Closer water monitoring needed as wildfires increase

Burned trees in Santa Cruz Mountains
Researchers studied stream chemistry in watersheds impacted by the 2020 CZU Lightning Complex Wildfires. (Photo courtesy of Christina Richardson)
With climate change leading to increases in the size and frequency of wildfires, UC Santa Cruz researchers warn that such natural disasters can change the chemistry of nearby streams that people and wildlife depend on for drinking water. However, the researchers found that the baseline water-chemistry data needed to detect such changes aren’t always available.

“Wildfires are becoming more common, yet the effects of wildfire on streams and their water quality remain unclear,” they explain in their recently published study. “Changes in stream water quality following a wildfire can have consequences for drinking water and aquatic ecosystems.”

The study, “Exploring the Complex Effects of Wildfire on Stream Water Chemistry: Insights from Concentration-Discharge Relationships,” was led by Christina Richardson, a postdoctoral fellow in UC Santa Cruz’s Department of Earth & Planetary Sciences. She researches water in coastal, estuary and river systems in the biogeochemical lab run by Professor Adina Paytan.

Understanding the impact of wildfires on stream-water quality is important for effectively planning and managing wildfire-prone areas, the study’s authors state. Three of the four creeks and rivers that the researchers focused on are used as local drinking water sources for communities nestled in the southern Santa Cruz Mountains, as well as the city of Santa Cruz.

Gaining insights from the ashes

Specifically, one month after the CZU Lightning Complex Wildfires – that destroyed over 86,000 acres across Santa Cruz and San Mateo counties in 2020 – Richardson and her colleagues began collecting samples at four different watersheds impacted by the massive, month-long fires. Over the course of two years, her team ventured into the ravaged mountains and measured stream-water chemistry, coupled with analysis of burned soils and ash from the same areas.

They measured for more than 20 different elements, including arsenic and lead. And while the study didn’t find changes in stream-water chemistry that would be harmful to humans, Richardson said the ability to make that finding was a significant accomplishment in itself – made possible by the many partnerships they formed with local and federal organizations to access what baseline chemistry and water-flow data were available.

“These collaborations on this project really showcase how multiple organizations and groups can come together with a shared purpose that benefits our local community and science at large,” the researchers wrote. Such effective partnerships between researchers and public agencies don’t always occur, Richardson said.

More proactive water monitoring needed

However, they were not able to report definitive water-chemistry changes at one of the sites studied due to a lack of data on chemical levels prior to the fire – the kind of valuable information that would be collected if ongoing water-quality monitoring were more commonplace. With climate change raising the incidences of wildfires and the harms they inflict on surrounding communities, Richardson said this study highlights the importance of more routine water-chemistry monitoring.

“Our understanding of how disturbances like wildfire impact stream water quality is limited by a paucity of pre-fire data,” Richardson explained. “Without these baselines, it is challenging to understand not only the primary drivers of post-fire change in aquatic systems, but also to even define what constituents are changing in terms of stream-water quality.

“This study is helping to fill this critical data gap as wildfires become more common due to climate change and shifts in land-management practices,” she added.

Going forward, the next step in this line of research is for deeper exploration of why water-chemistry changes are influenced by so many variables: from a watershed’s topological features, to flow-volume fluctuations, and even the time of year. Ultimately, Richardson said these insights are critical for effective planning and management of water resources as wildfires become more frequent.