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.
