A. Y. Cantillo, NOAA/NOS/ORCA,Silver Spring, MD; L. Pikula, NOAA/Miami Regional Library, Miami, FL; J. Beattie , E. Collins , NOAA/Central Regional Library, Silver Spring, MD; K. Hale, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL; T. Schmidt, Everglades National Park Research Center, Homestead, FL.

Florida Bay is a coastal lagoon, on average less than 3 m deep, approximately 1,000 square miles in area, located between the South Florida mainland and the Florida Keys. In recent years, adverse environmental changes have been noted in the Bay. Currently, a multi-agency multi-year effort is underway to restore the ecosystem of South Florida, including that of Florida Bay. To assist in determining the Bay's former condition and to catalogue changes, events that may have affected or have occurred in the Bay are described, listed and graphically displayed in a common time scale. The time coverage begins in 1910 with construction activities along the Florida Keys, and in what later became the Everglades National Park. Included are global scale atmospheric, geological and astronomical phenomena such as El Niño events, volcanic eruptions and solar activity that may affect local weather. On local scales, documented are dieoffs of species such as seagrasses, sponges and fishes; environmental occurrences of algal blooms, coral reef degradation, fishery catch changes and soil subsidence; and human activities such as population increases, and construction. Awareness of the environmental importance of the Bay is documented in legislation affecting environmental regulations nationwide and in the Bay area; and environmental programs and studies performed currently and in the past by Federal, state, municipal, academic and civic organizations.

Robert B. Halley, Leanne M. Roulier, USGS 600 4th St. South , St. Petersburg, FL 33701.

Recurring hypersalinity in Florida Bay has raised questions about the possible influence of onshore water management practices on salinity of the bay. The primary forcing factors of salinity in the bay are seasonal precipitation and evaporation which vary so widely that salinity changes are difficult to specifically characterize. The fossil record of the bay offers the potential for providing a salinity record with resolution of decades, or better, during the past century and a half under natural conditions. To test the hypothesis that older shells can be used to characterize salinity before the turn of the century, we have used carbon and oxygen isotope ratios (d13C and d18O) of mollusk shells from surface sediment as a proxy for physical and chemical water characteristics.

A four-inch diameter core was taken in each of five sub-basins in Florida Bay. These sub-basins are located in Long Sound, Buttonwood Sound, Alligator Bay, Whipray Basin, and Old Dan Bank northwest of Long Key. The selected sub-basins range from being strongly influenced by freshwater runoff (Long Sound) to being dominated by Gulf of Mexico and Atlantic Ocean water (Long Key) . In each sub-basin except Long Sound and Alligator Bay a core was taken in scattered turtle grass (Thalassia testudinum) growths to obtain organisms that grow attached to the grass. Turtle grass was not present in Long Sound and Alligator Bay but other grasses were present that might serve as substrate for many organisms commonly attached to Thalassia testudinum.

The coarse fraction of the sediment from the upper 10 cm of each core was washed and separated into two size fractions: 425 um - 1 mm and > 1 mm. Working primarily with the 425 um - 1 mm fraction, commonly occurring species were identified and separated from each sample. Seven species of mollusks, two species of foraminifera, and a serpulid worm were identified in most samples. On average, 15 individuals of each species were selected for analyses. If at least three individuals could not be found in a sample, the species was considered absent. Individual shells, or several portions of an individual, were crushed using a mortar and pestle, split and then analyzed in the USGS mass spectrometry laboratory in Denver, CO. More than 700 analyses allow the evaluation of species that are best for retrospective analyses and provides for the statistical characterization of the samples from each sub-basin.

Grouping the data by location (Figure 1) shows that each sub-basin has distinctive characteristics. Mollusks from near Long Key and Long Sound have mutually exclusive d18O and d13C values that compose end-member distributions. The widest range in d18O values is seen in Long Sound where the most positive d18O values reflect greater net evaporation and the more negative d18O values occur in response to increased fresh-water input. In contrast, more "normal marine" values are maintained near Long Key where variations in temperature and salinity and thus d18O and d13C are relatively small due to the more open exchange with the Gulf of Mexico and Atlantic Ocean. Moving toward the exterior of the bay, from Long Sound to Long Key, the intermediate sub-basins including Buttonwood Sound, Alligator Bay and Whipray Basin exhibit quite a bit of overlap, but show progressively more marine-like isotopic characteristics. The degree to which all of these areas are influenced by evaporation and fresh water may also be related to the slope defined by the regression through data for each sub-basin. These results indicate that it is conceivable to evaluate salinity based on mollusk shell isotopic composition, even though salinity variations in Florida Bay are complex and not as quantitatively well-defined as in other coastal settings. It follows that the isotopic analyses of mollusks from successive samples taken down carefully dated cores will provide a measure of natural, long-term salinity change in Florida Bay.

Halley, R. B. , Shinn, E. A. , USGS, St. Petersburg, FL 33701; Holmes, C. , USGS, Denver, CO 80225; Robbins, J. A. , NOAA, GLERL, Ann Arbor, MI 48105; Bothner, M. K. , USGS, Woods Hole, MA 02543; Rudnick, D. T. , South Florida Water Management District, West Palm Beach, FL 33406 .

Recent rapid ecological change in Florida Bay is widely believed to result from long-term changes in water quality, particularly salinity and nutrients, that have been influenced by onshore flood control and drainage projects completed during the last century. Overlooked, however, is the natural rise of sea level (30 cm since 1850) and the increased depth of Florida Bay. Because sediment production rates are insufficient to compensate for the added volume of the bay, more marine water covers the bay than did a century ago. Therefore, even if the same amount of freshwater had been delivered to Florida Bay, salinity would have increased simply because there is more marine water to dilute.

