Surface film of cyanobacteria (formerly called blue-green algae)
Until recently, this surface film was considered a form of “blue-green algae”. We now know that there is no such thing as “blue-green algae”. Blue-green algae are actually classified as bacteria and are correctly called cyanobacteria. As bacteria, they are mobile and can rise and sink through the water column. They have chlorophyll and can produce food for themselves through photosynthesis. Possible colors range from yellow to red to violet to green to deep blue, blue-green, gray and black.
Probably the oldest living forms of life, cyanobacteria are not well understood. They exist everywhere. Nevertheless, nuisance blooms are increasingly troublesome throughout the Southeast. Cyanobacteria blooms are nuisances because they are ugly, smell bad and can produce toxins. Rarely the toxins have been associated with deaths of fish and livestock drinking the water. The blooms are not very stable and often crash in a relatively short period of time.
Unlike desirable plankton, cyanobacteria do not contribute significant amounts of dissolved oxygen. Cyanobacteria reproduce relatively slowly, about 1 time per day. Dead decomposing cells consume available dissolved oxygen. They are also not good oxygen producers like green plankton algae. The slow recovery of low oxygen levels contributes to occasional fish kills.
Excessive blooms are not likely in lake and ponds we manage. As a result of “Preventive Year-round Service” (our routine management), you are not likely to see fish kills and toxicity. We usually see short-lived thin surface films that are simply unattractive. Managing cyanobacteria is very important to us. We’ve diligently researched the physical/chemical and biological factors that may potentially provide control. The factors include:
Agitation – Flushing, mixing and turbulence all reduce cyanobacteria growth. If water flushes through the lake faster than the nuisance can bloom, problems are reduced. If mixing can overcome the ability of the bacteria to maintain its position in relation to light and available nutrients, growth is reduced. Shear turbulence can disrupt colonies and break up filaments. Aeration with fountains, and even diffused air bubbles, can significantly reduce surface film formation.
Shading – With limited light available, photosynthesis is inhibited. The concentration of the bloom and the composition of the species present are affected by the amount of light available and the depth of light penetration through the water. Shading can be effective for reducing numbers. Lake colorants are one way to provide shading.
Temperature – Warm water temperatures, above 80oF. are associated with cyanobacteria blooms. Warm water is less dense than cooler water. Therefore, the warm water actually “floats” causing stratification allowing surface water to warm dramatically. Through contact with the air at the surface of the water, nitrogen and carbon dioxide can be used by cyanobacteria as food sources.
Excess nutrients – High levels of phosphorus are associated with cyanobacteria blooms. If the nutrients are reduced for months and years, blooms have been shown to diminish.
pH – Low pH (acidic water) tends to inhibit growth of cyanobacteria. When the pH is above 8.0 problems increase. Regular additions of lime can buffer the pH and reduce high pH conditions.
Salinity (or salt content) – Although cyanobacteria occur in salt water, research shows the nuisance species can be controlled by 1 – 5 parts per thousand of salt. Therefore, each acre-foot of water would require 270 – 1,350 pounds of salt. We have been very unimpressed with results from using salt for control.
Iron – Apparently, cyanobacteria are capable of out-competing algae for limited levels of iron. When high nitrogen and phosphorus levels exist in the lake, adding iron may encourage the growth of desirable green algae. We are still trying to learn more about possibly adding iron.
Fish: Tilapia are fish that eat algae and will grow while eating cyanobacteria. However, the fish are tropical and will die when water temperatures drop below about 50oF. Therefore, they have to be stocked each spring. We have found that if we stock 50 – 100 tilapia per acre in the Spring, they will effectively control nuisance growth of some algae. Tilapia reproduce abundantly. However, availability is limited and predators may eat small fish. The fish cannot be stocked until the water temperature is consistently above 70oF in the Spring. We have had trouble maintaining effective populations in some lakes and ponds.
Beneficial bacteria concentrates: Although results are somewhat inconsistent, beneficial bacteria concentrates may compete with cyanobacteria for available nutrients. Revive is the product we use. It is a dry powder with 25 billion viable microorganisms and 18 billion spores per gram. A bran carrier contains a “conditioned” media that serves as nourishment when the powder is mixed with pond water. Supposedly, this allows the bacteria to double every 20 minutes. Furthermore, the spores germinate to the vegetative, active growing form.
Barley straw: We are not allowed to claim barley straw might “control” algae growth since it has not been registered as a pesticide by the United States EPA. However, it’s popularity for “clarifying” ponds in Europe for generations has spread to the United States. We use it in some situations, but results have not been consistent.
All of these factors are considered in our control activities. The surface film types of cyanobacteria actually represent a very small volume of material in lakes/ponds. If you could strain it out, it would only be a “handful”. It is simply very noticeable. We are fairly successful sometimes at controlling the volume, but we have not been able to entirely eliminate the persistent species. We believe many times treating cyanobacteria with chemicals simply makes it persist longer. Often we find that if the client is willing to live with it for a week or two, it will go away.
As the summer progresses the problem will be going away as the water cools and the sun gets lower in the sky. Depending upon your lake’s characteristics, our strategy for next year may include:
· Adding a phosphorous binding chemical that reduces one essential nutrient required for cyanobacteria growth.
· Adding an algaecide that kills the cyanobacteria cells and includes a phosphorous binding chemical to reduce the essential nutrient.
· Adding barley straw twice per year.
· Apply the Revive beneficial bacteria/enzyme concentrate at 3 pounds per acre-foot in March and at least 1 pound per acre-foot each month through September. Treatments lost to flushing will be re-applied. We expect the beneficial bacteria to consume the nutrients required by the cyanobacteria.
· We will continue to add the colorants as necessary to limit light penetration.
· Depending upon size, we may stock 50 – 100 blue per acre in May. The fish will be filtering the cyanobacteria from the water and growing.
· We will monitor stratification of the water column. Aeration with diffused air or fountains is always advantageous. If we find the fountains are not mixing the lakes, we can often add a sleeve so the fountain water intake is close to the lake bottom.
· If determined to be effective, algaecides will be used at a higher rate as a last result. We believe our past methods allowed a resistant species to endure at relatively low but ugly levels.
Additional options to consider include liming the lakes and reducing the amount of fertilizer entering the lakes. Adding lime should buffer the water chemistry and reduce the high pH levels often found during the afternoon. We have specifically formulated lawn fertilizer available for use in lake watersheds. Adding non-invasive shoreline plants or particularly floating plant rafts should reduce nutrients. Very shallow ponds can benefit from dredging to make them deeper. We will be happy to provide more information if you are interested.
Foster Lake & Pond Management provides the full range of lake, pond and stormwater BMP services and products. These include: construction, repairs, maintenance, certified inspections, fish stocking, fisheries management, lake mapping, vegetation management, docks, fountains and aeration.
We have provided aquatic and stormwater solutions to our North Carolina customers for 30 years. Call us at: 919-772-8548 or visit: www.FosterLake.com.