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中的营养循环。在阿拉斯加的东部北坡，泉水流入的溪流常年流动，水温几乎恒定(3-7摄氏度)，在那里，其他源头溪流一年中有六个月以上是结冰的。驱动假设之一是，由于温度全年保持几乎恒定，异养生物活动的速率(例如，二次生产、生态系统呼吸)在夏季和冬季不会有差异。然而，初级生产量的速率将受到光照的限制，因此由于昼长的极端年度周期(24小时光照到24小时黑暗)，不同季节之间将有很大差异，这可能会迫使相关生态过程发生循环。此外，据推测，越冬鱼类(北部Dolly Varden char Salvelinus Malma)进出泉水的迁徙活动会影响捕食率和营养供应。因此，迁徙模式是应该进一步加剧社区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夏季结构和过程对假设的冬季条件的外推，而没有冬季观测的好处。这项研究的第一个目标是通过将生态系统新陈代谢、分解速率、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，测试调查生物活动的季节性变化。实验将在两年的时间里，在一条具有代表性的泉水中，大约每月进行一次。该研究的第二个目标是通过将碳种群结构、产量、捕食率和养分排泄率与观察到的生物生产力模式联系起来，将鱼类迁徙的假想后果与其他驱动因素区分开来。拟议的研究将为预测了解北极春季生态系统潜在的不成比例的景观作用提供基础，北极春季生态系统的季节性变化从该地区流动的溪流栖息地的1%到100%。这两个目标的结果将结合起来，评估泉水作为全年生物生产力和分类丰富度“热点”的作用与迁徙的碳水化合物种群之间的相互作用，迁徙碳水化合物种群的运动将泉水溪流与整个北坡景观的水生生态系统连接起来，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)的科学伙伴关系造福社会。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溪流群落季节性避难所的作用，可能对未来管理南水北调淡水资源至关重要。该项目还将通过两项主要活动促进教学、培训和学习，从而将研究和教育结合起来。首先，作为该项目的一部分，一名博士生和一名博士后研究助理将接受培训。第二，本科生将参与实验室活动，并将寻求暑期REU支持本科生参加暑期实地考察工作，在此期间，他们将开展与该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.