Florida Bay is a shallow lagoon subdivided by mudbanks into several dozen subbasins, that vary from nearly normal marine to estuarine. Poorly documented transport processes erode fine-grained sediment from subbasins and leave many sediment starved (floored by exposed Pleistocene limestone). Mudbanks are eroding on their northern and eastern slopes, probably in response to winter storms. Newly produced, as well as older, eroded sediment preferentially accumulates in the lee and on top of mudbanks at rates as great as 1-4 cm/yr, as indicated by 210Pb and 222Ra analyses. These observations suggest the elevations of banktops are maintained during sea-level rise by a balance of erosion and deposition resulting in overall buildup and migration. Mudbank segmentation and restriction of the bay have outpaced sea-level rise and have allowed subbasins to remain highly variable in water quality. Thus, two natural processes, sea-level rise and sedimentation, require evaluation in order to understand ecosystem-scale change in Florida Bay and to plan related onshore restoration activities.

Philip A. Kramer, Peter K. Swart , Marine Geology and Geophysics, RSMAS, University of Miami, Miami, Fl 33149; T.C. Juster , H.L.Vacher, Department of Geology, University of South Florida, Tampa, Fl 33620.

Over 230 small mangrove islands are found along the mudbanks and basins of Florida Bay. They serve an important role in the overall trophic dynamics of the Bay, as well as provide critical nesting and foraging habitat for a variety of birds, reptiles, and aquatic invertebrates. While it has long been recognized that these environments are saline to hypersaline, little is known about their flooding frequency, hydroperiod, rates of horizontal and vertical porewater movement, or porewater geochemistry.

This study has examined the hydrological and physical environmental conditions which lead to the formation of hypersaline pore waters on these islands. The overall goals of this study were three fold: 1) understand the basic surface hydrology and rates of water flux through the islands 2) to characterize the spacial and seasonal variability of the early diagenetic processes, and 3) to document the controls on the dissolution and precipitation of carbonate minerals in these high ionic strength sediments. While largely motivated by geochemical interest, this study has shed light on many of the important hydrogeological processes occurring on these islands which directly impacts the vegetation, birds, and aquatic invertebrates inhabiting them.

Two islands were examined in detail for this study: Cluett Key (located in western Florida Bay), and Jimmy Key (located in eastern-central Florida Bay). These two islands were chosen because of major differences in their physiographic characteristics, sedimentology, developmental history, and porewater chemistry. Each appears to represent the two extremes of island-types within the Bay.

Field logistics and the unconsolidated properties of the sediments necessitated using a variety of hydrological and geochemical sampling methods. Both islands were extensively instrumented in Spring, 1993 with pressure transducers, rain gauges, and sampling wells. The pressure transducers were placed in vertical nests along a transect 50-75 meters long and surveyed to a common datum using sight and transit. Water levels in the ponds, adjacent bay, and underlying limestone were also monitored using pressure transducers. All instruments were connected to remote data loggers. Sampling wells (1 1/4" diameter pvc pipes) were placed in nests of 5 (depths 25, 50, 100, 150, 200 cm) adjacent to nests of pressure transducers to allow rapid porewater collection. The islands were visited every other month beginning in Spring 1993 to July 1994. On each visit, data was downloaded, wells were pumped and sampled, and cores were taken. Water samples were analyzed for alkalinity, pH, salinity, and cations (Ca++, Mg++, Sr++, K+) and anions (Cl-, SO4--). In addition, tritium (half life 12.43 years) and d18O was measured in selected water samples. Cores were squeezed and analyzed as above, as well as for H2S, bromide, ammonia, and phosphate. Sediments examined for water content, permeability, porosity, and mineralogy.

The islands were flooded by bay water during the new and full moon spring tides that arrive every two weeks. Annual changes in Florida Bay water levels, short term wind effects, and the elevation of an island's levee are the major controls on the flooding frequency. During the study period, mean water levels in Florida Bay were about 20 cm higher in the fall than in the spring. This resulted in a much higher flooding frequency during the fall months. High water levels were maintained in the ponds through most of the year, dropping only during spring and early summer, when the interior ponds dried out completely. The groundwater table dropped substantially during these dry periods. On Cluett Key, the water table fell by as much as 50 cm below the pond surface forming large unsaturated zones. On Jimmy Key the groundwater table only dropped 10 cm below the pond floor due to the lower amount of exposure those sediments endured.

Rainfall mainly affected the surface waters during periods of low flooding frequency and limited tidal exchange (February through July). The shallow depth of the island ponds, coupled with the large seasonal changes in flooding frequency, rainfall, and rates of evaporation allow for rapid changes in surface water salinities. Highest salinities coincide with times when the evaporation- to- recharge deficit is at it's peek during the late spring and summer. A decrease in the late summer and early fall occurs when heavy rains begin, and Florida Bay water levels rise so that frequent flooding is assured.

The limestone groundwater beneath Cluett Key is hydraulically "linked" to the surrounding Florida Bay water. The movement of surface and porewaters on the islands are influenced by this hydraulic link. During the wet season a net downward gradient of .1 exists between the interior ponds and the adjacent bay, after short term tidal variations are subtracted. This substantial head gradient can potentially move water downward through island sediments during this time of year. In contrast during the spring, the groundwater levels in the islands drops below that of the adjacent bay and conditions for upward flow combined with upwards evaporative capillary movement exist. The extent of movement is limited by the low hydraulic conductivity of the sediments, which decreases from 10-2 m-day-1 to 10-4 m-day-1 at greater depths due to compaction and root void filling as sediments are buried. Horizontal movement is insignificant due to the vertical nature of many of macropores and root voids, and the small (<30 cm) topographic gradients of the island terrain. Tritium measurements confirm this general vertical movement, and indicate that the porewaters on these islands are all less than 40 years old.

