Wildfires devastate forests and watersheds leaving behind contaminants that continue to pollute rivers and streams longer than previously estimated. A new study offers the first large-scale assessment of post-wildfire water quality. It analyzed water quality in over 500 watersheds, aiming to identify trends in post-wildfire water quality across the entire US West.
Fire ash and degraded post-fire soil quality can negatively impact water quality. Past research often remained localized leaving it to local authorities to test water quality in streams after large fires. This new study significantly expands that scope.
The research team for this study analyzed over 100,000 water samples from 500 sites. Half came from burned river basins, half from unburned ones. They measured levels of organic carbon, nitrogen, phosphorus, and sediment. Turbidity, or cloudiness, was also assessed. Using data models they measured how contaminants changed in each basin before and after wildfires.
The results show watersheds take longer to recover after fires than earlier studies indicated. Organic carbon, phosphorus, and turbidity remain significantly elevated for one to five years post-fire. Nitrogen and sediment show notable increases for up to eight years. Fire-driven impacts were more severe in areas with denser forest cover and large storms were shown to potentially mobilize leftover contaminants years later.
Each watershed in the study experienced different impacts. This variability likely relates to the fire's proximity to the river. A fire closer to the river causes more severe issues than one upstream. Additionally, varying soils, vegetation, and weather patterns change the impact in each watershed. Despite this variability, the study provides concrete numbers providing insights for future planning efforts aimed at enhancing wildfire resilience.
