Factors controlling seasonal changes in the structure and function of food webs of perennial spring streams in Arctic Alaska

这项研究将调查阿拉斯加北部泉水溪流的营养循环。常年流动且水温接近恒定（3- 70摄氏度）的泉水溪流在阿拉斯加的东北坡上相对广泛，在那里，其他源头溪流一年中有6个多月都是冻结的。其中一个重要的假设是，由于全年温度几乎保持不变，异养生物活动（如次生生产、生态系统呼吸）的速率在夏季和冬季之间不会有差异。然而，初级生产的速度将受到光照的限制，因此由于日照长度（24小时光照到24小时黑暗）的极端年周期，不同季节之间的差异会很大，这可能会迫使相关生态过程发生循环。此外，越冬鱼类（北多利Varden char Salvelinus malma）进出春季溪流的迁徙假设会影响捕食率和营养供应。因此，迁移模式是一个应进一步加剧群落和生态系统动态的季节性模式的过程。这些假设在很大程度上是基于对夏季结构和过程的外推，以假设冬季条件，没有冬季观测的好处。本研究的第一个目的是通过将生态系统代谢、分解率、大型无脊椎动物群落结构和生产与潜在的非生物驱动因素联系起来，测试研究生物活性的季节性变化。在两年的时间里，实验将在一个有代表性的春季溪流中进行，大约每月一次。该研究的第二个目标是通过将鱼类种群结构、产量、捕食率和营养物质排泄率与观察到的生物生产力模式联系起来，将鱼类洄游的假设后果与其他驱动因素分开。拟议的研究将为预测北极春季生态系统可能不成比例的景观作用提供基础，春季生态系统在该地区流动溪流栖息地的季节性变化从1%到100%。这两个目标的结果将结合起来，以评估春季溪流作为全年生物生产力和分类丰富度的“热点”的作用与迁徙的鲑鱼种群之间的相互作用，它们的运动将春季溪流与整个北坡景观的水生生态系统联系起来，从布鲁克斯山脉到沿海的波弗特海。该项目将通过与北极国家野生动物保护区（ANWR）的科学合作造福社会。对北坡未来温度和降水模式的预测表明，了解多年生泉水作为河流群落季节性避难所的作用，可能对ANWR未来淡水资源的管理至关重要。该项目还将通过两项主要活动促进教学、培训和学习，将研究和教育结合起来。首先，一名博士生和一名博士后助理研究员将作为该项目的一部分接受培训。第二，本科生将参与实验室活动，并寻求暑期REU支持本科生参加暑期实地考察工作，在此期间，他们将开展与本项目相关的独立研究。

This research will investigate nutrient cycling in spring-fed streams in northern Alaska. Spring-fed streams with perennial flow and near-constant water temperatures (3- 7oC) are relatively widespread on the eastern North Slope of Alaska, where other headwater streams freeze solid for more than six months of the year. One of the driving hypotheses is that, because temperatures remain nearly constant year-round, rates of heterotrophic biological activity (e.g., secondary production, ecosystem respiration) will not differ between the summer and winter. Rates of primary production, however, will be limited by light and so will differ dramatically between seasons due to extreme annual cycles in day length (24-h light to 24-h darkness), potentially forcing cycles in related ecological processes. Additionally, the migratory movement of overwintering fish (northern Dolly Varden char Salvelinus malma) in and out of spring streams is hypothesized to affect predation rates and nutrient supply. Therefore, migration patterns are processes that should further exacerbate seasonal patterns of community and ecosystem dynamics. These hypotheses are based largely on the extrapolation of summer structure and processes to assumed winter conditions, without the benefit of winter observations. The first objective of this study is to test investigate seasonal changes in biological activity by relating ecosystem metabolism, decomposition rates, and macroinvertebrate community structure and production to potential abiotic drivers. Experiments will be coducted approximately monthly in a single, representative spring stream over a two-year period. The second objective of the study is to separate the hypothesized consequences of fish migration from other drivers by relating char population structure, production, and rates of predation and nutrient excretion to observed patterns of biological productivity. The proposed research will provide the basis for a predictive understanding of the potentially disproportionate landscape role of Arctic spring ecosystems, which shift seasonally from being 1% to 100% of the region's flowing stream habitat. The results of the two objectives will be combined to assess interactions between the role of spring streams as "hot spots" of year-round biological productivity and taxonomic richness, and that of migratory char populations, the movements of which connect spring streams to aquatic ecosystems across the whole North Slope landscape, from the Brooks Range to the coastal Beaufort Sea. This project will benefit society through a scientific partnership with the Arctic National Wildlife Refuge (ANWR). Predictions of future patterns of temperature and precipitation on the North Slope suggest that understanding of the role of perennial springs as seasonal refugia for stream communities may prove critical to future management of the freshwater resources of ANWR. This project will also integrate research and education by promoting teaching, training, and learning through two primary activities. First, one Ph.D. student and one Postdoctoral Research Associate will receive training as part of this project. Second, undergraduate students will be involved in laboratory activities and summer REU support will be sought for undergraduates to join summer fieldwork efforts, during which they will develop independent research related to this project.