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 depressions, pinnacles, and VEGETATION islands along the coast (Rupert and Big Bend tidal marshes have a Arthur, 1990). In addition to these thin veneer of sediment, 0-3 m deep, obvious local effects, regional variations over the limestone. Slightly elevated in the morphology of the marsh coincide limestone outcrops support sabal palm with the different units that have been hammocks within the marsh, and to a described in the area (Plate 1). In large extent the marsh is buffered on the particular, the occurrence of barrens, the interior edge by the hydric hammock, a smoothness of the coast, and the hardwood and sabal palm forest, limited presence of hammocks, islands and primarily to the Coastal Lowlands and sawgrass appear to vary with the other wet, flat sites (Vince et al, 1989; underlying geologic formations. FNAI/FDNR, 1990). The marshes are The major rock units are the dominated by Juncus romerianus (black Ocala Limestone (sometimes called the needlerush), which are flooded primarily Ocala Group) of late Eocene age (38 - by high tides. Spartina alterniflora 41 million years), the Suwannee (cordgrass) thrives on the regularly Limestone of Oligocene age (25-33 flooded banks facing the gulf and million years old), and the St. Marks Cladium jamaicense (sawgrass) thrives Formation of the early Miocene age (16 at the marsh interior where fresh water - 25 million years). More details and flows, replacing S. alterniflora in low references on the geology of this coast elevation, low salinity areas. The large are found in Rupert and Arthur (1990). expanses of tidal marsh plants The St. Marks Formation effectively trap sediment and buffer storm surge (FNAI/FDNR, 1990). Salt The marsh over the St. Marks barrens occur in some regions at the Formation in Wakulla County (Plate 1) border between marsh and upland. The contains several spring-fed rivers, and barrens are hypersaline environments displays a markedly irregular shoreline. that have sparse vegetation ofBatis, Springs and sinks are commonly Salicornia species, and other salt- associated with this water-bearing tolerant vegetation. Patches of bare rock limestone (Rupert and Arthur, 1990). develop on the edges of hammocks, Salt barrens are present in this area, particularly where the hammocks have possibly because of a quartz sandy formed on rock crests having gentle component in this formation (Rupert ard relief. Arthur, 1990). Plate 2 illustrates the St. Marks River and adjoining marshes. This area is forested as well and is GEOLOGIC CHARACTERISTICS subject to prescribed burning as part of a The bedrock along the Big Bend management program. Note the salt coast lies at or near the surface. The barrens to the northwest of the marshes. Tertiary limestone units in this area are This feature, unique to limited areas of an important part of the Floridan aquifer the coast, helps to identify regional system. The shallowness of the rocks characteristics related to underlying results in significant control on features geology. in the marsh. The limestone has a karst topography generating sinkholes, Plate 2. St. Marks, Wakulla County (Landsat TM April 1986) The Suwannee Limestone This area of extensive hammocks, The region of the Suwannee islands, and springs corresponds to the Limestone (Plate 1) in Taylor County to region described as the 'Crystal River the north, and Pasco and Hernando formation' (Vernon, 1951; Puri, 1957). Counties to the south (Yon and Hendry, The salt barren feature is uncommon 1972) has a moderately wide marsh with here, pure stands of sawgrass occur, and a relatively linear coastline. The exposed areas are usually rock outcrops, Suwannee is a hard limestone with a not yet colonized by marsh vegetation. minor sand component and may be Mangroves not present in the 1986 and dolomitized in Taylor County in the 1991 imagery are currently recovering Keaton Beach area (Cooke, 1945). The along the gulf edge. surface of the Suwannee is karstified The central region of the Ocala, with associated solution pipes and in Levy and Dixie Counties from the sinkholes (Yon and Hendry, 1972). Withlacoochee River to north of the Some hammocks are present and Suwannee, includes the lower member sawgrass may occur mixed with Juncus. of the Ocala Formation and has been Barrens occur in southern Taylor County referred to as the 'Inglis and Williston which appears to have a discontinuous formations' (Vernon, 1951). The zone between the Suwannee Limestone limestone north of the Withlacoochee and the ' Steinhatchee dolomite' River is highly soluble (White, 1970). (abandoned; Puri, 1957) of the Ocala Small springs and hammocks are Limestone to the south. common, the marsh is broad and is dissected by numerous tidal creeks The Ocala Limestone reaching 1-3 