Large temporal changes in soilwater salinity were observed in the upper 50 cm of both islands, with profiles "hinging" back and forth. The highest salinities occurred during dry periods and were measured in excess of 250‰. The lowest salinities occurred during frequent flooding and after heavy rains diluted surface waters. These salinity changes are consistent with surface soils undergoing seasonal evaporation and dilution by flood waters and rainfall. The depth to which these short term changes are propagated coincides with the average depth that the water table falls in a given area during dry out.

Below 50 cm, pore water salinity variations become damped out and begin to approach a constant value representative of the time-averaged mean of the changes occurring in the soilwaters above. In nearly all profiles examined, this time-averaged maximum salinity occurred between 75 and 150 cm beneath the surface. Concentrations of salt in soilwaters gradually decrease to the limestone contact, 1 to 2 meters below. No significant changes in pore water salinity at these greater depths were recorded over the study period.

The chemical changes in porewaters reflect both microbial and early diagenetic processes. The major driving force in determining the direction and magnitude of the chemical changes is the amount of exposure the sediments receive, and the input and types of input of organic carbon to the sediments. These chemical pathways generally correlate to processes occurring within distinct vegetation zones. In the mangrove fringe there are high inputs of leaf detritus, and frequent flooding of the soils. This results in extensive sulfate reduction within the upper sediments. This sulfate reduction is coupled to moderate amounts of high magnesium calcite and aragonite dissolution, and limited amounts of calcite/dolomite precipitation. In the high hammock zone, extensive dissolution was also documented, but through a different process of organic matter oxidation. Meteoric water and salts derived from sea-spay collects in the upper sediments and initially dissolves aragonite and high magnesium calcite as it comes into equilibrium with the sediments. Oxidation of organic carbon using oxygen, nitrate, and sulfate within the root zone of the shrubs and trees elevates the pCO2 which further promotes dissolution of aragonite and High magnesium calcite. Some of the highest rates of carbonate dissolution occur in the high hammock zones of the islands. In the ponded interiors, pore waters have much higher salinities. Gypsum formation occurs in the most exposed sediments, but that very little sulfate reduction or pyrite formation was found.

This study has demonstrated for the first time the mechanisms which control the flooding and hydrology of the mangrove islands which play an integral part of the ecology of Florida Bay. These studies reveal that the high salinities in the islands are unrelated to the salinity in the bay, but are controlled by the height of the levee surrounding the island and the amount of evaporation on the island. In future work we propose to study the hydrological connections between adjacent basins and implications that these connections may have on the geochemical flux from the sediments.

Richard P. Stumpf, US Geological Survey, Center for Coastal Geology, St. Petersburg FL 33701.

Water turbidity produced by resuspension events have a potentially significant impact on water quality and various bottom communities in Florida Bay. We are using satellite imagery in conjunction with field observations to describ the frequency and extent of turbidity events.

Several types of satellite will be examined in the course of the project. The primary source will be AVHRR data, which is available almost daily at 1 km pixel size. Landsat data, at 80 m, is available sporadically from 1973, Landsat TM at 30m from 1984; and ocean color sensors, such as SeaWiFS and OCTS are anticipated for launch in 1996. Imagery will be processed to water reflectance by correcting for atmospheric affects and sun angle, and removing bottom albedo. Field observations will be used to establish diffuse attenuation and total suspended solids.

At present, AVHRR imagery is being evaluated, about 400 suitable scenes (of over 1800 data sets) are in hand and processed for aerosols and sun angle from December 1989 to the present. The AVHRR data sets have also been processed for sea surface temperature.

Meteorological observations from NOAA CMAN stations are also being examined with the imagery. The impact of the cold fronts on water clarity is evident in the Bay. Recent imagery is being made available in preliminary form on the Internet for use in Florida Bay studies. The effort over the next year will be establishing light attenuation coefficients from the satellite imagery and incorporation of Landsat data to look at some early time periods.

Peter K. Swart, University of Miami, 4600 Rickenbacker Causeway, Miami FL 33149; Genny Healy, MGG/RSMAS, University of Miami, 4600 Rickenbacker Causeway, Miami FL 33149; Richard E. Dodge, Nova Southeastern University, Oceanographic Center, 8000 North Ocean Dr., Dania FL 33004.

In order to investigate historical variations in the water quality of Florida Bay we have utilized changes in the oxygen and carbon isotopic composition of the skeletons of scleractinian corals growing in Florida Bay. The oxygen isotopic ratio (18O/ 16O) of the coral skeleton records changes in salinity and temperature, while the carbon isotopic ratio (13C/ 12C) indicates the overall physiological condition of the coral as well as the ambient ratio in the dissolved inorganic carbon (DIC) of the prevailing water. Oxygen and carbon isotopic ratios are usually reported in the conventional d notation as parts per thousand (‰) relative to an international standard (PDB).

In our studies we are using two different species of corals, Solenastrea bournoni and Siderastrea radians. The specimens of S. bournoni we are using are large (120 to 150 years in age) and are as far as we know restricted to Lignumvitae basin. These corals were originally cored in 1986 and their growth rates and fluorescence descibed by Hudson et al. (1989) and Smith et al. (1989). The corals were cored again in 1993 and 1994 by our group and the d13C and d18O have been correlated with recent high resolution salinity, temperature, and nutrient data obtained from Florida Bay. In order to extend our interpretations to other basins where the Solenastrea corals are not present, we are using specimens of the species Siderastrea radians, a small grapefruit sized coral which grows to an age of between 20 to 40 years.

