Controlling Algae?


The most important parameters regulating algal growth are nutrient quantity and quality, light, pH, turbulence, salinity and temperature. Light is the most limiting factor for algal growth, followed by nitrogen and phosphorus limitations, but other nutrients are required including carbon. Biomass is usually measured by the amount of chlorophyll a in the water column.  Water temperature influences the metabolic and reproductive rates of algae. Most species grow best at a salinity that is slightly lower than that of their native habitat,  The pH range for most cultured algal species is between 7 and 9, with the optimum range being 8.2-8.7. Through photosynthesis, algae produce oxygen in excess of respiratory requirements during daylight hours. Conversely, during low light or nighttime periods algae respire (consume) dissolved oxygen, sometimes depleting water column concentrations. Thus, high algae concentrations may lead to low dissolved oxygen concentrations.

A common solution for algae is copper sulfate.  Copper Sulfate works to kill the algae, but when it dies, it settles to the bottom of the water body where it becomes a carbon source for bacteria and future algae.  One will often see shallow ponds with rising algae.  But there is significant concern about copper in coastal water bodies.  Copper is toxic to marine organisms so USEPA and other regulatory bodies are considering the limits on copper use.  Such a limitation would severely limit options in dealing with algal blooms near coastal waters.

Mixing is necessary to prevent sedimentation of the algae, to ensure that all cells of the population are equally exposed to the light and nutrients.  So oxygenation can help (it also mixes the water.  The depth of south Florida water bodies is problematic (shallow and therefore warmer than normal).  But oxygen will help microorganisms on the bottom consume the carbon source on the bottom, which might slow algal growth.  Analysis is ongoing.

Two other conditions work against controlling blue-green algae outbreaks: climate change and political/regulatory decision-making.  Lake Okeechobee has routine algal blooms from the nutrients introduced from agriculture and runoff around the lake, which encouraged an artificial eutrophication of the lake years ago.  It continues today.  Warmer weather will encourage the algal blooms in the future.  The decisions to discharge the water without treatment is a political one.  From a regulatory perspective, algae is seen as a nuisance issue, not a public health or environmental issue.  But algal blooms consume oxygen and kill fish, so the ecosystem impact is considerable – it is not a nuisance .

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