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In 2020 the Bush Fire burned approximately half of the Sycamore Creek watershed in central Arizona. Sycamore Creek has been the subject of more than 40 years of research and the stream has been monitored by NEON since 2017. We studied the effects of fire on biogeochemistry of the stream and its watershed. We deployed autosamplers to monitor stream chemistry during storms on the mainstem and in ephemeral tributaries draining burned and unburned watersheds. The storm sampling program commenced nearly a year following the fire because absence of summer monsoon or winter storms in 2020-21 resulted in no flow in tributaries and intermittent flow in the mainstem. Water chemistry was measured during 14 monsoon storms of 2021 and winter frontal storms of 2021-22 with samples of baseflow collected in the mainstem during intervening periods. Water samples were analyzed for dissolved organic carbon, nitrogen, phosphorus, and major anions and cations. We also measured nutrient content of ash and chemistry of ash leachate as a potential source of solutes to stream biota. 

Abstract Wildfires have increased in size, frequency, and intensity in arid regions of the western United States because of human activity, changing land use, and rising temperature. Fire can degrade water quality, reshape aquatic habitat, and increase the risk of high discharge and erosion. Drawing from patterns in montane dry forest, chaparral, and desert ecosystems, we developed a conceptual framework describing how interactions and feedbacks among material accumulation, combustion of fuels, and hydrologic transport influence the effects of fire on streams. Accumulation and flammability of fuels shift in opposition along gradients of aridity, influencing the materials available for transport. Hydrologic transport of combustion products and materials accumulated after fire can propagate the effects of fire to unburned stream–riparian corridors, and episodic precipitation characteristic of arid lands can cause lags, spatial heterogeneity, and feedbacks in response. Resolving uncertainty in fire effects on arid catchments will require monitoring across hydroclimatic gradients and episodic precipitation.