nitrogen

Just days after the Trump administration completed millions of dollars in renovations on the Lincoln Memorial Reflecting Pool to make it American flag-blue, residents and online users noted it had turned a phosphorescent green.

Here’s why:

The calm, still waters of the Reflecting Pool make it an ideal nursery for algae growth. Algae need nitrogen and phosphorus to grow, and the Reflecting Pool is primarily fed by the Potomac River, which gets heavy doses of those nutrients from nearby urban and agricultural lands.

The Potomac also absorbed one of the largest sewage spills in U.S. history earlier this year when a pipe burst five miles upstream of Washington, although that event probably happened too long ago to contribute to the algal bloom today.

Untreated sewage is high in nitrogen and phosphorus. When nutrient levels are high, feasting algae can quickly reproduce.

The Department of the Interior said when the algae first appeared that it was “residual,” from the supply lines to the pool.

Experts also speculate that the darker blue color may be helping the Reflecting Pool absorb more heat. The higher temperatures promote algae growth by allowing their metabolisms to shift into overdrive.

Summer temperatures in D.C. aren’t helping. This week, temperatures are as high as 95 degrees in the city, prompting a heat alert.

The combination probably explains the excessive growth, turning the water surface an opaque green and preventing onlookers from seeing the new blue hue of the concrete basin.

Algae are important and beneficial organisms when the ecosystem is in balance. They’re the base of the aquatic food chain, fed on by herbivores of all shapes and sizes, including shrimp and juvenile fish, which in turn feed organisms higher up the food chain. The single-celled organisms use the power of the sun to produce energy through photosynthesis, similar to houseplants on your balcony.

In an effort combat the algae in the Reflecting Pool, employees of the National Park Service were seen pouring in gallons of hydrogen peroxide, a chemical commonly used in pool maintenance.

The Department of the Interior also is employing a “high-tech nanobubble ozone technology” to destroy the cells of the algae.

Ozone — yes, the same irritant that is in smog — is a gas composed of three oxygen molecules, and the small size of the bubbles allow the most gas transfer into the water, where it can damage algal cells, similar to how it irritates our lungs.

This only treats the symptoms, however. Generally, ozone nanobubbling is effective as a temporary solution for algae blooms. Longer-term fixes would have to address what makes the Reflecting Pool so ideal for algae, such as its depth, darker color and inflow of nitrogen and phosphorus.

In California, ozone nanobubbles also have been used in a project to improve water quality in the Tijuana River. The 120-mile river that runs near the border in northern Mexico and Southern California was the site of a pilot study in 2025. The U.S. section of the International Boundary and Water Commission reported that the nanobubbling reduced “odors and bacteria,” but the project concluded prematurely after a flood swept some of the instrumentation into the river.

Judge Emily Marks had previously allowed the execution to proceed, arguing that no execution is entirely without pain.

A federal judge in the United States has permanently blocked Alabama from executing an inmate with nitrogen gas, after declaring that the method violates the ban on cruel and unusual punishment.

On Tuesday, US District Judge Emily C Marks permanently enjoined the state from executing Jeffery Lee by nitrogen gas. Lee was scheduled to be executed Thursday at an Alabama prison.

Her decision came a day after an appeals court reversed her earlier ruling that the method is constitutional.

The case centres on how to interpret the US Constitution’s Eighth Amendment, which bars the government from inflicting “cruel and unusual punishments”.

A spokesman for Alabama Attorney General Steve Marshall said the state is reviewing the decision and considering next steps, including an appeal. The case will likely end up before the US Supreme Court, which has previously let nitrogen executions proceed.

A spokeswoman for Lee’s legal team said they did not have an immediate comment.

In her 26-page ruling, Marks said litigation is a constant in death penalty cases.

“Were Alabama to adopt firing squad as a method of execution, that method would likely be challenged as well. Indeed, there is likely no method — no matter how humane — that would be immune to constitutional challenge,” Marks wrote.

“But the Constitution does not guarantee a painless death, and human life cannot be purposefully extinguished without some risk of pain. The Court, the condemned, and the State must all confront that sobering reality.”

Marks noted that the state has two other authorised execution methods: lethal injection and the electric chair. She said Lee is “not entitled to an injunction barring the State from executing him using one of those methods”.

Marks also ruled that the state could switch to Lee’s preferred method, a firing squad. Inmates challenging execution methods are required to suggest an alternative method.

“The State can readily obtain rifles, ammunition, and other materials necessary to carry out a firing squad execution,” Marks wrote.

“Additionally, the State would be able to modify space at Holman to carry out executions by firing squad. The State is also able to source and train volunteers willing to carry out such an execution.”

Lee is currently housed at Holman Correctional Facility in Atmore.