LATE HOLOCENE SEA LEVEL RISE IN SOUTHWEST FLORIDA: IMPLICATIONS FOR ESTUARINE MANAGEMENT AND COASTAL EVOLUTION

Dana Derickson, Figure 2 FACULTY Lily Lowery, University of the South Mike Savarese, Florida Gulf Coast University Stephanie Obley, Flroida Gulf Coast University Leonre Tedesco, Indiana University and Purdue Monica Roth, SUNYOneonta University at Indianapolis Ramon Lopez, Vassar College Carol Mankiewcz, Beloit College Lora Shrake, TA, Indiana University and Purdue University at Indianapolis VISITING and PARTNER SCIENTISTS Gary Lytton, Michael Shirley, Judy Haner, STUDENTS Leslie Breland, Dave Liccardi, Chuck Margo Burton, Whitman College McKenna, Steve Theberge, Pat O’Donnell, Heather Stoffel, Melissa Hennig, and Renee Dana Derickson, Trinity University Wilson, Rookery Bay NERR Leda Jackson, Indiana University and Purdue Joe Kakareka, Aswani Volety, and Win University at Indianapolis Everham, Florida Gulf Coast University Chris Kitchen, Whitman College Beth A. Palmer, Consortium Coordinator Nicholas Levsen, Beloit College Emily Lindland, Florida Gulf Coast University LATE HOLOCENE SEA LEVEL RISE IN SOUTHWEST FLORIDA: IMPLICATIONS FOR ESTUARINE MANAGEMENT AND COASTAL EVOLUTION

MICHAEL SAVARESE, Florida Gulf Coast University LENORE P. TEDESCO, Indiana/Purdue University at Indianapolis CAROL MANKIEWICZ, Beloit College LORA SHRAKE, TA, Indiana/Purdue University at Indianapolis

PROJECT OVERVIEW complicating environmental management are the needs of many federally and state-listed Southwest Florida encompasses one of the endangered species, including the Florida fastest growing regions in the United States. panther and West Indian manatee. Watershed The two southwestern coastal counties, Collier management must also consider these issues and Lee Counties, commonly make it among of environmental health and conservation. the 5 fastest growing population centers on nation- and statewide censuses. Although not Water management in Southwest Florida is heavily industrialized, urban and suburban overseen by the South Florida Water growth has taxed water resources, and Management District (SFWMD). This state agricultural development has both increased agency is empowered with this difficult task of freshwater demands and created point source compromising freshwater needs, storm water pollution. Consequently, management of management, and the maintenance of freshwater is a major societal concern. ecological health. Water delivery is Because rainfall is seasonal, water managers principally controlled by a system of storm must both retain freshwater for use during the water retention ponds, canals, and weirs. dry season (winter and spring) and prevent Typically management practices function to storm flooding during the wet season (summer hold as much water a watershed can maintain and fall). to recharge groundwater aquifers until some critical threshold level is achieved when water Counter to water management constraints are is then abruptly released from the weirs. Such environmental concerns. Southwest Florida, if practices, though effective for society’s left unaltered, would exist as a network of concerns, can be harmful to life within the wetlands that drain principally through sheet estuaries downstream of the freshwater flow into coastal estuaries. Freshwater and release. Although estuarine ecosystems can brackish water ecosystems are delicately handle large fluctuations in salinity and the adapted for these conditions. Water quality is water quality alterations that accompany them, germane for their health. These habitats are sudden and persistent changes can be somewhat unique. Southwest Florida sits detrimental (i.e., an ecological phenomenon within a narrow strip of the West Indian known as “pulsing”). The practice is also biogeographic province that is separated from wasteful of freshwater. The canal system was the majority of the province’s real estate by designed before Southwest Florida’s the Straits of Florida. Consequently, there are population boom, when freshwater was not numerous endemic species, relict biotas, and viewed as a limiting resource. Consequently, ecosystems perched for extinction. Further improved water management practices are These environmental problems are needed to account for these risks and to exacerbated by longer term, natural variability minimize waste. occurring along the Southwest Florida coast. Superposed upon the decadal environmental What this conflict means is that Southwest variability generated by human alteration of Florida is an ideal laboratory for coastal environments are natural, longer experimentation – a venue for better period, centennial and millennial scale understanding the scientific basis for fluctuations that are seriously impacting “research-founded” resource management and coastal geomorphology and the distribution of environmental restoration (often referred to as environments. Although these are arguably “best management practices”). If we are uncontrollable through standard practices of willing to accept the inevitability of environmental management, they are of vital development, then scientifically sound concern to regional planning. First, Southwest management practices are necessary. Rookery Florida must anticipate the longer-term Bay National Estuarine Research Reserve environmental effects. It would be futile to (RBNERR), managed by the Florida State develop management strategies or restoration Department of Environmental Protection and plans that were discordant with those less one of NOAA’s National Estuarine Reserves, controllable effects. Second, many of the is centered within much of this critical planet’s longer-term environmental problems estuarine habitat (Figure 1). The Reserve is stewarded with the management and (e.g., sea level rise, greater storm frequency and intensity) are at least partial indirect preservation of over 100,000 acres of tidally consequences of anthropogenic change. influenced land. Because an estuary is nothing more than the downstream sum of its Among the assortment of global problems, sea freshwater parts, the Reserve is also interested level rise is perhaps the greatest threat to in affecting the practices that go on higher up estuarine environmental change. In southern in the watersheds. Consequently, the Reserve Florida, Holocene sea level rise has had manages a large, public lands acquisition significant control on the geomorphology of project whereby sensitive headlands are the coast (Wanless & Parkinson, 1989; purchased and placed into public trust. Wanless et al., 1994). Barrier islands are common, but not unique to Southwest Florida. A number of watersheds within Rookery Bay Reserve are targeted for restoration as part of However, the anastamosing geometry present within the protected inner bays, a by-product the Comprehensive Everglades Restoration of the development of oyster reefs and Plan (CERP). Most of these efforts strive to restore the prehistoric patterns of sheet flow subsequent mangrove settlement (details to follow), is unique to our region. Mangrove- that existed prior to water resource management for suburban and agricultural rimmed estuaries are only found within the needs. Two basic types of estuarine West Indian biogeographic province, making the southern tip of the Florida peninsula environmental problems exist as a consequence. Some estuaries are robbed of environmentally different from the rest of freshwater as an effect of freshwater storage or North America. Persistence of this diversion (e.g., Blackwater River; Figure 1). geomorphology depends upon a moderate rate Other estuaries are inundated or pulsed with of sea level rise (Parkinson, 1989). A sea freshwater during the rainy season due to level rise rate that grossly exceeds rate of storm water management practices or the sedimentation destabilizes oyster reef and mangrove island development. Recent draining of wetlands through channelization of measurements of sea level rise rates (Maul & flow (e.g., Henderson Creek, Faka-Union Bay; Martin, 1993) suggest that this critical Figure 1). Restoration projects for these estuaries, and their respective watersheds, are threshold has been exceeded since the beginning of industrialization in the late 19th in various stages of development, with most Century. Rates over the last century have still in the planning phases. been measured between 20-40 cm / 100 years, Blackwater Faka-Union and bays, were the sites used by most of student projects. estuaries, and the intervening Aerial photograph mosaic of estuarine environments in Southwest Florida. Ten Thousand Islands are located southeast Marco Island.

an order of magnitude higher than the rate that Figure 1. has persisted for the last 3000 years (Figure 2; mangrove forest development. Mangroves are Wanless et al., 1994). Recent historical able to tolerate high salinities and, therefore, measurements of sea level have only been recruit to tidally influenced areas. made since the installation of tide gauge Additionally, their production of leaf litter and monitoring stations. In southern Florida, this root mass results in a sedimentation rate that amounts to less than 100 years of recording slightly exceeds the modest rate of sea level (Figure 3). Consequently, it is difficult to rise (Cahoon & Lynch, 1997). (Three species assess whether or not the recent higher rates of mangroves predominate, Rhizophora are merely a natural anomaly or if this truly mangle (red mangrove), Avicennia germinans represents the anthropogenic forcing of (black mangrove), and Laguncularia climate change. If the latter is true, the racemosa (white mangrove), though the red geomorphology that has dominated Southwest mangrove is most responsible for coastal Florida for the last 3000 years may quickly agradation.) As a result, the coastal margin degrade. The implications of such a change progrades despite rising sea level (Figure 4). are great. Much of southern Florida’s Mangrove islands within interior bays will biodiversity and many of its endangered proliferate in a slightly different fashion. If a species depend upon mangrove and wetland bay floor begins to shoal upward into intertidal habitat, and the urban planning associated with depths, mangrove propagules (seeds that begin coastal development needs reassessment. to germinate on the parent plant that are then The unique geomorphology of southern released and float with the tides as potential recruits) will settle and develop into saplings. Florida (often referred to as the Everglades Shoaling can occur through longshore geomorphology) is a product of the net effects of sea level rise rate and the rate of transport, from tropical storm delta or overwash fan formation, or, most commonly sedimentation. Because of its subtropical in Southwest Florida, through oyster reef climate and microtidal influence, southern development. The eastern oyster, Crassostrea Florida’s coastal systems are dominated by

Sea Level Compilation 2. 3. 1. 23 cm / 100 yrs 2. 4 cm / 100 yrs 1. 3. 30-40 cm / 100 yrs

Figure 2. Sea level rise rates compiled by Wanless et al. (1994) from Stratigraphic studies throughout South Florida. Ft Mye r s Tid e Data 1966-1997 0.2 5 12 cm / 1 0 0 y rs 0.2

0.1 5 0.1

0.0 5

0

MSL (m) 0 50 100 150 200 250 300 -0.0 5 -0.1

-0.1 5 y = 0.0 001x - 0.0 007 -0.2 2 R = 0.0 155 -0.2 5 Number of Mont hs Figure 3. Tide gauge data from Ft. Myers, FL, measured relative to mean sea level (to NGVD), recorded between 1966-1997. Slope of regression line provides estimate of sea level rise rate, equal to 12 cm / 100 yrs. Comparable analyses for other locations in south Florida yield rates between 12 – 48 cm / 100 yrs. virginica, is prolific is Southwest Florida’s assumes the estuarine and wetland facies estuaries. Oyster recruitment and growth rates merely transgress landward through time can be so high that huge expanses of bay floor while maintaining their overall character, this will develop reefs. Once these deposits reach spatial shift must be considered in matters of intertidal depths, they become sites for environmental management, restoration mangrove recruitment. With time oyster reefs planning, and urban development and growth. develop into mangrove forested islands. For example, it is common, and often These two phenomena, coastal progradation prescribed by law, for regional planners and the filling of estuarine bays with oyster (county and local governments) to leave reefs and mangrove islands, combine to mangrove coastal fringes undeveloped. produce the Everglades coastal morphology. Coastal development is then typically The Ten Thousand Islands region of permitted immediately landward of this fringe. Southwest Florida, and the site for this Keck Mangrove forests and salt water marshes are project, is so named for this geomorphology protected as a result, but no space is left for (Figure 1). the future migration of these habitats. Ultimately the stability of Southwest Florida’s Accommodation space for future wetlands is coastal geomorphology and its environmental much reduced as a consequence. Landward management and restoration planning are shifts in the brackish water ecotone have already been observed locally throughout dependent upon these relative rates of sea level change and sedimentation. Southwest southern Florida, and mangrove and wetland habitats have migrated accordingly and have Florida must recognize that its entire estuarine fragmented as a response to sea level rise and wetland system may radically change in (Ellison & Stoddart, 1991; Snedaker, 1993; character over the next couple of centuries. Abbott & Nath, 1996; SFWMD, 2001). These Even without radical change and if one occurrences, however, exist in preserve and Transgressive & Regressive Systems Tracts