We have correlated changes in the d18O of the coral skeleton of Solenastrea with salinity over the past 30 years and developed a statistically significant association between these two variables; the skeletal d18O increases with increasing salinity. Based on an analysis of the d18O of the Solenastrea bournoni in Lignumvitae Basin we have concluded that while there has been no long term increase in salinity in this basin of Florida Bay over the past 160 years (Figure 1), there is an increase in d18O coincident by the construction of the Florida East Coast Railway from Miami to Key West between 1905 and 1912. The construction of the railway resulted in the restriction of the exchange of water between the Florida reef tract and the Gulf of Mexico causing Lignumvitae Basin to become slightly more saline. From 1910 to 1986 there has been no obvious increase in the skeletal d18O and therefore we conclude there has been no increase in salinity. Large changes also occurred in the skeletal d13C values coincident with railway construction. After 1910 the skeleton contained more 12C, a phenomenon which is related to the increased contribution of the products of the decay of organic material to the dissolved inorganic carbon pool . We suggest that the railway construction process, which restricted the exchange of water, also allowed more organic material to be retained within Florida Bay. The organic material eventually degrades to CO2 producing a characteristic signature in the water column.

Natural events also appear to have influenced the water in the Bay. Between 1912 and 1948, frequent hurricanes had the effect of increasing exchange of water between the Bay and reef tract and removing large quantities of organic rich sediments (Figure 2). However, since 1948 the number of hurricanes affecting the area has decreased and the products of the oxidation of organic material have been increasingly retained within the basin promoting the initiation of eutrophic conditions. The interpretation of this work have been accepted for publication (Swart et al., In Press).

In order to better calibrate changes in the water quality of Florida Bay to the skeletal coral record, we have used the high resolution environmental data collected by the Everglades National Park and Florida International University in conjunction with their water quality monitoring program over the past several years. As data on the d18O and d13C of Florida Bay water has not been available, we have also started to collect this information. These data combined with high resolution sampling of the coral skeleton have allowed us to improve the correlations between salinity and skeletal d18O. Based on the new calibration and an independent indicator of temperature, such as the Sr/Ca ratio of the coral skeleton, we feel that it should be possible to obtain an unambiguous record of salinity in Lignumvitae Basin for the past 160 years.

One criticism of our interpretation of the data from Lignumvitae Basin has been that the results from this basin might not be representative of other portions of the Bay. In order to assess how the record in Lignumvitae Basin relates to other basins, we are using the small coral Siderastrea radians. This coral appears to be widespread throughout the bay growing in areas with rocky bottoms. Some of these specimens can be up to 30-40 years in age. Our first analyses of this coral show good agreement between the d18O and the salinity of the water.

References

Hudson, H.D., Powell, J.V.D, Robblee, M.B. and Smith, T.J., 1989. A 107-year-old coral from Florida Bay: barometer of natural and man-induced catastrophes, Bull Mar. Sci., 44:283-291.

Smith T.J., Hudson, JH, Robblee, M.B., Powell, G.V.N., and Isdale, P.J., 1989. Freshwater flow from the Everglades to Florida Bay: A historical reconstruction based on fluorescent banding in the coral Solenastrea bournoni, Bull. Mar. Sci., 44:274-282.

Swart, P.K. Healy, G. Richard, Dodge,R.E. Kramer ,P. Hudson,H. Halley, R. & Robblee , M. (In Press) The Stable Oxygen and Carbon Isotopic Record from a Coral Growing in Florida Bay: A 160 Year Record of Climatic and Anthropogenic Influence, Palaeo, Palaeo, Palaeo

H.R. Wanless, Dept. Geological Sciences, University of Miami; T.A. Nelsen, AMOL, NOAA; L.P. Tedesco, Dept. Geology, Indiana/Purdue University at Indianapolis; J. H.Trefry , Dept. Oceanography, Florida Institute of Technology; P.L. Blackwelder , J.A. Risi, Rosenstiel School of Marine and Atmospheric Science, University of Miami.

The investigators are involved in two projects in and proximal to Florida Bay. One is to document the fate of hurricane deposits and evolution of hurricane impacted environments. The second is to assess the viability of using sedimentologic, geochemical and paleoecological records in layered sediment sequences to document historical changes in the environments influencing Florida Bay.

The project studying fate of hurricane deposits is in its second of three years of funding and involves sampling strata from historical hurricanes (principally Andrew, Betsy, Donna, and the Labor Day Hurricane of 1935), documenting changes in deposited storm layers, substrate subsidence, and recolonization or evolution of biotic communities. We are focusing on Biscayne Bay, Florida Bay and the Everglades west coast north to Chatham River. Over 150 cores have been collected to characterize Andrew, Betsy, Donna and the Hurricane of 1935. Aerial photographs from 1927 to present have been analyzed.

With respect to Florida Bay, a most important finding of this study is the recognition that hurricane-destroyed mangrove swamps may undergo a period of rapid substrate subsidence (we are measuring 2-4 cm per year following Andrew). Large volumes of detrital and dissolved organics are being released from the decaying mangrove swamp substrate. On the west coast, some of this released organic detritus has formed thick (0.5-1.5 meters in 3 years) post-event deposits in the inner bays and in side channels. Much is being carried seaward to the offshore environment. Winter storm resuspension and transport processes are moving these offshore particulates southward into northwest Florida Bay and southward through the Keys to the reef tract.