km into the interior. The The Ocala Limestone is a more tidal creeks drain surface flow from the complex unit and is highly karstified coastal hammocks and seepage from the (Vernon, 1951). It had originally been Floridan aquifer system (Rupert, 1991). considered a Group with several The Cedar Keys area is an anomaly, formation members (Puri, 1957), being composed of large sand bodies although these members had (White, 1970) and limestone islands traditionally been differentiated on fossil (Vernon, 1951). The adjacent marsh has type rather than lithology and have not developed on an extensive complex of been maintained as preferred usages oyster reefs supported by freshwater (Rupert and Arthur, 1990). However, from the Suwannee River, the largest the 'abandoned' members, the river in the region. Steinhatchee dolomite, the The marsh changes appearance in Inglis/Williston, and the Crystal River northern Dixie and southern Taylor formations, appear to affect coastal Counties. This region of narrow marsh morphology. The Ocala Formation with extensive salt barrens and a linear underlying the marsh in Hernando and shoreline corresponds to what Puri et al. Citrus Counties shows a strong karst (1967) described as the 'Steinhatchee topography (Plate 3), unlike the dolomite' member of the Ocala Suwannee Limestone region to the Formation (Plate 4). The dolomitization south. Springs are abundant in this area, of limestone decreases its primary and the marsh has the "archipelago" porosity (Rosenau et al, 1977) which feature described by Davis et al. (1985). may decrease the flow through of aquifer waters and contribute to the development of barren areas at the high HYDROLOGIC CHARACTERISTIC" water line where salts accumulate. This marsh/barren complex continues north and extends into an area tentatively The tidal marshes occupy a low identified as Suwannee Limestone. This gradient limestone shelf flooded by a area in southwestern Taylor County is one meter tidal range. Meandering tidal the only area where the marsh creeks carry gulf waters up to 3 km morphology and the rock formations do inland. Marsh elevations and the low not match well (see Plate 1). However, tidal range prevent tidal flooding of the the break between the Ocala Group and marsh interior except at high tide and the Suwannee Limestone in Taylor during storm surge. Aside from the tidal County is uncertain and may be influence, the hydrology of the marsh is discontinous (Frank Rupert, oral tied directly to the underlying geology, commun.1995; Campbell, 1993). the thinly covered carbonates exposed to The association of the underlying the process of dissolution, and the rocks with characteristics such as coincidence of the coast with the surface extensive barrens suggest that these of the Floridan aquifer system (Scott, features will tend to remain associated 1992). It is noteworthy the tidal marshes with the rock types. The St. Marks are absent to the south and west of the region with a broad marsh and Big Bend where the top of the Floridan convoluted shoreline exhibits aquifer drops 50 feet below the land characteristic salt barrens and numerous surface (Vernon, 1973). springs. The harder Suwannee Rivers along the coast are small Limestone is characterized by a linear and spring-fed with the exception of th? shoreline, a moderately wide marsh, Suwannee River with an average annual tidal creeks of limited size and seepage discharge of 298 m3/s (1941-1994, from the Floridan aquifer system. The USGS Water Resource Division third region, the Ocala Limestone, has records). All other rivers have an three geomorphic subregions, the average annual discharge of 30 m3/s and 'Steinhatchee dolomite', the less. The Floridan aquifer system 'Inglis/Williston', and the 'Crystal River discharges significant freshwater along formations'. The Steinhatchee is the marsh coast through seeps and identifiable by a narrow band of marsh, springs, some springs producing tidal a linear form and numerous barren areas. streams (Rupert and Arthur, 1990). First The Inglis/Williston subregion has a order coastal springs, > 3 m3/s, are characteristically broad marsh with concentrated between Citrus and numerous and long meandering tidal Hernando County with one exception in creeks, and extensive discharge from the Wakulla County (Plate 1). Lower order aquifer through seeps, springs and coastal springs are scattered across the solution channels. The Crystal River counties of the Big Bend coast. Reports member exhibits a highly complex indicate artesian flow from the aquifer shoreline with many springs, tidal occurs intermittently along the coast creeks, scattered limestone outcrops (Rupert and Arthur, 1990; Vernon, supporting coastal hammock vegetation, 1951). and virtually no salt barrens. Water Marsh Forest Barren/Developed

