Redox potential as an important characteristic of the chemical and biological state of surface waters (review)

This review summarises literature data on redox potential (Eh) as an essential characteristic of surface waters affecting their ecological and chemical state. We consider the influence of Eh on the migration of nutrients, metals, and metalloids in the 'bottom sediments – water' system and its role in the secondary pollution of water bodies. Hypoxia, anaerobic conditions, and reduced Eh leads to an increase in the concentration of nutrients, reduced forms of manganese and iron, due to their migration from bottom sediments to the aquatic environment. This, in turn, contributes to enhanced eutrophication of water bodies. We reviewed the data on the transformation of metal and metalloid compounds depends on the intensity of redox processes resulting their bioavailability, and toxicity to aquatic organisms. Humic substances, as the most common group of dissolved surface water organic substances, exhibit reducing properties and affect the coexisting metals and metalloid species. The intensity of redox processes in surface water will increase under climate change. The issue of redox transformation of elements will need to be considered in the context of developing measures to reduce surface water loading with primarily nutrients and metals, taking into account the possibility of internal pollution of water bodies.