PARENT SESSION
Poster Session # 4: Paleoecology.

Monday, August 4 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Tracking effects of salt-water encroachment on community migration in coastal South Florida wetlands using mollusks.

Zafiris, Angelikie^*,1, Gaiser, Evelyn¹, Ross, Michael¹, ¹ Southeast Environmental Research Center, Miami, FL

ABSTRACT- Coastal wetland communities of South Florida have been cut off from freshwater sheet flow for decades and are contracting and migrating landward due to salt-water encroachment. We conducted a paleoecological study to determine the effect of salt-water encroachment on the location of boundaries between fresh- and salt-water ecotones in the southeastern saline Everglades. Wetland soils were cored to bedrock at 8 locations in two transect perpendicular to the coast. Transitions from basal marl soils to peat were evident throughout the transect, with a deepening of the peat layer toward the coast indicating increased production and interior expansion of the fringing mangrove forest. Mollusks were abundant throughout the cores and the 24 collected taxa served as useful paleoecological indicators. Modern distributions among 86 sites in the same wetland were used to determine local habitat affinities, which were then applied to infer past settings from the sequence of sedimented mollusks. Sites located between the drainage canal and the coast showed signficant upcore increases in the ratio of marine to freshwater taxa, while sites to the interior of the canal showed the opposite trend. Terrestrial taxa have also increased in the interior sites, indicating a transition from shallow gramminoid marsh to the current shrub-forest community. Together with historic accounts and aerial photograph archives, the paleoecological data are showing an interior migration of the fringing mangrove ecotone within the past 60 years, replacement of a mixed gramminoid-mangrove zone by a dense monoculture of dwarf mangroves, and a confinement of the freshwater gramminoid marsh to landward areas between urban developments and drainage canals.

Key words: Paleoecology, Salt-water encroachment, Mollusks, Everglades