Analysis of historic vegetation changes Dr. Merryl Alber University of Georgia

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

malber@uga.edu https://marsci.uga.edu/directory/people/merryl-alber https://orcid.org/0000-0002-9467-4449 Georgia Coastal Ecosystems LTER Project

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

gcelter@uga.edu https://gce-lter.marsci.uga.edu/ Dr. Merryl Alber University of Georgia

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

malber@uga.edu https://marsci.uga.edu/directory/people/merryl-alber https://orcid.org/0000-0002-9467-4449 Principal investigator 1999-01-01 2001-12-31 Dr. Alice G. Chalmers University of Georgia

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

achalme@uga.edu Research scientist Ms Carrie Beth Smith University of Georgia

Graduate research assistant 2026

Aerial photographs and GIS analysis were used to map the distribution of tidal marsh vegetation along the salinity gradients of the estuaries of the Altamaha and Satilla Rivers. Vegetation maps were constructed from 1993 U.S. Geological Survey Digital Orthophoto Quarter Quads, 1:77,000-scale color infrared photographs taken in 1974 and 1:24,000-scale black and white photographs taken in 1953. Changes between years were identified using a GIS overlay analysis. Four vegetation classifications were identified and groundtruthed with field surveys: salt marsh (areas containing primarily Spartina alterniflora), brackish marsh (Spartina cynosuroides and S. alterniflora), Juncus ( Juncus roemerianus), and fresh marsh (Zizania aquatica, Zizaniopsis miliacae, and others). There was no evidence for an upstream shift in marsh vegetation along the longitudinal axis of either estuary over the time frame of this analysis, which implies there has not been a long-term increase in salinity. Although the inland extent of each marsh zone was further upstream in the Satilla than the Altamaha, they corresponded to similar average high tide salinities in each estuary: areas classified as salt marsh occurred from the mouth up to where average high tide salinity in the water was approximately 15 psu; Juncus ranged from 21 to 1 psu; brackish marsh ranged from 15 to 1 psu; and fresh marsh was upstream of 1 psu. Approximately 63% of the 6,786 ha of tidal marsh vegetation mapped in the Altamaha and 75% of the 10,220 ha mapped in the Satilla remained the same in all 3 yr. Juncus was the dominant classification in the intermediate regions of both estuaries, and shifts between areas classified as Juncus and either brackish or salt marsh constituted the primary vegetation change between 1953 and 1993 (87% of the changes observed in the Altamaha and 95% of those in the Satilla). This analysis suggests that the broad distribution of tidal marsh vegetation along these two estuaries is driven by salinity, but that at the local scale these are dynamic systems with a larger number of factors affecting the frequently changing borders of vegetation patches.

Question 2: How do the spatial and temporal patterns of biogeochemical processes, primary production, community dynamics, decomposition, and disturbance vary across the estuarine landscape, and how do they relate to environmental gradients? (more information)

LTER NSF Altamaha River Georgia Satilla River GCE Juncus Spartina aerial photographs brackish marsh fresh marsh GIS salintiy salt marsh tidal marsh vegetation Overall geographic extent of the research project -81.582311 -81.237936 31.401403 31.296034 1999-01-01 2001-12-31

National Science Foundation grant number OCE-9982133. Additional funding: Coastal Incentive Grant, Georgia Deptartment of Natural Resources

estuary marsh complex Altamaha River - Altamaha River transect used for GCE quarterly hydrographic monitoring surveys. Nominal profiling stations are defined every 2km from -4km to 40km (relative to station 0km at the line of demarcation), based on an estimated Thalweg line running up the main river channel. -81.582311 -81.237936 31.401403 31.296034 Triangles mark the locations of point samples and Ts mark the locations of transects. Circles (and corresponding numbers) mark the location of sampling stations from the Georgia Rivers LMER program and denote the distance from the mouth (in km) along the main axis in each estuary. https://gce-lter.marsci.uga.edu/public/resources/projects/AltamahaEsutaryAlberQ3.png Higinbotham, C.B., Alber, M. and Chalmers, A.G. 2004. Analysis of Tidal Marsh Vegetation Patterns in Two Georgia Estuaries Using Aerial Photography and GIS. Estuaries. 27(4):670-683. Smith, C.B. 2001. Analysis of historic vegetation changes in two Georgia estuaries using aerial photography and GIS. M.S. Thesis, University of Georgia, Athens, Georgia. 93 pp. Smith, C., Alber, M. and Chalmers, A.G. 2001. Linking shifts in historic estuarine vegetation to salinity changes using a GIS. Pages 615-618 in: Hatcher, K.J. (editor). Proceedings of the 2001 Georgia Water Resources Conference. Institute of Ecology, University of Georgia, Athens, Georgia. http://gce-lter.marsci.uga.edu/public/files/pubs/Smith_gwrc.pdf Smith, C.B., Alber, M. and Sheldon, J.E. 2000. Poster: Analysis of historic vegetation changes in two Georgia estuaries using a GIS. Southeastern Estuarine Research Society Meeting. Southeastern Estuarine Research Society, Oct 01, 2000, Tampa, Florida. Vegetation classifications of the Altamaha River estuaries in 1993. https://gce-lter.marsci.uga.edu/public/resources/projects/AltamahaVegClassAlberQ3.png Spreadsheet: Landsat imagery analysis of Spartina alterniflora aboveground biomass patterns in the Altamaha estuary zone of the GCE research domain https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=1015