Sediment records of phosphorus-driven shifts to phytoplanktondominance in shallow Florida lakes |
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| Authors: | William F Kenney Matthew N Waters Claire L Schelske Mark Brenner |
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| Institution: | (1) Department of Geological Sciences, University of Florida, Gainesville, USA;(2) Department of Fisheries and Aquatic Sciences, University of Florida, 7922 NW 71st Street, Gainesville, USA |
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| Abstract: | Primary producer community structure (PPCS) in shallow lakes isinfluenced by phosphorus (P) load and water column P concentration.Theoretically PPCS may shift between phytoplankton and macrophyte states withintermediate P loading, but phytoplankton dominate when P loading exceeds acritical threshold. We analyzed sediment cores from five shallow, eutrophiclakes (size range: 0.6 to 125 km2) that arephytoplankton dominated to determine whether the development of the currentstate was associated stratigraphically with an increase in sediment total P(TP) and a shift in PPCS. We used sponge biogenic silica(BSiSponges) concentrations and total carbon to total nitrogenratios (TC:TN) as proxies for macrophyte abundance and sediment organic mattersource, respectively. Three stratigraphic groups of sediments were identifiedwith k-means cluster analysis. These samples were grouped by increasing TPconcentrations and decreasing age and identified as macrophyte, transitionaland phytoplankton sediments. Results show that as P loading increased in thelate 19th and early 20th centuries, the lakes producedsediments with an increasing contribution from phytoplankton. Four of our lakesmay represent a subset of shallow lakes because of their large size (30 to 125km2) and relatively rapid historic P enrichment. Inthese Florida lakes, PPCS shifted to phytoplankton dominance with nopaleolimnological record of lake-wide alternating stable states or of lake-widephytoplankton dominance before anthropogenic P enrichment. |
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| Keywords: | Alternative Stable States Eutrophication Lake Apopka Lake Jesup Little Lake Jackson Macrophytes Newnans Lake Orange Lake Phytoplankton Sediment |
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