Preventative Measures for Cyanobacterial HABs in Surface Water
Preventative measures are the preferred approach to managing HABs. The most effective preventative measures are those that seek to control the primary drivers of HABs, most importantly discharge or runoff of excess nutrients. Management practices for nutrients, specifically nitrogen and phosphorus, should have the goal of reducing loadings from both point and nonpoint sources, including water treatment discharges, agricultural runoff, and stormwater runoff.
Nutrient Pollution Control to Prevent and Reduce HABs
The EPA continues to work diligently to combat nitrogen and phosphorus pollution in U.S. water bodies. The agency’s comprehensive Nutrient Pollution program offers a wide range of actions and tools that the public and our Tribal, state and territorial partners can use to prevent and reduce nutrient pollution. Learn about these activities and tools on EPA’s Nutrient Pollution website:
You can also learn what EPA is doing to reduce nutrient pollution and, in turn, help reduce HABs and other negative effects:
EPA’s efforts on nutrient reduction to mitigate HABs occur not only at the national scale but also in particular geographic areas. For example, EPA’s Great Lakes National Program Office coordinates U.S. efforts with Canada under the Great Lakes Water Quality Agreement to restore and maintain the chemical, physical and biological integrity of the Great Lakes Basin Ecosystem, including focused efforts on nutrient pollution control to reduce HABs in Lake Erie:
Learn more about ways to prevent blooms and protect water resources:
- Preventing Eutrophication: Scientific Support for Dual Nutrient Criteria Fact Sheet (pdf)
- Great Lakes Water Quality Agreement, Nutrient Annex 4- Recommended Binational Phosphorus Targets to Combat Lake Erie Algal Blooms
- US EPA Watershed Framework Approach
- US EPA Watershed Analysis and Management (WAM) Guide for States and Communities
- Strategies for Preventing and Managing Harmful Cyanobacterial Blooms (HCB-1), Chapter 6. Management and Control Strategies for HCBs. Interstate Technology Regulatory Council
Other Prevention Measures
While controlling nutrient pollution is the main way to prevent HABs, there are other approaches that can also be used at certain sites to prevent HABs from occurring or reoccurring. For example, because nutrients can be stored in sediments and cycle through the water column periodically (called “internal loading”), contributing to the formation of HABs, there may be need for HAB prevention approaches to be used while nutrient reduction efforts proceed.
One approach uses devices that mix the layers of water in lakes (for example, by air bubbling), resulting in enhanced vertical mixing of the phytoplankton and minimized formation of surface blooms made of floating cyanobacteria. Increasing water flow through lakes might also be used to prevent cyanobacteria blooms. Table 1 provides some examples of waterbody measures to prevent HABs in surface waters. These site-specific examples can be expensive and are best suited to small, affected water bodies.
Learn about other HAB prevention strategies:
DISCLAIMER: U.S. EPA does not endorse any of the measures presented on this page.
Table 1. Examples of Waterbody Management Measures to Prevent HABs
| Waterbody Management Measure to Prevent HABs | Description | Benefits | Limitations |
|---|---|---|---|
| Biological Measures | |||
| Floating Treatment Wetlands (FTW) | Consists of emergent wetland plants growing on floating mats on the water’s surface. The plant’s roots provide enough surface area to filter and trap nutrients. FTWs also encourage biofilm processes that reduce cyanobacteria levels. Periodic harvesting of mature plants is conducted to prevent stored nutrients from re-entering the aquatic ecosystem, mitigating risk of HABs by keeping nutrient levels in balance. |
Assimilates nutrients and encourages particle adsorption. Covered surface area minimizes light penetration and limits opportunity for algae growth. Able to tolerate fluctuations in water depth. Utilizes natural processes with minimal technical attention required. |
Often dependent upon the amount of input (i.e., the number of plants and mats). Excessive coverage can lead to de-oxygenation of the water. Plants only have access to nutrients in the water column and not ones in sediment. |
| Physical Measures | |||
| Aeration | Aerators pump air throughout the water column to disrupt stratification. Many operate by pumping air through a diffuser near the bottom of the water body, resulting in the formation of plumes that rise to the surface and create vertical circulation cells as they propagate outwards from the aerator. | Limits the accessibility of nutrients to the surface. Disrupts the behavior of cyanobacteria to migrate vertically. Reduces competitive advantage of cyanobacteria by maintaining healthy levels of dissolved oxygen. |
Individual devices have limited range; areas further away may remain stratified and provide a suitable environment for growth. De-stratification of the water column may harm aquatic habitats that rely on colder bottom temperatures. |
| Mechanical Circulation | Mechanical circulators operate by pumping water from the surface layer downwards or draw water up from the bottom to the surface layer. Similar to aerators, mechanical mixers interfere with stratification of the water column, intercepting conditions ideal for HABs to occur. | Limits the accessibility of nutrients to the surface. Disrupts the behavior of cyanobacteria to migrate vertically. Reduces competitive advantage of cyanobacteria by maintaining healthy levels of dissolved oxygen. |
Individual devices have limited range; areas further away may remain stratified and provide a suitable environment for growth. Certain algae prefer an unstable environment and are benefitted by circulation. |
|
To increase oxygen concentrations in the hypolimnion layer. Mechanisms include submerged oxygen chambers, side stream oxygenation and direct oxygen injection. |
High oxygen delivery rates reduce potential for sediment to release nutrients. Minimizes impact to hypolimnion by maintaining water column structure and temperature (thermocline, pycnocline, etc.). |
Techniques are relatively expensive. Requires a significant understanding of system in order to operate. | |
| Chemical Measures | |||
| Alum, ferric salts, clay (Coagulation and Flocculation) | Alum, ferric salts, or clay can be applied to the water body as coagulants that cause cyanobacteria to settle down away from the top layer of the water body. When applied to water, alum forms an aluminum hydroxide precipitate called a floc. As the floc settles, it removes phosphorus and particulates (including algae) from the water column. The floc settles on the sediment where it forms a layer that acts as barrier to phosphorus. Phosphorus, released from the sediments, combines with the alum and is not released into the water to fuel algae blooms. | Injection of aluminum compounds can be effective at reducing phosphorus levels in the water body. | Effectiveness varies with amount of alum added and depth of water body. The addition of aluminum can impact pH levels of the water body. Best suitable for well-buffered hard water. Buffering soft water lakes with either sodium aluminate or carbonate type salts to prevent undesirable pH shifts that can be toxic to biota may be needed. |
| Barley Straw | Barley straw, when exposed to sunlight and in the presence of oxygen, produces a chemical that inhibits algae growth. Barley straw bales are broken apart and placed in a buoyant net deployed around the perimeter of the water body to facilitate the necessary chemical reactions and natural processes that prevents algae growth. | A low-cost method to preventing HABs. | Amount used depends on size of water. 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 water body due to decay. |