Carbohydrates, uronic acids and alkali extractable carbohydrates in contrasting marine and estuarine sediments: Distribution, size fractionation and partial chemical characterization

Concentration, size fractionation and monosaccharide composition of carbohydrates and uronic acids were investigated in contrasting sediments of the Mandovi estuary (ME), Arabian Sea (AS) and the Bay of Bengal (BOB). Concentrations and monosaccharide composition of carbohydrates and uronic acids varied spatially. Average yields of carbohydrates and uronic acids were higher for the estuarine compared to marine sediments. Interestingly, yields of carbohydrates and uronic acids increased in sediments with water column depth, implying preferential removal of other constituents, selective preservation and/or lateral input of carbohydrate rich material. Analysis of monosaccharide biomarkers indicates that carbohydrates were derived from terrestrial plants, bacteria and phytoplankton, however, the influence of the former was relatively greater in sediments of the ME and BOB, as well as in residual sediments of ME. Approximately 11–21% of total carbohydrates could be extracted using hot alkali extraction followed by sonication. Irrespective of the depositional environment, carbohydrates and uronic acids were greater in the very high molecular weight size fraction (>30 kDa). The abundance of glucose increased with the decrease in molecular size of extracted organic matter. This probably indicates its association with less degradable carbohydrates.