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A 2,500-year record of environmental change in Highlands Hammock State Park (Central Florida, U.S.A.) inferred from siliceous microfossils
Authors:Christof Pearce  Holger Cremer  Emmy Lammertsma  Friederike Wagner-Cremer
Institution:1. Centre for Past Climate Studies, Department of GeoSciences, Aarhus University, H?egh-Guldbergs Gade 2, DK-8000, Aarhus C, Denmark
3. Palaeoecology, Laboratory of Palaeobotany and Palynology, Institute of Environmental Biology, Faculty of Science, Utrecht University, Budapestlaan 4, 3584 CD, Utrecht, the Netherlands
2. Netherlands Organization for Applied Scientific Research TNO, Geological Survey of the Netherlands, Princetonlaan 6, 3584 CB, Utrecht, the Netherlands
Abstract:Analysis of siliceous microfossils of a 79 cm long peat sediment core from Highlands Hammock State Park, Florida, revealed distinct changes in the local hydrology during the past 2,500 years. The coring site is a seasonally inundated forest where water availability is directly influenced by precipitation. Diatoms, chrysophyte statospores, sponge remains and phytoliths were counted in 25 samples throughout the core. Based on the relative abundance of diatom species, the record was subdivided into four diatom assemblage zones, which mainly reflect the hydrological state of the study site. An age-depth relationship based on radiocarbon measurements of eight samples reveals a basal age of the core of approximately 2,500 cal. yrs. BP. Two significant changes of diatom assemblage composition were found that could be linked to both, natural and anthropogenic influences. At 700 cal. yrs. BP, the diatom record documents a shift from tychoplanktonic Aulacoseira species to epiphytic Eunotia species, indicating a shortening of the hydroperiod, i.e. the time period during which a wetland is covered by water. This transition was interpreted as being triggered by natural climate change. In the middle of the twentieth century a second major turnover took place, at that time however, as a result of human impact on the park hydrology through the construction of dams and canals close to the study site.
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