Freeze or famine: do uncoupled temperature and light regimes drive unique seasonal production-demand relationships in arctic spring-stream ecosystems?

研究人员将研究季节性光照和温度之间的相互作用，以及这些如何通过利用春季喂养的栖息地来影响生态系统过程，这些栖息地在冬季保持在冰点以上，否则季节性强烈的北极地区。在阿拉斯加，常年水流和相对稳定的温度的溪流广泛分布，为多莉瓦登（Dolly Varden）（一种重要的生存鱼类）等物种提供了冬季栖息地，否则这些物种可能无法生存。这些系统还提供了一个独特的机会来研究季节性光和温度模式的解耦。该项目将研究与冬季相对温暖的温度相关的能源成本，当没有高生产力的支持时，通常伴随着温暖和充满阳光的夏季，影响北极生物，种群和食物网。研究人员将重点关注阿拉斯加的十个地点，冬季平均气温在1到13摄氏度之间，并在所有季节对这些地点进行采样。研究结果将有助于评估重要水生物种的栖息地质量，研究人员将与联邦和州资源管理人员分享研究结果。此外，该项目将支持一名早期职业教师和两名研究生，四名本科生将参与夏季实地考察。这项研究将促进对北极科学和生态学领域的基本理解。数据将在阿拉斯加的10个春季溪流收集，跨越温度梯度，覆盖所有季节。总体目标是评估光和温度对生态系统过程（总初级生产，生态系统呼吸，营养吸收，次级生产，食物网属性）和生物生长速率，代谢和组织化学计量学在这些栖息地的相互作用的影响。在阿拉斯加的北极地区，常年流动的春季河流和稳定的温度每年只有3-4摄氏度的波动，其他类型的河流在冬季可能会冻结。这些生态系统的特点是相对温暖的热制度嵌入在一个强烈的季节性北极景观，是高生产力和关键物种（如多莉瓦登炭，红点鲑）提供关键的冬季栖息地。它们还提供了一个独特的研究背景，特别是在年度光照和温度制度的解耦方面，以及对季节性生态系统过程的后续影响。之前在阿拉斯加州Ivishak Spring的研究表明，与大多数其他生态系统不同，在这些生态系统中，光驱动的初级生产总值（GPP）和有机碳（C）需求的季节性周期与夏季的高产量和需求以及冬季的低产量和需求密切相关，北极春季溪流的周期是季节性分离的。换句话说，在GPP受光照限制的季节，暖冬温度会推动消费者对C的高需求率。因此，尽管这些泉水提供了一个必要的冬季避难所（一个“冻结或饥荒”的情况），但它们带来了巨大的生物能量成本。由于北极春季溪流的冬季平均温度在1到13摄氏度之间，冬季生物能源成本的严重程度可能很广，在最温暖的溪流中，代谢受到惩罚，以至于一些分类群可能无法成功越冬。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

The investigators will examine the interactions between seasonal light and temperature and how these affect ecosystem processes by taking advantage of spring-fed habitat that remains above freezing in winter during the otherwise intensely seasonal Arctic. Streams with year round water flow and relatively stable temperatures are widespread in Alaska and provide winter habitat for species such as Dolly Varden (an important subsistence fish) that might otherwise be unable to survive. These systems also provide a unique opportunity to study the uncoupling of seasonal light and temperature patterns. This project will examine how the energy costs associated with relatively warm temperatures in winter, when not supported by high productivity that would typically accompany warm and light-filled summer months, affect Arctic organisms, populations, and food webs. The investigators will focus on ten sites in Alaska with average winter temperatures ranging from 1 to 13 degrees C and sample these in all seasons. Results will help evaluate habitat quality for important aquatic species, and the investigators will share findings with federal and state resource managers. In addition, the project will support an early career faculty member and two graduate students, and four undergraduates will be involved with summer fieldwork.This research will advance fundamental understanding in both Arctic sciences and the field of ecology. Data will be collected at 10 spring-streams in Alaska across a thermal gradient and covering all seasons. The overarching goal is to assess the interactive effects of light and temperature on ecosystem processes (gross primary production, ecosystem respiration, nutrient uptake, secondary production, food-web attributes) and organismal growth rates, metabolism, and tissue stoichiometry in these habitats. Spring-fed streams with perennial flow and stable temperatures with annual fluctuations of only 3-4 degrees C are widespread in arctic Alaska, where other stream types can freeze solid during winter. These ecosystems, characterized by relatively warm thermal regimes embedded in an intensely seasonal arctic landscape, are highly productive and provide critical winter habitat for key species (e.g. Dolly Varden char, Salvelinus malma). They also provide a unique research context, particularly with regard to the uncoupling of annual light and temperature regimes, with subsequent effect on seasonal ecosystem processes. Prior research at Ivishak Spring, Alaska, has shown that unlike most other ecosystems where light-driven seasonal cycles of gross primary production (GPP) and organic carbon (C) demand are closely coupled with high production and demand during summer and low production and demand during winter, arctic spring-streams have cycles that are seasonally uncoupled. In other words, warm winter temperatures drive high rates of C demand by consumers during the season when GPP is light-limited. Consequently, these springs impose significant bioenergetic costs despite providing an essential winter refuge (a "freeze-or-famine" scenario). Since mean winter temperatures among arctic spring-streams range from ~1 to 13 degrees C, the range in severity of winter bioenergetic costs is likely to be wide, with metabolic penalties in the warmest streams to the point that some taxa may be unable to overwinter successfully.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.