Paper No. 4
Presentation Time: 9:00 AM


COLLINS, Laurel S., Dept. Earth and Environment, and Dept. Biological Sciences, Florida International University, Miami, FL 33199, HAYEK, Lee Ann, Smithsonian Institution, NHB MRC-121, Washington, DC 20560 and WACHNICKA, Anna, Southeast Environmental Research Center, Florida International University, Miami, FL 33199,

Much research on Florida Bay, in Everglades National Park, has focused on the degradation of coastal water quality and the history of environmental change since permanent human occupation began in the late 1800s. The relative extent of perturbations to the Everglades ecosystem by human activities (e.g., beginning of agriculture, canal construction) versus natural events (e.g., hurricanes, droughts) has been debated. This study compares the timing of perturbations in the records of preserved microbiotas and physical conditions to known human and natural events over the past 120 years to infer their relative strengths.

Six sediment cores taken in 2002 from four areas of Florida Bay (near the mainland, the central bay and near the Gulf of Mexico) were dated with 210Pb and analyzed for proxy variables of water quality and environmental change. For each variable, the number of sediment samples and the cores sampled ranged from <100 to >300. We used an adaptation of impulse-response functions, a procedure from signal-processing, to track the responses of the variables to the impulses of the time-dependent shocks or occurrences of disruptive events, both anthropogenic and natural. We were able to identify where larger breaks and smaller perturbations occurred in time within the dated sediment cores. The physical variables did not produce definitive responses but the foraminiferal and diatom assemblages did. We used the biotic variables alone to identify six times of major breaks and perturbations that correspond in timing to the following documented events: 1) 1906-1910 construction of the Flagler Railroad; 2) 1926-1935 hurricanes; 3) 1954-1959 strongly negative phases of the El Niño/Southern Oscillation and Pacific Decadal Oscillation, and associated extensive drought events; 4) 1977-1980 negative Atlantic Multidecadal Oscillation and ENSO, strong drought and institution of a Monthly Allocation Plan for controlling water release; 5) 1987-1994 seagrass die-off that began with hot, still conditions; and 6) 1997-1999 seagrass recovery and increased water flow. This study is being continued with new approaches of reducing the number of species in whole assemblages to those that are ecologically meaningful for each event, and testing the hypotheses of the causes of the breaks against what is predicted for each event.