Repeated low-dose copper algaecide treatments promote beneficial phytoplankton and zooplankton communities

Authors: MCDONALD, M - Auburn University; HENNESSEY, A - Auburn University; JOHNSON, P - Auburn University; GLADFELTER, M - Auburn University; MERRILL, K - Auburn University; TENISON, S - Auburn University; GANEGODA, J - Auburn University; HOANG, T - Auburn University; Torbert Iii, Henry; Beck, Benjamin; WILSON, A - Auburn University

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2025
Publication Date: 10/4/2025
Citation: Mcdonald, M.B., Hennessey, A.V., Johnson, P.P., Gladfelter, M.F., Merrill, K.L., Tenison, S.E., Ganegoda, J.S., Hoang, T.C., Torbert III, H.A., Beck, B.H., Wilson, A.E. 2025. Repeated low-dose copper algaecide treatments promote beneficial phytoplankton and zooplankton communities. Journal of Environmental Management. 394:127502. https://doi.org/10.1016/j.jenvman.2025.127502.
DOI: https://doi.org/10.1016/j.jenvman.2025.127502

Interpretive Summary: Effective harmful algal bloom (HAB) control is critical for improving and maintaining water quality. Common treatment strategies, such as copper sulfate pentahydrate treatment with alkalinity-based dosing, often prescribe higher doses than may be necessary to achieve HAB control in many systems. A study evaluated the performance of a previously developed multiple linear regression (MLR) based copper dosing method that uses only pH and dissolved organic carbon (DOC) to determine an optimal dose when compared to alkalinity-based doses after repeated copper treatments. A 42 day field based mesocosm experiment was conducted in a hypereutrophic aquaculture pond where an MLR based dose and half of this dose and the alkalinity-based dose common application practices in aquaculture were compared. Initially, all copper treatments saw an identical ~95% reduction in cyanobacteria, indicating that lower doses are as effective as the higher alkalinity-based doses for HAB control. Moreover, the lower, MLR-based doses caused less harm to beneficial chlorophytes and zooplankton. Overall, these results demonstrate that the MLR-based Cu dosing strategy offers superior long-term control of HABs with less ecological impact than higher, alkalinity-based Cu dosing.

Technical Abstract: Effective harmful algal bloom (HAB) control is critical for improving and maintaining water quality. Common treatment strategies, such as copper sulfate pentahydrate treatment with alkalinity-based dosing, often prescribe higher doses (> 0.25 mg/L Cu) than may be necessary to achieve HAB control in many systems. This study evaluated the performance of a previously developed multiple linear regression (MLR) based copper dosing method that uses only pH and dissolved organic carbon (DOC) to determine an optimal dose when compared to alkalinity-based doses after repeated copper treatments. A 42 day field based mesocosm experiment was conducted in a hypereutrophic aquaculture pond where an MLR based dose (80 µg/L Cu), half of this dose (40 µg/L Cu) and the alkalinity-based dose (350 µg/L Cu) were applied every 14 days (3x across the experiment) to mimic common application practices in aquaculture, recreational pond, and drinking water management. Initially, all copper treatments saw an identical ~95% reduction in cyanobacteria, indicating that lower doses are as effective as the higher alkalinity-based doses for HAB control. Moreover, the lower, MLR-based doses caused less harm to beneficial chlorophytes and zooplankton over the course of the experiment. Notably, it was observed that the alkalinity-based dose showed decreasing efficacy with each subsequent treatment, indicating that lower doses offer better control of harmful phytoplankton genera over time. Overall, these results demonstrate that the MLR-based Cu dosing strategy offers superior long-term control of HABs with less ecological impact than higher, alkalinity-based Cu dosing.