The solubility of manganese in natural water is strongly influenced bychemical equilibria involving Mn+2, Mn+3and Mn+4species, redox potential, pH, and dissolved species of bicarbonate and sulfate. The solubility of manganese is shown by graphs as a function of Eh and pH in the absence of sulfate and in the presence of several different fixed activities of bicarbonate and sulfate ranging from 10 to 2,000 ppm (parts per million). Solubility is increased by the complexes MnHCO+3and MnSO4aq. whose association constants are 63 and 190, respectively.