An Example from Biscayne National Park

Geodiversity & Geoconservation Application of Paleoecologic Methods to Coastal Resource Management: An Example from Biscayne National Park G. Lynn Wingard Introduction THE NATION’S COASTAL ECOSYSTEMS HAVE CHANGED PROFOUNDLY during the last century due to human activities. The Estuary Restoration Act was passed by Congress in 2000 and a component of the act was to develop a National Strategy to Restore Coastal and Estuarine Habitat (NOAA 2002). The national strategy identifies the importance of establishing historical or baseline conditions within estuarine ecosystems “to determine rates of loss, evalu- ate threats and predict future trends for various habitat types and areas within the system” (NOAA 2002:2). The report continues: “The availability of historical information varies greatly from place to place. For some estuarine systems, historical maps ... along with anecdotal information on previous centuries may be available. For other systems, only limited anecdotal information may be available.” Understanding natural patterns and estuaries of Biscayne Bay and Florida Bay. cycles of change that have occurred in a system prior to significant human disturbance Approach is a critical component of restoration; how- An integrated approach to interpreting ever, land managers do not have to rely on ecosystem history provides significant ben- historical maps or anecdotal information, as efits. Data from different groups of plants the above report suggests. Changes in and animals enhance the reliability of the ecosystems take place at many time scales, results and provide an averaging effect to from diurnal to millennial, and it is not smooth out species-level responses. Data practical or even possible to directly from different scientific disciplines allow observe change at these longer time scales. researchers to derive information on many Basic paleoecologic methods have been aspects of an ecosystem and to determine if successfully used in ecosystems around the synchronous changes have occurred in dif- country to determine short- and long-term ferent components of the system. For exam- patterns of change in the physical and bio- ple, if sediment geochemistry analyses logical components of ecosystems. In South detect an increase in nitrogen, paleoecolog- Florida, these methods have been utilized to ic assemblage analyses of the same sample establish the ecosystem history of the will indicate if a corresponding change Everglades, and those of the downstream occurred in the fauna. While these data do Volume 22 • Number 3 (2005) 13 Geodiversity & Geoconservation not prove cause-and-effect relationships, ment at the time of deposition, including they point to areas where observation or the range of salinities that existed, sub- experimentation in the living system might strates, and availability of freshwater. (See be worthwhile. Brewster-Wingard et al. 2001; Cronin et al. The process begins by locating areas 2001; Ishman et al. 1998; Willard, Holmes, that have sufficient sedimentary cover and and Weimer 2001; and Willard, Weimer, as little bioturbation, storm disruption, and and Riegel 2001 for examples of paleoeco- erosion as possible, within the area being logic studies in South Florida.) evaluated. Once sites are identified, cores Biogeochemical analyses of the calcium are collected using methods that minimize carbonate tests of ostracodes, mollusks, or sediment disruption. Cores are x-rayed and forams provide another method for deriving described, then cut into samples 1 to 5 cm numerical salinity values for each segment thick. of a core. A combination of ostracode and An age model for each core is derived mollusk shell analyses can provide a power- using three methods, where possible. Lead- ful tool to reconstruct seasonal and annual 210 analysis establishes the chronology of salinity variations. Ostracode adult tests the upper portions of the cores (see Holmes represent essentially instantaneous secre- et al. 2001 for explanation of the methodol- tions recording the salinity and temperature ogy). Radiocarbon ages on shells or wood at that point in time. Mollusks provide a fragments provide data points for the lower nearly continuous record throughout the portion of the cores. Additional confirma- span of the individual’s life. Experiments to tion of the age model comes from pollen of calibrate molluscan shell chemistry to water exotic flora with documented dates of intro- chemistry are currently ongoing; however, duction into the system. For South Florida, calibration curves for the ostracodes have the first occurrence of Casuarina (Aus- been successfully developed and utilized for tralian pine) pollen, an exotic introduced South Florida (Dwyer and Cronin 2001; around the beginning of the 20th century Dwyer et al. 