Transformation of dissolved organic matter and related trace elements in the mouth zone of the largest European Arctic river: experimental modeling

The relationship between dissolved organic matter (DOM) and heterotrophic bacterioplankton controls the ecological status of freshwater ecosystems and the fate of metals in aquatic environments. To improve our understanding of physicochemical and biological processes controlling the DOC and related trace elements in the Arctic estuary, we conducted experiments of the biodegradation and physicochemical coagulation of DOM and associated trace elements. For the experiments, water from the estuarine zone of the Severnaya Dvina River in Russia, the largest pristine European Arctic river, was mixed with sterile river water from the freshwater zone, sampled during spring flood in June and summer base flow in August. We revealed a lack of transformation of allochthonous organic matter in spring and measurable degradation of more autochthonous DOM in summer. According to their behavior during incubation experiments, several groups of trace metals were distinguished, comprising (1) nonconservative Fe, Mn, A...