ABSTRACT
The abundance of manganese in the Earth’s crust has been estimated to be 0.1% (Alexandrov, 1972, p. 670). The element is, therefore, only 1/50th as plentiful as iron in this part of the Earth. Its distribution in the crust is by no means uniform. In soils, for instance, its concentration can range from 0.002 to 10% (Goldschmidt, 1954). An average concentration in freshwater has been reported to be 8 µg kg−1 (Bowen, 1979). Concentrations slightly in excess of 1 mg kg−1 can be encountered in anoxic hypolimnia of some lakes. In seawater, an average concentration has been reported to be 0.2 µg kg−1 (Bowen, 1979), but concentrations more than three orders of magnitude greater can be encountered near active hydrothermal vents at midocean spreading centers.
