Changes in water chemistry in a macrophyte-dominated lake before and after herbicide treatment

Abstract

Lake Istokpoga is the fifth largest freshwater lake in Florida, and is widely renowned for its abundance of sport fish. By 1988, an infestation of the exotic aquatic weed hydrilla, had severely impacted many water related functions on Lake Istokpoga. Beginning in 1988, the lake was treated with fluridone to control hydrilla. Five years (1988–1992) of water chemistry data are presented in this paper, representing pre- (Feb.-Dec. 5, 1988) and post- (Dec. 20, 1988-Dec. 1992) herbicide application periods. Trophic state variables were calculated to characterize lake condition. Reductions in hydrilla populations through herbicide treatments caused increases in total phosphorus and chlorophyll a concentrations, and decreases in Secchi depth. No significant increases in the total nitrogen concentrations were observed between the before and after treatment periods. Fluridone treatment of Lake Istokpoga cost approximately $3.7 million (through 1992), and was only temporarily effective at controlling hydrilla. © 1995 Taylor & Francis Group, LLC.