Figure 4. Diagram showing the transgressive (5500-3200 ybp) and regressive (< 3200 ybp) systems tracts for Southwest Florida (taken from Parkinson, 1987). Slowing of sea level rise rate at 3200 ybp permits the progradation of oyster and mangrove facies, thereby producing the Ten Thousand Islands coastal geomorphology. national park lands where accommodation whom have limited experience in space for habitat migration is available. environmental science and geology. Lastly, providing a deeper-time database of coastal A second possible effect concerns a shift in the spatial distribution of habitat type. evolution helps modelers improve the accuracy of predicting future environmental Freshwater wetlands in Southwest Florida change. This would improve long-range often sit at the same topographic elevation as brackish water wetlands but are spared from environmental planning and forecasting. salt water inundation by their distance from Monitoring paleoenvironmental change in the coastal edge and the tidal head loss due to Southwest Florida is readily accomplished overland friction. Consequently, a simple through the hand- and vibracoring of estuarine transgressive shift in the distribution of habitat unconsolidated sediments. Because types across the landscape, even if environmental characteristics change accommodation space were available, is appreciably over short geographic distances highly unlikely. The spatial mosaic of future within estuaries, sedimentary facies are easily habitat types as a result of sea level rise will distinguished. Considerable be controlled by topography and distance from paleoenvironmental detail can be inferred the coastal edge. based upon sedimentary characteristics (e.g., Both the geomorphologic and environmental grain size, sorting, percent organics, percent carbonate, sedimentary structures), faunal management implications of sea level rise in assemblages (e.g., reflecting different Southwest Florida necessitate a firm understanding of this region’s late Holocene salinities), and the presence of critical indicator facies, like mangrove peats and history. The last 3000-5000 years of history provides precedents for the coastal system’s oyster reefs. The spatial position of sea level can be tracked using oyster reef and mangrove response and insights into how Southwest peat facies, because these environments follow Florida might respond in the future. Arguably an appreciation of this history is even more the temporal shifts in the brackish water ecotone (for example, see Macintyre et al., important in the hands of regional planners, 1978). Geochronology was obtained using managers, and decision makers, many of radiocarbon AMS and standard counting the late Holocene? What are the techniques. In addition, some dates were implications for future environmental obtained using amino acid racemization on change? subfossil oysters (Goodfriend, 1989; Lily Lowery, University of the South, Steph Kowaleski et al., 1998). A number of seminal Obley, Florida Gulf Coast University, Monica studies concerning present-day Roth , SUNY at Oneonta: How has Southwest geomorphology and sedimentology of Florida’s estuarine geomorphology and Southwest Florida have been conducted environmental context responded to late (Perlmutter, 1982; Parkinson, 1987) upon Holocene changes in sea level which this project was founded. Nick Levsen, Beloit College: How do mollusc This Keck, summer of 2001 project, funded by assemblages change over modern estuarine the Keck Geology Consortium, Florida Gulf environmental gradients? Does this have Coast University, and Rookery Bay National utility for recognizing late Holocene Estuarine Research Reserve, employed the paleoenvironments? talent, intellect, and labor of 14 individuals to further the understanding of the effects of late Chris Kitchen, Whitman College: How have Holocene sea level rise on the coastal estuarine biofacies changed over the late evolution and environmental management of Holocene? Does this reflect historical Southwest Florida. Each individual student environmental change? project served this common goal. (The list of Ramon Lopez, Vassar College: How have individual student research questions follows.) estuarine biofacies changed over the late Keck students and faculty, because of their Holocene? Do some biofacies show evidence training in more traditional aspects of geology for mixed, transported assemblages indicative (e.g., sedimentology, stratigraphy, of storm activity? paleoenvironmental reconstruction, geochronology), have made a significant Theme #2: How does the environment contribution to the region’s research mission. affect oyster reef development? How do The results from all these studies will be oyster reefs affect the environment? submitted to Rookery Bay NERR, Florida Margo Burton, Whitman College: Are oysters Gulf Coast University, and the South Florida accumulating and concentrating metals within Water Management District to help better various components of oyster reefs? serve the region’s environmental management needs. Dana Derickson, Trinity University: How does substrate sedimentologic composition and STUDENT PROJECTS texture affect the foundation and development Each student project was self-conceived with of oyster reefs? guidance from the project faculty and from Leda Jackson, Indiana – Purdue University at environmental professionals at Rookery Bay Indianapolis: What are the dynamics of NERR and Florida Gulf Coast University. estuarine water mixing in a tropical setting Project topics fell into one of two categories. where freshwater input varies seasonally? The first concerned questions that addressed Emily Lindland, Florida Gulf Coast the details of environmental change through University: Is there a correlation between the late Holocene and the implications this has taphonomic grade and the age of an oyster for the future of estuarine environments. The shell? How much time averaging occurs second grouping focused on the role oysters within an oyster reef? and their reefs play in the geomorphologic development and environmental alteration of ACKNOWLEDGMENTS Southwest Florida’s coastal system. Funding for this project was provided by the Theme #1: How has Southwest Florida Keck Geology Consortium, Rookery Bay evolved in response to sea level change over National Estuarine Research Reserve, and Florida Gulf Coast University’s College of Arts & Sciences. Many people on staff at Maul, G. A., and Martin, D. M.. 1993. Sea Rookery Bay NERR provided help, including level rise at Key West, Florida, 1846- Gary Lytton, Michael Shirley, Judy Haner, 1992: America’s longest instrument Leslie Breland, Dave Liccardi, Chuck record? Geophysical Research Letters McKenna, Steve Theberge, Pat O’Donnell, 20:1955-1958. Heather Stoffel, Melissa Hennig, and Renee Parkinson, R. W. 1987. Holocene Wilson. A number of FGCU faculty members sedimentation and coastal response to helped mentor students, including Joe rising sea level along a subtropical low Kakareka, Aswani Volety, and Win Everham. energy coast, Ten Thousand Islands, The College’s lab managerial staff, Michael Southwest Florida. Ph.D. dissertation. Lucas, Rhonda Holtzclaw, Mary Newman, University of Miami, Florida. and Aixa Chaves-Nieves, provided assistance with lab work. Parkinson, R. W. 1989. Decelerating Holocene sea-level rise and its influence REFERENCES CITED on Southwest Florida coastal evolution: a Abbott, G. C. and Nath, A. K. 1996. transgressive/regressive stratigraphy. Hydrologic restoration of Southern Golden Journal of Sedimentary Petrology Gate Estates: conceptual plan. Final 59(6):960-972. Report. Big Cypress Basin, South Florida Perlmutter, M. A. 1982. The recognition and Water Management District. 206 p. + reconstruction of storm sedimentation in appendices. the nearshore, Southwest Florida. Ph.D. Cahoon, D. R. and Lynch, J. C. 1997. dissertation. University of Miami, Florida. Vertical accretion and shallow subsidence Snedaker, S. C. 1993. Impact on mangroves. in a mangrove forest of southwestern Pp. 282-305. In: Maul, G. (ed.). Climatic Florida, U.S.A. Mangroves and Salt Change in the Intra-Americas Seas, Marshes 1: 173-186. Edward Arnold, London. South Florida Ellison, J. C. and Stoddart, D. R. 1991. Water Management District (SFWMD) Mangrove ecosystem collapse during Big Cypress Basin and U.S. Department of predicted sea-level rise: Holocene Agriculture Natural Resources analogues and implications. Journal of Conservation Service 2001. Southern Coastal Research 7: 151-165. Golden Gate Estates watershed planning assistance cooperative study. Final Goodfriend, G. A. 1989. Complementary use Report. of amino acid epimerization and radiocarbon analysis for dating of mixed Wanless, H. R. and Parkinson, R. W. 1989. age assemblages. American Journal of Late Holocene sea level history of Science 3: 1041-1047. Southern Florida: control on coastal stability. Proceedings of the Eighth Kowalewski, M., Goodfriend, G. A., and Symposium on Coastal Sedimentology, Flessa, K. W. 1998. High-resolution Coastal Sediment Mobility, p. 197-214. estimates of temporal mixing within shell beds: the evils and virtues of time- Wanless, H. R., Parkinson, R. W., and averaging. Paleobiology 24:287-304. Tedesco, L. P. 1994. Sea level control on stability of Everglades Wetlands. Macintyre, I. G., Pilkey, O. H., and Everglades, the Ecosystem and Its Stuckenrath, R. 1978. Relict oysters on Restoration. St. Lucie Press, p. 199-222. the United States Atlantic continental shelf: a reconsideration of their usefulness in understanding late Quaternary sea-level history. Geological Society of America Bulletin 89:277-282. COPPER AND MERCURY IN AN OYSTER REEF SYSTEM, TEN THOUSAND ISLANDS, SOUTHWEST FLORIDA

MARGO BURTON Geology Dept., Whitman College Sponsor: Bob Carson, Whitman College

INTRODUCTION detrimental. Copper is recognized to cause gastrointestinal, cardiovascular and liver Oysters are often used as indicators of estuary toxicity. Prenatal exposure can also be health. Since oysters are suspension feeders harmful (www.scorecard.org/chemicalprofiles/ that filter water, they can retain small particles summary.tcl?edf_substance_id=7440-50-8). within their bodies (Day, 1989). If these particles have heavy metals attached to them, Oysters live in clumps that combine to make this filtering would lead to a concentration of up a larger oyster reef. A single reef with heavy metals within the oyster body. The hundreds to thousands of oysters could Rookery Bay National Estuarine Research potentially have significant filtering and Reserve in the Ten Thousand Islands area in accumulation effects. My research focused on southwest Florida is currently focusing on answering the question of where in an oyster restoring its estuary to pre-anthropogenic reef system the heavy metals that are filtered conditions. For these reasons, any information out accumulate. An oyster reef system about oysters and oyster health in the area includes sediment upstream, within, and would be helpful to the reserve in determining downstream of the reefs, as well as oyster estuary health. shell and tissue samples from within the reef. Generally, oysters accumulate heavy metals in Because the reserve is adjacent to agriculture their tissue. My hope is that this work will be and other development, heavy metal pollution significant in helping to understand more is a potential threat. Heavy metals, especially about oyster reefs in the Rookery Bay estuary, copper and mercury, are a concern for both which will help resolve the larger problem of environmental and human health. In addition determining the estuary’s health. to being a carcinogen, mercury affects the nervous system and can permanently damage PROJECT METHODS the brain. It can also harm unborn children if Henderson Creek Bay was chosen as the study ingested by the mother (www.epa.gov/pbt/ area because it is the waterway within mercury.htm). Mercury biomagnifies though Rookery Bay that is the most affected by the environment, and causes death in fish, agricultural development, and will likely have shellfish, and birds. This biomagnification higher metal concentrations as a result. Reefs can cause the mercury concentration in fish A and B are each about 2 meters long and are and shellfish to be tens of thousands of times located along the margins of Henderson greater than the concentration of mercury in Creek, about a kilometer from the mouth of the water (www.epa.gov/owow/oceans/airdep/ the creek. Reef C is a large circular reef, air2.html). Copper is a necessary nutrient for about 15 meters in diameter, and is located humans, but excessive levels of it can be where Henderson Creek Bay opens into a matter content has been measured in all larger bay system. sediment samples to determine the role that The sampling procedure was designed so that organic matter had in absorbing and the filtering effects of the oyster reefs could be concentrating copper and mercury. Figure 1 tested. Sediment from both upstream and shows the graphed correlation for heavy downstream of the reefs was sampled to see if metals and organic content. No significant the oyster reefs had a significant impact on the correlation was found. water quality. Reef sediment, oyster tissue, and oyster shell were tested to see if oysters managed to concentrate the heavy metals in their shells or tissue, or if metals were passed through their system. Five components were tested at each of the three reefs: external sediments (upstream), internal sediment from the middle of the reef, shells and tissue from the middle of the reef, and external sediment downstream of the reef. Three samples were taken of each component to ensure a large enough sample size. Oyster samples were collected by hand, reef sediment was collected with a sanitary scoop, and coated cocktail shakers were used to collect external sediment. All sample devices were rated for trace metal analyses. Samples were tested for mercury at the organic chemistry lab at Florida Gulf Coast University using their mercury analysis system. Testing the samples for copper was done at a chemistry lab at Whitman College using their atomic absorption instrument. Percentage of organic matter was found at Whitman College by ashing the sediment and then using 3% hydrogen peroxide. RESULTS AND DISCUSSION Mercury Concentrations There are two main factors that control Table 1 lists the mean concentrations of mercury and copper concentrations in mercury in sediment, oyster tissue, and oyster sediment. The first factor is distance from shell. Reefs A and B, the small reefs that are source area. For metal source areas located close together upstream in Henderson Creek upstream of the test reef, metal concentration show similar absolute concentrations, while would likely decrease from reefs further reef C, the large reef downstream where upstream to reefs further downstream. Henderson Creek Bay opens into a larger bay Another factor that influences heavy metal system, has lower absolute concentrations. In concentration is the amount of organic matter all of the reefs, the concentration of mercury within the sediment. Rickabaugh (1999), in oyster tissue is much higher than the while working in the same estuarine system, concentration in the sediment. Reef C, which observed that organic-rich sediment had has the lowest absolute mercury increased capacity to concentrate heavy concentrations in sediment, has the highest metals. Temminghoff and others (1997) also mercury concentration in tissue. For all the found that organic matter significantly absorbs reefs, the mercury concentration in the oyster heavy metals, especially copper. Organic Table 1. Mercury (Hg) and copper (Cu) concentrations (ppb) [reported concentrations are mean of the three samples measured at each position] Upstream Reef Downstream Oyster tissue Oyster shell sediment sediment sediment Hg Cu Hg Cu Hg Cu Hg Cu Hg Cu Reef A 10.6 115 11.4 173 8.16 77 30 1374 BDL 162 Reef B 8.78 138 14.8 101 10.9 139 16 1299 BDL 242 Reef C 1.37 329 3.29 464 3.16 533 39 88 BDL 69 Reefs A,B = middle Henderson Creek Bay Reefs Reef C = Hall Bay Reef (where Henderson Creek Bay opens into a larger bay system) shells is below the detection limits of the instrument. Levels of Concern Fortunately, none of the copper or mercury A reef filtering effect is not observed when levels in the sediment, oyster tissue or oyster sediment is compared between upstream and shell is at a level of concern. The EPA has set downstream sites on a reef. However, internal the minimum cleanup levels for copper in sediment from the inside of a reef has a higher marine sediment at 390 ppm (parts per mercury concentration than external sediment. million), and for mercury in marine sediment This increased concentration is probably due at 0.59 ppm (590 parts per billion). to the high amount of oyster feces within a reef’s interior. COPPER AND MERCURY Because higher mercury concentrations are found in the middle of Henderson Creek at SOURCES reefs A and B as opposed to where Henderson While mercury is found naturally in the Creek Bay opens into a larger Bay system at environment, the Environmental Protection reef C, the source for mercury is probably Agency estimates that human activities are freshwater runoff from higher up in the responsible for 75% of worldwide mercury watershed. emissions. The initial source of mercury is difficult to determine because mercury can be Copper Concentrations deposited and re-emitted several times in the Copper concentrations (Table 1) among reefs environment (www.epa.gov/owow/oceans/ A, B, and C are opposite of what is observed airdep/air3.html). However, there is strong for mercury concentrations. Copper evidence that the majority of the mercury concentrations in sediment from reef C are found in southwest Florida comes from local significantly higher than copper sources. The majority of mercury (one model concentrations in sediment from reefs A and estimates 71+8%) comes from local sources B. Previous research done in Galveston Bay, such as municipal waste and medical waste Texas shows a positive relationship between incinerators and oil combustion in Broward increased salinity and increased copper and Dade Counties in southeastern Florida concentration (Tang, 2001). This is a possible (Dvonch, 1999). Other sources of mercury are explanation for the higher concentrations of not as easily determined, and are probably in copper at reef C, since reef C is further from the atmosphere as a result of both global and the freshwater source, and is likely to have regional sources. Mercury is transported higher salinity concentrations than reefs A and through the atmosphere from eastern to B. western Florida by the trade winds that dominate during the stormy wet season, and is then deposited in the Everglades area by precipitation during the wet months (Guentzel, www.epa.gov/pbt/mercury.htm, Priority 2001). PBTs: Mercury and compounds, 10 Feb The greatest outputs of copper contamination 2002. in the United States are from mining and www.epa.gov/owow/oceans/airdep/air2.html, smelting operations and municipal incinerators What atmospheric deposition pollutants (www.epa.gov/safewater/dwh/c- pose the greatest problems for water ioc/copper.html). Copper is also a main quality?, 10 Feb 2002. ingredient in many pesticides and in marine www.epa.gov/owow/oceans/airdep/air3.html, paint, so likely sources in southwest Florida What are the major effects of common are from pesticides used in agriculture in the atmospheric pollutants on water quality, area, and from boats (www.scorecard.org/ ecosystems, and human health?, Feb 10 chemical-profiles/summary.tcl?edf_substance 2002. _id=7440-50-8). REFERENCES CITED ACKNOWLEDGMENTS I would like to thank my project directors, Dr. Day, J.W., Hall, C.A.S., Kemp, W.M., and Mike Savarese, Dr. Lenore Tedesco, and Dr. Yañez-Arancibia, Alejandro, 1989, Carol Mankiewicz for their help in developing Estuarine ecology: New York, John Wiley my project and helping me carry out my & Sons, 558 p. research, Dr. Joe Kakareka and Matt Benolkin Dvonch, J.T., Graney, J.R., Keeler, G.J., and of Florida Gulf Coast University for their help Stevens, R.K., 1999, Use of elemental in the lab, Dr. Pat Spencer and Dr. Bob Carson tracers to source apportion mercury in south of Whitman College for their help in putting Florida precipitation: Environmental all of my research together, and the other Keck Science Technology, v. 33, p. 4522-4527. students in Florida for their help and support Guentzel, J.L., Landing, W.M., Gill, G.A., in the field and in the lab. Pollman, C.D., 2001, Processes influencing deposition of mercury in Florida: Environmental Science Technology, v. 35, p. 863-873. Tang, Degui, Warnken, K.W., and Santschi, P.H., 2001, Organic complexation of copper in surface waters of Galveston Bay: Limnology and Oceanography, v. 46, p. 321-330. Temminghoff, E.J.M, Van Der Zee, S.E., and De Haan, F.A.M., 1997, Copper mobility in a copper-contaminated sandy soil as affected by pH and solid and dissolved organic matter: Environmental Science & Technology, v. 31, p. 1109-1115. www.scorecard.org/chemical-profiles/ summary.tcl?edf_substance_id-7440-50-8 Chemical profile for copper, 25 Feb 2002. www.epa.gov/safewater/dwh/c- ioc/copper.html, National primary drinking water regulations, 10 Feb 2002. CHARACTERIZATION OF ESTUARINE ENVIRONMENTS AND SUB-ENVIRONMENTS USING MOLLUSK ASSEMBLAGES

