EFFECTS OF METALS ASSOCIATED WITH WILDFIRE ASH ON WATER QUALITY

Abstract:

The forests of the western United States are impacted dramatically by climate change and have suffered from large-scale increases in wildfire activity. This rise in wildfires introduces additional ash to ecosystems and can represent a serious and ongoing threat to water quality in streams and rivers from storm event runoff in burn areas. The effect of metals associated with wildfire ash (from wood collected from the Valles Caldera National Preserve, Jemez Mountains, New Mexico) on solution pH and dissolved oxygen was assessed through a series of laboratory experiments. Microscopy and spectroscopy analyses were conducted to characterize the elemental content and oxidation state 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. The initial pH after conducting batch experiments reacting ash with water started at 9.9 and the alkalinity of the water was 110 mg L^-1 as CaCO₃. Solution pH decreased to 8.0 after 48 hours of reaction, which is almost a delta of two pH units. 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. This presentation will discuss how redox-active metals, such as Fe and Mn, could contribute to the increased dissolved oxygen demand and fluctuation of the oxidation/reduction potential in the system.