Wildfire Impacts on Water Quality and Implications for Disinfection Byproduct Formation
Forested watersheds are used worldwide as sources of high-quality drinking water. These areas have coevolved with wildfire, but climate change-induced increases in temperature and drought, plus mismanagement of forested areas are increasing the frequency and severity of wildfires. These can have adverse effects on drinking water quality by destroying vegetation, altering hydrologic regimes, and increasing erosion and nutrient loading into surface water. Another aspect of wildfire is the alteration of organic matter. Fire is known to increase the aromaticity of dissolved organic matter (DOM) and decrease its molecular weight. This affects various aspects of water treatment, including disinfection. The addition of disinfectants, such as chlorine, to water containing wildfire-affected DOM has been shown to increase concentrations of the regulated disinfection byproducts (DBPs) known as trihalomethanes (THMs) and haloacetic acids (HAAs), though questions remain about changes in the reactivity of fire-affected DOM to form these. Less attention has been paid to unregulated nitrogenous DBPs (N-DBPs), such as haloacetonitriles (HANs), and currently, no studies have investigated the effect of wildfire on haloacetamide (HAM) formation. This warrants further investigation to inform water utilities so that they may better treat these waters and protect public health.The aims of this dissertation were to 1) understand watershed-scale impacts of wildfire on water quality and DBP precursor loading in mountain streams and rivers during storm flushes and winter, spring, summer, and fall flow regimes, 2) investigate the effect of both oxygen concentration and temperature on DBP precursor transformation in soil, and 3) understand the effect of soil heating on DOM hydrophobicity, molecular weight, and the relation to DBP precursor reactivity. Watershed scale impairment of water quality and DOM changes caused by wildfire were confirmed at the bench scale. Wildfire and simulated wildfire conditions cause changes in the reactivity of DOM to form C- and N-DBPs. To identify the DOM fractions responsible for these changes, hydrophilic and hydrophobic DOM fractions were isolated to study their changes in DBP formation potential, optical properties, and molecular weight distribution after thermal alteration. Conclusions from this research may aid in tailoring treatment for improving public health and meeting regulatory requirements.
Disinfection Byproducts, Forest Fire, Haloacetamides, Haloacetonitriles, Trihalomethanes, Wildfire
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