NICHOLAS LEVSEN Geology Dept., Beloit College Sponsor: Carol Mankiewicz, Beloit College

INTRODUCTION indicators for specific estuarine environments and sub-environments. It will also provide an An estuary is simply defined as the region of index of indicator species for use in interaction between inland freshwater sources identification of modern and paleo- and the salt waters of the open ocean (Hobbie environments. 2000, p. 1). Within such a region a number of environments and sub-environments occur that METHODS are characterized by various environmental factors including salinity and substrate Sample Site (Parkinson 1987). These factors create the I conducted this study primarily within the boundaries of habitat for a multitude of Rookery Bay National Estuarine Research estuarine organisms. Mollusca is such a class Reserve, located in southwestern Florida. of organisms, occurring in great ubiquity This area is characterized by brackish rivers throughout an estuary and in such diversity opening into a chain of coastal bays that are that each of the molluscan species requires a sheltered from the ocean by numerous oyster unique set of environmental parameters reefs, mangrove islands, and barrier islands. I (Davies 1972). It is this diversity, ubiquity, took 19 samples from three major salinity and high potential for preservation that make environments identified by Parkinson (1987) mollusks ideal for use in characterizing many as open-ocean shoreface (OOS), inter-island estuarine environments. bays (IIB), and chain of bays (CB). A fourth The characterization of environments becomes salinity environment, riverine (R), was unique important when determining rate and direction to this study. These samples also included of sea level oscillations. Wanless, Parkinson, sub-environments characterized by sediment & Tedesco (1994) reported a modern grain size. transgressive phase of sea level rise at a rate of Procedure 23 cm/100 years. In a transgressive phase I determined possible sample sites using there should be evidence of environment Parkinson’s (1987) site map. I took each migration inland; low- salinity indicator sample from a skiff using two modified species would be found preserved under the cocktail shakers bolted together and attached modern depositional environments of the open to a sixty-foot rope. For each sample, I cast ocean. Molluscan indicator species may aid in the shakers into the water at a radius from the identification of estuarine paleo-environments. boat of approximately 25 feet. I pulled the The purpose of this study is to test the shakers along the floor of the waterway and up hypothesis that molluscan species serve as to the boat. I repeated the sampling process, indicate significant differences in the diversity casting the shakers in numerous directions of the four salinity environments and also the around the boat in order to collect 3600 mL of distribution of members of a mollusk species sediment. An additional sample was taken for throughout these salinity environments. analysis of grain size, percent carbonate, and Figure 1 shows that in the fragmented fraction percent organic matter. Each 3600 mL sample of shells the riverine salinity environment had was sieved to obtain a 2-mm and a 1mm significantly lower diversity values than the fraction. I then separated the 2-mm fraction of other three environments. The complete sieved shells into complete individuals (fully fraction showed no significant differences in articulated, closed bivalves or complete diversity among the salinity environments. gastropods), hinged (articulated open Some mollusk species did show differential bivalves), and fragmented (one valve or less in distribution throughout the four salinity bivalves and less than 85% complete environments. There were five such species in gastropod) shells. I identified all shells the complete fraction that showed significance measured anterior to posterior lengths in the in mean number of individuals (Figure 2). bivalves with at least one complete valve and Nucula proxima, Terebra protexta, and the apical to aperture lengths in all full length Parvilucina nassula all appear in the greatest gastropods. numbers in the open-ocean environment, while the majority of Anomalocardia Sedimentary Analysis auberiana and Tellina tampaensis individuals Each sediment sample was analyzed for appear in the chain of bays and riverine percent calcium carbonate with a treatment of habitats. 20% HCL and for percent organic material Twelve mollusk species from the fragmented using the procedure described in Moore and fraction showed significant differences in Reynolds (1989). mean number of individuals among the The percent sand, clay, and silt were salinity environments. Anomalocardia determined by wet sieve and pipette analysis auberiana again appears in the greatest as described in Folk (1974). numbers in the riverine environment as does Mytilopsis leucophaeta (Figure 3). The inter- Statistical Analysis island bay environment is shown to have the highest concentration of the species I calculated the Shannon-Weaver diversity Carditamera floridana of all the other habitats indice H’ for each sample using the formulas (Figure 3). The other species are significantly found in Zar (1999). Because I could not meet the assumption of normality to perform an ANOVA, I ran a nonparametric Kruskal- Wallis test on JMP (SAS Institute) to determine if the means of the diversity indices in each salinity environment were statistically different. I also compared the means of the numbers of individuals of each mollusk species found in the four salinity environments, but I could not meet the assumption of normality. I also ran a Kruskal- Wallis test for these data to determine statistical differences. RESULTS I identified approximately 3500 individuals representing about 110 mollusk species from Figure 1: Shows the means of Shannon-Weiner diversity both the complete and fragmented fractions of indices for fragmented samples found in each salinity the nineteen samples. The statistics did environment. greater in number in the open-ocean shore face of fragmented individuals than the other than any other environment (Figures 3 and 4). environments. The low relative salinity The statistical significance among the means concentration and the low-energy system that of these species in the salinity environments prevail in this environment are most likely the

allows me to draw conclusions on what

Figure 3: Shows the distribution of mollusk species (fragmented individuals) over four salinity environments. Figure 2: Distribution of mollusk species (complete The values represented are the mean number of individuals individuals) over four salinity environments. The values occurring in all samples of that environment. Only species represented are the mean number of individuals occurring in that show statistical significance are presented. all samples of that environment. Onlyspecies that show cause of this difference in diversity (Barnes statistical significance are presented. 1989) and fragmentation. The chain of bays mollusks will most likely be found in a environment is characterized by a high relative particular environment. Of the thirty-five concentration of complete individuals of T. major mollusk species tested from both tampaensis. Likewise, a high relative fragmented and complete fractions, eighteen concentration of C. floridana can be a showed no statistical significance in the mean descriptor of the inter-island bay environment. number of individuals among the salinity The open-ocean environment has greater environments. I did not include these in the concentrations of A. aequalis, P. nassula, C. graphical representation of data. cancellata, T. acropora, T. proxima, N. acuta, C. caribeae, T. divisus, and T. similis than any The sedimentary data were not included in this of the other environments. This assemblage analysis as there were no differences in the can be said to characterize the open-ocean grain sizes among the tested samples. Also, the calcium carbonate and organic material content of the sediment showed no statistical relationship to the distribution of mollusks. DISCUSSION In accordance with Parkinson (1987), I found that salinity is a primary factor acting on the distribution of mollusk species throughout the Rookery Bay estuary. The riverine environment can be characterized by a high relative concentration of complete and fragmented individuals of the species A. auberiana and fragmented individuals of M. Figure 4: Shows the distribution of mollusk species leucophaeta. T. tampaensis (complete) and C. (fragmented individuals) over four salinity environments. floridana (fragmented) also contribute to the This graph is similar to graph 3 and shows the distributions of the other five statistically significant species of the mollusk assemblage of the riverine salinity fragmented fraction of shells. environment. This environment is also characterized by a significantly lower diversity salinity environment. would result in an effective and thorough Davies (1972) showed that mollusk species index for the identification of paleo- live along a physical environmental gradient environments and current environmental as an effect of environmental stress. This health. study has used one of those environmental REFERENCES CITED stresses, salinity, and determined the preferred habitats of a number of mollusk species. Barnes, R.S.K., 1989, What, if anything, is a Those mollusks that are constrained to a very brackish – water fauna? Transactions of narrow saline environment can be used as the Royal Society of Edinburgh, Earth indicator species for that environment. The Sciences, 80, 235-240. results of this study have provided a number Davies, T.T. 1972, Effect of Environmental of examples of such indicator species. The Gradients in the Rappahannock River indicator species from the fragmented fraction Estuary on the Molluscan Fauna in Nelson, demonstrate the highest preservation potential B., Environmental Framework of Coastal as many of these species maintain high Plain Estuaries: Boulder, Colorado, population numbers in high energy TheGeological Society of America. environments. These indicator species as complete individuals would be preferred for Folk, R.L., 1974, Petrology of Sedimentary use in characterizing modern and paleo- rocks: Austin, Texas, Hemphill. environments because they are the most likely Hobbie, J., 2000, Estuarine Science: A to be preserved in large quantities. synthetic Approach to Research and The major limitation of this study originated in Practice: Washington, D.C., Island Press. the low number of sample replications from Moore, D.M., and Reynolds, R.C., Jr., each environment. Because of the lack of 1989, X-Ray diffraction and the replication, the number of individuals of many identification and analysis of clay species is too low to statistically analyze. An minerals: Oxford, Oxford University increase in the number of replicates would Press, 332p. also allow for more generalized conclusions Parkinson, R.W., 1987, Holocene about particular environments than can be Sedimentation and Coastal Response To made from this study. Ordination, a type of Rising Sea Level Along A Subtropical multivariate analysis, is the optimal analysis LowEnergy Coast, Ten Thousand Islands, for a study of this kind as it has been generally Southwest Florida: Miami, Florida, used for similar ecological studies as this. The University of Miami. nonparametric analysis that I performed leads Wanless, H.R., Parkinson, R.W., and Tedesco, to a greater degree of inference as to what L.P., 1994, Sea Level Control on Stability assemblage is characteristic of an environment of Everglades Wetlands, in Davis, S.M., than would be preferred. and Ogden, J.C., eds., Everglades, the Also two of the four environments had only ecosystem and its restoration: Delray one mollusk species that could be used to Beach, FL, St. Lucie Press, p. 199-222. characterize them. An effective index should Zar, J.H. 1999, Biostatistical Analysis: New include many more indicator species. Jersey, Prentice Hall. This study served as a preliminary investigation into the feasibility of environmental characterization by mollusk assemblage. I would suggest that future studies perform many more replications in many more environments and sub- environments. Also these studies should employ ordination to analyze those data that are collected. I believe that such a study TIME ACCUMULATION ON AN OYSTER REEF: IMPLICATIONS FOR THE MONITORING OF ENVIRONMENTAL CHANGE

