Efficacy of three algaecides on algal blooms in hypereutrophic lakes -

Abstract

Cyanobacterial blooms are an emerging problem worldwide, affecting many important freshwater systems. The proliferation of these blooms has been linked to public health concerns and to the impairment of the designated uses of several fresh water systems. Several studies have linked the increase in bloom frequency to anthropogenic activities, particularly increased nutrient loading. While basin-level management measures that aim to control nutrient loading are the most effective on the long-term, they are hard to implement given socio-economical constrains. As such, the use of chemical algaecides can provide a viable short-term mitigation measure that aims to control these blooms. In this study, the efficacy of three algaecides, namely Copper Sulfate, Potassium Permanganate, and Diquat, was examined with regards to controlling two toxin-releasing cyanobateria, Aphanizomenon flos-aquae and Microcystis aeruginosa. The efficacy of each algaecide was quantified under laboratory conditions over a range of selected dosages. The results showed that Diquat and Copper Sulfate were significantly more effective than Potassium Permanganate in controlling Microcystis; yet all three algaecides were found to be effective in controlling Aphanizomenon blooms. Reduction rates for both cyanobacteria varied temporally, with the largest drop in concentration recorded between 48 and 72 hours of treatment. Following algaecide application, regrowth was observed for Microcystis aeruginosa but not for Aphanizomenon flos-aquae. The experimental findings are then used to provide recommendations on optimal dosages for each algaecide taking into account the type of cyanobacteria bloom.