Control Measures for Cyanobacterial HABs in Surface Water
Measures can be employed once blooms have already started occurring to reduce the magnitude, extent or frequency of blooms. The table provides a summary of common physical and chemical measures for cyanobacterial bloom control in surface waters and their respective effectiveness and limitations.
To learn more about ways to manage cyanobacterial blooms visit: Report: Solutions for managing cyanobacterial blooms: A scientific summary for policy makers (PDF) or the ITRC's Strategies for Preventing and Managing Benthic Harmful Cyanobacterial Blooms Management Criteria Tool.
DISCLAIMER: U.S. EPA does not endorse any of the measures presented on this page.
A Summary of Waterbody Management Measures for Cyanobacterial Blooms
| Waterbody Management Measure | Description | Effectiveness | Limitations |
|---|---|---|---|
| Physical Controls | |||
| Aeration | Aerators operate by pumping air through a diffuser near the bottom of the waterbody, resulting in the formation of plumes that rise to the surface and create vertical circulation cells as they propagate outwards from the aerator. This mixing of the water column disrupts the behavior of cyanobacteria to migrate vertically in addition to limiting the accessibility of nutrients. | Successfully implemented in small ponds and waterbodies. May also provide more favorable growth conditions for competing organisms. | Generally more efficient in deeper water columns. Also highly dependent upon the degree of stratification and the air flow rate. |
| Hydrologic manipulations | Manipulation of inflow/outflow of water in the system to disrupt stratification and control cyanobacterial growth. | Easy to implement in controlled systems (i.e., reservoirs, dams, treatment facilities). | Requires sufficient water volume and the ability to control flow. Oftentimes can be expensive. Unintended consequences for other aquatic organisms are likely. |
| Mechanical mixing (circulation) | Mechanical mixers are usually surface-mounted to disrupts the behavior of cyanobacteria to migrate vertically in addition to limiting the accessibility of nutrients. | Successfully pump water from the surface layer downwards or draw water up from the bottom to the surface disrupting the bloom. | Individual devices have limited range; areas further away may remain stratified and provide a suitable environment for growth. |
| Reservoir drawdown/desiccation | Reservoirs and other controlled waterbodies can draw down the water level to the point where cyanobacteria accumulations are exposed above the waterline. Subsequent desiccation and/or scraping to remove the layer of cyanobacteria attached to sediment or rock is required, in addition to the reinjection of water into the system. | Easy to implement in controlled systems (i.e., reservoirs, dams, treatment facilities). | Can have a significant impact on other aquatic organisms in the system. May be expensive and requires a significant input of resources. |
| Surface skimming | Cyanobacterial blooms often form surface scums, especially in the later stages of a bloom. Oil-spill skimmers have been used to remove cyanobacteria from these surface scums. This technique is often coupled with the implementation of some coagulant or flocculant. | Useful method for blooms that are in later stages and have formed surface scums. | This technique cannot be effectively employed until the later stages of a bloom, at which point many of the harmful aspects of a bloom have materialized. Requires proper equipment prior to implementation. |
| Ultrasound | An ultrasound device is used to control HABs by emitting ultrasonic waves of a particular frequency such that the cellular structure of cyanobacteria is destroyed by rupturing internal gas vesicles used for buoyancy control. | Successfully implemented in ponds and other small waterbodies. A single device can cover up to 8 acres. Non-chemical; inexpensive. | Also disrupts cellular functioning of green algae. Effectiveness is dependent upon waterbody geometry and cyanobacteria species. Further research of method is required. |
| Chemical Controls | |||
| Algaecides | Algaecides are chemical compounds applied to a waterbody to kill cyanobacteria and destroy the bloom. Several examples are:
|
Wide range of compounds with a history of implementation. Relatively rapid and well-established method. Properties and effects of compounds are typically well-understood. | Risk of cell lyses and the release of toxins. Thus, is often used at the early stages of a bloom. Certain algaecides are also toxic to other organisms such as zooplankton, other invertebrates, and fish. |
| Barley straw | Barley straw bales are deployed around the perimeter of the waterbody. Barley straw, when exposed to sunlight and in the presence of oxygen, produces a chemical that inhibits algae growth. Field studies suggest significant algistatic effects. Several causes for the observed effects have been suggested; however, the exact mechanism of this process is not well understood. | Studies have shown that decomposed barley straw inhibits the growth of cyanobacteria Microcystis sp. | Does not kill existing algae, but inhibits the growth of new algae. May take anywhere from 2 to 8 weeks for the barley straw to begin producing active chemical. Potential to cause fish kills through the deoxygenation of the waterbody due to decay. |
| Coagulation | Coagulants are used to facilitate the sedimentation of cyanobacteria cells to the anoxic bottom layer of the water column. Unable to access light, oxygen, and other critical resources, the cells do not continue to multiply and eventually die. | Several studies have shown that cells can be coagulated without damage; however, further research is required. Successfully implemented in several treatment facilities. | Subject to depth limitations. Coagulated cells become stressed over time and lyse, releasing toxins to the waterbody. |
| Flocculation | Flocculants are used to facilitate the sedimentation of nutrients to the anoxic bottom layer of the water column, thereby limiting nutrient levels in the waterbody and inhibiting cyanobacterial growth. | Successfully implemented in larger lakes and ponds. | Subject to depth limitations. |