Study of the formation of anthropogenically induced additional migration pathways for manganese

The article examines the equilibrium of the system: dissolved manganese (Mn2+) ⇔ undissolved manganese in the water column of rivers of the Amur River basin in Outer Manchuria. The study focuses on the mobilisation of geogenic manganese from bottom sediments and iron-manganese nodules, rather than direct anthropogenic pollution. Rivers draining these territories are characterised by high Mn2+ concentrations reaching up to 2600–2700 μg/l. Hydrochemical parameters have been established at which Mn2+ does not accumulate and its concentration does not exceed background values (up to 40 μg/l). However, due to anthropogenic influence in this territory, Mn2+ becomes the dominant form of manganese (from 69 to 92%). It has been shown that the main factors statistically associated with this mobilisation process are the influx of Corg of likely anthropogenic origin, as well as oxygen depletion. It is likely that most of the Corg is not directly involved, but rather acts enzymatically with the participation of microorganisms. NH4+ and H2S were identified as the best markers indicating a favourable hydrochemical environment for manganese release. A Bayesian network was constructed to predict the concentration ranges of Mn2+. The model allows accurate prediction of the degree of environmental risk associated with manganese release due to anthropogenic impact and the subsequent emergence of the danger of manganese intoxication.