Abstract
Wildfires increase runoff and sediment yields that impact downstream ecosystems. While the effects of wildfire on stream water quality are well documented, oceanic responses to wildfire remain poorly understood. Therefore, this study investigated oceanic responses to the 2018 Woolsey Fire using satellite remote sensing and in situ data analyses. We examined 2016–2020 turbidity plume (n = 192) and 2008–2020 fecal indicator bacteria (FIB, n = 15,015) measurements at variable proximity to the Woolsey Fire. Shifts in coastal water quality were more pronounced in the “inside” region, which drained the burn area. The inside region experienced 2018–2019 plume surface area monthly means that were 10 and 9 times greater than 2016–2017 and 2017–2018 monthly means, respectively. Further, linear regressions showed that 2018–2019 three-day precipitation totals produced plumes of greater surface area. We also noted statistically significant increases in the inside region in 2018–2019 total coliform and Enterococcus monthly means that were 9 and 53 times greater than 2008–2018 monthly means, respectively. These results indicate that sediment and microbial inputs to coastal ecosystems can increase substantially post-wildfire at levels relevant to public and environmental health, and underscore the benefit of considering remote sensing and in situ measurements for water quality monitoring.
Highlights
In the western United States, wildfire activity has increased since the late twentieth c entury[1,2] in frequency, duration, and season length[3,4]
Satellite remote sensing can be used to help resolve gaps in spatial and temporal sampling of water quality to help evaluate coastal conditions following wildfire events. Water quality variables, such as turbidity, can be derived using optical data acquired through remote sensing platforms including Landsat and Sentinel-2
Results indicate that the 2018 Woolsey Fire impacted the physical water quality
Summary
In the western United States, wildfire activity has increased since the late twentieth c entury[1,2] in frequency, duration, and season length[3,4]. At the onset of rainfall, runoff is unable to infiltrate burned soils, resulting in soil erosion via rill networks and debris flows[21] These processes produce heightened runoff and sediment yields[16,17,22] that mobilize and transport contaminants to downstream ecosystems. Satellite remote sensing can be used to help resolve gaps in spatial and temporal sampling of water quality to help evaluate coastal conditions following wildfire events. Water quality variables, such as turbidity, can be derived using optical data acquired through remote sensing platforms including Landsat and Sentinel-2. This study did show consistency between satellite-derived turbidity and coincident in situ light transmissivity measurements (Supplementary Text S1, Supplementary Fig. S1)
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