EMILY LINDLAND Dept. of Biology, Florida Gulf Coast University Sponsor: Mike Savarese, Florida Gulf Coast University

INTRODUCTION prolific throughout the Mesozoic and Cenozoic periods. As brackish water ecotone indicators, oyster reefs are potentially useful for the To better understand time averaging on oyster reconstruction of sea level curves and for reefs, three questions were addressed by this determining anthropogenic effects on water study. How much time is represented within quality. Their acute sensitivity to change in an oyster reef? The shorter the time water quality also makes them strong indicator represented, the more value the structure has species for the assessment of estuarine to problems of coastal evolution and ecosystem health. For oyster reefs to fulfill ecosystem health. Is there a more economical this potential, the magnitude of time averaging and methodologically simple proxy for must be relatively short. If oyster reefs assessing the magnitude of time averaging? If accumulate shell material over long periods of there is a correlation between the taphonomic time, their presence might misrepresent the grade and age of an oyster shell, this method position of sea level or the timing of may be acceptable as a gauge of time environmental change. For example, if reefs averaging. Does a correlation between the persist at the sediment-water interface after the shells preservational status and its age brackish water ecotone has transgressed improve or worsen under certain beyond the reef’s position, then their location environmental conditions? An oyster reef may have little relevance for sea level tracking located in an exposed environment may or current conditions of environmental health. display worse preservational status than one I therefore examined the relationship between located in a protected environment. taphonomic grade (state of shell preservation), Understanding taphonomic grade variations absolute age of dead oyster shells, and the within and between reefs of varying energies magnitude of time averaging on modern oyster will help determine a reef’s usefulness in reefs, a previously taphonomically unstudied tracking sea level change. The hypotheses ecosystem along the Southwest Florida coast. tested in this study are: the degree of time averaging is less for oyster reefs than for other Time-averaging studies have been conducted coastal intertidal communities; oyster reefs previously in coastal settings (Flessa et al. from protected bays exhibit less time 1993; Koweleski et al. 1998, Parsons-Hubbard averaging than those from more exposed et al. 1999). However, to date, no study environments; and the taphonomic grade of specifically addressing time averaging on oyster reefs has been attempted, yet they are oyster shells directly correlates with time averaging on oyster reefs. MATERIALS AND METHODS Time averaging was compared between two environments, a protected bay and an exposed bay reef. Both reefs were composed solely of the oyster species Crassostrea virginica. They . were both located in the Blackwater River Figure 1: Examples of taphonomic grades. system on the Southwest coast of Florida Grade1 represents the best preservation and grade (figure 1 in Savarese herein) to control as 4 represents the worst preservation. many unforeseen variables as possible. Using RESULTS a tape measure, a transect was oriented on the exposed reef, traversing the most exposed sub- The oldest shell sampled from both the environment to the most protected sub- exposed and protected reef came from the environment. The north to south width of this exposed reef. This shell’s age was 520 years reef was 63 m; the east to west length was 180 old indicating a time averaging minimum on m. The transect was replicated 5 months later the high-energy reef of 520 years. The oldest for a second set of data. Because the protected shell sampled from the low energy reef was reef was comparatively narrow, it required two 280 years old indicating a time averaging 13-m transects in order to increase the sample minimum of 280 years. These results differ size. Both were oriented in a parallel manner, from those of Flessa et al. (1993), Macintyre one on the north end of the reef and one on the et al. (1978), and Meldahl et al. (1997) who south end of the reef. These transects were found significantly higher time averaging also replicated 5 months later. magnitudes. Approximately 1400 oyster shells were Histograms of taphonomic grade distribution collected, one every 10 cm along the transects. were used to compare protected and exposed No living shells and no clumps containing reefs. The average taphonomic grade of 866 three or more cemented oysters were specimens analyzed from the high-energy reef collected. The oysters were 3-7 cm in length, was 3.2 (the replicate sample was whole, fragmented, or articulated. A total of indistinguishable). The combined average 880 shells were collected from the high- grade of the 258 specimens from the low- energy reef and 520 shells from the low- energy reef was 2.6. The replicate sample energy reef. Four taphonomic grades were yielded an average taphonomic grade of 2.4. established using a set of preservational The average taphonomic grade on the high- criteria described by Flessa et al. (1993). energy reef was significantly greater (less well Specimens were graded on a scale of 1 to 4 by preserved) than that of the low-energy reef three people (1 representing the best (Wilcoxon Signed Ranks Test [p<0.0001]). preservation and 4 the worst) (Fig.1). Grades On the high-energy reef, the topographic were averaged for each oyster shell and 32 height of a facies along the profile and each samples (16 from each reef, 4 from each facies’ sedimentary characteristics correlated grade) were chosen for amino acid with taphonomic grade. Facies located at high racemization dating (Goodfriend 1989). elevations along the profile had higher energy A topographic profile was measured along the sedimentary characteristics and had oysters transects of each reef to assess the relationship with worse taphonomic grades (Fig. 2). between the shells’ taphonomic grade and the Regression analyses of an oyster shell’s amino specific environmental energy where it was acid racemization age versus its taphonomic collected. The environmental energy of each grade showed a high positive correlation for topographic position was determined through both the high- and low-energy reefs (high: facies analysis. slope = 156.0, y-intercept = – 166.9 [R=0.91];

Facies Facies Facies Facies Facies

A A A A A B B B B B C C C C C D D D D D E E E E E F F F F F G G G G G

Number Number Number Number Number

24 24 24 24 24 34 34 34 34 34 22 22 22 22 22 115 115 115 115 115 59 59 59 59 59 61 61 61 61 61 64 64 64 64 64

Mean Grade Grade Grade Grade Grade Mean Mean Mean Mean Mean

3.18 3.18 3.18 3.18 3.18 3.28 3.28 3.28 3.28 3.28 3.32 3.32 3.32 3.32 3.32 3.11 3.11 3.11 3.11 3.11 3.06 3.06 3.06 3.06 3.06 3.21 3.21 3.21 3.21 3.21 3.33 3.33 3.33 3.33 3.33

Description Description Description Description Description

Small Small Small Small Small Small Disart Disart Disart Disart Disart . . . . . Imbric Imbric Imbric Imbric Imbric . . . . . Lg Lg Lg Lg Lg live live live live live Oyster Oyster Oyster Oyster Oyster Imbric Imbric Imbric Imbric Imbric . . . . . Shell Shell Shell Shell Shell

live live live live live live valves valves valves valves valves shells shells shells shells shells clumps clumps clumps clumps clumps gravel gravel gravel gravel gravel shell shell shell shell shell frags frags frags frags frags

clumps clumps clumps clumps clumps

100

50 0

Height (cm)

0 10 20 30 40 Transect Position (m) Position Transect Figure 2: Topographic profile of the high energy reef. The taphonomic grades vary directly with the environmental energy. and low: slope = 85.1, y-intercept = – 96.2 overall grades among the reefs indicate that [R=0.88]). Shells with a higher taphonomic the shells on the high-energy reef are grade have an older age than those displaying undergoing longer or more intense weathering better preservation. Conversely, those with a processes than those of the low-energy reef. lower, better taphonomic grade have a The discordant results found between two younger age. reefs of different energies are also found at DISCUSSION smaller spatial scales within a reef. The taphonomic grade of oyster shells within a reef The degree of time averaging is less for oyster varies directly with its topographic position reefs than for other coastal intertidal and the facies sedimentary texture in which it communities. Both oyster reefs sampled lies (indicative of energy level). Shells that exhibited better than millennial-scale were sampled in a higher energy section of the resolution with a maximum age on the high- reef displayed worse grades than those energy reef of 520 years and 280 years on the sampled in lower energy facies. Again, this low-energy reef. indicates that the relative energy of the Flessa et al. (1993) found a much higher environment in which a shell sits has an magnitude of time averaging (~3500 years) for impact on the shell’s ability to maintain intertidal bivalve cheniers from Bahia La preservation before burial. Choya, Gulf of California. The bivalves The regression analysis of amino acid composing these cheniers live unattached and racemization age versus taphonomic grade infaunally while oysters are sessile and demonstrated a high positive correlation for cemented together. These differences in life both the high and low energy reefs (R=0.91 mode, coupled with the differences in and R=0.88 respectively), suggesting environmental conditions may explain our taphonomic grade is a reasonable proxy for incongruent results. time averaging. This correlation differs from The protected bay oyster reef environments those obtained by MacIntyre et al. (1978), exhibited not only a better than millennial Flessa et al. (1993), and Meldahl et al. (1997). scale resolution, but also better taphonomic These results indicate that the magnitude of grades than the more exposed oyster reef time averaging on an oyster reef holds a better environments. The differences in average than millennial scale resolution and a shell’s taphonomic grade correlates with its absolute age. With precaution, therefore, oyster reefs could be used to track the historic position of sea level as well as assess the anthropogenic forcing of climate change and ecosystem health. REFERENCES CITED Flessa, K.W., A.H. Cutler, K.H. Meldahl. 1993. Time and taphonomy: Quantitative estimates of time-averaging and stratigraphic disorder in a shallow marine habitat. Paleobiolgy 19(2): 266-286. MacIntyre, I.G., Pilkey, O.H., Stuckenrath, R. 1978. Relict oysters on the United States Atlantic continental shelf: A reconsideration f their usefulness in understanding late Quanternary sea-level history. America Bulletin 89: 277-282. Meldahl, K. H., Flessa K.W., Cutler, A.H. 1997. Time-averaging and postmortem skeletal survival in benthic fossil assemblages: Quantitative comparisons among Holocene environments. Paleobiology 23(2): 207-229. Kowalewski, M. Goodfriend, G.A., Flessa, K.W. 1998. High resolution estimates of temporal mixing within shell beds: The evils and virtues of time-averaging. Paleobiology 24(3): 287-304. Goodfriend, G.A. 1998. Recent barrier beach retreat in Georgia: Dating exhumed salt marshes by aspartic acid racemization and post bomb radiocarbon. Journal of Coastal Research 14: 960-969. Parsons-Hubbard, K.M., Callender, W.R., Powell, E.N., Brett, C.E., Walker, S.E., Raymond, A.L., Staff, G.M. 1999. Rates of burial and disturbance of experimentally deployed mollusks: Implications for preservational potential. Palaios 14: 337- 351. SEDIMENTARY EVIDENCE OF COASTAL RESPONSE TO HOLOCENE SEA-LEVEL CHANGE, BLACKWATER BAY, SOUTHWEST FLORIDA

LILY E. LOWERY University of the South Sponsors: Donald B. Potter, University of the South Lenore P. Tedesco, Indiana/Purdue University at Indianapolis