This post-event redistribution is still occurring for mangrove swamps damaged by the Great Labor Day Hurricane of 1935 and Hurricane Donna (1960). The large areas of coastal and interior mangrove forest on northern Cape Sable damaged by these storms have not recovered. Rather, as the peat substrate has decayed, the surface has subsided into the lower intertidal zone where burrow excavation, grazing and tidal processes are completing the transfer of the storm-destroyed mangrove swamp to the subtidal. Large volumes of detrital and dissolved organics are still episodically discharged from this degrading environment.

The second study, using layered sedimentary sequences for paleoenvironmental reconstruction, is focusing on finding meaningful stratified sediment sequences which contain an interpretable historical record. Most accumulating sediment sequences are formed layer by layer. This stratification (layering) is preserved in the shallow marine environments of south Florida where environmental conditions inhibit bioturbation. The stratified records, however, vary with respect to continuity of record, persistence of sediment deposition, local reworking, and presence/absence of erosional hiatuses. The nature of the sediment-biotic-geochemical record is dependent on the style of sediment deposition in the area. Six styles are recognized.

(1) Daily Sediment Deposition. A few areas receive significant sediment on a day to day basis and accumulate a detailed sediment record, though short lived because of rapid sediment buildup. (2) Winter Storm Deposition. Some deltas, banks and isolated depressions receive thin sediment laminae from episodic winter storms and tropical storms. Supratidal levees and berms receive depositional laminae from certain of the winter storm and tropical storm events. (3) Hurricane Deposition. Hurricane events produce a significant sediment layer across much of the affected subtidal and supratidal environments. Layers vary in thickness from less than one mm to greater than one meter. (4) Post Event Deposition. Major hurricanes and major mangrove or seagrass dieoffs may initiate a phase of sediment reworking of material both from unstable areas and released from destabilized bottoms. Redistribution of this sediment results in accumulation of thick deposits in sediment sinks. Post Andrew sediment deposition is greater than 1.5 meters in a few areas. This post event redistribution may last a few years or decades, depending on the nature of the environmental disturbance. (5) Autochthonous Biogenic Sediment Deposition. Subtidal algal mats, Halimeda opuntia banks, and coral-coralline algae layers rarely preserve in situ. Supratidal mats have higher preservation potential. Seagrass recolonization can produce distinct epifaunal and infaunal communities that preserve in situ. (6) Allochthonous Biogenic-influenced Sediment Deposition. Seagrasses, algal mats, and scum mats modify the bottom energy, cohesiveness and stability. They provide conditions for deposition or stabilization of sediment that would normally not be deposited or retained.

These different styles of sedimentation have different sediment textures, fabrics, constituent composition and type of sedimentary structure(s). It is imperative that the style(s) of sediment deposition be distinguished in sequences being used for paleoenvironmental reconstruction as each records the local and regional physical, biotic and chemical environmental history differently. As many styles of sedimentation are not continuous through time or space, it is generally not meaningful to project average rates of sediment accumulation.

Different styles of sedimentation have very different rates and continuity of sedimentation. It is critical to accurately define the style or styles of sedimentation within a sequence before evaluating rates of sedimentation and the significance of geochemical and paleontological studies therein.

Other aspects must also be resolved in using sediment sequences for detailed paleo-environmental analysis. These include: physical and biogenic mixing, selective deposition or erosion, selective dissolution based on variations in mineralogy and skeletal microstructure, deep excavation and infill structures, biotic changes resulting from local substrate changes, and apparent chemical changes related to differing texture or constituent composition.

Despite the potential pitfalls, fine-scale analysis of shallow marine sediment sequences provide an unequaled potential to reconstruct detailed local and regional hydrologic and paleoenvironmental history along a continuum of environments from fresh to marine.

During the first year of funding, we have used stratified sequences from four sites to evaluate the potential for detailed dating and paleoenvironmental reconstruction. These cores are from areas adjacent to Florida Bay that influence or reflect the environments of Florida Bay. Three core sites are on a gradient from the mouth of Shark River Slough (mouth of Avocado Creek) through lower Shark River (a laminated filled bay sequence in adjacent Whitewater Bay) to Ponce de Leon Bay (laminated bank in the northeastern sector). This transect has the potential to represent the changing influence of discharge from Shark River Slough to the adjacent marine environment. A fourth layered sediment sequence site in northwestern Coot Bay has provided an opportunity to evaluate how the sediment sequence has recorded known historical changes and influences (opening and closing of Coot Bay Canal connection with Florida Bay; Hurricane of 1935 and 1960).

Analyses of cores has included, style of stratification, degree and type of burrowing, constituent composition and texture, visual erosion or discontinuity surfaces; x-ray and color enhanced photography of cores; radiometric dating by 210Pb, 137Cs, and excess 228Th; analysis for Al, Cu, Hg, Pb, Zn, organic N, organic C, P; evaluation of contained pollen contained molluscs, foraminifera, arenaceous foraminifera, octracods, diatoms and other skeletal grains and fragments. Sampling for this first (reconnaissance) year was at 2-5 cm intervals spaced through the cores to look for presence and trends of the above listed components.

In the layered cores selected and analyzed, we have 80-120 cm thick sequences that record environmental history from about 1850-1900 to the present. All cores record a progressive upwards increase in Hg and Hg/Al, with the dramatic increase occurring in the 1940's. There is a progressive decrease in Hg from the mouth of Shark River Slough seaward to Ponce de Leon Bay. Coot Bay contains high levels of Hg and Hg/Al. This indicates an aerosol source for the pollutant, as Coot Bay is not in the main freshwater transport pathway from Shark River Slough.