G U

Mexico

<**»»*«'&;*&

Homos as&a

10km Plate 3. Ozello archipelago, Citrus County (Landsat TM April 1986) Water Marsh Deadmarz Forest Bay " Barren/Developed

G U 1

O f Mexico

10 km Pe pp e rf is h Keys

Plate 4. Steinhatchee dolomite, Dixie County (Landsat TM April 1986)

6b their place are not the salt barrens of the CHANGE ANALYSIS St. Marks and the Steinhatchee areas, but exposed surfaces of karstified Change analysis based on a limestone. Field reconnaissance suggests simple classification shows no net loss the pocked surface gradually fills with of marsh between 1986 imagery, 1991 imagery and earlier estimates of marsh fine sediment and is colonized by Juncus, Distichlis or Salicornia spp. acreage (table 1). Although there is no net loss, initial analysis of vegetation An increase of greenness (NDV increase) in 1991 along the marsh edge change based on vegetation indices at Waccasassa Bay may be an indication shows a loss of greenness at the marsh of recovery from wrack deposited during transition zone and the gulf edge, and Hurricane Elena in 1985. The surge of increases in greenness primarily as a high water during storms carries an recovery response to short-term accumulation of plant material that is disturbance. Seasonal and short term deposited in the marsh as the flood disturbance from which vegetation may waters subside. The gulf edge of the recover include fire, storm wrack deposits, and low temperatures, as Fenholloway area in contrast shows a discussed earlier with respect to distinct loss of greenness, an indication mangroves. Fire is a common of decreased vegetation health and vigor. disturbance in the vast Juncus marsh, It is possible this area had not yet both naturally occurring and as part of recovered in 1991 from previous storm management programs. Recovery may wrack deposits. Field reconnaissance indicates such recovery can take from 2- occur in a few years and has been documented with satellite imagery. 5+ years and may include colonization by alternative species, depending on It appears that vegetation local conditions. The coincident succession may be occurring along the coast, not at the expense of marsh, but of decrease and increase of NDVI values ?.t upland and transitional species. The the Fenholloway marsh interior indicate decline of greenness at the marsh that in key locations marsh and interior suggests the hydrology of the transitional species may be area has changed, either by the increase successionally following the decline of in sea level and/or fluctuations in upland species (Plate 5). This location precipitation and fresh water flow. It is near the Fenholloway may be at the likely that species not adapted to tidal most advanced position in a landward flushing are in distress, including trend of marsh migration. fresh/brackish marsh species, transitional species (Ivd) and the evergreen coastal hammock species, sabal and cedar. CONCLUSION Examples of this may be seen at The common traits that link the Waccasassa Bay where the coastal Big Bend marshes in a cohesive unit hammock is in severe decline (Plate 5). include a rocky limestone shore covered The marsh interior, dotted with coastal with a thin veneer of sediment and hammocks, shows a consistent NDVI colonized by Juncus romerianus. decline. Aerial survey and field However, the rocky shelf itself is reconnaissance document high morbidity variable enough to create regional of these forest islands. What remains in patterns distinguishable in satellite imagery and distinctive enough in REFERENCES CITED character to cause variations in marsh morphology. The variations in the Campbell, K.M., 1993, Geologic Map of bedrock appear to control marsh width, Taylor County, Florida: Florida the presence of barrens, islands and Geological Survey #192. hammocks, and combined with the Cathey, H.M., 1990, USDA Plant Floridan aquifer system, the character of Hardiness Zone Map: USDA the tidal creeks. For instance, areas of Agriculture Research Service Miscellaneous Pub. #1475, porous, karstified limestone with Washington, D.C. dissolution channels more readily Cooke, C.W., 1945, Geology of Florida: transfer alterations in hydrologic Florida Geological Survey Bulletin conditions to the marsh, including No. 29, Tallahassee, Fl. changes in aquifer discharge and tidal Davis, R.A., Hine A.C., and Belknap, flushing. D.F., 1985, Geology of the Barrier The initial data sets indicate that Island and Marsh-dominated Coast, the effects of long-term sea level rise West-central Florida: University of and alterations in hydrology may first South Florida, 119 pp. appear as a decline of marginal upland FNAI/FDNR, 1990, Guide to the Natural Communities of Florida: plant communities and successional Florida Natural Areas Inventory and changes at the marsh interior. Florida Department of Natural Preliminary analysis of satellite imagery Resources, 111 pp. shows regional variations in the response Henry, J.A., Portier, K.M. and Coyne, and recovery of vegetation following J., 1994, The Climate and Weather of disturbance. Further field work and Florida: Sarasota, FL, Pineapple examination of April 1995 imagery, Press, Inc. which we are performing, will clarify Lewis, in, R.R., Gilmore, Jr., R.G., Crewz, D.W. and Odum, W.E., 1988, these trends. Knowledge of underlying Mangrove Habitat and Fishery characteristics such as the geology and Resources of Florida, in Florida hydrology will assist in anticipating and Aquatic Habitat and Fishery understanding the patterns of change Resources: W. Seaman, Jr., ed., Florida Chapter of American Fisheries observed along the coast. Society, pp 281-336. Puri, H.S., 1957, Stratigraphy and Zonation of the Ocala Group: Florida Geological Survey Bulletin No. 38, ACKNOWLEDGMENTS Tallahassee, Fl. Puri, H.S., Yon, Jr., J.W., and Oglesby, We extend our appreciation to Frank W.R., 1967, Geology of Dixie and Rupert of the Florida Geological Survey Gilchrist Counties, Florida: Florida for his expert advice and thoughtful Geological Survey Bulletin No. 49, Tallahassee, Fl. critique of this material and to Karen Morgan for her untiring assistance on Rosenau, J.C., Faulkner, G.L., Hendry, C.W., and Hull, R.W., 1977, Springs graphics. of Florida: Florida Geological Survey Bulletin, No. 31, Tallahassee, Fl. NDVI decrease # & ®

