UCLA

Wildfires are becoming more frequent and intense due to climate change, especially in the southwestern US. Wildfires occur in vulnerable urban areas prone to intense droughts and extreme floods, exacerbating water scarcity issues. Polluted runoff from wildfires can contaminate the limited surface water available for drinking water. To protect downstream water quality, green infrastructure such as stormwater biofilters could be implemented to remove pollutants from post-fire runoff. However, the impacts of wildfire residues on their functions remain unknown. This dissertation aims to understand how green infrastructure can mitigate wildfire impacts on water quality and how to design innovative wildfire-resilient stormwater biofilters.This dissertation specifically addresses four research questions. (1) How and to what extent are wildfires impacting surface water quality? (2) How do wildfire residues affect the physical and chemical functions of stormwater biofilters? (3) How do wildfire residues affect the biological function of stormwater biofilters? (4) Can waste-derived amendments remove pollutants from wildfire residues? Finally, a study explored whether a cohort-based research experience can increase STEM engagement and persistence. To address these questions, I used a combination of field experiments, bench-scale laboratory experiments with column setups, physical-chemical processes, and geochemical and spectroscopic techniques, as well as quantitative and qualitative research methods. Natural stormwater was collected from Ballona Creek in Los Angeles, CA, and wildfire residues were collected from the Santa Monica Mountains, CA. Results showed that wildfires can have a lasting impact on water quality, releasing pollutants into surface water even years after the wildfire. Deposited wildfire residues can negatively affect the infiltration capacity of biofilters by clogging filter media but do not affect their pollutant removal capacity. Wildfire residues did not appear to impact the germination and growth of plants, although sensitivity to wildfire residues varied among species. Drinking water treatment residuals (WTR) enhanced biofilter capacity to remove wildfire-associated pollutants such as phosphate released from fire retardants. Engaging undergraduate students in cohort-based research fostered their science identity, increasing STEM retention, particularly among underrepresented minority students. Overall, the results inform when, where, and how green infrastructure may be used to reduce the negative impacts of wildfires on water quality.