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

2020年6月，亚利桑那州有记录以来第五大火灾烧毁了索诺拉沙漠和Sycamore Creek分水岭的高海拔森林，Sycamore Creek是一个已经研究了40多年的生态系统。像火灾这样的干扰，当与季风和冬季暴雨相结合时，可能会导致径流携带大量沉积物、溶解碳和营养物质。这些径流事件也会降低溶解氧的浓度。较高的沉积物、碳和营养负荷以及较低的溶解氧降低了水质，最终为下游城市凤凰城的供水做出了贡献。然而，生态系统可能会通过捕获沉积物和吸收养分来吸收这些影响，从而减少火灾对下游生态系统的影响。这个快速奖将研究季风和冬季锋面风暴期间燃烧的支流与未燃烧的支流相比，燃烧后的沉积物、碳和营养物质的输入。他们将在风暴发生后和火灾发生一年后立即观察溪流生态系统的潜在变化，包括植物群落和无脊椎动物群落、碳和氧气的处理以及河道形状。索诺兰沙漠很少发生大火，但由于入侵草类的生长和人类活动，预计大火将变得更加常见。这项研究将帮助森林和市政水资源管理人员预测干旱土地火灾的后果，并帮助支持一名技术人员、一名研究生和一名本科生的专业发展。2020年6月的一场大规模野火烧毁了亚利桑那州780平方公里的索诺拉沙漠和更高海拔的林地和森林，包括近一半的Sycamore Creek分水岭，40年溪流生态研究的地点和一个霓虹灯水生地点。沙漠西南部的大规模火灾在历史上是罕见的或根本不存在的，但由于入侵的草地和人类活动，火灾正变得越来越常见，但人们对火灾对沙漠溪流结构和功能的影响知之甚少。Sycamore Creek的源头和主干在2020年的大火中没有被烧毁，但所有东部支流都被烧毁；因此，火灾对河流生态系统的潜在影响将是间接的，并受到被烧毁的高地和溪流之间时断时续的水文联系的驱动。在即将到来的夏季季风和冬季锋面风暴季节，这种联系为研究一种新的扰动的影响和观察扰动如何在生态系统之间传播提供了直接机会。拟议的研究将利用连续的传感器记录和基于事件的采样，调查干旱土地火灾对风暴期间水流、沉积物和养分负荷以及有机碳输入的影响，这些风暴将连接沙漠高地和溪流。立即和一年后对河流中的反应进行审查，将确定接受生态系统吸收和减轻这种干扰的能力。对溪流响应的观察将包括大型无脊椎动物群落；溪流新陈代谢的模拟和微生物吸收有机碳的措施；以及河道形态、地表水范围和湿地植被沿主干12公里的分布的变化。这项研究的数据和发现将与负责管理森林和凤凰城大都市区供水的机构分享。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.