INTRODUCTION Initial studies of sedimentary sequences in Studies of Holocene coastal sedimentary SOUTH FLORIDA SEA-LEVEL HISTORY sequences in southwest Florida have provided important clues in determining coastal response to sea-level changes (Parkinson, 1989; Wanless et al., 1994). Much of the southwest Florida coast is a mangrove- dominated estuarine system with chains of mangrove-capped oyster bars that provide a barrier between the bay and open marine influences. This low energy, low relief system provides an ideal environment for the deposition and preservation of sedimentary sequences that record relative sea-level fluctuations. The mangrove fringe is a major control on shoreline facies, as reported by Davis (1940) and summarized by Parkinson (1989), sometimes resulting in local shoreline changes in opposition to regional trends. In an early study of the southwest Florida coastal system, Davis (1940) described the sedimentation processes specific to mangrove dominated systems: the trapping of sediment Figure 1: Holocene sea-level rise curve results in rapid aggradation of peat, illustrating deceleration of rate of rise and present rapid rise from tide-gauge records. (from Wanless progradation of the shoreline, and local marine et al., 1994). regression in a rising regional system (Parkinson, 1989). Conversely, mangrove southwest Florida (Davis, 1940) documented control in these systems can actually allow the coastal submergence during relative sea-level opposite effect, when the destruction of the rise. Later studies (Scholl et al., 1967, 1969) vegetation in a storm or period of storm events created a submergence curve for southwest causes shoreline retreat and a punctuated rise Florida for the last 7000 years that delineated in relative sea level (Wanless et al., 1994). continual, but decelerating rise in sea level, which was later modified (Wanless et al., RESULTS 1994) to assign specific rates of rise and dates of changes in rate (Figure 1). More recent Using the textural composition classification work in the Everglades and Ten Thousand of Perlmutter (1982), we found the cores Islands regions presents a two-phase relative revealed a consistent stratigraphy across the sea-level model within the decelerating entire bay (Figure 3). Pliocene limestone eustatic system, consisting of (1) transgression bedrock (Parkinson, 1987, 1989), at the base with rapid eustatic rise, followed by (2) of cores 6 and 1, is overlain oldest to youngest regression beginning at approximately 3200 by units A to D. These units were classified y.b.p. as sea-level rise slowed and biogenic (Table 1) as sediment type A (quartz sedimentation kept pace with or outpaced packstone or a clayey quartz sand), sediment eustatic rise (Parkinson,1987,1989). type B (quartz grainstone), sediment type C (Rhizophora, red mangrove, peat), and During June, 2001, a northeast/southwest sediment type D (shelly quartz packstone to transect of four sediment cores was taken, wackestone). The base of the peat in core 1 roughly perpendicular to the shoreline across was dated at 4170 + 40 y.b.p. using Blackwater Bay (Figure 2) using a vibracore radiocarbon techniques, and the upper surface of the peat in core 6 was dated at 1090 + 40 y.b.p. (Figure 3). DISCUSSION Vertical and lateral relationships of units A to D in the four cores suggest that Blackwater Bay has undergone three phases of local sea- level change during the eustatic Holocene transgression. Each sedimentary sequence represents a time transgressive unit, as changes in sea level caused migration of depositional environment. Sediment types A and B formed during the early transgressive phase, as interpreted by Parkinson (1987, Figure 3: Core transect across Blackwater Bay showing correlated stratigraphy. Note 525 times vertical 1989), as shoreline approached the study site. exaggeration: slope of all actual contacts is less than The thick peat sequences represent the Figure0.15°. 2:Radiocarbon Map showing dates study for peatssite, Blackwater in cores 6 and Bay, 1 are shoreline intersection with the site, then a shownand location by arrows. of the four cores. relative shallowing or at least a temporary stabilization of shoreline. The facies change mounted on a pontoon boat. Coring recovered to sediment type D at a uniform elevation the entire Holocene sequence (units B, C, D in indicates a return to deepening. Figure 3), in addition to upper Pleistocene sediments (unit A), with negligible loss and Transgression little compaction. Preliminary descriptive analysis was performed with open cores Parkinson (1987, 1989) suggests that Pliocene during the summer, and subsequent lab limestone was exposed, eroded, and then analysis determined percent carbonate, organic unconformably overlain by the Pleistocene content, and grain size. aged clayey sand of unit A, as the terrestrial environment evolved to a salt water marsh. Based on these cores from Blackwater Bay, The small grain size and low carbonate we believe that this portion of the southwest percentage of this unit (Table 1) indicates that Florida shoreline has experienced three major the finer grains are terriginous clays. Unit A phases of relative sea-level change during the is sharply and unconformably overlain by the Holocene eustatic rise: (1) transgression, (2) clean quartz sands of unit B, which we regression with accumulation of thick peat interpret as fluvial deposits of the ancestral sequences, and (3) a return to transgression. Blackwater River. Stabilization/Regression Previous work (Boettner, 2000) has The base of the peat, unit C, represents the documented an upstream carbonate mud levee initiation of an intertidal regime as sea level in the Blackwater River, containing marine reached that elevation, and the coastal faunal fragments 1069 + 99 y.b.p. to 990 + 84 mangroves continued to migrate landward y.b.p. in age. One possible interpretation of with the shoreline. The base of the peat in the this levee involves landward transport of most seaward core (7) is 462 cm below Mean marine sediment and fauna during a violent High Water (MHW), an elevation that storm event or a period of high storm corresponds to a 4750 y.b.p. shoreline on the frequency. These dates coincide with the Wanless et al. (1994) curve, (Figure 1). submergence of the mangroves in Blackwater Growth in the three most landward cores Bay at 1090 + 40 y.b.p. (the radiocarbon date began shortly before the 4170 + 40 y.b.p. of upper peats in core 2), suggesting that the basal peat radiocarbon date, in good same events may have inundated the coastal agreement with a 4100 y.b.p. intersection on mangroves, resulting in destabilization of the the South Florida sea-level curve, Figure 1 mangrove system and subsequent (Wanless et al., 1994). transgression. During the first stage of peat accumulation Sediment type D, which forms the modern prior to 3200 y.b.p., the mangrove aggradation sediment surface, exhibits a deepening phase may have been in a precarious equilibrium followed by a shallowing phase (Kitchen, with rapid sea-level rise of 23 cm/100 yr. At 2002, this volume): oysters, indicative of 3200 y.b.p., as sea-level rise decelerated to 4 intertidal conditions, overlie finer muds of a cm/100 yr, peat accumulation rates may have deeper depositional environment. Cores taken slowed in response, resulting in a temporarily in previous studies contain sequences of stabilized shoreline. If peat aggradation mangrove-capped oyster bars over these muds continued at a pace comparable to the more (Parkinson, 1987, 1989). When the mangrove system was first inundated, waterflow and Table 1: Averaged grain size and compositional characteristics of sedimentary units. Sediment Quartz Quartz Type Description % Mud Mean Mode % Carbonate A Clayey quartz sand 6.76 2.1 2.1 7.63 B Quartz grainstone 1.47 2.2 2.2 2.11 C Mangrove peat ------D Shelly quartz pack/wackestone 15.37 2.0 2.9 50.55 rapid rate of rise, a relative regression may sedimentation processes may not have been have occurred. ideal for oyster habitation, but a slight increase in depth may have allowed initiation of oyster Transgression colonization and sediment aggradation. The upper contact of unit C, where peat is Tide gauge records for the past 60 years in sharply overlain by the shelly carbonate muds South Florida (Wanless et al., 1994) and of D, indicates a relatively sudden inundation studies of worldwide sea level over the past of the mangroves and destruction of the century (Barnett, 1990) indicate an increase in mangrove dominated system across the 1.5 km sea-level rise rates ranging from 10 to 40 length of this transect at 1090 + 40 y.b.p., as cm/100 yrs. We expect that this acceleration shown by the radiocarbon date from core 2. It would contribute further to the deepening is unlikely that the slow eustatic rise was represented by unit D. sufficient to inundate the coastal mangroves, or result in the modern submerged condition CONCLUSIONS of Blackwater Bay. The four units sampled in our cores from Blackwater Bay document that the area experienced an early Holocene transgression, the Nearshore, Southwest Florida [unpubl. followed by a stabilization and possible Ph.D. dissert.]: Coral Gables, Fla., Univ. regression of the shoreline at approximately Miami, 230 p. 4100 y.b.p. with the accumulation of thick peat sequences. At approximately 1000-1090 Scholl, D.W., Craighead, F.C., Stuiver, M., y.b.p., a significant event, possibly a storm or 1969, Florida submergence curve revised- series of storms, inundated the mangroves in Its relation to coastal sedimentation rates. all cores, reinitiating a relative sea-level rise Science, v. 163, p. 562-564. that eventually brought Blackwater Bay to approximately its current size and depth. If Scholl, D.W., Stuiver, M., 1967, Recent the acceleration of sea-level rise recorded in submergence of southern Florida: a the last century in South Florida (Wanless et comparison with adjacent coasts and al., 1994) and worldwide (Barnett, 1990) other eustatic data: Geological Society continues, the transgressive phase of the past of America Bulletin, v. 78, p. 437-454. 1000 years will be accentuated in the study area: intertidal mangroves will be slowly Wanless, H.R., Parkinson, R.W., Tedesco, inundated as the shoreline moves landward L.P.,1994, Sea Level Control on Stability and Blackwater Bay deepens. of Everglades Wetlands. Davis, S.M. (editor), Ogden, J.C. (editor). Everglades; REFERENCES CITED the ecosystem and its restoration., St. Barnett, T.P., 1990, Recent changes in sea Lucie Press, p. 199-222. level: A summary. In Sea-Level Change, National Research Council, Geophysics Study Committee, National Academy Press, Washington D.C., p. 37- 51. Boettner, A.R. 2000, The Geochemistry and Sedimentology of Selected Coastal and Wetland Environments of Southwest Florida, MS Thesis, Indiana/Purdue University at Indianapolis,198 p. Davis, J.H., 1940, The ecology and geologic role of mangroves in Florida: Washington, D.C., Carnegie Institute, Publication 517, Papers of the Tortugas Library, v. 2, no. 16, p. 307-409. Parkinson, R.W., 1989, Decelerating Holocene sea-level rise and its influence in southwest Florida coastal evolution: A transgressive/ regressive stratigraphy: Journal of Sedimentary Petrology, v.59, p. 960-972.Parkinson R.W., 1987, Holocene Sedimentation and Coastal Response to Rising Sea Level Along a Subtropical Low Energy Coast, Ten Thousand Islands, Southwest Florida [unpubl. Ph.D. dissert.]: Coral Gables, Fla., Univ. Miami, 224 p. Perlmutter, M.A., 1982, The Recongnition and Reconstruction of Storm Sedimentation in THE INFLUENCE OF SEA LEVEL RISE ON THE HISTORY OF ESTUARINE ENVIRONMENTS IN SOUTHWEST FLORIDA

STEPHANIE P. OBLEY Florida Gulf Coast University Sponsor: Michael Savarese

INTRODUCTION examine changes in Estero Bay’s geomorphology over time in response to sea Sea level has been rising since the last glacial level rise and to compare these changes with maximum, 18,000 years ago, in response to those seen in the Ten Thousand Islands area, a global warming and thermal expansion, region in the westernmost Everglades inundating ancient shorelines and creating (Parkinson, 1989; other papers in this those seen today. In South Florida, this rise volume). Radiocarbon dates show that as has not been constant (Scholl, 1969; Wanless much as 4345 years are represented in the et al., 1994). The fastest rise rate (greater than cores. 23 cm per 100 years) continued until 5500 years ago, slowing to 23 cm per 100 years METHODS until 3200 years when sea level rise slowed A total of 10 3-inch diameter gravity cores, again to 4 cm per 100 years (figure 2 in with depths ranging from 1 to nearly 4 meters, Savarese et al., herein). The more recent, were taken along an offshore to onshore slower rate has allowed shorelines to stabilize. transect within Estero Bay and Estero River This stabilization led to the present-day coast, using both manual and vibracore techniques. characterized by mangroves that have An offshore to onshore transect was chosen in outpaced the rate of sea level rise (Parkinson, order to capture the changes in sea level rise 1987, 1989). throughout the river and estuary system. Five This unique geomorphology depends upon a cores were taken inside the bay, and five were sea level rise of modest rate, however, some taken either near, at the base of, or beyond the studies suggest sea level rise could be mangrove fringe along the river. returning to the faster rate of as much as 20 to Cores were cut lengthwise and sedimentary 40 cm per 100 years (Maul and Martin, 1993; facies were defined based on sediment type, Wanless et al., 1994). Understanding the abundance and type of shell material, color response of coastal systems to previous and grain size of sediment, and sedimentary changes in rise rate will help predict the structures. potential consequences if rise rate again increases. The following sedimentary analyses were conducted when appropriate: radiocarbon Estero Bay and River, located in Lee County, Florida, are part of an estuarine system of dating via AMS and standard counting mangrove and barrier islands, and oyster reefs through Beta Analytic of Miami using shell (Figure 1). The goals of this study were to material from 4 identified facies; coarse grain Fig. 1. Map showing location of Estero Bay and River on the Southwest Coast of Florida, located south of Fort Myers. Core transect is indicated with a white line. sieve analysis (Figure 2); fine grain sequence appears in the lower portion of the sedimentary analysis by pipette method core. (Figure 2); percent carbonate by selective acid In the cores closest to the Gulf (1, 5, 6 and 9), dissolution of carbonates; percent organics by the interlaminated fine sand sequence is oxidation at 550°C ignition loss; and fossil capped by either very fine sand or fine sand identification. with marine or brackish mollusks (Figure 3). RESULTS In Cores 2, 4 and 7 (located along the river or near the mouth), the sequence is overlain by All cores include a sequence of interlaminated, mangrove peat. In Cores 3 and 10 (both at the white fine sand with little or no shells or river’s mangrove fringe) the sequence is marine indicators. In all but one core, this located near the top of the core, directly above estuarine sediments with oysters, and topped by mangrove peat in Core 3 and detrital mud in Core 10. The upper portions of the cores vary throughout. Cores 1 and 9 (most seaward cores) include coarse silt with vermetids, giving way to coarse silt with oysters. Cores 1, 5 and 6 (middle bay) include shoal sediments in the uppermost facies, while Cores 2 and 7 (river mouth) have very fine sand with abundant mollusks. The sites of cores 3, 4 and 8 (river sites) are currently colonized by mangroves and include peat at the top. Fig. 2. Chart showing cumulative weight percent and grain size distribution from near the top of Radiocarbon dates Core 2, Facies E, as determined from coarse- Shells from 4 locations within 3 cores were grain sieve and fine-grain pipette sedimentary used to obtain calibrated intercept radiocarbon analyses. dates. The results are reported below, with depths below the sediment surface for each and mangroves are ultimately able to colonize sample: this region. The timing of this slow down is Core 1, 80-90 cm, 2880 ybp (+/- 80) between 2400 and 2880 ybp based on radiocarbon dates in Cores 1 and 3, which is Core 1,165-175 cm, 4345 ybp (+/- 40) consistent with the timing of the slow down in Core 2, at 65 cm, 1260 ybp (+/- 40) other studies (Wanless et al., 1994). Core 3, at 177 cm, 2400 ybp (+/- 80) This progradation of Estero Bay’s coastline is consistent with the model developed by Using these dates and the depth of the initial Parkinson (1987, 1989) in the Ten Thousand flooding surface from present-day sea level in Islands region, and further documented by Cores 1 and 2, a rise rate of 5.2 cm/100 years other papers herein. The calculated sea level was calculated. rise rate of 5.2 cm/100 years found in this CONCLUSIONS study is comparable to that found for the same time period in other studies (Wanless et al., An inundation/transgression of Estero Bay can 1994). be seen in all 10 cores as supratidal and subaerial sediments give way to either There is some evidence to suggest this area mangroves or bay environments, and grain may no longer be prograding due to an size becomes finer moving up through the acceleration of sea level rise. The most bottom portions of the cores (Figure 3). In the landward core was taken in an area that was a case of Cores 3 and 10, the sequence begins at freshwater marsh, but is now being colonized bedrock, shifting to subaerial sediments and by white mangroves. In Cores 2 and 7, then immediately to oysters. The encroaching mangrove peat lies in the middle of the core, sea has pushed back the environments in the and is overlain by bay sediments founded on a Estero Bay and River system. shell-rich tempestite. This suggests the mangrove forest in this area may have been This transgression occurs through destroyed by a storm and did not re-establish. approximately 2,400 to 2880 ybp, when the If indeed sea level rise rate is returning to 20 location of the most seaward Cores 1 and 9 to 40 cm/100 years, as some studies suggest, (now located in the middle of the bay) was an the characteristic mangrove island open coastal environment, characterized by geomorphology of Southwest Florida may be coarse silts with vermetid gastropods present. unable to keep pace and could begin to Vermetids require salinities of at least 25 ppt, degrade. strong currents for bringing food and hard substrate to colonize (Shier, 1969). This, REFERENCES CITED coupled with the grain size of the facies where Maul, G.A., and Martin, D.M., 1993, Sea vermetids appear, indicates a deeper water, marginal environment. These facies are found Level Rise at Key West, Florida, 1846-1992: in no other cores, suggesting this area was in a America’s Longest Instrument Record?: deeper subtidal setting that never extended to Geophysical Research Letters, v. 20, no. the location of the other cores. The 18, p. 1955-1958. transgression can also been seen clearly in Parkinson, R.W., 1987, Holocene Cores 3 and 10 (now located at the edge of the Sedimentation and Coastal Response to Rising river’s mangrove fringe), once the site of low Sea Level Along a Subtropical Low intertidal oysters. Energy Coast, Ten Thousand Islands, Evidence also exists for a regression due to Southwest Florida: doctoral dissertation, progradation of mangroves as the rise rate of University of Miami, Florida. sea level slowed. The vermetid facies give Parkinson, R.W., 1989, Decelerating Holocene way to oysters, and in Core 1 the coarse silt Sea-Level Rise and Its Influence on and oysters give way to a very fine sand shoal Southwest Florida Coastal Evolution: A environment. In Cores 3 and 10, a supratidal Transgressive/Regressive Stratigraphy: environment overlies the oyster environment Journal of Sedimentary Petrology, v. 59, 485-508. no. 6, p. 960-972. Wanless, H.R., Parkinson, R.W., and Tedesco, Stuiver, M., 1969, Florida Submergence Curve L.P., 1994, Sea Level Control on Stability Revisited: Its Relation to Sedimentation of Everglades Wetlands: Everglades, the Rates: Science, v. 163, p. 562-564. Ecosystem and Its Restoration, St. Lucie Press, Delray Beach, FL, p. 199-222. Shier, D.E., 1969, Vermetid Reefs and Coastal Development in the Ten Thousand Islands, Southwest Florida: GSA Bulletin, v. 80, p.

