Understanding the Lincoln Reflecting Pool Algae Bloom

Preview

The incident with the algae bloom in the Lincoln Memorial Reflecting Pool highlights significant ecological principles. Following a $16 million renovation that darkened the pool’s bottom surface, the National Park Service utilized hydrogen peroxide and nanobubbler technology to kill the algae. Critics questioned whether these treatments effectively addressed the underlying causes, such as the effect painting the pool’s bottom surface a dark bluel. School kids know that warm water temperatures and nutrient levels promoting algae growth. Experts suggest that improving water circulation, controlling nutrient input, and reconsidering the aesthetics of the pool could provide a more sustainable solution, emphasizing that understanding basic ecology is crucial in addressing such environmental issues.

The recent algae bloom in the Lincoln Memorial Reflecting Pool has become an unexpected lesson in ecology, engineering, common sense and school science. Mr. Dalton Pierce, CEO of American Monument Restoration Systems, the company awarded the $16 million Reflecting Pool contract, maybe needs to study a bit of school biology or consult with a local high school science department.

After a $16 million renovation that included repainting the pool, officials found themselves confronting a familiar problem: green algae spreading through the water. The response was dramatic. National Park Service crews poured hydrogen peroxide into the pool while specialized “nanobubbler” machines injected microscopic ozone bubbles into the water to kill the algae.

The technology sounds impressive.

But the larger question remains:

Why did the algae bloom in the first place?

Ironically, the answer involves principles that many elementary school students learn during their first science lessons about ponds and aquatic ecosystems. In the Global Thinking Project, that I co-directed with Dr. Julie Weisberg, we engaged student around the world in a cluster of environmental inquiries.

One of the inquiries was called Project Water Watch. In the project, students collect data on the physical & chemical characteristics of a river, collect and identify macroinvertebrates of the river, analyze the physical, chemical, and biological qualities of the river, learn how to take action to protect bodies of water. Students in the U.S., collaborated using telecommunications with students in Australia, Czech Republic, Russia, Spain, as well as many other countries that joined the project. Students and teachers in the GTP leaned to value communication, experiential learning, and cultural exchange, aiming tos develop global citizens committed to environmental sustainability. Students who participated in the GTP would have known the effects of painting the floor of the reflecting a dark color.

Most kids know that algae thrive when three conditions come together: sunlight, nutrients, and warm water. Explore Figure 2 to see how students might investigate conditions that affect algae growth.

Remove one of those ingredients and algae growth slows. Increase them and algae multiply rapidly. Every summer, ponds, lakes, aquariums, and even neglected birdbaths demonstrate this simple biological rule.

How did painting the floor of the pool lead to a green slime?

In Figure 3, I’ve shown how you might think about the ecological conditions that lead to an algae bloom. Note the affect of changing any of the variables that affect algae growth. Increasing the temperature of the water in the reflecting pool is one way to get the algae to go crazy and cover the pool with green in a couple of days. What were the adults in the pool thinking?

According to numerous reports, the renovated Reflecting Pool was painted a dark blue color. Dark surfaces absorb more solar energy than light-colored surfaces. Anyone who has walked barefoot across black asphalt on a summer afternoon understands this principle instantly.

A darker pool absorbs more sunlight, which increases water temperature. As temperatures rise, algae reproduction accelerates.

This is not controversial science. Warmer water consistently promotes algae growth. Environmental scientists have documented this relationship for decades. It is one reason harmful algal blooms become more common during hot summers and during periods of climate warming.

Imagine two shallow pans of water sitting in the sun. One has a bright, reflective bottom. The other has a dark bottom that absorbs heat. Which one gets warmer?

Most children could answer that question correctly.

Now imagine adding sunlight and trace nutrients to both pans. Which one is more likely to experience algae growth?

Again, the answer is obvious.

Yet when the algae appeared in the Reflecting Pool, the response focused largely on treating the symptom rather than addressing the underlying cause.

What did the Trump administration do to solve the problem?

To combat the bloom, officials used hydrogen peroxide rather than chlorine bleach. The Department of the Interior explained that hydrogen peroxide was selected because it is less caustic and breaks down into water and oxygen.
In addition, the National Park Service deployed advanced nanobubbler technology that injects microscopic ozone bubbles into the water. Ozone is a powerful oxidizer that damages algae cells and can rapidly clear contaminated water.

Federal officials later declared the effort a success, noting that the algae had been killed and that crews were vacuuming dead material from the pool. This was simply not true.

Critiquing the Administrations Solution

But many observers questioned whether the treatment addressed the real problem.

Pool maintenance experts noted that the Reflecting Pool contains approximately 6.75 million gallons of water. Videos showing workers pouring ordinary gallon jugs of hydrogen peroxide into a body of water that size sparked skepticism. Critics argued that the quantity appeared insignificant compared with the volume of the pool itself.

Others raised concerns about wildlife. The Reflecting Pool is not merely a decorative feature; it is also a habitat used by ducks, migratory birds, and other urban wildlife. While hydrogen peroxide and ozone are generally considered less harmful than chlorine, any chemical intervention in a living ecosystem invites questions about unintended consequences.

More importantly, critics argued that even a successful algae treatment does nothing to eliminate the conditions that allowed the bloom to develop.

If warmer water remains the fundamental driver of algae growth, then killing one bloom simply resets the clock until the next one appears.

Ecological solution.

• The first step is reducing excessive heating. Increased water circulation can distribute heat more evenly and prevent stagnant warm zones from developing. Improved aeration can also help stabilize water quality.
• The second step is controlling nutrients. Algae feed on nitrogen and phosphorus that enter through dust, runoff, bird droppings, and decaying organic matter. Better filtration and maintenance reduce the food supply available to algae.
• The third step is recognizing the role of sunlight absorption. If the dark coating contributes significantly to higher water temperatures, then managers may need to reconsider whether aesthetics and ecological performance are working against one another.

None of these approaches is as dramatic as nanobubblers or chemical treatments. They are slower, less visible, and less likely to generate headlines.

But they address causes rather than symptoms.

The Reflecting Pool episode is ultimately a reminder that nature does not care how much money was spent on a renovation. Water, sunlight, temperature, and microorganisms obey the laws of biology, not construction budgets.

In fact, a fifth-grade science class studying pond ecosystems might have predicted the outcome before the first bucket of paint was opened. Warm water tends to produce more algae. Cooler water tends to produce less.

Sometimes the most expensive problems arise when we overlook the simplest lessons.

The hydrogen peroxide and ozone treatments may temporarily clear the water. But unless the environmental conditions that favor algae growth are addressed, the bloom will likely return. The long-term solution is not found in a jug or a machine. It is found in understanding the basic ecology that schoolchildren have been learning for generations.

Conclusion

The incident with the algae bloom in the Lincoln Memorial Reflecting Pool highlights significant ecological principles. Following a $16 million renovation that darkened the pool’s surface, the National Park Service utilized hydrogen peroxide and nanobubbler technology to kill the algae. Critics questioned whether these treatments effectively addressed the underlying causes, such as warm water temperatures and nutrient levels promoting algae growth. Experts suggest that improving water circulation, controlling nutrient input, and reconsidering the aesthetics of the pool could provide a more sustainable solution, emphasizing that understanding basic ecology is crucial in addressing such environmental issues.