).

Overview:
The purpose of this study was to use aerial photographs and GIS analysis to determine if the location of the brackish water interface in two Georgia estuaries has changed over the last 50 years in response to increases in upstream freshwater withdrawal. Current vegetation maps of the Satilla and Altamaha estuaries were constructed from 1993 USGS Digital Orthophoto Quarter Quads (DOQQs). Vegetation was outlined and classified as Juncus roemerianus, brackish marsh, fresh marsh, salt marsh, or other. Historic vegetation maps were similarly constructed from 1:77000-scale color infrared photographs taken in 1974 and 1:24000-scale black and white photographs taken in 1953. Change maps between all years were constructed for each river.

Findings:

  • Most of the marsh vegetation classifications remained the same in both estuaries between 1953 and 1993.
  • There was a net increase in Juncus in both estuaries.
  • The ability of Juncus to flourish in a wide variety of salinity regimes made it unsuitable as an indicator of salinity variation.
  • Median high-tide salinity values were found to correlate with changes in vegetation. For example, the measured location of a high-tide salinity value = 18 ppt in both the Satilla and the Altamaha Rivers corresponds to the location on the map where brackish marsh plants meet the more downstream salt marsh vegetation.  

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This page was updated October 13, 2006