Fig. 3. Fence diagram showing sediment characteristics of each core, correlation of facies between cores, and correlation of general environmental suites of all cores. GROWTH AND DEVELOPMENT OF HOLOCENE OYSTER REEFS, SOUTHWEST FLORIDA

DANA DERICKSON Geosciences Dept., Trinity University Sponsor: Dr. Edward C. Roy Jr., TU

INTRODUCTION more marine setting. Knowing the preferred substrate on which oyster reefs develop could An estuary is defined as “a semi enclosed also help in restoration efforts that are coastal body of water which has a free currently underway in that area. By connection with the open sea and within which understanding the sedimentology of oyster sea water is measurably diluted with fresh reefs, new reefs could be planted in bays and water derived from land drainage” (Shier have a better chance of survival. 1969). They are one of the world’s most productive and delicate ecosystems. Estuarine METHODS environments, like the Ten Thousand Islands in southwest Florida, display a balance Field Work between wave, tidal, and fluvial processes. The area seaward of the Blackwater River in Human influences, as well as millennial scale Ten Thousand Islands was chosen for the fluctuations of sea level, threaten this balance. study because it is an area of low human Oyster reefs are an essential part of estuarine influence (see Figure 1). The control reef, ecosystems, especially in the Ten Thousand located in Blackwater Bay, is an optimal Islands area. Oysters filter the water, thus environment for a healthy oyster reef. Three raising water quality and lowering turbidity, other reefs were chosen in the outer fringe they provide food and habitat for the coastal environment just south of Blackwater numerous aquatic species, and they provide Bay. They are all influenced by marine stable ground for the roots of mangrove trees. surroundings because they are exposed to the Knowing how and where oyster reefs develop Gulf of Mexico. is key to the preservation of the reefs, and it also provides useful information for any Using a vibracore and three-inch diameter restoration effort that may be attempted in the aluminum tubes, a core was extracted from future. each reef. The sediments were described and stratigraphic columns were drawn. Oyster The watersheds of southwest Florida are shells and sediments were sampled at selected currently endangered because of urban, intervals throughout each core. agricultural, and coastal development. For example, Faka Union canal to the southeast and Henderson Creek to the northwest of the Laboratory Work study area have been drastically altered as a Sediments from five to ten centimeter result of human influence. This study will help intervals were wet sieved into the following to decide if oyster reefs can survive rapid size fractions; <1F , 1F to 2F , 2F to 3F , 3F changes of environment and then persist in a to 4F , and >4F . Each fraction was dried and weighed. Each fraction was then evaluated for sediments do not show a characteristic mean its percentage of shell, quartz, mud and root grain size. hairs. The ratio of sand to mud was also Microscopic analysis shows that the sediment calculated and graphed. Stratigraphic columns less than 1_ was mostly broken oyster shells were prepared and a fence diagram was along with gastropod and bivalve shells. The constructed. Oysters were individually 1_ to 2_ fraction contained varying amounts of examined and each received a taphonomic carbonate mud lumps, oyster shells, grade so that comparisons could be made foraminifera and some angular to sub-angular vertically within each core as well as from quartz. The 2_ to 3_ sized sediments were core to core. A bar graph was constructed mostly angular to sub-angular quartz with comparing the oyster’s grade compared to its minor carbonate amounts. The 3_ to 4_ range depth. consisted mostly of sub-angular quartz as well as sponge spicules and a few carbonates. RESULTS Anything greater than 4_ was considered to be carbonate mud. Sediment The sand-mud ratio varied between cores but Stratigraphy the three fringe reef cores displayed similar The stratigraphic sections of the three outer ratios between 40cm and about 150cm. reefs have very similar units that correlate well Overall there was an average of about 60% (See Figure 2). At all three outer reef sand in this section. locations, the reefs began to develop on a According to weight percents, a general shelly wackestone. The cores that were drilled pattern shows that the percent coarse sand and deeper show that the wackestone formed on a gravel (<1_) in each core was high in the mangrove peat layer. The oysters that make up upper 20-30 cm and diminished with depth. It the control reef in the inner bay developed on also shows the 2_ to 3_ sized fractions at a top of mangrove peat. The fact that peat was low percent in the upper sections and an found in the cores of the outer reefs suggests increased percent with depth. However, the that the area was once in an inner bay where mangrove trees grew. The oysters appear in CONCLUSION the core either directly above the peat or above a shelly wackestone layer deposited on the By comparing an oyster reef that has always been located in a protected inner bay to three peat. It is therefore probable that the reef first reefs in the outer fringe of the islands, it can formed while the environment was still be suggested that the more marine reefs estuarine. actually developed in an inner bay of an Taphonomic Grading estuary and then persisted through the transgression into a more marine environment. In theory, there should be a low degree of This was confirmed by analyzing each reef’s oyster shell fragmentation, disarticulation and stratigraphy along with the oysters themselves corrosion for a shell that is in a lower energy and the sediment surrounding them. Studies environment and the physical characteristics from Chester (1979) and Shier (1969) use of the shell should worsen as the environment different techniques but also agree that oyster becomes more unprotected. To prove that the reefs in the Ten Thousand Islands area more marine oyster reefs had in fact developed developed on either peat or a clastic layer in a protected bay environment there should be overlying the peat. a pattern present that shows better preserved oyster shells in the older section of the oyster REFERENCES CITED reef, and a progressively worse grade as the Andrews, J., 1994, A field guide to shells of the Florida reef gets younger. coast: Gulf Publishing Co., Houston, TX. After examining the results there seems to be Chester, M., 1979, The stratigraphy of a modern oyster no apparent patterns at all. Individual cores do reef in the ten thousand islands area: Masters thesis, University of Toledo, p. 1-66. not display the theoretical pattern, and no two cores exhibit similar results. This does not Shier, D.E., 1969, Vermetid reefs and coastal prove or disprove the theory that the reefs development in the ten thousand islands, Southwest Florida: Geological Society of America Bulletin, v. developed in an estuarine setting. 80, no. 3, p.485-508. DETERMINATION OF HOLOCENE SEA LEVEL CHANGE BY ANALYSIS OF MOLLUSKS, BLACKWATER BAY, SOUTHWEST FLORIDA

CHRIS KITCHEN Keck Geology, Whitman College Sponsor: Bob Carson

INTRODUCTION features. Relative sea level rise is a competition between the rate of Estuaries are the most productive ecosystems sedimentological and biological processes on earth and the fastest diminishing ones too. versus the rate of sea level rise. If the rate of These two facts make protection and sedimentation and biological accumulation is restoration of estuaries a top priority. One of greater than that of sea level rise, relative sea the potentially most destructive forces to level drops (regression) and vise versa. From estuaries is rapid sea level rise, which is 7,500ybp to 5,500ybp sea level was rising at a currently being accelerated by global warming. The Environmental Protection Agency (EPA) forecasts a sea level rise of 55- 335cm (average150-210cm) by the year 2100 (Wanless et al. 1994). This rise will have serious environmental impacts on Florida’s estuaries and urban centers, most of which are not more than a meter above sea level. In this paper I will describe the effects of Holocene sea level rise on Florida’s estuary environments. I will focus on the relationship between Holocene sea level rise and the effects it has on mollusk fauna of the time. SEA LEVEL HISTORY During the Pleistocene period in southwest Florida limestone platforms were submerged and subaerially exposed due to glacial and interglacial periods (Tedesco 2001; Parkinson 1987; Wanless et al. 1994). About 120,000 years before the present (ybp), sea level was 100m-150m below today’s level. Approximately 20,000ybp sea level began to very fast rate of 50cm/100yrs and from rise inundating the limestone platforms and 5,500ybp to approximately 3,200ybp sea level causing landward migration of coastal rise was 23cm/100yrs ( Tedesco 2001; Parkinson 1987; Wanless et al.1994). This rapid sea level rise was sufficient to cause shoreline retreat, flooding and deepening of

