Comparison of physical characteristics between created and natural estuarine marshes in Galveston Bay, Texas

Five natural and ten created Spartina alterniflora marshes in the Lower Galveston Bay System were compared to determine if there were significantly different physical characteristics associated with each type of marsh. The saltmarshes were compared on the basis of microhabitats, length-width ratio, area-perimeter ratio, marsh-water edge ratio, total size of S. alterniflora plant communities, fetch distances, angle of exposure, orientation, and elevation. All physical measurements, except for elevation, were obtained from photography analyzed with the use of a Geographic Information System with digital image processing capabilities. Differences existed between natural and created marshes. The natural marsh sites in this study were characterized by highly undulant marsh-water edges, island-like S. alterniflora plant stands, concave shorelines, and low elevations. Created marshes were characterized by relatively smooth marsh-water edges, an unbroken shoreline morphology, convex to straight shoreline configurations, and elevations on the edge and inner portions of the marsh higher than those of natural marshes. The low elevations of the natural marsh appear to be due to coastal subsidence in the Galveston Bay area along with rising sea level. Reticulated marshes and undulant shorelines appear to be caused by consequent drowning of the natural marshes. High elevations in some of the created marshes are related to erosion of the low elevation marsh or deposition of coarse sediments at the marsh-water edge