Nanobubbles one idea for ending toxic blooms in lake

The recent closure of Lone Lake on South Whidbey due to toxic blue-green algae is nothing new but part of what has become an annual summertime event.

It’s a cycle residents, scientists and government officials are hoping to break, possibly with “nanobubbles,” a solar-powered contraption that makes ultrasonic waves or large piles of a chemical that has been used since antiquity as deodorant.

The series of events that led to the toxic problem likely started in the late 1990s when someone emptied an aquarium with fish and aquatic plants into Lone Lake. The fishies probably didn’t live long, but a waterweed native to South America proliferated.

People combated the non-native weed by introducing an Asian carp that can grow up to 80 pounds, but that venture resulted in too many carp and a seasonal overabundance of a blue-green algae that’s not really algae — and may have been key to life on Earth — but can nevertheless be toxic to people and other mammals.

Bowfishing and eagle predation has largely controlled the unwanted fish, but now officials are looking for solutions to the blue-green algae.

The Whidbey Island Conservation District, with a grant from the state Department of Ecology, prepared a detailed Lone Lake Algae Management Plan that outlines the complex causes of the problem and possible fixes.

“Lake management needs to be focused on achieving the appropriate balance between algae and plants since too much of either can be problematic,” the plan states.

In addition, Island County, also with the help of a state grant, has a project to identify and hopefully diminish the source of the phosphorus that is flowing into the lake and contributing to the problem.

The management plan explains that, between 1996 and 2003, the lake was invaded with an exotic water plant called Egeria densa, which entangled boat propellers and reduced the quality of the habitat for trout.

In response, a homeowners association, in cooperation with the county noxious weed board and the state, developed a weed-control plan that started with herbicide followed by the stocking of the lake with grass carp. Unfortunately, the preferred food of the carp turned out to be a native plant, the plan states.

The resulting eradication of native underwater plants, due to the one-two punch of herbicide and carp, was a shift to an algae-dominated lake and an increase in phosphorus. Its nitrogen-limited state benefits blue-green algae, a cyanobacteria that produces anatoxin-A and microcystins and may have oxygenated primordial Earth.

Anatoxin-A, also called “very fast death factor,” is a neurotoxin that can cause lethargy, muscle aches, confusion, memory problems and, at sufficiently high levels, even death in animals and people.

The Department of Ecology reports that a sample from Lone Lake tested at 16 times the limit under the state recreational guideline for anatoxin-A on July 22. Matthew Colston, an Island County environmental health specialist, said the lake will remain closed for public recreation until a test shows the toxin level is below the guideline.

According to historical data from the Department of Ecology, the lake was closed due to anatoxin-A for the past five years.

The Conservation District’s new Lone Lake Algae Management Plan explains that the high amount of nutrients in the lake leads to periodic periods of low oxygen. Then the low oxygen causes a substantial release of phosphorus in the sediment, which in turn fuels the blue-green algae bloom.

An analysis concluded that the sediment is the source of 75 percent of the phosphorus in the lake during the summer.

The plan offers a list of possible ways to control phosphorus and algae. Among the alternatives is a proposal to spill $290,000 worth of alum into the lake to remove phosphorus and blanket the sediment.

There are several high-tech proposals, including aeration with nanobubbles, which are 2,000 times smaller than a grain of sand and greatly increase oxygen transfer, which both prevents phosphorus release and reduces the amount in the sediment.

It would cost an estimated $200,000 or more. A slightly less expensive idea is a system that creates ultrasonic waves to prevent algae from going towards the light.

The cheaper alternatives are herbicides, which kill both algae and native plants, or just waiting to see if nature will fix the problem with the reestablishment of native aquatic plants.

“This no-action alternative would allow for nature to take its course, and, given the high costs of the active management options, may be the most likely to happen,” the plan states.

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