Rapidly deposited storm and post-storm layers, burrowing, and style of sedimentation all affect the vertical radiometric, geochemical, and paleontologic profiles in the cores analyzed. Rates of sedimentation are not uniform in the sequences.

For year two, we are initiating a detailed analysis of layered sediment sequences from lower Shark River (bay fill in adjacent Whitewater Bay), northwestern Coot Bay, and First National Bank area in northwestern Florida Bay. We consider the approaches of these demonstration projects to have opened the door for future detailed paleoenvironmental reconstruction throughout Florida Bay and adjacent environments.

G. Lynn Wingard, T.M. Cronin , D.A. Willard , S.E. Ishman , L.E. Edwards , C. Holmes , S.D. Weedman , U.S. Geological Survey, Reston, VA.

Recent negative trends have been observed in the ecosystem of Florida Bay, including algal blooms, seagrass die-offs, and declining numbers or shellfish, adversely affecting the fishing and tourist industries. Many theories of cause and effect exist to explain the adverse trends, but these theories have not been scientifically tested. Prior to finalizing plans for ecosystem restoration, the relative roles of human activities versus natural ecosystem variations need to be established. This project addresses this need by focusing on two primary goals. First, to determine the characteristics of the ecosystem prior to significant human alteration, including the natural range of variation in the system; this establishes the baseline for restoration. Second, to establish the extent, range, and timing of changes to the ecosystem over approximately the last 150 years and to determine if these changes correlate to human alteration, meteorological patterns, or a combination of factors. In addition, data on recovery times of certain components of the ecosystem will be obtained allowing biologists to estimate responses to proposed restoration efforts. This project is planned as a five year study, to be completed in 1999.

This project is one segment in a group of coordinated USGS projects examining the biota, geochronology, geochemistry, sedimentology, and hydrology of southern Florida, Florida Bay and the surrounding areas. Data are being compiled from terrestrial, marine, and freshwater environments in onshore and offshore sites in order to reconstruct the ecosystem history for the entire region over the last 150 years.

Methods: In cooperation with other USGS projects, and other state and federal agencies, a series of shallow piston cores (~1-2 m) have been collected in the central and northeastern areas of Florida Bay. The cores are x-rayed and examined to determine the degree and extent of sediment disruption. Cores that appear to contain relatively undisturbed sediments are submitted for 210Pb analysis to determine the age and degree of disruption of the sediments. An independent support for the age model is obtained by analysis of the pollen in the core; key introduced species include Casuarina, Schinus, and Melaleuca.

Cores that have a good stratigraphic record are sampled at closely spaced intervals (2 cm) for all macro- and micro-fauna and flora present. The primary biota analyzed are 1) benthic foraminifera, 2) ostracodes, 3) mollusks, 4) dinoflagellate cysts, 5) pollen and macro-plant material. The faunal and floral groups are compared by means of quantitative down-core assemblage diagrams. Determinations of salinity, bottom conditions, nutrient supply and various other physical chemical parameters of the environment are made for each sample based on the fauna and flora present.

Examination of the diversity and distribution of the fauna and flora over time allows us to infer the nature and extent of changes that have occurred in the ecosystem. In the marine environment, benthic foraminifera and ostracodes are used to suggest changes in salinity and substrate; micromollusks indicate substrate changes and general changes in salinity patterns; dinoflagellate cysts may indicate algal blooms and current patterns; pollen reflects the composition of onshore vegetation, therefore providing an indication of regional changes, such as climate, hydroperiod or nutrient supply.

Data from all cores are being integrated to search for regional patterns of change in diversity and distribution of the fauna and flora; data from Florida Bay will be correlated to data obtained in the corresponding USGS onshore ecosystem history project. The integrated data set will be analyzed to see if detected changes in biota correlate to alterations in physical parameters and/or historic records of human-induced modifications of the environment.

In addition, modern core-top living assemblages are being collected twice a year (in the wet and dry seasons), over a period of several years, from the central and northeastern portions of the bay, in order to provide data on seasonality, habitat distribution, and preferred substrates of the living biota for interpretation of the down-core assemblages.

Preliminary Results: Two shallow cores have been examined to date: 1) Bob Allen #6A Core (172 cm total depth), located on a grass covered mud bank near the southern end of the Bob Allen Keys; 2) Taylor Creek Core T-24 (90 cm total depth), located near the mouth of Little Madeira Bay. The age model developed using 210Pb established a 1.1 cm/year sedimentation rate for the Bob Allen #6A core; the ages discussed below are estimates based on that rate.

The Bob Allen #6A core can be divided into five zones based on the benthic fauna. The ostracodes, mollusks, and benthic foraminifera in the lower portion of the core (172-135 cm; ~1850-~1890) show moderate diversity and abundance; they indicate that the salinity ranged from 20-30 ppt and the subaquatic vegetation was present in moderate amounts. The dinoflagellate cysts were low in abundance and the terrestrial vegetation, as indicated by the pollen, was pine-dominated upland forests. The portion of the core from 135-75 cm (~1890-~1930) is characterized by a very low diversity, low abundance, benthic faunal assemblage dominated by sand dwellers; subaquatic vegetation was low to absent, and the salinities ranged from 15-25 ppt. In contrast, dinoflagellate cysts were relatively abundant in this portion of the core, and the assemblage was dominated by one species, Polysphaeridium zoharyi. The terrestrial vegetation began to shift to typical wetlands species, with more salt-marsh, slough, and hardwood pollen present. All five biotic elements examined show corresponding changes at approximately the 135 cm and 75 cm sections of the core.

