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Contributed Poster

Session: Fire/Fire Management

PS 28-135 - Temporal analysis of wildfire ash in Sycamore Creek

Tuesday, August 8, 2023
5:00 PM – 6:30 PM PDT
Location: ESA Exhibit Hall
Abstract: Wildfires contribute to heavy sediment and solute loading in streams and rivers, where one of the major contributors is ash. Wildfire ash composition can range from highly organic, scarcely burned material to fully combusted material with little residual carbon. This study examines the basic characteristics of ash resulting from the 2020 Bush Fire in central Arizona, and its effects on stream water quality in a spatially intermittent watershed in the Tonto National Forest. The fire, which burned ~785 km² of Sonoran desert scrub, chaparral, pinyon-juniper, and higher-elevation coniferous forest, burned much of the eastern portion of the Sycamore Creek watershed and its tributaries but left the main channel, headwaters, and west side of the watershed unburned. Ash was collected for two years post-fire at three sites along the creek. We examined the chemical properties of the ash to answer two questions: what is the elemental composition of ash? and is the carbon in the ash labile? Carbon content of ash was found to be at an average range of 4.9-8.4%, varying with the year of collection. To examine the usability of organic carbon for microbes within the stream, we conducted carbon lability incubations over a 21-day period, using ash leachates. Dissolved organic carbon (DOC) utilization by the microbes was 45-80% over the three-week timespan, which is comparative to previous studies of lability of stream DOC following the fire. Fires in the Sonoran Desert have recently become more prevalent due to climate change and introduction of flammable, non-native grasses such as buffel grass and red brome. An understanding of the effects of fire and its contributing load of burnt material entering rivers and streams is imperative to mitigating climate risks from increased frequency of disturbances like fire.