USE OF GIS SPATIAL ANALYSIS FOR IDENTIFICATION OF TEMPORAL CHANGES IN SEDIMENT DISTRIBUTION AND CONTAMINANTS IN GULF COAST ESTUARIES

The availability of relatively inexpensive algorithms capable of performing spatial analysis on gridded data has provided researchers with an invaluable tool that greatly simplifies interpretation of changes that have taken place in bays, estuaries, etc. over time. Arc View’s Spatial Analyst® module is one such program that has been successfully used to identify a number of changes in the sediment regimen of Mobile Bay, Alabama and Apalachicola Bay, Florida and to evaluate changes in heavy metal distributions that have taken place over the past 30 years. Prior to the advent of this type of software, the researcher could only view maps showing variables from two different time periods and visually try to assess the changes that had taken place. Using the Spatial Analyst® module, however, areal changes in sediment texture within both bays were easily discerned and it was then possible to tie these changes to both natural phenomena and anthropogenic causes. The effects of major Gulf Coast hurricanes were clearly apparent, as were also changes caused by trapping of coarse sediment behind dams and the accelerated downstream lateral erosion that also resulted from construction of dams within the watershed area. In addition, by using the GIS methodology, it was also possible to identify changes in specific contaminant point sources over time and to relate heavy metal levels in sediments to factors such as particle size distribution, clay mineralogy, and organic carbon content. Further, the GIS algorithms allow the magnitude of changes to be assessed and also quantitization of the areas that have been affected by such changes.