The Arctic LTER research site is in the foothills region of the North Slope of Alaska and includes the entire Toolik Lake watershed and the adjacent watershed of the upper Kuparuk River, down to the confluence of these two watersheds. This area is typical of the northern foothills of the Brooks Range, with continuous permafrost, no trees, a complete snow cover for 7 to 9 months, winter ice cover on lakes, streams, and ocean, and cessation of river flow during the winter. Tussock tundra is the dominant vegetation type but there are extensive areas of drier heath tundra on ridge tops and other well-drained sites as well as areas of river-bottom willow communities. The North Slope is divided into the Coastal Plain (6,000 km2), the Foothills (95,000 km2), and the Mountains (40,000 km2). The Arctic Long-Term Ecological Research (ARC-LTER) project is one of 24 LTER projects in North America, Puerto Rico, and Antarctica. The Arctic LTER's field research site is based at University of Alaska's Toolik Field Station, Alaska, in the northern foothills of the Brooks Range (68° 38'N, 149° 43'W, elevation 760 m). The foothills are characterized by continuous permafrost, no trees, 24 hour sunlight during short cool summers, periods of complete darkness during long cold winters (graph) and numerous pristine lakes and streams. Tussock tundra is the dominant vegetation but there are extensive areas of wet sedge tundra, drier heath tundra on ridge tops and other well-drained sites as well as areas of river-bottom willow communities. The year-round base of the Arctic LTER project is at the Ecosystems Center of the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts. The Principal Investigator of the Arctic LTER is Gus Shaver while Breck Bowden, Laura Gough, Anne Giblin, Phaedra Budy and George Kling form an executive committee and direct the four main components of the research including groups focused on tundra, streams, lakes, and landscape interactions. The goal of the Arctic LTER project is to predict the future ecological characteristics of the site based upon our knowledge of the controls of ecosystem structure and function as exerted by physical and geologic factors, climatic factors, biotic factors, and the changes in fluxes of water and materials from land to water. To achieve this goal the Arctic LTER uses several approaches: Long-term monitoring and surveys of natural variation of ecosystem characteristics in space and time. Includes: climate, plant communities and productivity, thaw depth, stream flow, chemistry of streams and lakes, temperatures of streams and lakes, lake chlorophyll lake productivity, zooplankton abundance. Experimental manipulation of ecosystems for years and decades. Includes: tundra warming, shading, and fertilizing, grazer exclusions, fertilization of lakes and streams, addition and subtraction of predators. Synthesis of results and predictive modeling at ecosystem and watershed scales. Includes: stream N cycling, lake physics, bioenergetics of fish populations, water movement and transfer of DOC and nutrients from land to water, soil respiration, cycling and storage of C in tundra under different scenarios of future climates.