Copper Compounds as Algaecides

Copper Sulfate Use in Algae Control: Short-Term Benefits, Long-Term Consequences

Copper sulfate and related copper compounds have long been used to control unwanted algae in lakes and ponds. These treatments involve spreading copper sulfate crystals or powder in affected areas or spraying a slurry over the water surface. While copper sulfate is generally effective at quickly killing floating algae mats, its control effects are very short-lived, and its negative impacts can persist much longer.

How Copper Sulfate Works and Its Limitations

After application, copper ions in the water become highly reactive for about two hours. During this time, copper binds with carbonate ions to form copper carbonate, which then settles out of the water column. This means copper is only actively toxic to algae for a brief period. Research by Button et al. (1977) in Ohio ponds showed that copper levels return to normal within two hours after treatment. While algae exposed during this window may die, new algae begin to grow soon after as nutrients from the decaying algae are released back into the water, fueling further growth.

Impact on Beneficial Organisms and Algae Growth

Copper sulfate doses needed to kill algae are 10 to 100 times higher than those that harm beneficial zooplankton—tiny aquatic animals that naturally filter algae. Killing these algae-grazing organisms can lead to increased algae blooms following treatment. Cooke and Kennedy (2001) highlight that low copper levels are toxic to zooplankton, causing a rebound effect where algal biomass surges after copper precipitates out of the water.

Risks in Drinking Water Ponds

Copper sulfate treatments can also trigger the release of toxins from blue-green algae, some of which are harmful to humans and pets—causing symptoms ranging from gastrointestinal distress to liver failure or death (Hitzfeld et al. 2000). Blue-green algae blooms tend to worsen when algae-grazing zooplankton are reduced, a common consequence of copper use. Moreover, copper can cause blue-green algae cells to rupture, releasing dangerous hepatotoxins into the water (Lam et al. 1995). Since these toxins are difficult to remove through standard water treatment, preventing their production is critical.

Effects on Bottom-Dwelling (Benthic) Organisms

Copper ions quickly precipitate and accumulate in bottom sediments, where they reduce the diversity and abundance of benthic organisms essential for ecosystem health. In particular, copper inhibits beneficial bacteria that decompose organic matter. Without these microbes, dead material builds up on the pond bottom, accelerating pond filling and degradation. In contrast, healthy microbial communities slow this process by breaking down organic debris.

Conclusion: Rethinking Copper Sulfate Use

While copper sulfate can provide a rapid but temporary fix for algae problems, the long-term ecological consequences are significant. Its use can upset pond ecosystems, accelerate sediment buildup, and increase risks associated with toxic algae blooms. For sustainable algae control, it is better to avoid copper treatments and adopt a Holistic Approach combining aeration, microbial augmentation, and physical removal of algae.

References:
Button, K.S., Hostetter, H.P., & Mair, D.M. (1977). Copper dispersal in a water supply reservoir. Water Research, 11, 539-544.
Cooke, G.D., & Kennedy, R.H. (2001). Managing drinking water supplies. Lake and Reservoir Management, 17(3), 157-174.
Hitzfeld, B.C., Hoger, S.J., & Dietrich, D.R. (2000). Cyanobacterial toxins: Removal during drinking water treatment, and human risk assessment. Environmental Health Perspectives, 108, 113-122.
Lam, A.K.-Y., Prepas, E.E., Spink, D., & Hrudey, S.E. (1995). Chemical control of hepatotoxic phytoplankton blooms: Implications for human health. Water Research, 29, 1845-1854.