Collaborative Research: RAPID: Quantifying the response of stream ecosystems to a punctuated cold-stress disturbance across a semi-arid to sub-humid gradient

合作研究：RAPID：量化河流生态系统对半干旱到半湿润梯度间断冷应激干扰的响应

• 批准号: 2128280
• 负责人: Amber Ulseth
• 金额: $ 2.21万
• 依托单位: Sam Houston State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-05-15 至 2023-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2128280&HistoricalAwards=false
• 关键词: Collaborative; Research; RAPID; Quantifying; response

Climate change is expected to result in increased global mean temperatures that will lead to movement of tropical and sub-tropical species toward the poles, a process known as “tropicalization”. Changes in precipitation patterns are predicted to be spatially variable, with some regions becoming drier and others wetter. The ecology and health of stream ecosystems are particularly susceptible to changes in rainfall and temperature. Simultaneously, the frequency and intensity of extreme weather events are expected to increase, and it is unknown how these extreme events will interact with gradual changes in temperature and precipitation to affect stream ecosystems. This research evaluates how a recent extreme event, the February 2021 “polar vortex” in Texas, interacts with changing mean climate conditions to predict how climate change will impact the structure and function of U.S. stream ecosystems in the coming decades. The research leverages a steep, natural rainfall gradient that features an abrupt shift in stream community composition and ecosystem functioning between semi-arid and mesic ecosystems. Repeated field measurements are being made for one year after the polar vortex and these data compared to prior data collected from these streams over the last 4 years. This work greatly increases our understanding of how climate change will affect sub-tropical stream ecosystems and their biota. Training of undergraduates (including minority) and graduate students along with community outreach via an established K–12 program contribute to the project’s broader impacts for society.The goals of this research are to characterize the direct and indirect impacts of an extreme cold event (ECE) on stream ecosystem structure and function and to examine the role of organism traits and local environmental features that drive these effects. Punctuated low temperatures below an organism’s thermal limits can result in physiological, behavioral, and fitness consequences. These events are particularly important in the context of understanding tropicalization. Warm-adapted species are expanding poleward but lack adaptations for cold conditions, and thus may be more vulnerable to ECEs, driving mass mortality events. The impact of mass mortality events on ecosystem functioning may last for months to years and result in population declines, changes to community composition, and the contribution of dead individuals to the organic matter pool. The following hypotheses are being tested: 1) mesic streams will have greater thermal buffering capacity than semi-arid sites due to their greater discharge per unit watershed and greater tree canopy that creates a microclimate above the water surface; 2) taxa in semi-arid streams will have greater cold tolerance because many of them have adaptations to cope with harsh conditions; 3) taxa with neotropical ancestry will have lower cold tolerance due to a lack of adaptions for cold stress; 4) fish and invertebrate mortality will indirectly affect the abundance of algae and benthic organic matter, impacting stream metabolism. Because ECEs may become more common in the future, studying this historically rare event may help us understand how ECEs may interact with “tropicalization”. Furthermore, the utilization of a steep rainfall gradient provides an exceptional opportunity to study the interaction between extreme disturbance and long-term climate conditions.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.

气候变化预计将导致全球平均气温升高，从而导致热带和亚热带物种向两极移动，这一过程被称为“热带化”。预计降水模式的变化会在空间上发生变化，一些地区变得干燥，另一些地区变得湿润。河流生态系统的生态和健康特别容易受到降雨和温度变化的影响。同时，极端天气事件的频率和强度预计将增加，但尚不清楚这些极端事件将如何与温度和降水的逐渐变化相互作用，从而影响河流生态系统。这项研究评估了最近发生的极端事件，即 2021 年 2 月德克萨斯州的“极地涡旋”如何与不断变化的平均气候条件相互作用，以预测未来几十年气候变化将如何影响美国河流生态系统的结构和功能。该研究利用了陡峭的自然降雨梯度，其特征是半干旱和中等生态系统之间溪流群落组成和生态系统功能的突然转变。在极地涡旋发生后一年内进行了重复的现场测量，并将这些数据与过去四年从这些流中收集的先前数据进行了比较。这项工作极大地增加了我们对气候变化将如何影响亚热带河流生态系统及其生物群的理解。通过既定的 K-12 计划对本科生（包括少数民族）和研究生进行培训以及社区外展，有助于该项目对社会产生更广泛的影响。这项研究的目标是描述极冷事件 (ECE) 对河流生态系统结构和功能的直接和间接影响，并研究驱动这些影响的生物体特征和当地环境特征的作用。低于生物体热极限的间歇性低温可能会导致生理、行为和健康方面的后果。这些事件对于理解热带化尤其重要。适应温暖的物种正在向极地扩展，但缺乏对寒冷条件的适应，因此可能更容易受到 ECE 的影响，从而导致大规模死亡事件。大规模死亡事件对生态系统功能的影响可能持续数月至数年，并导致人口下降、群落组成发生变化以及死亡个体对有机物库的贡献。正在测试以下假设：1）中等河流比半干旱地区具有更大的热缓冲能力，因为它们每单位流域的流量更大，并且树冠更大，在水面上方形成了小气候； 2）半干旱河流中的类群将具有更强的耐寒性，因为其中许多类群具有适应恶劣条件的适应性； 3）具有新热带血统的类群由于缺乏对冷应激的适应而具有较低的耐寒性； 4）鱼类和无脊椎动物的死亡将间接影响藻类和底栖有机物的丰度，影响河流的新陈代谢。由于 ECE 未来可能会变得更加普遍，研究这一历史上罕见的事件可能有助于我们了解 ECE 如何与“热带化”相互作用。此外，利用陡峭的降雨梯度为研究极端干扰与长期气候条件之间的相互作用提供了绝佳的机会。该奖项反映了 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。