Costs and efficacies vary, and there are many competing considerations, some site-specific. The methods themselves, and the science of when, whether, and how to use them, are works in progress.
Algaecides: This method uses chemicals to control algae and cyanobacteria in water supplies. Many chemical treatments are inexpensive compared to other methods, but can affect other species, trigger release of toxins from within algal cells, accumulate in the environment, or entail other problems. Only EPA- and state-approved algaecides are legal, and many states require certification prior to application.
Barley Straw: Decomposing barley straw produces biological compounds that can control algae and cyanobacteria. It is generally affordable and has been used in many reservoirs and dams in the United Kingdom with positive results. Other results in the lab and the field, however, are ambiguous. The decomposition of barley straw consumes oxygen, of potential concern in those water bodies where dissolved oxygen is already low.
Biologically Derived Control: Barley straw byproducts are only some of the plant-derived substances that limit the growth of cyanobacteria. In aquatic environments, these degrade more quickly than algaecides but can have low efficiency, and cyanobacteria may adapt to their effects. Biological control substances are still in early stages of development as an HCB control method and many substances are still difficult to obtain.
Circulation: Lakes that thermally stratify during warm summer weather are often susceptible to some of the highest concentrations of cyanobacteria. Artificial methods to increase circulation and limit stratification, such as aerators and mixers, can inhibit the growth of blooms. These methods generally are deployed before blooms appear.
Flocculants: Flocculants such as aluminum sulfate, sodium aluminate, native clays, chitosan, and lanthanum clay limit HCBs by binding and settling out biologically available phosphorus, a key nutrient on which cyanobacteria feed. Some products may prove toxic to aquatic life if improperly applied. In addition to other considerations, some form high-volume masses of flocculent material that can coat sediment at the bottom of the water body if not removed after treatment.
Ultrasound (Sonic Blasters): Ultrasound in water can be used to damage cyanobacteria cell walls and membranes, killing the cells or rupturing the gas vacuoles that allow them to move vertically in the water column. Bacteria so injured cannot take advantage of both light at the surface and nutrients below the surface. Treatment must be repeated to be effective, and like many other methods, the cost is proportional to water body size. Cell disruption may lead to the release of cyanotoxins that may affect other organisms.
Adapted from “Harmful Algal Bloom Control Methods Synopses,” developed by the NEIWPCC HAB Workgroup’s Control Methods–Best Management Practices Focus Team.
This adaption is a companion piece published with “A Study in Cyan” in the March, 2016, issue of the Interstate Water Report. The Cyan article looks at the problem of cyanobacteria and is available online and as a reprint.
The reprint includes “Controlling and Treating Cyanobacteria Blooms.” The Interstate Water Report is the predecessor of Interstate Waters, NEIWPCC’s twice-annual magazine.