Florida Coastal Everglades Long Term Ecological Research
Florida Coastal Everglades LTER - Project Information
Project Information

Anthropogenic and climate caused changes of habitats and water quality along a coastal gradient in Florida Bay, USA

Short-term project
Start date: Jan-2002          End date: Jan-2009
Contact person: Anna Wachnicka

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Although water quality conditions in Florida Bay have been fluctuating for thousands of years due to the natural processes and sea-level changes caused by the changing climate, the ecological conditions in the bay start deteriorating at the increasing rate in last few decades as a result of fast urban development in South Florida. Fluctuating water quality conditions greatly affected seagrass population abundance in Florida Bay, which was demonstrated by numerous studies. Changes in salinity, water total nitrogen (WTN), water total phosphorus (WTP) and water total organic carbon (WTOC) were inferred from diatoms preserved in four sediment cores collected from a coastal gradient in Florida Bay. The position of the cores along the estuary gradient helped to determine which water quality condition fluctuations were related to natural and climate-driven processes, and which to human processes. The main goals of this research were to reconstruct the historical changes in water quality conditions (salinity, WTN, WTP, WTOC) and diatom assemblage types (epipelon, epiphyton, plankton), and look for possible relationships between them. Assemblages in each core were grouped into stratigraphically distinct clusters. Changes in species turnover (beta diversity ) were recorded in late 1800's in the Bob Allen and the Russell Bank cores, followed by changes in early 1900's in the Trout Cove and the Ninemile Bank cores. A second period of change in beta diversity occurred in Bob Allen, Russell Bank and Trout Cove in the mid- 1950's and Ninemile Bank in the mid-1980's. Inferrence models indicate that salinity in the last 100 years at the Trout Cove location was higher in early 1900's than in recent time, decreased between 1900-1920 and then started increasing to the modern record. At Ninemile Bank salinity varied little untill the 1980's when it began to decrese, while at Russell Bank it increased untill the mid-1960's then slightly decreased in 1970's before increasing again after the early 1980's. Salinity at Bob Allen had slowly decreased since the beginning of the 20th century. The reconstructions indicate that the central and western parts of the bay experienced fluctuations earlier in the record. Nutrient and TOC conditions were variable throughout the records without linear trends, although peaks were observed in 1980's and 1990's that might be related to seagrass die-offs and algae blooms that happened in the bay during the same time. Reconstructions of the abundance of diatom assemblages typical of different ecosystem types revealed that physical processes such as erosion, deposition, sediment transport and water circulation significantly influence species composition at the coring sites. Reconstructions of the abundance of dominant assemblage type (plankton, epiphyton, epipelon) were inconclusive due to the very dynamic hydrology of Florida Bay that induces significant assemblage mixing.

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National Science Foundation logo This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DEB-1237517, #DBI-0620409, and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
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