Summary
A semi‐quantitative method is described for the determination of free sugars in lake sediments. The method involves extraction with 70% ethanol, deionization with ion exchange resins, and separation and estimation of the sugars on paper chromatograms. The following sugars were detected in extracts of sediments from three Ontario lakes: maltose, sucrose, glucose, fructose, galactose, arabinose, ribose, xylose, and two unknowns. Total amounts of free sugar ranged from traces up to 2.9 g/kg of sediment ignitable matter. Maltose and glucose were usually the dominant sugars. Analyses of two surface cores of mud revealed decreasing concentrations of free sugars from the mud surface down to a depth of 50 cm. The sedimentary sugars are quantitatively held by the mud particles, and are lacking in the pore water of the mud. Lake mud sorbs small amounts of sugars from dilute aqueous solution, but the problem of sorption requires more detailed investigation before its importance can be assessed. Analysis showed that tendipedid larvae were not the source of the mud sugars, and theoretical arguments were presented to show that neither were the living bacteria in the sediment.
Three samples of seston contained 2.3, 3.9, and 42.4 g of total sugar per kg dry weight respectively, with glucose and maltose present in the greatest amounts. The concentration of free sugars in seston decreased by over 90% during aerobic decomposition in the laboratory. Seston is considered to be the main source of the sedimentary sugars, both by directly contributing free sugars to the mud as well as by producing starch‐like polysaccharides which can be hydrolysed in situ to produce free sugars.
The results of a culture experiment with lake mud showed complete disappearance of sedimentary sugars after 24 days of anaerobic culture in the presence of Bacto‐Yeast‐N‐base. Without the addition of Bacto‐Yeast‐N‐base, more sugar was found after 24 days than was initially present, both in aerobic and anaerobic cultures. Some factor in the Bacto‐Yeast‐N‐base enhanced the disappearance of sugars from mud.
Methodology
Sediment cores, culture experiment