assigned to individual layers, normally to the top sedimentary unit of each core. The cores were then cut open, and the stratigraphy was described. Five-centimeter thick samples were taken at intervals of 5cm-15cm from unit E (Figure 2) which is a shelly, muddy quartz packstone. Each sample was sieved through 2mm and 1mm sieve, leaving only the molluskan assemblage, which was then bays. At approximately 3,200ybp this rate sonically cleaned. Next all the fauna was slowed to 4cm/100yrs, which allowed identified, and unit E was broken up into coastlines to stabilize, marine environments to shallowing (regressive) and deepening shallow, and oyster and mangrove (transgressive) phases (Figure 4). Fauna was colonization to proceed seaward. There is assigned to a depositional environment based disagreement as to when exactly the rate on habitat preference including brackish, slowed and many believe that the rate was intertidal and subtidal marine from Andrews decreasing before 3,200ybp. (1994), Abbot (1974) and Morris (1973). Some of the key species and their habitat that METHODS were used to assign fauna assemblages to Cores were taken with 3in. diameter irrigation depositional environments can be seen in tubes (732cm in length) at the locations figure 3. It was not practical to base these indicated (Figure 1). Using a vibrator head the depositional environments on the presence of cores were driven 2–5m into the sea floor and individual mollusks because there was a large pulled out with an extensive winching system. variety of fauna and associated habitats in All cores (Figure 2) were located in relation to each 5cm unit. Instead I compared the faunal mean high tide, which was determined by assemblage with the habitat reflected by the locating the sediment surface relative to the bulk of the fauna in that unit to assign the core highest occurrence of barnacles or oysters. interval to a habitat. Where barnacles and oysters were not present, CORE DESCRIPTIONS the lowest mangrove leaves, which were determined to be 20cm higher than the mean Six different sediment packages were high tide mark, determined mean high tide. identified (A-F). Unit A is limestone bedrock Compaction was determined from the distance from the Pliocene and it is covered by a from the surface of the water to the sediment Pleistocene sticky clay packstone (unit B) surface inside the core minus the distance (Parkinson 1987). The fact that Pleistocene between the water surface and the sediment sediments are present in most cores indicates surface outside the core. Compaction was then two things: one, that our cores contain the entire Holocene sediment record; and, two, In core 8 transgression began in the E unit that initial coastlines were widespread and (Figure 4) for the first 90cm of deposition uniform (Parkinson 1987). Unit C is a quartz resulting in a change from an intertidal to sand grainstone that gradationaly changes marine environment. A regressive phase from a clean quartz sand near the contact with occurs in the top 85cm going from marine unit B to a dirty sand which contains mud, intertidal to a brackish, somewhat intertidal peat remnants and mollusks as it grade upward environment. In core 6 a peat forms, starting to its contact with Unit E or D. Unit C is at approximately 4120ybp (dated wood believed to be a nonmarine deposit. Unit D is fragment found at base of peat), indicating that a mangrove peat. Unit E is a shelly quartz a regressive phase had began sometime before packstone, rich in mollusks. This unit is then. At 1040ybp, (dated Macoma shell found clearly a lagoonal/ bay deposit. The faunal just above the peat), the peat was inundated by analysis of unit E indicates that it can be bay deposits indicating that a transgressive broken into a lower deepening phase and an phase had begun. No faunal samples were upper shallowing phase (Figure4). Unit F is an taken from this core because the E unit is less oyster bindstone, which is essentially an old than 40cm thick; however it is assumed that oyster reef. this unit would show a regressive phase in the All the cores in figure 2 show at least one full upper portion like all the other cores. The first regressive /transgressive/ regressive sequence, regressive phase in core 3 ends about 2300ybp whether it is in the major units or confined in (dated angel wing shell just above the peat). A the shelly quartz packstone (E) unit, with the transgressive phase in the bottom 141cm of exception of core 9 which is fluvial in nature unit E results in brackish intertidal to open (Figure 1). The first regressive cycle allowed marine conditions. About 140cm from the top of the core a regressive phase causes a change from a marine subtidal environment to its present shallow brackish water bay (Figure 4). In core 4 a transgressive phase occurs at the top of unit C to allow for the deposition of the lagoonal muds of unit E. In unit E a transgressive phase occurs in the bottom 142cm. This section of unit E appears to oscillate between intertidal and subtidal environments. This could be due to the difficult nature of determining mollusk environments from sediment packages or could indicate high frequency sea level oscillations. Gelsanliter and Wanless (1995) (in Tedesco 2001) found evidence for high frequency sea level oscillations between 3200ybp and 2400ybp. The upper 122cm of core 4 shows a regressive phase from marine subtidal to a shallow sea grass brackish for peat to form. From the radiocarbon dates it environment of today. Core 11 shows the two can be determined that the peat began to form transgressive / regressive cycles most before 4850ybp. This indicates that the first completely. The first transgression occurs as regressive phase probably began 5000- unit C is covered by unit E. A regressive 6000ybp. These dates coincide with the phase occurs in unit E and continues through decreasing sea level, rise that occurred about unit F, oysterbindstone, and unit D, a peat. the same time. The second transgressive/ The top of this peat layer is dated at 4850ybp. regressive phase can bee seen in unit E in all The second transgression began about this the cores (Figure 4). time, which can be seen in the bottom 122cm of the second unit E. The top 40cm of unit E Florida’s fragile fresh water environments and shows a regressive phase up through the fresh water sources for human needs. A rise of oysterbindstone (unit F) above it. this magnitude will not only damage natural environments but also human population DISCUSSION centers most of which are less than a meter The slowing sea level rise that occurred at above sea level. Small changes in faunal 5,500ybp allowed sedimentary and biological assemblages (i.e. disappearance or appearance processes to dominate over erosional ocean of species) and depositional environments processes creating the regressional features of along with retreating coastal features could be barrier islands, oyster bars and mangrove an early indicator and warning of a rapid forests. Evidence of transgression appears at transgression and the effects of global 4850ybp in core 11, 2300ybp in core 3 and warming. The information in figures 2, 3, and 1040ybp in core 6. The difference in 4 can be used as a reference for the possible transgression ages is due to time transgressive future effects of global warming and sea level phenomena. This transgressive phase is rise on Florida’s estuarine environments. It is present in the lower section of unit E. The my hope that this study will help bring to light regressive phase that occurred in unit E is the serious effects of global warming and a rather abrupt and appears to occur at about the major sea level rise. same time in all the cores in figure 4. This REFERENCES CITED indicates that, unlike the previous regressive/transgressive phase that occurred as Abbott, Tucker 1974, American Seashells: sea level rise rate decreased gradually, this one Van Nostrand Reinhold Company, New was abrupt. This is due to a major decrease in York. the rate of sea level rise from23cm/100yrs to Andrews, Jean 1994, A Field Guide to the 4cm/100yrs. This was probably a rapid change Shells of the Florida Coast: Gulf unlike the gradual rate change that occurred Publishing Company, Houston, Texas. 5,500ybp. Michaels, Brian 2001, Holocene Stratigraphy IMPLICATONS and Geomorphic Evolution of the Cape Although sea level has been rising during the Sable Region, Southwest Florida: Holocene, relative sea level has been Evidence for Late Holocene Sea Level oscillating due to different rates of rise and Dynamics: University of Miami sedimentological and biological processes. It Morris, Percy 1973. A Field Guide to the can be seen that once sediment and biological Shells of the Atlantic and Gulf Coasts: processes gain a foot on sea level rise it takes Houghton Mifflin Company, Boston. a long time to overcome these processes. Of Parkinson, Randall 1987. Holocene particular concern today is the fact that sea Sedimentation and Coastal Response to level has been rising extremely fast again Rising Sea Level Along a Subtropical, since 1930 (Wanless et al. 1994). It has increased to a rate of 23cm/100yrs, which is Low Energy Coast, Ten Thousand Islands, the same rate that caused the last major Florida: Dissertation, University of Miami. transgression from 4800ybp to 1000ybp that Tedesco, Lenore 2001. An Introduction to inundated the mangrove forests and cause Southwest Florida’s Natural Environment massive landward retreat of all coastal IUPUI Department of Geology and Center features. The EPA’s prediction of a 55cm- for Earth Environmental Studies. 355cm sea level rise by 2100 due to global Wanless, Harold, Parkinson, Randall and warming far exceeds the rate that caused that Tedesco, Lenore.1994. Sea Level Control last major transgression. This rise will cause on Stability of Everglades Wetlands: major retreat of coastal features and could Everglades, the Ecosystem and Its inundate Florida’s lowlands and fresh water Restoration: St. Luci Press, Delray Beach, complexes. This would be devastating for Florida. WINTER AND TROPICAL STORM EVENT IDENTIFICATION BASED ON LATE HOLOCENE SHELL BEDS, TEN THOUSAND ISLANDS, S.W. FLORIDA

RAMON J. LOPEZ JR Department of Geology, Vassar College Sponsor: Friedrich Pflueger, Ph.D.

INTRODUCTION shell beds should be evident. This hypothesis is based on the assumption winter storms carry Determination of storm frequency through significantly less energy than larger tropical tempestite identification over the past 5, 000 storms. A winter storm would produce years is key to understanding how coastal relatively smaller shell bed with shells having geomorphology of southwestern Florida will relatively better taphonomic condition as be affected in the future (emphasis mine). opposed to those generated by hurricanes. Arguably, a global warming trend is likely to Understanding the difference(s) between produce more hurricanes of increased tropical and winter storm deposits allows for a intensity. Higher occurrences of Hurricane better understanding late Holocene climate Andrew-type storms (Category IV) will and how storms will affect southwest Florida drastically affect mangrove island health and in the future. thus have serious implications for property values and human development in and around METHODOLOGY AND one of the fastest growing areas of the United STUDY SITES States. A model describing two types of shell beds Research indicates that mangrove islands are was developed for this study. Type I shell responsible for shoreline stabilization and beds are those occurring within a “parent” progradation. Since mangrove roots are facies or geologic unit. Type II shell beds are known to trap sediment, they slowly prograde found on a facies contact and are indicative of seawards as new seedlings take root. a change in paleoenvironment (i.e. increased Parkinson (1991) reports mangroves have kept wave energy associated with rising sea level, pace with Holocene sea level rise and are thus or amalgamated storm deposits). The responsible for an apparent late Holocene sea depositional mechanism responsible for the level regression. Parkinson (1987) states shell bed is a separate matter; this is based on numerous studies on the Ten Thousand Island the organization of material within the bed. A conclude hurricane landfall is the major generic storm generated shell bed would show control mechanism for sedimentation and thus a fining upwards grain size trend with geomorphology. articulated, imbricated shells in hydraulically The identification of storm events based on stable positions in the lower zone of the bed. shell deposits in the stratographic is the focus Shells of poor taphonomic condition are of this study. Several observable differences expected to be deposited in the upper zone of between winter and tropical storm generated the bed, as they are less dense than articulate on the amount of shell material. The ones. preliminary facies analysis (based on observation) is: (1) slightly shelly to shelly Coring Program quartz packstone, (2) quartz wackestone with A series of two transects— three cores from shell debris, and (3) slightly shelly quartz Barfield Bay and two from Blackwater grainstone (core BB-1 only). River— were hand cored in areas where These cores are associated with open marine tempestites preservation is most likely, that is, sequences. Sufficient material for absolute a waterway of constricted flow opening into a age dating is not available for any cores within relatively larger area. (Parkinson, 1989 and this study. Purlmutter, 1982). Strain on program resources and the risk of attracting large Discussion predators were the main reasons for not using Two occurrences of sea-level change, the a vibracore. Lower Holocene transgressive and Upper Holocene “regressive” sequences (Parkinson, Barfield Bay, and Blackwater River 1991), have been identified within the Barfield Bay is mostly likely a non-carbonate Blackwater River transect. The Lower inter-island bay (IIB) within the TTI Holocene transgressive sequence is identified mangrove island complex (MIC) coastal zone by the first four facies in cores BW-1 and BW- (Parkinson, 1991). Known sediment types for 2 (figure 1). The following paleoenvironment chain-of-bays, and inter-island bay systems reconstruction of the facies is based on are: (1) soft organic-rich shelly quartz sedimentary evidence: (1) sub-aerial (mottled, mudstone, (2) mollouscan quartz packstone, organic rich quartz packstone), (2) red (3) shelly quartz packstone, and (4) oyster mangroves (peat), (3) shallow marine (shelly rudstone and bindstone (Parkinson, 1987). A quartz packstone, or muddy oyster bindstone), transect of three cores was taken down the and (4) high energy marine (shelly quartz middle of a smaller, submerged flood delta in rudstone). Barfield Bay. The study site is located on a The Upper Holocene “regressive” (or rather sand bar in the seaward most area of the shoreline progradation) sequence is identified mainland shore (MS) coastal zone (Parkinson, by the fifth facies, quartz grainstone. The 1991). The predominant sediment within this moment in geologic history where mangrove area is red mangrove peat, quartz, and progradation begins to match the rate of sea occasionally calicitic muds. The mineralogy level rise is difficult to determine from this of the Blackwater River study area is data. The quartz grainstone unit, although an predominately quartz in nature. open marine sequence is part of the Upper RESULTS Holocene regression as a red mangrove forest surrounds the study site—this indicates a The Blackwater transect, consisting of two return to more shallow marine conditions. cores (cores BW-1 and BW-2, figure 1) were interpreted to have five distinct sedimentary The shelly quartz rudstone unit exhibits units: (1) mottled organic rich quartz several interesting features making an packstone, (2) red mangrove peat, (3)shelly interpretation of the depositional mechanism marine quartz packstone or muddy oyster problematic. The sharp basal, non-bioturbated bindstone, (4) very shelly quartz rudstone, and contact with the underlying shelly quartz (5) quartz grainstone with shelly debris. packstone lends evidence of rapid erosion and re-deposition. The lower zone of the rudstone The Barfield Bay transect exhibits two major facies also contains a higher concentration of geologic units in cores BB-2 and BB-3 with a broken shells while the upper zone has an third distinct unit in core BB-1 (figure 1). increased concentration of articulated Several subunits are also described within specimens—this suggests a coarsening these cores; classification of a subunit is based upwards sequence of shell material. Based on the shell bed model developed for energy wave action is a certainly a plausible this study, the shelly quartz rudstone unit of explanation for the poor taphonomic condition the Blackwater transect partially fits the of bivalves, gastropods, and oysters. In either criteria of a Type II shell bed generated by case, these interpretations support a sea level storm activity since it occurs on a facies transgression described by Parkinson (1991). boundry. It is unlikely this unit represents a Rising sea level would result in increased singular storm deposition event but rather an wave action thus exposure to larger waves is amalgamation of tropical storm layers expected.

