A 5-year artificial-tracer study was used to mimic bioturbation of foraminifera in the back-barrier marshes of Folly and Rat Islands, South Carolina. Mixing rates decrease with subenvironment elevation, and decadal- to centennial-scale ecological signals and smaller hurricane deposits would not survive passage through the low-marsh mixing zone. However, the lower mixing rates in the high-marsh subenvironment allows for the preservation of such signals in the stratigraphic record. Bioturbation rates correlate poorly with plant density (primarily Spartina alterniflora). The Pearson correlation coefficient between mixing rate (Im in centimeters) and halophyte density (stems per square meter) is only 0.46, while the correlation between mixing and burrow density (apertures per square meter) is a much stronger 0.83. This corroborates earlier reports that spatiolateral variability in bioturbation is primarily a result of bioturbator (Uca spp.) preference for the low marsh and not halophyte distribution.
Two factors contribute to the preservation of storm layers in the marshes behind Folly Island: (1) Hurricane deposits are laterally continuous and deposited across both low and high marsh, and (2) the coarser grain size of the washover sediments and the thickness of the larger storm deposits inhibit crab burrowing. Although the extensive paleostorm record from Folly Island appears to show a decrease in category 4 and 5 hurricanes through time, this record may reflect change in marsh paleosubenvironment. In a transgressive setting, where a formerly high marsh is submerged into low marsh, the preservation potential of storm deposits decreases through time.