Hydrogeochemistry of the surface waters of the Mackenzie River drainage basin, Canada—II. The contribution of amino acids, hydrocarbons and chlorins to the Beaufort Sea by the Mackenzie River system

Abstract

Abstract A major portion of the organic matter deposited on the continental shelf of the Beaufort Sea in the Canadian Arctic is from the drainage basin of the Mackenzie River. 101 samples of surface waters from the Mackenzie River drainage basin were collected in mid-summer of 1969. Sixteen amino acids were determined in selected samples using gas chromatography. The bulk of the acids were present in combined form in suspended particulate material. Suspended solid material contained 635 to 2260 gmg/g of total amino acids, corresponding to 15 to 220 μg/1 of river water. Filtered waters ranged from 11.1 to 78.6 μg/l, with combined acids ten times more abundant than free acids. The distribution pattern for individual amino acids in the filtrates was significantly different from that in the particulate matter. Fluorescence analysis for chlorins showed emission at 672 nm for excitation at 410 nm. The principal pigments were uncomplexed pheophytins, about 80 per cent of which appeared to be associated with the suspended sediment rather than in true solution. Abundances of chlorin pigments in the water ranged from 0.5 to about 100 ng/l with a median value of 7 ng/l. Neither amino acids nor chlorins experienced appreciable degradation in the drainage basin. Six samples of sediment, collected from mud flats along the rivers and lakes, were examined for saturated hydrocarbons. The amount of normal alkanes, C 14 to C 34 , varied from a total of 0.5 μg/g, in a sample from a mountain stream to a total of 9.4 μg/g in a shallow lake sediment. The CPI ranged from 2.9 to 5.1. Isoprenoid hydrocarbons, phytane and pristane, were also present. It is estimated that 5.9 × 10 10 g of amino acids, 2.8 × 10 6 g of chlorins and 2.4 × 10 8 g of normal alkanes annually enter the Beaufort Sea from the Mackenzie River.