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Pyrogenic Remobilization And Transport Of Toxic Metals


The effects of wildfires and deforestation on the remobilization of persistent inorganic contaminants are not completely understood. In forests, trace metal contaminants (e.g., lead) are sequestered in terrestrial sediment, soil organic matter, and vegetation, where they are relatively immobile. However, the combustion of soil organic matter and vegetation releases these contaminants in more labile forms. The associated deforestation and accelerated weathering increase the mobilization of trace metals from forests by simply increasing rates of erosion. These remobilized contaminants are transported to water bodies, increasing the loads of contaminants in these aquatic systems.

This project used analyses of trace metal inventories and lead isotopic compositions to study the remobilization and transport of toxic metals with respect to forest fires and deforestation associated with land-use. Chapters 2 and 3 present the results of investigation of the pyrogenic remobilization of trace metals at two contrasting sites in California: the relatively pristine Santa Barbara and the more populated and industrialized Los Angeles Metropolitan Area. The results indicate that wildfires are increasing the remobilization and transport of persistent contaminants (e.g., lead) in both study areas. Chapter 4 presents the results of a similar study conducted in Chile, in which geochronology and lead isotopic compositions were used to investigate the impact of historic (about a century ago) slash and burn practices on the deposition of trace metals in Lake Thompson, Patagonia. The results show a positive relationship between fire size and the flux of metals to the lake. These findings are significant because the frequency and intensity of wildfires are expected to increase with global climate change. Chapter 5 presents the results of a study in which contaminant remobilization was linked to land-use practices by characterizing temporal changes in the flux of trace metals to Lake Tanganyika, Africa. The results indicate that deforestation is the predominant factor accelerating trace metals transport to the lake. This land-use associated remobilization of contaminants is projected to increase with population growth and industrialization in Africa.

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