Setting Water Quality Goals for Restoration of Lake Apopka: Inferring Past Conditions

ABSTRACT

Lake Apopka is a large (12,500 ha), hypertrophic lake in central Florida which is the subject of a state-sponsored restoration program. We used three quantitative methods in concert with an analysis of the history and general character of the lake and drainage basin to infer the past conditions. We specifically examined two past conditions: 1) pristine (before any major anthropogenic disturbance) and 2) antecedent (before a specific, major anthropogenic disturbance). For Lake Apopka the pristine condition ended in the 1890s when a canal was dug which lowered the elevation for surface water outflow. The antecedent condition ended in the late 1940s when most of the lake's 8,900 ha of floodplain marsh was drained for farming. History, general lake and basin characteristics, and the quantitative analysis indicate that Lake Apopka was mesotrophic; with clear-water and native, submersed macrophyte beds; in both the pristine and antecedent conditions. The three quantitative methods (reference lakes, empirical models, and a loading model) were used to infer the ranges of most probable values in the antecedent condition for total phosphorus, chlorophyll a and Secchi depth. These ranges were 32–51 mg·m⁻³ for total phosphorus, 8–38 mg·m⁻³ for chlorophyll a, and 1.39–0.76 m for Secchi depth. Lake Apopka has had a history strikingly similar to that described for Dutch lakes affected by cultural eutrophication with proliferation of macrophytes in the clearwater state preceding a rapid transition to the turbid, algal-dominated state induced by a large increase in the phosphorus loading rate.

Key Words:

• lake restoration goals
• water quality
• Lake Apopka
• hypereutrophic