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Research Project: Sustaining Productivity and Ecosystem Services of Agricultural and Horticultural Systems in the Southeastern United States

Location: Soil Dynamics Research

Title: Investigating the role of pH effects on the efficacy of copper sulfate pentahydrate in mitigating harmful algal blooms and off-flavors

Author
item HENNESSEY, A - Auburn University
item MCDONALD, M - Auburn University
item JOHNSON, P - Auburn University
item GLADFELTER, M - Auburn University
item MERRILL, K - Auburn University
item TENISON, S - Auburn University
item GANEGODA, J - Auburn University
item HOANG, T - Auburn University
item Torbert, Henry - Allen
item WILSON, A - Auburn University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/20/2024
Publication Date: 3/19/2024
Citation: Hennessey, A.V., Mcdonald, M.B., Johnson, P.P., Gladfelter, M.F., Merrill, K.L., Tenison, S.E., Ganegoda, J.S., Hoang, T.C., Torbert III, H.A., Wilson, A.E. 2024. Investigating the role of pH effects on the efficacy of copper sulfate pentahydrate in mitigating harmful algal blooms and off-flavors [abstract]. Auburn University Climate Symposium, March 22, 2024, Auburn, AL.

Interpretive Summary:

Technical Abstract: Harmful algal blooms (HABs) have significant impacts on aquatic ecosystems, threatening water quality, aquatic organisms, and generating off-flavor compounds. Copper sulfate pentahydrate (CuSO4·5H2O) has been utilized as an algaecide for decades due to its affordability and its status as one of the only chemicals permitted by the FDA for aquaculture use. Concerns about the non-target environmental effects and efficacy of routine treatments have prompted the exploration of alternative strategies. This project aims to assess the potentially synergetic effects of low-dose CuSO4·5H2O treatments after manipulating pH with carbon dioxide (CO2). Copper sulfate pentahydrate becomes more effective at lower pH; therefore, when the addition of CO2 reduces the pH in the water column as CO2 converts to carbonic acid, it is hypothesized to increase the toxicity of CuSO4·5H2O to cyanobacteria. To test this hypothesis, twenty ~1600L in-situ mesocosm enclosures were placed in a eutrophic pond and treatments were added once in a full dose (330 µg/L CuSO4·5H2O) or quarter dose (82 µg/L CuSO4·5H2O) relative to untreated control, with half of each of these treatments receiving CO2 additions at the beginning of the experiment. After treatment, the enclosures were monitored for 28 days. The CO2 addition dropped the water column pH in the enclosures from 9.1 to 7.5 and it remained that low for the first 3 days. By day 7, pH had slowly recovered to 8.3 and continued to rise throughout the remainder of the experiment. Results indicated that the addition of CO2 for the quarter dose of CuSO4·5H2O resulted in 15% more removal of cyanobacteria and 23% more removal of off-flavors in the first 24 hours. After day seven, enclosures with both CuSO4·5H2O and CO2 additions dramatically promoted beneficial green algae while successfully mitigating cyanobacteria and off-flavors, compared to enclosures that were treated with only CuSO4·5H2O (no CO2). The results of this experiment provide valuable information to water resource managers on how to best utilize CuSO4·5H2O in the mitigation of HABs.