Did the Thomas fire contaminate the ocean? Ask the algae

As smoke from the Thomas fire blanketed Ventura and Santa Barbara counties, USC earth sciences Prof. Seth John and his colleagues chartered a fishing boat and motored out towards the Channel Islands. 

Ash fell from the sky, the shore disappeared behind a thick curtain of smoke, and the crew began gathering ocean water with the hope that they'd be able to quantify how much of an impact the largest wildfire in California's history was going to have on the ocean ecosystem just off the coast.

They measured the amount of trace metals, like lead and copper, deposited in the ocean by the smoke.

When wildfires burn, it's not just carbon dioxide and fine particulate matter that's released, but also small amounts of metals buried deep inside plants and the landscape around them. The metals go airborne and then end up on our houses, in our yards and in the ocean.

As the trace metals mix with water they can act as either nutrients or as potential toxins to algal populations in coastal regions, according to John. Lead, copper and cadmium, for instance, are toxic and can kill algae, whereas iron and zinc can be beneficial and lead to growth.

Many of these metals are naturally occurring. Copper, for instance, can be found in dust blown in from the desert, according to John. Lead, on the other hand, has been building up in the environment for decades, because of the use of leaded gasoline. As cars burned the fuel, lead was released into the environment, landing on leaves and sprinkled across the ground. When wildfires roll through, that lead is released again, spreading further.

"By studying those populations of algae, we'll be able to see whether those toxic metals are building up in the algae," John said. "And then [we'll] have a much better understanding of whether any of those toxic metals could move up the food chain into the fish that we eat or the other animals that are living in the Santa Barbara Basin."

A few weeks after the Thomas fire was contained, the first major storm of the season rolled through Southern California, causing the devastating mudslides in Montecito and giant rivers of water draining into the ocean.

"We realized that rainy season was coming and that could be another important pathway for metals to get into the ocean," John said. "There's a lot of previous work that's shown that some contaminants, especially lead are very elevated in river runoff, particularly in burned areas after wildfires."

His colleague Josh West and graduate student Rachel Kelly gathered runoff from the Ventura river, every three hours for three days during the storm, with the hope that they could measure trace metals in those samples as well. 

"Fire are something that are recurring in California and are likely to get more common with future climate change scenarios," John said. "So, it's something that we need to study now in order to asses how not only the Thomas fire, but any future fires may be impacting the local ecosystem and fisheries."

John and his colleagues expect to get the results of their samples later this week.