Date of Award

Fall 2025

Document Type

Open Access Dissertation

Department

Environmental Health Sciences

First Advisor

Mohammed Baalousha

Abstract

Wildfires are natural processes that have played a vital role in ecosystems for millions of years. However, with increasing anthropogenic activities and climate change, wildfires' frequency and intensity have increased. A wildfire is an uncontrolled fire that burns forests, grasses, and savannas. In addition to vegetation combustible materials, wildfire burn structure items such as homes, stores, and storage sheds in areas where the transition zone between urban and wildland is defined as the wildland-urban interface (WUI). Moreover, wildfires in WUI can burn vehicles, including automobiles, tractors, and boats on trails. Recently, there have been concerns regarding the metals, metalloids, and nanomaterials produced by WUI fire and their environmental impact, particularly on marine ecosystems.

In this dissertation, ash samples were collected after a massive wildfire in California, from the North Complex Fire and LNU Lighting Complex fire, which are considered the sixth and seventh most destructive fire in California's history. The ash was collected from three different burn sources: vegetation, structure, and vehicle. Metals, metalloids, and incidental nanomaterial were determined using a microwave acids-assistance digestion system followed by inductively coupled plasma-time of flight-mass spectrometry. In the Ash from the structure and vehicle-burned sources, Ti, Zn, Cu, Ni, Pb, Sn, Sb, Co, Bi, Cr, Ba, As, Rb and W concentrations are generally higher than in vegetation-derived ashes and soils. Interestingly, the combustion completion of black, gray, and white ash has different concentration levels. This study found that some concentrations increased

with increased combustion completeness. For example, the concentrations of Ca, Sr, Rb, and Ag were higher in white ash than in black and gray ash. On the other hand, concentrations of C, N, Zn, In, and Pb are higher in black ash than in gray and white ashes, as those metals' concentrations decreased with increased combustion completeness. Ash produced from WUI fire mobilized and can transfer to the soil and underground water and eventually reach the marine ecosystem. Therefore, investigations of the impact of these ashes from different sources were required to provide a better understanding of their marine-environmental consequences.

In this study, laboratory experiments were conducted to simulate the effect of WUI fire on the marine environment. Recent studies suggest that wildfires will increase the growth of marine phytoplankton because they provide essential metals such as P, N, and Si. However, Ashes from WUI fire also have some toxic metals, as evidenced in chapter two of this dissertation such as Cr, Cu, Pb, and Zn. Accordingly, Marine diatom, Thalassiosira weissflogii, was exposed to ash samples originating from three different sources: vegetation, structure, and vehicle burnings. Thalassiosira weissflogii were cultured in F/2 media without adding trace metals solution to investigate the effect of metals in ash on marine diatom T.weissflogii. The growth of T.weissflogii was measured daily using Turner Designs 10-AU fluorometer. Remarkably, the ash produced from the structure and vehicle inhibited the growth of T.weissflogii because of the presence of toxic elements such as Cu, Zn, As, and Ni. Ash from vegetation sources shows no significant effect on the growth of T.weissflogii.

The overall study shows that WUI fire has produced different metals and metalloids in the form of incidental nanomaterials. This study also provides valuable insights into the possible effect of those pollutants on marine ecosystems. Moreover, the study identifies the need for an adaptive management strategy that can change to reduce the future impacts of WUI on aquatic ecosystems. Further research is required to assess the fate, reactivity, and transformation of ashes produced from WUI and investigate the long-term effect of post-fire occurrence on marine environment.

Rights

© 2025, Talal Abdullah Alshehri

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