Resuspension of Florida Bay sediments is not a simple process, it is the result of a complex set of parameters and processes, including wind strength and direction, the presence and density of seagrass growth, local basin geometry, exposure to incoming wave energy, depth, and sediment composition. Investigation of the characteristics of the modern sediment surface, distribution of seagrass, and the typical wind/wave regime reveal how these influences interact within the Florida Bay system. An understanding of these processes will allow us to better explain the spatial and temporal patterns of turbidity in the Bay, how sediments have and will periodically be redistributed, and to predict how the ecosystem will respond to future alterations.

Previous research indicates that resuspension within Florida Bay is principally controlled by wind generated waves. Computer simulation of wave generation in Florida Bay reveals that in addition to wind strength and direction, the depth and geometry of local basins within the Bay exerts a strong control on wave derived near-bottom flow. Because of the limited depth and fetch within some of the smaller basins in Florida Bay, only relatively weak near-bottom flow occurs, even under relatively high wind conditions. In basins that have a larger fetch in the direction of strong winds, downwind mud banks are subjected to higher wave energy, and stronger flow in the central portion of the basin is expected. These results may explain why some of the smaller, central basins have thicker accumulations of mud, as compared to other larger basins, floored by sand and bare bedrock.

Observations and modeling results indicate the importance of wave damping by seagrass growth. An extensive survey was conducted in Florida Bay to determine the distribution of seagrass and other bottom types which would effect wave propagation. Based on over 650 surveyed sites, combined with aerial photography and satellite imagery, a map of Florida Bay bottom types was completed. The major bottom types delineated are hardbottom, open mud or sand, sparse seagrass coverage, intermediate seagrass, dense seagrass, and a bank top suite. Observations suggest that seagrass growth is often concentrated along bank margins. Using data acquired during a brief deployment of pressure gauges in the Bay and from the results of previous research, variations in bottom friction in the Bay were assigned relative to the mapped bottom type distributions and incorporated into the wave model. Model results and observations in the Bay both suggest that bank margin seagrass significantly dampens incoming wave energy, thus greatly reducing the potential erodibility of the mud banks. Seagrasses also modify the composition of the sediments; they baffle fine-grained muds and support a mollusk community which becomes a source of gravel-sized shell material.

As a result of the multiple effects of seagrass, mortality events probably have several consequences. When seagrass dies, the wave energy which can potentially impinge on a bank edge is greatly increased. At the same time, the surface sediments, mud, sand, and gravel (shell) are more readily available for transport. It is hypothesized that emergent shell ridges found in the Bay and coarse layers observed in mud bank cores may be the result of seagrass die-off, intensified wave energy and the increased supply of readily transported shell material. A shell ridge which has formed on the bank north of Calusa Key since 1970 may be the end product of this sequence of events. If this process is reflected by coarse shell layers found in cores throughout Florida Bay, then periodic seagrass mortality may have occurred in the past and be a characteristic of naturally varying Bay conditions.

Analysis of 120 surface sediment samples suggests 12 distinct sediment types in Florida Bay. Grain size distribution, mud, water, organic and carbonate content have been analyzed for each sediment sample. Using cluster analysis techniques, sediments were differentiated and classified. Approximately 60 percent of the surface sediments are dominated by sand, and 40 percent by mud. Current research is underway to investigate how each of these sediment types responds to turbulent flow. Once this aspect of the investigation is complete, the findings will be combined with wave modeling results to map the resuspension potential throughout Florida Bay. It will also then be possible to quantify annual resuspension of sediments and predict how changes in bottom type or depth will affect patterns of turbidity, sediment stability, and longer-term accumulation processes within the Bay.

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