Seasonality of Nutrient and Organic Matter Export from the North Slope of Alaska to the Beaufort Sea

Riverine fluxes of land-derived material from watersheds to the coastal ocean are tightly coupled with climate variables that control the water balance as well as biological and geochemical activity. In the Arctic, this coupling is exemplified by wide seasonal variations in river export. This presentation will focus on nutrient and organic matter export from the Sagavanirktok, Kuparuk, and Colville rivers to the Beaufort Sea. Together these three rivers drain most of the land area on the North Slope of Alaska. While the USGS measures water discharge near the mouth of the Kuparuk River, there are no gauging stations at downstream locations on the Colville or Sagavanirktok rivers. Water discharge was therefore modeled to support estimates of export from these two rivers. Water chemistry was measured at downstream locations on all three rivers during intensive field efforts in 2006 and 2007. Variations in water chemistry were most pronounced surrounding the spring freshet. Increased organic matter concentrations during high flow amplified organic matter export during this period. Ammonium and soluble reactive phosphorus exhibited similar patterns to those observed for organic matter. In contrast, dilution of nitrate during high flow diminished relative export of nitrate during the spring freshet. Organic matter quality (as demonstrated by C:N ratios and stable isotope values) also changed dramatically between spring and summer. River export estimates provide a basis for considering runoff contributions to productivity in coastal waters of northern Alaska. Changes in climate are likely to alter the timing and magnitude of river export from the North Slope in the future.