Above 75 cm in the Bob Allen #6A core a great deal of fluctuation occurs within the benthic fauna. This portion of the core is divided into three zones: 75-35 cm (~1930-~1970); 35-10 cm (~1970-~1985); and 10-0 cm (~1985 to the present). The 75-35 cm and 10-0 cm zones are characterized by moderate to high benthic faunal diversity and abundance, and low dinoflagellate cyst abundance. The benthic fauna indicate a period of extreme fluctuations in salinity, ranging from 20->50 ppt, and abundant subaquatic vegetation. The 35-10 cm zone is distinguished by a return to lower diversity and abundance for the benthic fauna, and low to moderate abundance for the dinoflagellate cysts. The salinities in this portion of the core appear more stable, fluctuating between 15-30 ppt, and the subaquatic vegetation was low. The pollen for the upper portion of the core, from 75-0 cm indicates greater abundances of onshore wetlands environments, dominated by hardwoods, mangroves and buttonwoods.

The benthic fauna seen in the upper 60 cm in the Taylor Creek T-24 core show the same kinds of fluctuations as those seen in the upper 75 cm of the Bob Allen #6a core. The dinoflagellate cysts show a significant increase in the dominance of Polysphaeridium zoharyi at 75 cm in the Taylor Creek T-24 core, which may correspond to the increase seen at ~ 75 cm in the Bob Allen #6a core (although the Taylor Creek T-24 core has a higher sedimentation rate). Taylor Creek T-24 core has approximately 20% more Polysphaeridium zoharyi than Bob Allen #6a throughout the core; this is consistent with the more restricted marine setting of Little Madeira Bay. The pollen record for Taylor Creek T-24 shows more subtle changes in the onshore terrestrial environment, primarily because of its closer proximity to land, but the general patterns are the same. The basal portion of the core (90-80 cm) indicates a pine-dominated upland, and above 80 cm wetland vegetation becomes more abundant.

Our results indicate that major environmental changes occurred in the Florida Bay and Everglades ecosystems over the last 150 years. Periods of decreased salinity correspond to intervals of decreased subaquatic vegetation, lower benthic faunal diversity, and lower benthic faunal abundance. Periods of increased salinity correspond to intervals of increased subaquatic vegetation, higher benthic faunal diversity, and higher benthic faunal abundance. The pollen and dinoflagellate cyst records show that changes in the terrestrial habitat and the pelagic realm are roughly synchronous to the marine benthic faunal record. This apparent synchroneity between the marine and terrestrial realm implies changes occurred in parameters that affect both habitats. Rainfall and/or human-altered hydroperiods may be possible explanations for the changes seen. Presently, there is no evidence of hypersalinity in Florida Bay prior to ~ 1930. The fluctuating salinities and periods of hypersalinity that we see are consistent with controlled discharge through the canal system and inconsistent with natural sheet flow.

Future Work: Analysis of cores and samples collected to date will be completed, and monitoring of the modern environment for our core-top data base will continue. In addition, we hope to begin geochemical analyses of the shell material. Initial efforts have been concentrated in the northern and eastern portions of the bay, the areas presumed to be most impacted, but as patterns and trends begin to emerge, we plan to continue sampling along rough transects moving west and south through the Bay. Coordination with other USGS projects focused on terrestrial biota, geochronology, geochemistry, sedimentology, and hydrology should enable reconstruction of the regional ecosystem over the last 150 years by the time the project is terminated.

M.G. Winkler , P.R. Sanford , S. W. Kaplan, Center for Climatic Research, Institute for Environmental Studies, University of Wisconsin, Madison.

Paleoecological research provides knowledge of the prehistory of the Everglades which is crucial to preservation and reconstruction efforts in southern Florida. The paleoenvironmental history of both the aquatic and hammock landscapes of the Everglades as interpreted from the biota preserved in sediment cores provides a chronology of hydrologic change, mid-Holocene sea level change, and upland vegetation change. Well-dated prehistoric sequences are still rare for the Everglades and, consequently, basic information about the past history of the Everglades is sparse. Our goal is to document in detail how anthropogenic activities in the last 100 years changed the Everglades environments and how climate change affected southern Florida before and during the Holocene. Knowledge of past changes in aquatic and upland plant communities in response to past climate change is also needed to predict the extent of future changes in the Everglades in light of possible carbon dioxide and methane-induced global warming.

Since 1993 we have been studying the paleoecology of sites in the Everglades National Park (ENP). We have 38 cores from 17 sites, mostly within ENP, although 4 sites are in Water Conservation Area 3 (WCA3), and 1 is at Lignum Vitae Key. Using radiocarbon dating and standard methods for paleoenvironmental research we have analyzed some of the sediments recovered for charcoal, pollen, diatoms, sponge spicules, cladocera, and Nymphaea and Cladium sclereids. The scarcity of pollen, diatoms, and other bioindicators in the sediments has slowed analyses and required modification of laboratory techniques. Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and other chemical analyses of the more recent sediments and of fish scales from the cores have been used to reveal changes in nutrients and heavy metals. Charcoal analysis provides fire history of the peatlands. Because differences in stable carbon isotope signatures of C3 and C4 plants provide independent evidence of plant community change, mass spectrometric analyses of peats and charcoal from cores and plants near coring sites have been done.

