Abstract
Five surface sediment samples (0–3 cm), two suspended sediment samples and a zooplankton sample from Lake Ontario were analysed for nitrogen-containing compounds. Amino acids, amino sugars, ethanolamine and urea were separated and characterized by ion-exchange chromatography. Free amino acids and soluble combined amino acids and amino sugars accounted for less than 0–25 per cent of the total nitrogen in the sediments. Insoluble combined amino acids and amino sugars were the most abundant nitrogen fraction in the sediments, making up from 49 to 55 per cent of the total nitrogen. Evidence is presented that asparagine, glutamine and citrulline are present in the interstitial waters and may make up part of the sediment organic nitrogen that was not characterized. The free amino acids released by the proteolytic enzyme, pronase, from the interstitial waters and sediment humic and fulvic acid extracts were determined. Pronase released 65 per cent of the soluble combined amino acids and 34 per cent of the fulvic acid amino acids as free amino acids. Enzyme activity was inhibited in the presence of the humic acid extract. The results indicate that the combined amino acids in the interstitial waters and fulvic acid extracts are intermediates between the primary aquatic detritus and the sediment humic acids. The enzyme experiments and infra-red data indicate that part of the sediment amino acids are combined through peptide linkages.
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