V

i;'"'" " w* [ I ForestAipland I | Barren/developed Water NDVI increase

Waccasassa 0 1 2km Bay

Plate 5. Changes in vegetation index (NDVI) at Waccasassa Bay and the Fenholloway River Rupert, F.R., 1991, The Geomorphology and Geology of Dixie County, Florida: Florida Geological Survey, Open File Report No. 45. Rupert, F.R., and Arthur, J.D., 1990, The Geology and Geomorphology of Florida's Coastal Marshes: Florida Geological Survey Open-File Report 34, Tallahassee, Fl. Scott, T.M., 1992, A Geological Overview of Florida: Florida Geological Survey Open File Report 50, 78p. Vernon, R.O., comp., 1973, Top of the Floridan Artesian Aquifer: Map Series No. 56, Bureau of Geology, Division of Interior Resources, Florida Department of Natural Resources in cooperation with U.S. Geological Survey, Scale: approximately 50 miles to 1.5 inches. ______, 1951, Geology of Citrus and Levy Counties, Florida: Florida Geological Survey Bulletin No. 33. Vince, S.W., Humphrey, S.R. and Simons, R.W., 1989, The Ecology of Hydric Hammocks - a community profile: U.S. Fish and Wildlife Service, Biological Report 85(7.26). 81pp. White, W.A., 1970, The Geomorphology of the Florida Peninsula: Florida Geological Survey Bulletin No. 51. Yon, J.W., Jr., and Hendry, Jr. C.W., 1972, Suwannee Limestone in Hernando and Pasco Counties, Florida with section on Petrography of the Suwannee Limestone: Florida Geological Survey Bulletin No. 54.