CLIMATE CHANGE, FLOWPATH, AND NUTRIENT FLUX IN A TREELINE WATERSHED, NOATAK NATIONAL PRESERVE, ALASKA

High latitude terrestrial ecosystems contain 30 - 45% of the global organic carbon pool. Soil warming may enhance release of carbon dioxide and the production and export of dissolved organic carbon (DOC) and nitrogen (DON), important energy and nutrient sources in the aquatic ecosystem. The export of DOC and DON can be affected by seasonal subsurface flowpath, soil temperature, moisture, total carbon (C) and nitrogen (N) pool size, and available inorganic N. In 1990, we began studies in the 800 ha treeline Asik watershed, Northwest Alaska. One objective was to define ecosystem response to change in climate and available N. Northern Alaska has warmed during the last decade. At Asik, soil respiration rates increased (p <0.05) with temperture. Depth to the soil active layer increased 60 cm seasonally. Soil water DOC concentrations differ (p <0.1) by vegetation with concentrations higher (p=0.07) beneath the taiga-tundra transition zone than spruce. Alpine and subalpine stream water DOC and DON concentrations were similar during spring runoff indicating much winter mineralization throughout the watershed despite large differences in soil C and N pool size. By mid-summer, subalpine stream water DOC concentrations and flux increased relative to the alpine. The seasonal change likely is the product of deep soil thawing, increased melt runoff and precipitation, and warming subalpine soils. Alpine stream water ion concentrations indicate melt waters quickly pass through surface porous soils and are well mixed before reaching the stream. Subalpine stream water ion concentrations show a pattern indicating the subsurface flowpath to the stream is shallow. Watershed ecosystem nutrient budgets vary because of seasonal changes in subsurface hydrologic flowpath and soil mineralization rates.