Chemical transformation of the runoff of dissolved matters in the mouth areas of the Onega and Mezen’ rivers

Abstract

Natural observations were analyzed to study the distribution of dissolved species of major and trace elements in the Onega and Mezen’ mouth areas and the tendencies in the chemical transformations of the is continental runoff in the river mouths of the White Sea drainage system. It is shown that the migration of major ions and dissolved species of Li, Rb, Cs, Sr, B, F and Mo is consistent with a conservative behavior and is controlled by hydrodynamic processes. The amounts of uranium and barium additionally supplying in the Mezen’ mouth exceed those removed with a continental runoff, whereas the Onega, Severnaya Dvina, and other rivers of the White Sea drainage system are characterized by the conservative behavior of uranium, while barium desorption from particulate matter reaches no more than 33% of its content in the riverine waters. The growth of concentrations of these elements in the Mezen’ mouth is caused by the long-term interaction of solid matters of the continental runoff with saline waters in the tide-affected estuary. 28–59, 12–63, 25–67 and 20–63% of concentrations of iron, aluminum, lanthanum, and cerium are removed from the riverine waters in the mouth areas of all studied rivers of the White Sea drainage system mainly owing to the coagulation and flocculation of organic and organomineral colloids. The distribution of dissolved species of mineral phosphorus and silicon in the Mezen’ mouth is presumably controlled by the remineralization of the organic matter in the bottom sediments, which due to the hydrological features of estuary are regularly stirred up and interact with vertically mixing water sequence. Up to 20–46% of dissolved phosphates and 3–22% of silicon are removed from the continental runoff during vegetation period in the mouths of the Onega, Severnaya Dvina, and other rivers of the White Sea drainage system mainly owing to their biological consumption.