Aquatic Ecosystems Aren’t Immune to Wildfire Impacts, Research Shows

Amid an unusual September heat wave, several major wildfires are raging simultaneously out West. 

As climate change fuels more severe infernos, a fairly new field of study has emerged to investigate how these blazes are interacting with a substance that would seemingly be immune to their path of destruction: water. Aquatic ecosystems—from tiny ponds to the ocean—could be vulnerable to the same fires that burn through millions of acres of land each year, scientists say. 

A string of recent studies has started to uncover some of the unexpected and sometimes problematic ways that wildfire and water are mixing in the environment—and what that could mean for us land-dwellers. 

Hazy Lakes: The majority of wildfires in the U.S. are currently concentrated in California and Nevada, but the smoke that they produce stretches far beyond their points of origin, posing air quality and health threats for individuals across the country. 

It turns out this haze can affect lake health, too, according to a study published in June. Researchers looked at data from more than 1.3 million lakes across North America and found that around 99 percent of them had experienced at least one “smoke day,” where wildfire haze can be seen blanketing the air above them, per year from 2019 to 2021. The majority of these lakes saw more than 30 days of smoke annually, even though many of them were located nowhere near a wildfire.  

“That was surprising, even to us,” the study’s lead author Mary Jade Farruggia, a scientist at the University of California, Davis, said in a press release. “With this study, we quantified for the first time the scope of the smoke problem. We show that it’s not just a widespread problem, but one that is long-lasting in a lot of places.”

The study found that these ashy clouds can block sunlight and deposit carbon, nutrients and toxic metals such as mercury or lead into lake ecosystems, which can alter their chemistry and sometimes fuel algal blooms. A separate study published in May looked specifically at smoke cover over lakes in California—one of the most fiery states in the U.S.—and found similar results. 

The iconic Lake Tahoe, which straddles the California-Nevada border, could be particularly vulnerable to these impacts, Stefan Lovgren writes for National Geographic. That’s largely due to excess tourism and the lake’s proximity to high-risk fire zones. On Tuesday, officials in Tahoe warned tourists and residents to remain on alert as the massive Davis Fire, burning in parts of Reno, creeps closer to the lake. 

Researchers note that individual lakes may respond differently to wildfires depending on a number of factors such as their size, depth and amount of smoke cover. 

“We’re seeing changes—often decreases—in photosynthesis and respiration rates that drive almost everything else,” Adrianne Smits, an aquatic ecosystem ecologist at UC Davis, said in a release. “Food webs, algal growth, the ability to emit or sequester carbon—those are dependent on these rates. They’re all related, and they’re all being changed by smoke.”

Booms and Busts: For life at sea, there may be winners and losers as climate change worsens wildfires. 

In 2017, smoke from one of the largest wildfires in California history billowed across the northeastern Pacific Ocean, infusing the seawater with a variety of chemical compounds and metals. Instead of triggering an ocean massacre, this plume provided “a veritable buffet for marine microbes,” Phie Jacobs writes for Science. A 2023 study found that the ash fed tiny phytoplankton floating near the surface, effectively fertilizing this region of the ocean. A similar phenomena occurred in 2019, when smoke from wildfires in Australia triggered algal blooms thousands of miles away. 

Marine microbes are crucial for sucking up and storing carbon from the atmosphere, which former Inside Climate News fellow Jenaye Johnson wrote about in July. While these tiny critters can help offset a portion of the emissions released from wildfires, some phytoplankton species such as dinoflagellates also produce toxins that can poison fish and crabs—and humans who consume them. 

Closer to shore, wildfires could spur toxic ash runoff on beaches or coral reefs. For example, the Lahaina fire in Maui last year torched more than 2,200 urban structures and cars, burning through hazardous materials that can leach into the ocean or coral reefs. Recent tests show that contaminant levels have drastically decreased since the fire, but scientists are still studying the long-term impacts of this type of event on coastal ecosystems. 

In some cases, even the efforts to fight fires can harm aquatic ecosystems: Evidence shows that the bright red flame retardant that the Forest Service scatters across fires to suppress flames can also kill fish.

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