Holocene paleolimnology and diatom (Bacillariophyta) succession in lakes of the central highlands region of Florida, United States of America.

Abstract

Quantitative analysis of siliceous microfossils was performed on four 1.5-m sediment cores (LA-2, LA-9, LA-25, and LA-31) from Lake Apopka (Lat. N 28&deg; 36&feet;49&inches;, Long. W 81&deg;38&feet;6&inches;) in Orange County, Florida. Stratigraphic changes in sediment texture, chemical composition and diatom successional patterns were observed in each core. Based on <super>210</super>Pb analysis, the top 65 cm of core LA-9 was estimated to contain 130 years of sediment accumulation. Diatom analysis indicated a succession of diatom taxa and an increase in absolute and relative diatom abundance in all core samples at the transition to unconsolidated-flocculent sediments. In surface sediments, <italic>Aulacoseira italica</italic> constitutes &sim;80% of relative abundance. Redundancy analysis indicated that increases in relative abundance of <italic>A. italica</italic>, <italic>Navicula radiosa</italic>, and araphid diatoms were positively correlated (r<super>2</super> = &sim;0.9) with total nitrogen and total phosphorus in the core. A 4.4-meter sediment core sample was obtained from Lake Apopka. Sediments were prepared for microfossil analysis. Five stratigraphic regions were identified based on physical sediment characteristics, diatom absolute abundance and successional changes in diatom assemblages. Sediments contained in diatom Zone 5 were carbon 14 dated to &sim;8540 +/- 220 years before present. Initial diatom assemblages were dominated by benthic-alkaliphilous forms and low absolute abundance. <italic>Mastogloia smithii</italic> var. <italic> lacustris</italic>, an epipelic-alkaliphilous diatom, reaches maximum relative and absolute abundance in diatom Zone 5. Diatom Zone 2 begins (&sim;2500 ybp) with a pulse in planktonic diatom abundance, <italic>Aulacoseira italica</italic> averaging &sim;50% relative abundance. Diatom floras in Zone 2 resemble modern floras, suggesting that a lacustrine zone had formed in Lake Apopka by 2500 ybp. Changes in aquatic chemistry and water balance in Lake Tulane during the Pleistocene-Holocene transition produced successional patterns of diatom assemblages. Overall, diatom floras contain over 50% alkaliphilous taxa. Intervals 2858 cm, 2846 cm and 2828 cm contain over 65% alkaliphilous taxa and were dominated by <italic>Cyclotella plitvicense</italic> and <italic>Aulacosiera crenulata</italic>, both planktonic-alkaliphilous taxa. Intense stratification of habitats based on pH regimes was suggested by the complex diatom flora contained in sediments of Lake Tulane.