Lyngbya wollei responses to copper algaecide exposures predicted using a concentration – exposure time ( CET ) model : Influence of initial biomass

Concentration–exposure time models (CET) are used to predict responses of aquatic vascular plants to herbicides and could be applicable for cyanobacterial responses to algaecides if the model captures appropriate variables. For the cyanobacterium Lyngbya wollei, initial biomass upon application may be an important parameter driving responses to copper algaecides. Objectives were to 1) discern an algaecide with sufficient potency and relationship between copper concentration and response for a L. wollei CET model, 2) develop a CET model for the algaecide and L. wollei, 3) determine the influence of initial biomass on measured responses, and 4) develop a new model to predict L wollei responses with biomass as a variable. Emulsified 3.8% copper ethanolamine had sufficient potency ( 90% response), and increasing copper concentrations resulted in increasing responses (R 1⁄4 0.99). Exposures of 0.4, 0.7, and 1.0 mg Cu L 1 for 24 h, exposures of 0.4, 0.7, and 1.0 mg Cu L 1 for 8 h, and exposures of 0.7 and 1.0 mg Cu L 1 for 1 h resulted in 87 to 100% response of L. wollei (percent damaged trichomes). Initial biomasses greater than those used for the CET model (52 g wet weight [WW] m ) decreased responses to nondetect (1,558 g WW m ). Because initial biomass influenced responses, a new model was developed with biomass as a variable (biomass, duration, and concentration [BDC] model). The BDC model increased the range of initial biomasses (13 to 104 g WWm ) in which performance of the copper algaecide for controlling the growth of L. wollei could be predicted.