Contribution of Nutrients from Sediments and Interstitial Water to Colville River System, Alaska

Abstract

Arctic regions differ from temperate areas in the extreme seasonality of climatic conditions. In 1971, water samples and bottom sediments were taken from the Colville River system in Arctic Alaska prior to breakup, during breakup, and during summer for nutrient study. Although sediments are primarily sandy, some silt and clay are also present especially in the oceanic portion of the delta. Clay minerals are primarily kaolinite and illite. Montmorillonite and small amounts of a chlorite-like mineral are also present. The organic content in the sediments was higher in the upper river channel than in the ocean, whereas interstitial nitrogen components showed the opposite trend. These interstitial components are the products of organic decomposition in sediments. Through diffusion and animal activity, some of these components may slowly enter the water column beneath the ice cover during winter when exchange of water throughout the river channel is blocked by bottomfast ice. During the flood period in early spring, interstitial components in the basin sediments are also contributed to river water by leaching.

Once flooding begins, river water, which consists of snowmelt from mudflats, sand dunes, and the tundra surface, moves under the sea ice as a wedge. It contains more nutrients than does the seawater beneath. This floodwater, rich in inorganic-N (N/P ratio = 23: 1 in 1971), is significant in contributing to the nitrogen-deficient seawater (N/P ratio = 3: 1), and provides a basic ingredient for phytoplankton production. During summer, depletion of nutrients prevails as a result of phytoplankton uptake and dilution by seawater. It was calculated that during spring the nutrient-enriched floodwater of the Colville River contributes 0.875×10⁶ kg of inorganic-N to the ocean. Such nutrient input is significant in the primary productivity of this nearshore zone, helping account for the abundance of fish found in the area.