SS3.06 Large Scale Change in Prominent Ecosystems
Date: Wednesday, June 12, 2002
Time: 4:45:00 PM
Location: Lecture Theatre
 
SchelskeCL, Univ. Fla., Land Use and Environmental Change Inst., Gainesville, FL, USA, schelsk@ufl.edu
Kenney, W, F, Univ. Florida, LUECI, Gainesville, FL, USA, kenney@ufl.edu
 
A NEW PERSPECTIVE ON RESILIENCE AND THE CATASTROPHIC SHIFT IN THE PRIMARY PRODUCER COMMUNITY IN LAKE APOPKA, FLORIDA.
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Lake Apopka, a shallow (1.6 m mean depth) hypereutrophic lake, forms the headwaters of the Harris Chain of Lakes. The catastrophic shift in primary producer community structure (PPCS) in 1947 was so rapid that anecdotal accounts report dominant rooted aquatic macrophytes were uprooted by a hurricane and replaced by phytoplankton within a few weeks. An alternate hypothesis is a nutrient-driven shift. PPCS shifted after wetlands were drained from 1942-47 for high-intensity agriculture changing 37% of the lake surface area from a phosphorus sink to a large phosphorus source. Possible factors to explain earlier resilience to nutrient enrichment include a small drainage basin relative to lake surface area and low nutrient content of the major hydrologic inputs (spring water and rainfall). In addition, the Apopka-Beauclair Canal constructed in 1893 established a permanent outflow that diverted wetland drainage to Lake Beauclair and lowered the mean lake level in Lake Apopka 1.0 m providing a competitive advantage for rooted macrophytes in this shallow lake. Sediment records from the two lakes provide evidence to support the new perspective.