U.S. DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Monitoring Tidal Marshes of Florida's Big Bend; regional variations and geologic influences by Ellen A. Raabe and Richard P. Stumpf OPEN-FILE REPORT 96-35 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards U.S. Geological Survey, Center for Coastal Geology St. Petersburg, Florida 33701 DISCLAIMER This publication was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in the report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Copies of this report may be purchased from: U.S. Geological Survey Center for Coastal Geology 600 4th Street South St. Petersburg, FL 33701 TABLE OF CONTENTS ILLUSTRATIONS ........................................................................^^ TABLES................................................................................................^^ ABSTRACT...................................................................................................................! INTRODUCTION.......................................................................................................... 1 IMAGE ANALYSIS........................................................................................... 2 WETLANDS DESCRIPTION........................................................................................2 VEGETATION................................................................................................... 4 GEOLOGIC CHARACTERISTICS.................................................................... 4 The St. Marks Formation......................................................................... 4 The Suwannee Limestone........................................................................ 5 The OcalaLimestone............................................................................... 5 HYDROLOGIC CHARACTERISTICS .............................................................. 6 CHANGE ANALYSIS................................................................................................... 7 CONCLUSION...............................................................................................................? ACKNOWLEDGMENTS..............................................................................................^ REFERENCES CITED................................................................................................... 8 ILLUSTRATIONS Figure 1. Sea level at Cedar Key, Florida 1939-1992..................................................... 3 Plate 1. Geologic and climatic features of the Big Bend tidal marsh coast.......... in pocket Plate 2. St. Marks, Wakulla County (Landsat TM April 1986) ......................................4a Plate 3. Ozello archipelago, Citrus County (Landsat TM April 1986)...........................6a- Plate 4. Steinhatchee dolomite, Dixie County (Landsat TM April 1986)...................... 6b Plate 5. Changes in vegetation index (NDVI)................................................................8a TABLES Table 1. Map accuracy for imagery classification depicted in this report......................... 2 Table 2. Tidal marsh acreage estimated for Wakulla to Hernando County...................... 2 11 Monitoring Tidal Marshes of Florida's Big Bend: regional variations and geologic influences By Ellen A. Raabe and Richard P. Stumpf ABSTRACT INTRODUCTION The marsh morphology of The tidal marshes of Florida's Florida's Big Bend coast, as observed Big Bend coast extend along a 250 km from Landsat TM satellite imagery, stretch of coast from Wakulla County tc corresponds to the underlying geology. Pasco County (Plate 1). This area is The major rock units have a direct relatively pristine, however rapid growth bearing on the width of the marsh, is occurring from both the north and the shoreline configuration, and the presence south. Changes in climate, sea level and of salt barrens, sawgrass and coastal land use may lead to potential long-terrr hammocks. Climate zones influence the changes along this coastline. While the presence of plant species, while sea level shoreline itself appears unchanged in change impacts vegetation succession over 100 years, vegetation change differentially along the coast. Tidal provides a key to detecting important creeks and freshwater from the Floridan alterations in the conditions of this aquifer system provide an additional coastline. Remotely sensed imagery is control on marsh variation. A used to characterize this coast and comparison of vegetation indices from document the changes. This report 1986-1991 imagery suggests a decline in describes factors shaping the vegetative health at the gulf edge and at characteristics of the marshes and the upland boundary. Further observations that may be used to identify comparisons with 1995 imagery will change due to natural climatic and elucidate the relationships observed in human factors. this analysis. IMAGE ANALYSIS Landsat Thematic Mapper (TM) WETLANDS DESCRIPTION imagery is the primary data source in this investigation. Aerial photography, SPOT imagery, National Wetlands The Big Bend tidal marshes Inventory (NWI) maps and other sources occur on a low and flat limestone are also investigated. The imagery is co- surface, which is physiographically registered, rectified to UTM (Universal referred to as the "Coastal Swamp" zone Transverse Mercator), radiometrically (White, 1970). The marsh is bounded on corrected, and corrected for atmosphere the interior by the Gulf Coastal using dark object subtraction. Analyses Lowlands, extending from Wakulla to include classifications and vegetation Pasco County. The low elevation indices (NDVI) of April 1986 and gradients make this area particularly February 1991 imagery. Seasonality is susceptible to alterations from sea level not significant in Florida tidal marshes, rise (Henry etal., 1994; White, 1970). although some non-marsh areas show The semidiurnal tide range is less than lower NDVI (Normalized Differenced one meter. The presence of marshes Vegetation Index) in the 1991 scene. along an open coast without barrier This paper employs a simplified beaches is unusual for the U.S. east classification with only four categories: coast. This is due to the lack of sand- water, tidal marsh, upland, and sized material (White, 1970), and this barren/developed. Upland includes all area should be considered a rocky coart. nontidal vegetation. A map accuracy The shoreline has been altered check is conducted using 120 stratified minimally and estimates of marsh area random samples of the four categories in recent years are remarkably similar and referring to CIR (Color Infrared) (table2). aerial photography from 1984 and 1988 (table 1). Some changes had occurred Table 2. Tidal marsh acreage between the dates of the imagery and the estimated for Wakulla to Hernando aerial photography. County Table 1. Map accuracy for imagery Source Marsh in acres classification depicted in this report 1982 NWI* 151,290 1986 Landsat TM 160,571 Land Cover Map Accuracy % 1991 Landsat TM 159,736 Water 100 "Lewis etal 1988 Tidal Marsh 85 Upland 85 B arren/Developed 96 Overall Map Accuracy 91 Annual precipitation for the estimated heights of one meter observed region averages 56-62 inches (142-157 in 1993-94 field reconnaissance and cm) from Henry et al. (1994). The detectable on 1993 satellite imagery. northern counties experience a wet Sea level along this coast has summer with moderate winter shown a trend upward over the last 50 precipitation, while to the south heavy years with fluctuations of up to 10 cm summer rainfall is followed by a drier over 10 year periods (Figure 1). Data winter. A climate zone boundary shown displayed is provided by NOAA NOS in Plate 1 (Henry et al., 1994) passes and referenced to the North American through the region. The frequency and Vertical Datum of 1988. The gradual severity of freezes increase north of the increase in sea level, if accompanied by boundary at Cedar Key. Although this marsh accretion, may have little negative region is marginal for mangrove impact on the marshes. However, establishment, it may be hospitable for shorelines may change where sediment considerable lengths of time as is unavailable. The landward migration documented by the distribution of of the tidally influenced zone will be mangroves in the mid-fifties (Plate 1). A limited by elevation gradient and land series of hard freezes in the 1980's use, and may impact upland vegetation eliminated all mangroves from the entire where the gradient is low. Big Bend marsh zone. Mangroves along the coast are reestablishing, with Figure 1. Sea level at Cedar Key, Florida 1939-1992. Water Level, Cedar Key, Fl. 0.00 - annual avg. ! rslr (1939-1992) = 1.4 mm/year -0.05 oo oo ON Q -0.10 oo -0.15 J-H -0.20 -0.25 Q 1940 1950 1960 1970 1980 1990 solution