After the CZU Lightning Complex fires tore through the counties of San Mateo and Santa Cruz in 2020, over 86,000 acres of land were left ravaged in its wake. Now, scientists from UC Santa Cruz are looking into the aftermath of the wildfires in nearby watersheds.
One month after the fires, coastal hydrologist Christina Richardson organized a team and scoured the mountains to assess any variance in the stream water composition. They spent over two years taking samples and analyzing water chemistry across four different sources: San Lorenzo River, Laguna Creek, Majors Creek and Scott Creek. The post-fire results were then compared with pre-fire data obtained from partnerships with organizations such as the Santa Cruz Water Department.
“With climate change, wildfires are becoming more common,” said Richardson. “There’s just a paucity of pre-fire data that has impaired our understanding of how fires are actually impacting stream water composition. And because streams are often used for drinking water, this is particularly important to understand.”
The study measured around 40 different components present in the streams, though did not find changes that would be considered harmful to humans. Even so, Richardson says the results are telling: the water chemistry is altered by wildfires, and a diverse range of chemicals can enter varying streams. Each watershed displayed a different response that could have depended on multiple factors, such as rainfall characteristics and topography.
“The one special thing about that specific research is we had all sorts of measurements in the same streams and rivers before the fire, so we can directly link the changes to the fire,” said Adina Paytan, a UCSC professor who works with Richardson in her biogeochemical lab.
Allison Myers-Pigg, an environmental scientist from the Pacific Northwest National Laboratory, particularly praises the work for its comprehensive and unique dataset. She points out the difficulty in designing a study around a disturbance event, and Richardson’s rapid response helped capture immediate and long-term impacts.
These impacts not only influence the composition of stream water but could affect aquatic wildlife as well. “There’s been a lot of attention on the effects of wildfire on terrestrial ecosystems (and) a lot less work done on aquatic ecosystems, even though they certainly will experience responses to wildfire,” said UCSC professor Eric Palkovacs.
Palkovacs researches how wildfires impact the ability of salmon and steelhead fish to detect chemical cues in their environment by impairing their sense of smell. He said that the changes in water chemistry following wildfires are going to affect the biodiversity of our streams, the fish we rely on for fisheries, and even threatened and endangered species.
“Every fire is a little different, every watershed is a little different, so it’s going to take more studies to really understand what these impacts are going to be,” said Palkovacs. “This study is an excellent start.”
Workers in water treatment are also slowly adjusting to the aftermath of the fires. “The CZU Lightning fire here in Santa Cruz was a real wake-up call for us,” said Chris Coburn, deputy director and operations manager of the Santa Cruz Water Department. He oversees the treatment and distribution of drinking water, and frequently works with the Graham Hill Water Treatment Plant.
Treating water is a complex multi-step procedure and requires drawing water from three of the four sources mentioned in Richardson’s study. Coburn highlights that forest fires can impact source water quality through increased amounts of sediments and fine materials that need to be filtered out. Knowing the chemistry of the water can help optimize the process by switching between sources and refining the treatment process.
“Studies like this, that help us better characterize and understand those source waters, are only going to help us better operate the treatment plant, choose our sources, and ultimately serve really high-quality water to our customers.”