Core sediment changes and 46 radiocarbon dates (by both AMS and standard bulk sediment techniques) provide a chronology for changes during the past 5000 years for ENP. Oldest dates, between 4900 and 5200 years before present (YBP) were obtained on cores from Rocky Glades, Pinelands trail, Castellow Hammock, L67C, and WCA3B. Freshwater marls were identified and dated for cross-correlation at most sites. Freshwater marl deposition results from lowered waterlevels. These deposits occur prior to 4000 YBP, between 2600 and 1900 YBP, and again after 1700 YBP. Overland flow may have been greatly diminished or confined to a few small channels during these periods. Relatively old dates on sediments near the upper part of some cores suggest that in the last centuries there were large water-level changes. These changes resulted in decomposition and loss of recent sediments during times of drought and the subsequent flushing of friable organic remains from sediments during times of high flow.

At Gator Lake pollen changes suggest a recent expansion of pinelands in the region. Pine also seems to have been abundant about 1500 YBP. Fluctuations between sawgrass and sedge pollen and aquatic macrophyte pollen, and pyrite framboid abundances indicate fluctuating water levels at Gator Lake. Diatom analysis indicates an inverse relationship between diatoms and sponges. Mercury analysis of fish scales found in the Gator Lake core revealed increased concentrations in the top sediments when compared to background (pre-European settlement) levels of mercury in both the fish scales and in the sediments surrounding the fish scales.

Cores from 2 wet prairie/Eleocharis marsh sites in Northeast Shark Slough (NESS), A06 (a long hydroperiod site) and A23 (a short hydroperiod site), have been studied in detail. In addition to sediment description and radiocarbon dating, these cores have been analyzed for charcoal, Cladium sclereids, cladocera, sponge spicules, and for A23 only, pollen and Nymphaea sclereids. A23 has an older basal date (2840 YBP) than A06 (2100 YBP). The lower elevation of A23 with respect to bedrock allowed a rising water table, coupled to rising sea level, to affect A23 before it affected A06. Marl and peat deposits began to build up earlier at A23 than at A06. Dark organic marl at the base of A06, dated at 2100-1960 YBP, probably corresponds to an A23 mid-core marl dated at 1890 YBP. In both cores peat layers overlie these time-equivalent marl layers and presumably are also time-equivalent. A06 peat continues to the modern surface, but A23 peat is succeeded by an algal floc marl, then another peat (1380 YBP), and a final surface marly peat. An old date so near the surface suggests that deposits in the area of the A23 core have been truncated by decomposition when deposits were exposed by low water levels and by burning. Charcoal analysis of A23 deposits supports this hypothesis. The mean for charcoal as % organic in the A23 core is 67.08% (n=5),whereas for A06 the mean value for charcoal as % organic is 21.31% (n = 13) and in the most recent sample of the A06 deposits, 7-0 cm, charcoal was only about 13% of organic weight.

Cladium sclereid analysis indicates 3 periods of locally increased Cladium near A06, all since 1960 YBP, while at A23 only one such period (1890-1660 YBP) is evident. The single A23 peak may correspond to the lowermost A06 peak, any subsequent Cladium increases in A23 having been removed by decomposition and burning. Cladoceran remains are fewer and less taxonomically diverse at A23 (17 taxa) than at A06 (28 taxa). In both sites cladoceran remains are scarce at the base of the cores and increase gradually over time with final sharp increases in the surface core samples. Cladocera may be tracking periphyton production, which is in turn responding to water level and nutrient increases. The distribution pattern of cladoceran remains in the cores may indicate that significant periphyton production has occurred only recently. Sponge spicules are less numerous in A23 sediments than in A06 sediments, but in both cores they follow a distribution pattern similar to that of cladocera, being scarce in older deposits and increasing upcore. However there is no direct relationship between cladocera and sponges over time in either of the cores. If cladoceran pieces are tracking periphyton production, then the lack of a relationship between sponges and cladocera may reflect a competitive interaction between sponges and periphyton. There appears to be an inverse (A23) or lag (A06) relationship between sponge spicule densities and Cladium sclereid densities. Such relationships may reflect changing water levels if high numbers of Cladium sclereids indicate lower water levels and shorter hydroperiods and high numbers of sponge spicules indicate higher water levels and longer hydroperiods. Pollen analysis of A23 sediments is complicated by the fact that pine and cheno-am pollen overwhelmingly dominate most samples. The basal sample, however, is dominated by Isoetes microspores suggesting standing water during the initial phase of sediment deposition at A23. Nymphaea pollen is present in every sample, while Cyperaceae pollen is present in all but the basal one. Pollen of both taxa increases gradually through time. An early Cyperaceae peak is succeded by a peak in Typha, which is succeded by a peak in Nymphaea + Sagittaria + Utricularia + Cyperaceae. The fact that deposits are thinner and microscopic remains fewer in the older A23 core suggests that this area has always had lower water levels, shorter hydroperiods, and perhaps lower productivity than A06. The study of A06 and A23 shows that the rate of surface water flow is not uniform at sites within the Shark River Slough because slight topographic differences can pool water or increase flow. Thus geomorphic changes can favor formation or degradation of peat or marl sediments and effect accompanying changes in local biota. These differences are evident in the formation and shaping of tree islands within the Shark River Slough, but they are also evident at more subtly different sites, as A06 and A23, by depositional differences in the past as well as today.

The modern hydrologic environment of the Everglades seems to be one of marl deposition. Recent hydrologic changes contrast with climate- and sea-level-induced changes over the past 5 millennia when deepwater peats formed, providing substrate for uplands, hammocks, and tree islands to enrich the landscape. The topographic highs in the landscape provide diverse habitat for both fauna and flora. The mosaic landscape of the Everglades could become less complex as long-term water-level changes may not favor production of peat today.

Work is continuing on this project. We are continuing detailed analyses of sediments from the sites with the longest records and hope to complete the study within the next year or two.

Last updated: 07/16/98
by: Monika Gurnée
gurnee@aoml.noaa.gov