BW-1 BW-2 BB-1 BB-2 BB-3 0 U Figure 1. Core data, geologic time Qg Qw Qw P scale, paleoenvironment. Scale in cm. Ms P Qw Q E Qg H Legend: g R O L BB* Barfield Bay Cores O MO BW Blackwater River Cores C “50” Core Depth (centimeters) E P Peat, Red Mangrove N r Qsp Qsp Qsp Qa Subaerial Quartz Packstone Qsr E Qg Quartz Grainstone Qop Quartz Oyster Packstone ME Qsp Shelly Quartz Packstone Qsr Qsr Shelly Quartz Rudstone Qw Quartz Wackestone

Ms L O Paleoenvironments: 100 W Ms Shallow Marine Qop E Mo Open Marine R ME High Energy Marine H Ps Mangrove Forest H S Subaerial O H Hiatus in Record L O *Open marine environment; Data inclusive C for determination of geologic age. P Qsp E Pr N Qa E 185 S 198 Qsp Qsp

215 Sand Bivalve 220 220 Mud Gastropod reworked during a period of rising sea level or A hiatus inPeat the Lower HoloceneOyster Blackwater rapidly changing climate. (It does not seem sequence was also observed. An animal likely winter storms carry enough energy to burrow embedded in red mangrove peat amalgamate large amounts of sediment and infilled with clean quartz packstone, is found shell material.) The poor taphonomic within core BW-2. Clean quartz packstone condition of shells within this layer (high was not found within any of the Blackwater degree of fragmentation and numerous bore cores. Quartz packstone and grainstone are holes) indicates the material was subjected to indicators of high energy conditions. Rising predation (i.e. parasites, worms, other sea level would deposit quartz sand top of the mollusks) followed by exposure to high red mangroves. A large errosional event then energy conditions before incorporation into occurred infilling the animal burrow and the facies. This lends evidence of a climatic erasing a portion of the geologic record. As change that may have proved catastrophic for sea level continued to rise and oyster oyster reefs within the Ten Thousands Islands. colonization began, tidal currents may have An alternative interpretation of this shell eroded any record of such a storm. Storm bed—a high energy oyster reef—is also a activity is a plausible explanation, as this is the consideration. Repeated exposure to high only mechanism capable of eroding large amounts of sediment in the Ten Thousand Gesanliter, S., 1996. Holocene stratigraphy of the Islands. This is strong evidence rising sea Chatham River region, southwest Florida; with a reevaluation of the late Holocene sea level level causing a catastrophic change to the Ten curve: Master of Science Thesis, University of Thousand Islands during the late Holocene. Miami, Coral Gables, Florida. The Barfield cores are too ambiguous to Kemp, A. E. S. (ed.), 1996. Palaeoclimatology and determine the nature of the depositional Palaeoceanopgraphy from Laminated system, although they are associated with open Sediments. Geological Society Special marine sequences. Barfield Bay may have Publication, No. 116: vii-xii. always been the regional seaward-most extent Parkinson, R. W., 1987. Holocene sedimentation and of the Ten Thousand Islands. coastal response to rising sea level along a subtropical low energy coast, Ten Thousand CONCLUSIONS Islands, southwest Florida: Ph.D. Dissertation, University of Miami, Coral Gables, Florida. Clear evidence for the generation of shell beds Parkinson, R. W., 1989. Decelerating Holocene sea- by tropical or winter storms have not been level rise and its influence on Southwest identified by this study. Shelly tempestites Florida coastal evolution: a showing singular depositional events were transgressive/regressive stratigraphy: Journal also not observed. The geomorphology of the of Sedimentary Petrology, 59(6): 960-72. study sites may not allow for preservation of Parkinson, R. W., 1991. Geologic evidence of net singular storm tempestites. However, there is onshore sand transport thoughout the Holocene evidence indicating at least two occurrences of marine transgression, southwest Florida: Marine Geology, 96(3-4): 269-77. rapid sea level rise and/or periods of high tropical storm activity affected the late Perlmutter, M. A. 1982. The recognition and Holocene ecosystem of the Ten Thousands reconstruction of storm sedimentation in the nearshore, southwest Florida: Ph.D. Islands. The first episode possibly killed off Dissertation, University of Miami, Coral the mangrove forests, and the second lead to Gables, Florida. the demise of oyster reefs. Further analysis Sexton, W. J., 1995. The post-storm Hurricane Hugo and coring is required to gain higher resolution recovery of the undeveloped beaches along the of any trends in storm activity over the late South Carolina coast, “Capers Island to the Holocene. Santee Delta:” Journal of Coastal Research, 11(4): 1020-5. REFERENCES CITED Sheridan, P. F., 1992. Comparative habitat untilization Carter, M. R., Burns, L.A., Cavinder, T.R., Dugger, K. by esturine macrofauna within the mangrove R., Fore, D. B., Revells, H. L., and Schmidt, T. ecosystem of Rookery Bay, Florida: Bulletin W., 1973. Ecosystems analysis of the Big of Marine Science, v. 50(1): p. 21-39. Cypress Swapm and esturaries: U. S. Tedesco, L.P. Wanless, H.R., Scusa, L.A., Risi, J.A., Environmental Protection Agency Region IV, and Gelsanliter, S., 1995. Impact of Hurricane Atlanta, Georgia. Andrew on South Florida's sand coastlines: Duever, M.J., Meeder, J. F., Meeder, L. C., and Journal of Coastal Research, Special Issue 21, McCollom, J. M., 1994. The climate of south p. 59-82. Florida and its role in shaping the Everglades Twilley, R. P., 1985. The exchange of organic carbon ecosystem: The Everglades Ecosystem and Its in basin mangrove forest in a southwest Restoration, Davis, S. M. and Ogden, J. C. Florida estuary: Estuarine Coastal and Shelf (eds), St. Lucie Press, Delray Beach, Florida. Science, 20: 543-57. Dunnam, R. J., 1962. Classification of carbonate rocks Wanless, H.R., 1981. Fining-upwards sedimentary according to depositional textures, in Ham, W. sequences generated in seagrass beds: Journal E., ed., Classification of carbonate rocks. of Sedimentary Petrology, 51(2): 445-54. American Association of Petroleum Geologist, Mem. 1: 117, Table 1. Yokel, B. J., 1975 B. Esturine biology: Rookery Bay Land Use Studies, Study No. 5. The Embry E. F., III and Klovan, J. E., 1972. Absolute Conservation Foundation, Washington, D.C. water depth limits of late Devonian paleoecological zones: Geology Rundschau, 61: 676, Figure 5. HOLOCENE STRATIGRAPHY AND EVIDENCE OF TRANSGRESSION IN THE TEN THOUSAND ISLANDS, SOUTHWEST FLORIDA

MONICA ROTH Earth Sciences Dept., SUNY Oneonta Sponsor: P.Jay Fleisher, SUNY Oneonta

INTRODUCTION Sea level changes have been recorded METHODS throughout geologic history. Florida’s Four 3” vibracores were obtained along a Southwest coastline has a thin veneer of transect from Blackwater River through the Holocene and Pleistocene sediments coastal bays to Gullivans Bay (see figure 1). (Parkinson, 1987) with ages no older than 1.8 This was done from a pontoon boat anchored million years. This unlithified material overlies to the substrate. At the time the core was a Pliocene limestone with a maximum age of 5 taken, the height of the water was measured million years (Parkinson, 1987). The current in reference to mean high tide as a base-level configuration of the coastal wetlands of Florida for the project. Using high tide as a developed during a slow rise in sea level reference elevation, comparisons could be (~4cm/100 years) over the past 3,200 years made among cores. Each of the four cores (Wanless et al, 1994). used in this analysis were cut, capped and This study was done in Southwest Florida’s Ten brought to the lab. Thousand Islands region, a complex of barrier The cores, which recovered all or nearly all islands along the coast, protecting a variety of of the Holocene sequence, were split open, depositional environments from storm waves in photographed, and described in detail. the Gulf of Mexico. Field work took place in Samples were extracted from the core for the area of Blackwater River and Bay (figure 1) sediment analysis. Weight percent carbonate which extends through the coastal bays toward from each sample was determined by the Gulf of Mexico. This site is part of Rookery removing the carbonate fraction with a Bay National Estuarine Research Reserve. The solution of 10% hydrochloric acid. Next, site was chosen because it is the portion of the organic material was removed from the estuary that is least disturbed by human impact. remaining sample using a 30% concentrated As the length of the estuary is nearly 5 hydrogen peroxide solution, allowing for a kilometers, a variety of recent environments are calculation of weight percent of organics seen. Unlithified sediments in and beneath these within the samples. Prior to each removal, environments record eustatic changes over the the sample was dried and weighed, and after Holocene. The dominant morphologic each removal samples were rinsed, dried, characteristics observed in the study area were and weighed. The remaining sample was the abundance of mangrove islands, oyster bars, placed in a series of sieves of 250, 125, and and lagoons. 62 microns to determine the weight percent of coarse grained and fine grained siliciclastics. 4. A shelly- muddy sand, an oyster boundstone, a mangrove peat, and another shelly-muddy sand are all overlain by the most recent layer, another oyster boundstone.

The mangrove peat of core 4.1 (275cm from the top of the core), which marks the initial flooding of the most distal location in the transect, was dated (4290+/-70ybp) by radiocarbon dating a single shell. The red mangrove peat found at the base of core 3 (2600+/-100ybp) marks the time in which the mangroves were drowned at this location. Due to the locations of the dated material within the two cores, and their locations along the transect, it is apparent that the distal site, from where core 4.1 was extracted, was first affected by the current transgression, with the more proximal sites (4, 3, then 8) inundated later.

All samples from each core contained organic, siliciclastic, and carbonate components. Carbonate material within the cores varied from less than 5 percent to over 50 percent in various samples. Each core displays a general trend of increasing carbonate percent mass with time (figure 2). Organic percentages remained low throughout the entire transect of cores with the exception of the few peaty samples. Sand sized particles in each sample Figure 1 – This air photo of the Blackwater predominate fine grained particles with the River section of The Ten Thousand Islands, exception of samples taken from 300-400cm Florida shows the relative locations from which depth in core 4.1, the outermost core. each of the four cores was taken. Fluctuations in the sand sized and fine RESULTS grained siliciclastic particles are inversely abundant along the length of each core The base of core 8 was represented by a clayey (figure 3). quartz sand that is Pleistocene in age (Parkinson, 1987). This was overlain by a SUMMARY shelly- muddy sand. Basal sediments in core 3 Core description and sediment analysis show were mangrove peats overlain by shelly-muddy that no two cores in this study are alike, sand. Core 4 penetrated the Pliocene carbonate owing to the time transgressive character of bedrock which was overlain by quartz sand, facies in the cores. This rise in sea level is topped with a shelly-muddy sand. Core 4.1, the indicated by sediments deposited in shallow distal core in the transect has a sequence water overlain by sediments deposited in beginning with the same Pleistocene clayey deeper waters, as determined by the sediment quartz sand as found in cores 8 and 4, overlain analysis. by the quartz sand which was also found in core In cores 8,4, and 4.1, an unconformity exists quartz sand that is found in cores 4 and 4.1. between the basal Pleistocene clayey quartz The mangrove peat of core 3 represents an sand and the overlying layers. Cores 4 and 4.1 environment that would be the first indicator both show quartz sand which has been in a sea level rise. The overlying shelly- determined to be terrestrial (Tedesco, 2002). muddy sand which is marine, records The presence of the shelly-muddy sand inundation of the peat. The dominant overlying the quartz sand records the rise in sea modern day sediments in the Blackwater level as marine waters drowned the terrestrial River and bay region are shelly-muddy

Figure 2 - These carbonate trend graphs show the mass percent of carbonate removed from various depths within the cores in relation to mean high tide. Core 8, which represents the most landward environment shows very low levels of carbonate until the upper half of the core, where there is an abrupt increase, likely indicating a sea level rise. Core 3, shows an increase in carbonate, a slight dip, then again an increase in the most recent sediments represented by the core. Cores 4 and 4.1 both show an increase in carbonate in the sediments to recent times, showing a trending rise in sea sediments. Shelly-muddy sands overlying the sands. Core 4.1, located in the outermost Pleistocene layer shows a flooding of the region of the transect shows a modern unit of Pleistocene unconformity allowing deposition oyster boundstone as the oysters have been to resume. Basal peats of core 3 may overlie the able to keep pace with the rate of sea level Figure 3 – These graphs represent the siliciclastic material found throughout each of the four cores. Samples A for each of the core represent the uppermost sample extracted from the cores. The upper most cores, cores 8 and 3 show a relatively steady balance between the sand size particles and those less than 62 microns. Cores 4 and 4.1 however express some variation in that there is some variance in the dominant sediment type. rise and establish a long-term standing. The rise in sea level is indicated by a transgressive facies sequence. Core 4.1 is an exception in that it shows an early transgression/regression package followed by the transgression recorded in the remaining core. REFERENCES CITED Parkinson, R.W. 1987, Holocene sedimentation and coastal response to rising sea level along a subtropical low energy coast, Ten Thousand Islands, Southwest Florida. A dissertation. P.45-140. Standard Mapping Services. Ten Thousand Islands Marco Island to Everglades City. (1996) Tedesco, L. P. 2002, Written communication. Wanless, H.R., Parkinson, R.W., and Tedesco, L.P., 1994. Sea level control on the stability of Everglades wetlands, in S.M. Davis and J.C. Ogden, (eds.), Everglades, the Ecosystem and its Restoration, St. Lucie Press, Delray Beach, Fl, p. 199-222.