The reactivity of metals associated with wildfire ash (from wood collected from the Valles Caldera National Preserve, Jemez Mountains, New Mexico) was assessed through a series of laboratory experiments. Climate change has caused dramatic impacts and stress that have resulted in large-scale increases in wildfire activity. Metals and other constituents in wildfire ash can negatively affect water quality in streams and rivers from storm event runoff in burn areas. Microscopy and spectroscopy analyses were conducted to determine the chemical composition of metals in unreacted and reacted ash. Certain metals (e.g., Ca, K, Al, Mg) were detected in ash from ponderosa pine, one of the dominant species in the Valles Caldera, with mean concentrations ranging from 400-1750 mg kg-1. Other metals (e.g., Na, Fe, Mn, V, Zn, Ni) were present at lower mean concentrations ranging from 12-210 mg kg-1. After the first minutes of reaction the solution pH was 9.9 caused by leaching of carbonates in the ash which resulted in water alkalinity to 110 mg L-1 as CaCO3. However, the pH decreased to 8.0 after 48 hours of reaction. Dissolved oxygen concentrations decreased by 2 mg L-1 over the course of 12 hours before the rate of reaeration surpassed the rate of consumption. Our results suggest that redox-active metals, such as Fe and Mn, could contribute to the pH decrease, increased dissolved oxygen demand, and fluctuation of the oxidation/reduction potential in the system. These results have important implications to better understand the negative impact of wildfire events on water quality.

Reactivity of metals from wildfire ash and effects on water quality

251st National Meeting (2016)

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