Compositions of ash, soil, sediment, water, and biota after the 2020 CZU Lightning Complex Wildfire, Santa Cruz Mountains, California

The CZU Lightning Complex Wildfire burned 86,500 acres of forested coastal watersheds in the Santa Cruz Mountains, CA, from August 16 to September 22, 2020. Ash, soil, and stream sediment were collected and characterized as soon as sites could be safely accessed to quantify potential environmental and public hazards from wildfire-related potentially toxic metals and polycyclic aromatic hydrocarbons (PAHs). Sites were chosen to reflect conditions with low, moderate, and severe soil burn severities. Repeated collections at regular intervals over three years showed temporal changes of in situ wildfire-related chemicals and changes related to transport of wildfire-materials in coastal watersheds. Stable isotopes, radiocarbon, and PAHs were measured in dominant plants, stream biota (steelhead and crayfish) and intertidal mussels to determine how wildfire constituents were taken up by organisms. Airborne wildfire particulates were collected and characterized downwind in Santa Cruz up to one month post-fire. Sediment provenance in Scott Creek and three of its tributaries was determined from geochemical fingerprinting of underlying parent rocks. In combination, these parameters show how the chemistry of hillslope soil and stream sediment and biota of forested coastal watersheds were affected by wildfire and how recovery progressed over three years.