Seasonal variability and geochemical significance of organic matter in the River Ganges, Bangladesh

Abstract

Asian rivers, particularly those originating in the Himalayas, contribute significantly to the annual global sediment discharge from the land to the sea¹. Although some data are available on the inorganic geochemistry of these rivers^2–6 little is known about their organic matter load^7,8. Over the past 4 years we have been studying the Ganges–Brahmaputra river system at locations in Bangladesh^9,10 with sampling intervals of 4 to 6 weeks. Here we report on the seasonal variability of organic matter in the dissolved and suspended loads of the Ganges during 1981 as revealed by data on particulate and dissolved organic carbon (POC and DOC) and their constituent fractions such as sugars, amino acids and n-alkanes. Organic matter associated with peak sediment discharge (July to November) appears to be dominated by a biodegraded fraction, presumably also resulting from biogeochemical processes occurring in the ox-bow lakes in Bangladesh, and, as a consequence, are less susceptible to further decomposition upon reaching the marine environment. We suggest that rivers such as the Ganges with their high sediment load are significant in terms of land-derived organic carbon burial in marine sediments.