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How Wildfires Affect Water Quality

Climate change is driving an increase in catastrophic wildfires; consumers can see, smell and taste the effects in the water. Water companies must prepare for worse times in the future. In recent decades, from the Amazon to Siberia, from Australia to the western United States, the number, scale and intensity of wildfires in many parts of the world have increased. The consequences of these fires provide a window for the future. Wildfires will have unprecedented harmful effects on ecosystems and the organisms that depend on them (including humans)-most importantly, they may cause serious damage to municipal water supplies. In 2013, the Rim fire-then the third largest wildfire in California history-burned down a large area of ​​Stanislaus National Forest near Hetch Hetch Reservoir, raising concerns about the safety of drinking water supplied from the reservoir to San Francisco.

The 2018 campfire not only destroyed vegetation, but also destroyed the buildings and water supply system in Paradise Township in north-central California, leaving piles of burnt electronics, furniture and cars scattered in the rubble. The heavy rain after the fire washed the debris and dissolved toxic substances in the burning materials into the nearby water body and polluted the downstream river. Residents who rely on these sources complain about the smell of smoke in their household tap water. In some cases, water companies have to stop using water from sources that are too close to wildfires and provide customers with alternative water sources. Climate change is expected to increase the frequency and severity of wildfires, thereby bringing new risks to water suppliers and consumers. The chemical properties of water exported from severely burnt watersheds may change greatly, and may contain high concentrations of pollutants and other undesirable substances that are difficult to remove.

Wildfires impact on water

Wildfires have had a documented impact on the quality of surface water. Fires polluted rivers, streams, lakes and reservoirs, which provide sediments for public drinking water facilities, nutrients and heavy metals that promote the growth of algae. However, few researchers have discussed the treatability of water—how easy it is to purify—or the quality of drinking water in treated water after wildfires (see video below). Due to forest fires, pollutants flow in the environment, which volatilizes biomass into gases such as carbon dioxide, and at the same time creates a layer of loose ash on the surface of the soil. Compared with DOM from unburned parent material, dissolved organic matter (DOM) leached from this burned or pyrolyzed material (PyDOM) has significantly different chemical properties [Chen et al., 2020]. Although wildfires can destroy forest ecosystems within a few days, changes in the number and composition of DOM can persist for decades in a burning landscape.

DOM itself is not a pollutant that has a direct impact on human health, but it can cause problems for water treatment. It causes deterioration of color and taste, and becomes a substrate for the growth of harmful microorganisms or membrane fouling. In addition, DOM will increase the processing cost and the level of chemical requirements, that is, the amount of added chemicals needed to disinfect water and remove DOM, such as chlorine and ferric iron. The treatment work may bring unexpected side effects: the disinfection process of DOM-contaminated water will form various carcinogenic disinfection by-products. The characteristics, processability, and duration of PyDOM from burned watersheds are poorly understood and more research is needed, but it is clear that this material constitutes several major challenges and health issues related to municipal water supply in wildfire-prone areas. In particular, it will have a negative impact on handleability and increase the possibility of algal blooms and the release of toxic chemicals.

Toxic chemicals in the water

When the forest vegetation burns, it will produce and directly release a variety of potentially toxic chemical substances, including polycyclic aromatic hydrocarbons and heavy metals, which provide a variety of toxic chemical substances for the source water. Fires can also destroy plastic water pipes in households connected to municipal water systems, potentially releasing harmful volatile organic carbon into larger water systems. For example, it is reported that the water supply pipes after the Tubbs fire in the urban area of ​​California contained up to 40 milligrams of benzene per liter, which is a known carcinogen [Proctor et al., 2020]. Benzene is one of many organic chemicals found in damaged water supply networks, and experts worry that over time, burning pipes may release many other toxic chemicals. Since these damaged pipelines are located downstream of the treatment facility, the best remedial option may be to completely replace the pipeline.



with information from: https://eos.org/science-updates/wildfires-are-threatening-municipal-water-supplies

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