SPATIAL VARIABILITY OF BIOTURBATION IN COASTAL SALT MARSHES: IMPLICATIONS FOR INFAUNAL FORAMINIFERAL DISTRIBUTIONS AND RECOVERY OF ECOLOGICAL SIGNALS

The conclusion of a three-year artificial tracer study from Rat Island, South Carolina has yielded bioturbation rates consistent with those measured using natural (foraminiferal) tracers from buried washover fans. Mixing rates increase from high marsh to low marsh and centennial-scale ecological signals would not survive passage through the low-marsh mixing zone. However, the lower mixing rates in the high-marsh subenvironment allow for the inclusion of such signals in the stratigraphic record.

Bioturbation rates correlate poorly with plant density (primarily S. alterniflora short and long form). The Pearson Correlation coefficient between mixing rate (Im in cm) and halophyte density (stems per m²) is only 0.46 while the correlation between mixing and burrow density (apertures per m²) is a much stronger 0.83. This corroborates earlier reports that spatio-lateral variability in bioturbation is primarily a result of bioturbator (Uca spp.) preference for the low marsh and not halophyte distribution.

The stratigraphic effects of mixing clearly influence post-mortem foraminiferal distributions; living populations are influenced by mixing as well. The percentage of foraminiferal populations living infaunally (primarily M. fusca and A. mexicana) strongly correlates to mixing rates (p=0.97) as burrows introduce more oxygen to the low-marsh sediments. Paleoenvironmental interpretations based on total (living + dead) foraminiferal populations should consider using cores taken in high-marsh subenvironments to increase stratigraphic resolution.