The mangrove forests of the southwest coast of Florida are a valuable coastal resource. Like most coastal ecosystems they provide important goods and services including fisheries production and shoreline stabilization (Costanza and others, 1997). The soils of the mangrove forest are deep peats (Gleason and Stone, 1994) produced by the below ground productivity of the mangrove trees themselves. Questions have arisen recently concerning the ability of mangrove ecosystems worldwide to keep pace with a rising sea level (Cahoon and Lynch, 1997). In southwest Florida the question is more complex because the effects of upstream hydrological modifications to the freshwater Everglades must also be considered. Added freshwater inflows to the mangrove zone may alter salinity and nutrient regimes which in turn may change the rate of peat accumulation.

Following Hurricane Andrew, in 1992, our research group began investigations into the hydrology and ecology of the mangrove forests of the southwest Florida coast including several State and federally protected areas: Everglades National Park, 10,000 Islands National Wildlife Refuge, and the Rookery Bay National Estuarine Research Reserve (Smith and others; Smith and Whelan; this volume). The present study is designed to take advantage of the network of permanent vegetation sampling plots and hydrological monitoring stations which are already in existence. It will add to the knowledge already being gained by providing key information on below-ground processes.

The study is establishing a network of Sediment Elevation Tables (SETs) to gain precise measurements (+ 1 mm) of elevation changes over time (Cahoon and others, 1995; Cahoon and Lynch, 1997). The network will eventually encompass three river systems on the southwest coast of Everglades National Park: the Shark, Lostman's, and Chatham. On each river, sites will be established at the upstream freshwater marsh end; at a mid-river, marsh and mangrove area; and in a downstream river mouth location dominated by mangrove forest. These sites are being co-located with the South Florida Global Climate Change hydrology stations (see Smith and others, this volume). The method involves inserting an aluminum pipe as deeply into the sediment as possible, preferably to bedrock (7 meters in some parts of the study area). This provides a stable platform which does not move in relation to the elevation of the sediment. Measurements using the SET are then made from this platform. The initial set of SETs where installed at sites in the mid to lower Shark River and at Big Sable Creek in July 1998. Additional sites were added in the freshwater portion of Shark Slough and in the lower Lostman's River in January 1999. Initial readings were made in July 1998. Subsequent readings have been made in October 1998 and January 1999.

These readings bracket the passage of Hurricane Georges and Tropical Storm Mitch. Thus an added advantage is to examine periodic storm events on sediment elevation changes in the mangrove environment. Because of the preliminary nature of the data gathered to date, no analysis will be presented here. However, it is clear that as the network is developed, in conjunction with ongoing studies of vegetation and hydrology, we will be able to measure effects of the South Florida Ecosystem restoration as the hydrology of Shark River Slough is restored.

A significant part of the funding for this research was provided from the U.S. Department of Interior South Florida Ecosystem Restoration Program "Critical Ecosystem Studies Initiative" (administered through the National Park Service) and from the U.S. Geological Survey, Florida Caribbean Science Center funds for the project "Disturbance Ecology of Tropical and Subtropical Mangrove Forested Wetland Communities." Additionally, this project is a unique research task within the larger overall project "Vegetation Dynamics of the land-margin Ecosystems: The Mangroves of South Florida."

REFERENCES

Cahoon, D.R., and others, 1995, Estimating shallow subsidence in microtidal salt marshes of the southeastern United States: Kaye and Barghoorn revisited: Marine Geology, v. 128, p. 1-9.

Cahoon, D.R., and Lynch, J.C., 1997, Vertical accretion and shallow subsidence in a mangrove forest of southwest Florida: Mangroves and Saltmarshes, v. 1, p. 173-186.

Costanza, and others, 1997, The value of the worldÌs ecosystem services and natural capital: Nature v. 387, p. 253.

Gleason, P.J., and Stone, P., 1994, Age, origin and landscape evolution of the Everglades peatland, in Davis, S.M., and Ogden, J.C., Everglades: The ecosystem and its restoration: Delray Beach, Florida, St. Lucie Press, p. 149-197.

(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)