Investigating the Chemical Composition and Bioavailability of Arctic River Dissolved Organic Matter (DOM) Using Biomarkers

Abstract

Arctic rivers are the dominant pathways for the transport of terrestrial dissolved organic matter (DOM) to the Arctic Ocean, but knowledge of lability, sources, and transformations of organic carbon and nitrogen in Arctic river watersheds is extremely limited. This study uses chemical analyses of enantiomeric amino acids and carbohydrates as biomarkers to investigate the chemical composition and bioavailability of DOM in five major Arctic watersheds. Carbohydrate-based indicators are sensitive to polysaccharide components derived from all plant sources; hydroxyproline and D-amino acids serve as indicators of plant and bacterial nitrogen, respectively. The results show the bioavailability of DOM in Arctic rivers is strongly correlated with seasonal discharge, vegetation topography, and water residence time. Pulses of bioavailable DOM were observed in the Siberian Rivers during the spring freshet, whereas the Mackenzie River exhibited extensively degraded DOM throughout all stages of the hydrograph. Freshet samples showed elevated input of plant-derived dissolved organic nitrogen. Bacterial organic matter comprised a significant fraction of riverine DOM (20-40%). These results demonstrate the importance of bacteria in regulating DOM composition and reactivity in Arctic rivers.