The salt marshes of the northwest Florida Big Bend coast form a prolific temperate ecosystem. These wetlands play a vital role in coastal ecology providing a natural sink for both upland and nearshore sediments, filter wastes and nutrients, buffer coastal areas against storms and provide essential habitat for wildlife, fish and waterfowl. Consequently, understanding the relationship between sediment accretion/erosion rates and changes in sea level is paramount in predicting the future of these marshland ecosystems, as they would be adversely impacted by a world-wide rise in sea level.
The Big Bend coast is characterized by low wave energy, minimal tidal influence and limited influx of marine and fluvial sediments to replenish eroding shorelines. Though the shoreline appears homogeneous, there are localized areas of increased deposition and erosion. This continuing study provides quantitative measurements of the rate of sediment gain/loss and provides a baseline so that areas of anomalous deposition may be identified.
The first five years of this investigation focuses on the coastline extending from Wakulla County, Florida, south to Dixie County, Florida, a distance of approximately 80 miles. Within this region the distributary systems of the Ochlockonee, St. Marks, Aucilla, Steinhatchee and Wacasassa Rivers were characterized with respect to their sedimentary make up. Samples from more than 100 cores were analyzed for percent organics, percent clay, and grain size distribution of sands. Marsh stability was addressed by measuring sedimentation and erosion rates. Among the techniques used for this were the installation of sedimentation-erosion tables (SET), lead-210 (210Pb) dating and Carbon-14 (14C) analysis.
Results of this continuing study show that the texture and composition of surface sediments in the study area are relatively uniform and the dynamic interaction of the marsh surface accretion rate and sea level rise is in tenuous balance. All lithologic units sampled in this study ranged in age from Eocene to present day. Low-energy depositional conditions dominate the study area, and have changed little during Holocene time.