The Woolsey fire impacted water quality for months

Today’s Image of the Day from NASA Earth Observatory features a massive burn scar left behind after the November 2018 Woolsey Fire in Southern California.

According to NASA, the fire also left unusually high levels of fecal bacteria and suspended sediment in the coastal waters off Los Angeles and Ventura counties.

A new study published in Nature Scientific Reports used satellite imagery, precipitation data, and water quality reports to assess coastal water quality after the fire. The researchers assessed two parameters of water quality: the presence of fecal indicator bacteria and the turbidity, or cloudiness, of the water.

“Fecal indicator bacteria originate in the gastrointestinal tracts of humans and other warm-blooded animals,” reports NASA. “While fecal indicator bacteria are not harmful, they can indicate the presence of other potentially harmful bacteria and pathogens found in feces. Turbidity has other implications: Cloudy, murky water results in less sunlight reaching marine life like kelp and phytoplankton.”

Study lead author Marisol Cira is a doctoral candidate at the University of California, Los Angeles, and an intern at NASA’s Jet Propulsion Laboratory (JPL). 

“Post-fire, we saw drastic water quality changes, particularly at beaches draining the burned area,” said Cira. “In those areas, both total coliform bacteria and enterococcus were far greater than pre-fire levels, as was turbidity plume size.”

The study revealed that the abundance of a large group of fecal indicator bacteria known as coliforms was ten times higher after the fire than it was in the previous twelve years. 

The presence of enterococci, bacteria that can cause gastrointestinal disease, was 53 times higher post-fire and well above what is considered safe.

“When a fire burns through a forest, it increases the amount of vegetation litter on the ground and changes the chemistry of the soils in a way that makes them unable to absorb water,” said study co-author and JPL scientist Christine Lee. “So rather than getting absorbed into the soil, rain runs off into local water bodies and coastal systems, carrying sediment and bacteria with it.”

The experts found that bacteria levels remained high through February 2019,  while turbidity remained high for three months before returning to previous levels.

“Usually when there’s a spike of bacteria in the water, it only lasts a day or two,” said study co-author Luke Ginger, a scientist with the nonprofit group Heal the Bay. “But after the fire, there were months of sustained high bacteria. So that was a big concern.”

“Climate change will likely exacerbate the effects we see here in terms of water quality as wildfire and rainfall patterns continue to change. A key part in protecting our ecosystems and communities is understanding these emerging threats and spreading awareness about them.”

Image Credit: NASA Earth Observatory 

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By Chrissy Sexton, Earth.com Staff Writer