RAPID: Indirect impacts of a novel wildfire on a well-studied desert stream: connectivity, carbon, and communities

点击翻译按钮获取中文摘要

In June 2020, the 5th largest fire on record in Arizona burned Sonoran Desert and high-elevation forests in the watershed of Sycamore Creek, an ecosystem that has been studied for over 40 years. Disturbances like fires, when combined with monsoon and winter rainstorms, can result in runoff that carries large amounts of sediments, dissolved carbon, and nutrients. These runoff events also can reduce the concentration of dissolved oxygen. High sediment, carbon and nutrient loads and low dissolved oxygen degrade the quality of water that ultimately contributes to the water supply for downstream metro Phoenix. However, ecosystems might absorb these effects by trapping sediment and taking up nutrients, diminishing the effects of the fire on downstream ecosystems. This RAPID award will study the inputs of sediments, carbon, and nutrients from burned compared to unburned tributaries during monsoon and winter frontal storms. They will observe potential changes in the stream ecosystem immediately following storms and one year after the fire, including plant and invertebrate communities, processing of carbon and oxygen, and channel shape. Large fires are rare in the Sonoran Desert, but are expected to become more common due to growth of invasive grasses and human activity. The research will aid forest and municipal water managers in predicting the consequences of arid land fires, and help support the professional development of one technician, one graduate student, and one undergraduate student.A large-scale wildfire in June 2020 burned 780 km2 of Sonoran Desert and higher-elevation woodland and forest in Arizona, including nearly half of the Sycamore Creek watershed, the site of 40 years of stream ecological research and a NEON aquatic site. Large-scale fire in the desert Southwest was historically rare or non-existent but is becoming increasingly common, owing to invasive grasses and human activity, yet little is known about the effects of fire on the structure and function of desert streams. The headwaters and mainstem of Sycamore Creek were unburned in the 2020 fire, but all eastern tributaries burned; thus, potential effects of the fire on the stream ecosystem will be indirect and driven by episodic hydrologic connections between the burned uplands and the stream. Such connections during the upcoming summer monsoon and winter frontal storm seasons present an immediate opportunity to study the effects of a novel disturbance and observe how disturbances are propagated between ecosystems. Proposed research will investigate the impacts of arid land fire on water flows, sediment and nutrient loading, and organic carbon inputs during storms that connect the desert uplands with the stream, using continuous sensor records and event-based sampling. Examination of in-stream responses, both immediately and after one year, will identify the capacity for receiving ecosystems to absorb and mitigate this disturbance. Observations of in-stream responses will include macroinvertebrate communities; modeling of stream metabolism and measures of organic carbon uptake by microbes; and changes in channel morphology, surface-water extent, and the distribution of wetland vegetation along 12 km of the mainstem. Data and findings from the research will be shared with agencies responsible for management of forests and water supply to the Phoenix metro area.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.