2002). (Langeland 1990), provides an excellent Geochemical analyses of sediments are stratigraphic marker for the early 1900s. conducted to examine historical changes in The basic principles of paleoecology nutrients, primarily carbon, nitrogen, phos- are utilized to interpret the faunal and floral phorous, and sulfur. Information on histor- assemblages in the core samples. Modern ical changes in nutrient elements in sedi- sites are established within the ecosystem ments reflects changes in nutrient load to for routine observation and sampling. Envi- the watershed from both natural and ronmental parameters such as temperature, anthropogenic sources (Orem et al., 1999; salinity, and pH of the water and the nature Zielinski et al. 2000). of the substrate are recorded along with information on the faunal and floral species Biscayne Bay living at each site. These data are entered Setting. Biscayne National Park is a into a database that is utilized for downcore unique subtropical preserve, sitting on the interpretations. Comparison of the living edge of the metropolis of Miami and con- biota to the core assemblage data allows us taining part of the only living barrier reef in to develop a general picture of the environ- North America and the third-longest barri- 14 The George Wright Forum Geodiversity & Geoconservation er reef in the world. The majority (95%) of mates the predevelopment conditions as the park’s 172,924 acres is underwater, closely as possible. The role of the U.S. making Biscayne the largest underwater Geological Survey (USGS) ecosystem his- park in the national park system. The park tory projects is to provide information on itself contains four distinct environments: the pre-development conditions of the the mangrove coastline, the shallow waters Everglades. of Biscayne Bay, the northernmost islands Ecosystem history results and dis- of the Florida Keys, and the reef tract. cussion. Nine sites within Biscayne Bay, The Greater Everglades Ecosystem Card Sound, and Barnes Sound have been encompasses most of southern Florida from cored. Four of the locations are within the the Kissimmee River southward, through park boundaries; the other five are located Lake Okeechobee, into the freshwater at sites selected to examine changes in marshes of Everglades National Park, and freshwater flow into the estuary (Figure 1). eventually into the estuaries of Biscayne Paleoecologic, biochemical, and geochemi- Bay, Florida Bay, and the southwest coast. cal analyses on these cores provide informa- Since the beginning of the twentieth tion on historical changes in salinity and century, Biscayne Bay and the Greater nutrient influx into the bay. Details of the Everglades Ecosystem have undergone dra- core analyses are available in Wingard et al. matic changes as the population of Miami- (2003; 2004), but a brief summary is pro- Dade County has grown from 4,955 resi- vided here. dents in 1900 to 2,253,362 in 2000 (U.S. Faunal and floral assemblages from Census Bureau). As the population cores at Middle Key and Manatee Bay increased, so too did demands for protec- (Figure 1) indicate that the southern end of tion from seasonal flooding and for potable the Biscayne system (Card Sound and water for the residents and for the growing Barnes Sound), had significantly more agricultural area. A complex series of canals freshwater influx prior to 1900 than in the and water control structures, built through- later half of the 20th century. Figure 2 illus- out the 20th century, have altered the natu- trates changes in percent abundance of key ral flow of freshwater through the wetlands indicator species throughout the core and and into Biscayne Bay. Along the shores of over time. The fauna in the lower portion of Biscayne Bay, power plants, water treatment Middle Key core, deposited prior to 1900, plants, solid waste sites, and large-scale are predominantly freshwater gastropods developments have stressed the ecosystem. (Figure 2, #1), but the environment begins During the 1980s and 1990s, momen- to shift around 40 cm and increasing num- tum began to build for restoration of a more bers of species typical of an upper estuarine natural freshwater flow throughout South environment appear (Figure 2, #2–4). Florida (National Research Council 2003), Between 30 and 20 cm (approximately which led to the development of the 1900), freshwater species begin to decline Comprehensive Everglades Restoration (Figure 2, #5), and concurrent increases Plan (CERP; USACE 1999). The primary occur in all estuarine species: mesohaline goal of the CERP is to restore the timing, (upper estuary; 5–18 parts per thousand quantity, quality, and distribution of fresh- (ppt) dissolved salts), polyhaline (middle to water to the ecosystem so that it approxi-

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