In situ field trial to evaluate the efficacy of Cutrine Ultra to manage a cyanobacteria population in a drinking water source

Algaecides can be used to effectively control a rise in cyanobacteria population. However, too high a concentration or long-term applications can pose detrimental effects on the ecosystem. This work investigated the potential of a copper-based algaecide to effectively manage the cyanobacteria population in a public water system when applied at a lower concentration. The cyanobacteria population (via phycocyanin) and chlorophyll-a concentration were tracked with optical probes over 14 days. The cyanobacteria population responded to the treatment within 2 days with the largest declines observed deeper in the water column and only marginal changes at the surface. The lowest cyanobacteria population was observed after 7 days for all depths in the water column with a 53% decrease at the surface. However, the cyanobacteria population increased by 14 days after treatment. The population at the 1 m depth increased by 151%, surpassing the initial population. There were notable differences between the cyanobacteria and chlorophyll-a data. For example, from 7 to 14 days, chlorophyll-a at the surface decreased by 26% whereas cyanobacteria exhibited a 74% increase. This may be highlighting a shift to cyanobacterial dominance in the phytoplankton community. This work produced strong evidence that algaecide application was successful in suppressing the in situ cyanobacteria population. However, it cannot be determined if the treated population rebounded or if new cyanobacteria entered the treatment area due to external environmental conditions such as flow and/or wind conditions. Careful application of lower algaecide concentrations may yield effective control of HABs with minimal harm to the surrounding ecosystem.