Who’s Winning The Algae War?

Blue-green algae have many weapons in their arsenal to defeat good, edible algae, including the ability to adjust their buoyancy. Blue-green algae can rise to the surface during the day for sunlight, and then sink into nutrient-rich bottom waters to access nitrogen and phosphorus.

Blue-green algae also have other advantages: they contain toxins that can kill zooplankton and other organisms, they can store phosphorus for later use, and they can convert nitrogen gas near the surface into a nutrient. In fact, they have so many advantages that once blue-green algae take over, it is difficult for any good algae to displace them.

When HABs occur, excessive nutrients–i.e., phosphorus–make the bloom grow that much larger. Large algae blooms near the surface also block sunlight to the deeper algae cells. When the deeper cells become light-limited, they can die off at once. As a consequence, bacterial de-composition of the dead algae cells can consume all the available oxygen, resulting in aerobic odor events and fish kills.

Advantages Of Edible Green Algae

Green algae also have major advantages: they start growing earlier in the season and can reproduce many times faster than blue-green algae. When they’re suspended in the water column, green algae can consume the available nutrients very quickly and remain viable throughout the season, making it harder for blue-green algae to gain any traction.

Wind-mixing alone is not enough to help the good algae out-compete blue-green algae because blue-green algae have adapted over millions of years to predictable wind-mixing patterns. Additional circulation may be necessary, and has been shown to be effective in improving water quality.

Limitations Of Chemical And Mechanical Methods As A Solution

Several methods exist for controlling blue-green algae. The most common is aquatic herbicides, such as copper sulfate. Chemicals can provide short-term relief from harmful blue-green algae, at a typical cost of $200 to $1,000 per acre per year, but they have serious ecological impacts, and the long-term effects are unknown. Algaecides can actually create copper-resistant algae, requiring more algaecide applications each year and eventually creating a sterile pond environment.

Devices such as bubblers, aerators and fountains do some mixing, and attempt to infuse a pond with dissolved oxygen, but in shallow ponds they are generally not effective at controlling blue-green algae over a large surface area. Solar-powered and grid-powered long-distance circulation equipment impacts a larger surface area, so the use of this type of equipment is growing in ponds with HAB problems.

Circulation Helps Edible Green Algae Survive

With a pond circulator, water is drawn to the intake from all directions (usually just above the thermocline in a deep pond and closer to the bottom in a shallow pond), pushed upward, and then sent out across the surface in a thin layer. This circulation provides gentle mixing and surface renewal over a large area. Because of this circulation, green algae and diatoms continue to receive sunlight, remaining viable and available to zooplankton all summer long.

The goal of circulation is not to add oxygen to a pond because that’s the work of green algae. Rather, the purpose of circulation is to help the green algae survive. When the green algae survive the levels of zooplankton, fish, dissolved oxygen and pH will stay in balance. The blue-green algae never take over, and the water will remain in a healthy state. It’s a low-maintenance and economical way to ensure that the pond or lake remains the focal point of municipal parks.

Joel Bleth is the president and a co-founder of SolarBee, Inc. The company manufactures solar-powered long-distance circulation equipment for solving water-quality problems freshwater, potable water and wastewater reservoirs.

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