Elevated levels of trace metals such as iron, lead, nickel and zinc were found in streams of the San Gabriel Mountains north of Los Angeles, California, at water-quality levels higher than the Environmental Protection Agency’s Aquatic Life Ambient Water Quality Criteria, according to a new U.S. Geological Survey study. Scientists linked the contaminants’ presence to the 2009 Station Fire in the Angeles National Forest.
The study examined the effect of the fire on trace metal contamination in nearby streams, and compared the post-fire storm water quality to criteria for aquatic life, seeking to understand if watershed runoff from the Station Fire burn area could harm local ecosystems.
“This study identifies how at-risk frog populations might be affected by water chemistry changes due to fire in their habitats,” said Robert Fisher, Research Ecologist with the USGS.
Results of this study will inform resource managers about the potential risks wildfires pose to fish and frogs that live in these watersheds, several of which are critically endangered and close to extinction.
Additionally, many of the creeks studied feed into public drinking water reservoirs. While water from these reservoirs is tested and treated before supplies are delivered to customers, results will help water treatment managers prepare for future water quality issues arising after fires and storms.
Scientists from diverse fields including hydrology, geology, geochemistry and biology worked together to examine water, soil and ash samples to determine the levels and types of contamination that may have resulted from the 2009 fire. Pre-storm and stormflow water-quality samples were collected from streams located inside and outside the burn area of the Station Fire. Ash and burned soil samples were collected and analyzed for metal content from several locations within the perimeter of the fire. By examining and comparing these samples, the researchers determined that concentrations of heavy metals in soil, ash and storm water were elevated as a result of either the fire or local storms, or a combination of both. The study also recorded extremely high pH levels, up to 12, in water leachates of ash samples collected from burned landscape areas prior to storm events.
These levels can adversely affect terrestrial and aquatic life. However, such high pH values were not found in the storm water samples, likely due to dilution and chemical reactions with rainfall.
The Station Fire in the Angeles National Forest was the largest of 20 wildfires in Southern California in 2009, burning from Aug. 26 to Oct. 16. It is the largest fire ever recorded in Los Angeles County. The USGS study area included portions of eight watersheds, of which approximately 680 square kilometers were burned by the fire.
Scientists from the USGS California Water Science Center, Western Ecological Research Center and the Crustal Geophysics and Geochemistry Science Center collaborated to publish their findings. “Trace Elements in Stormflow, Ash, and Burned Soil Following the 2009 Station Fire in Southern California” published in PLOS ONE is available online.