Relative Sensitivity of Cyanobacteria to Copper Herbicides and Effectiveness of Utilizing Copper Bioavailability Approach to Treat Harmful Algal Blooms in Pond Aquaculture Systems

Abstract

Harmful algal blooms (HABs) can pose ecological and economic risks to the aquaculture industry. Copper (Cu) has been widely used to treat HABs. Cu doses are usually calculated using a traditional alkalinity model, which might not be totally relevant because Cu toxicity to aquatic organisms is not only influenced by alkalinity but also other water quality parameters, such as pH, natural organic matter, hardness, and species of organisms. This thesis studied the different sensitivities of cyanobacterial species to Cu and the treatment efficacy when Cu bioavailability and species sensitivity approach was applied. Among three cyanobacterial genera studied in the laboratory condition, (Microcystis spp., Anabaena spp., Oscillatoria spp., and UTEX 3037) Oscillatoria spp. was the most sensitive to Cu. Microcystis spp. and UTEX 3037 displayed similar sensitivity to Cu and were most Cu tolerant genera. Based on the findings, pond trials were conducted to study the treatment efficacy using a bioavalability-based Cu dosing with the adjustment to species specific to the pond systems. Overall, post-Cu treatment monitoring revealed a fast and selective reduction in cyanobacterial populations, a subsequent increase in green algae, and no detrimental effects on zooplankton. The bioavailability-based method necessitated less copper than the traditional alkalinity model, hence decreasing treatment expenses and Cu load into pond systems. This thesis emphasizes the necessity of incorporating species-specific sensitivity and water chemistry into copper treatment methods to enhance efficacy and management of HABs in aquaculture pond systems.