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Study of Human Impacts on the Salinity Regimes of Coastal Georgia Estuaries

PIs: Richard Wiegert, Merryl Alber, Alice Chalmers (Dept. of Marine Sciences, Univ. of Georgia, Athens, GA, USA), and Jack Blanton (Skidaway Inst. of Oceanography, Savannah, GA, USA)

Support: Georgia Coastal Incentive Grant (GA Department of Natural Resources, Coastal Resources Division)

Timeframe: 1998 - 2000

Project Overview:
The overall goal of this project was to evaluate the evidence for changes in the salinity regimes of coastal Georgia Estuary over time. This was done by evaluating changes in the discharge record, water use patterns, land use, vegetation, and flushing times over time, as well as by conducting intensive field studies in the Satilla River Estuary. Although this study did not find conclusive evidence that salinity has changed over time, it did document the dynamics of vegetation patterns and salinity distribution in these systems. It also provided information regarding discharge, water use, and land use that will be useful as baseline information against which to compare future changes.

1) The discharge records of all 5 Georgia riverine estuaries (Savannah, Ogeechee, Altamaha, Satilla, St. Marys) was obtained from USGS. Although there were no significant long-term changes in the annual average flow of water that enters these estuaries, an analysis of more specific characteristics of the hydrogaphs suggested that there have been seasonal shifts in the discharge pattern, with increased winter flows and decreased summer flows.

2) Water use patterns in the watersheds of the rivers since 1985 were evaluated. Most of the water withdrawn in the region is from surface water. However, there was no evidence for increased withdrawal over this period.

3) Land use change was evaluted using published statewide landuse coverages. Comparison between data sets was complicated by the use of different classification schemes, but the primary differences were between watersheds rather than from year to year. There has been a slight increase in urban, developed areas at the expense of forested areas.

4) Changes in vegetation were evaluated by performing a GIS analysis of aerial photographs of both the Satilla and Altamaha River Estuaries that date from 1953, 1974, and 1993. There was evidence of dynamic changes in the patterns of marsh vegetation in both systems since 1953, and this study will be useful for the framing of future research regarding marsh vegetation in this system. However, there was no evidence for directional shifts in vegetation.

5) Changes in flushing times of these estuaries (the average amount of time it takes river water to transit from the head of tide to the mouth) were evaluated based on historic salinity values gathered by EPD. Although there was a lot of inter- and intra-annual variability in these estimates, there was no only limited evidence for temporal trends in flushing times.

6) Finally, intensive field studies of current salinity patterns in the Satilla river estuary were conducted. This data served to elucidate the processes that must be adequately simulated in numerical models of estuaries like the Satilla. First, they must correctly predict the changes in tidal elevations and currents. Secondly, cross-channel circulation patterns must be adequately represented. Both processes govern the transport and mixing of salt and freshwater.

Alber, M. and J.E. Sheldon. 1999a. Use of a date-specific method to examine variability in the flushing times of Georgia estuaries. Estuarine, Coastal and Shelf Sciences 49: 469-492

Alber, M. and J.E. Sheldon. 1999b. Trends in salinities and flushing times of Georgia Estuaries. In: K. Hatcher, ed. Proc. of the 1999 Georgia Water Resources Conference, pp. 528-531.

Alber, M. and C. Smith. 2001. Water use patterns in the watersheds of the Georgia Riverine Estuaries. 2001 Georgia Water Resources Conference, Athens, GA.  [Summary]

Blanton, J.O., G. Lin and S.A. Elston. Tidal current asymmetry in shallow estuaries and tidal creeks. Submitted to Continental Shelf Research.

H.E. Seim, J.O. Blanton and T.F. Gross.  Direct stress measurements in a shallow, sinuous estuary. Submitted to Continental Shelf Research.

C. Smith, M. Alber and A. Chalmers. 2001. Linking shifts in historic estuarine vegetation to salinity changes using a GIS. In: K. Hatcher, ed. Proc. of the 2001 Georgia Water Resources Conference.

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This page was updated October 13, 2006