The oxidation of manganese in seawater: Rate constants based on field data

Rate constants for the oxidation of dissolved manganese (II) are calculated from the distributions of dissolved manganese, particulate manganese, and dissolved oxygen in the Saguenay Fjord, Canada. Laboratory studies have described the oxidation using two different kinetic equations: − d[ Mn(II)] dt = k 1[ Mn(II)][ O 2]+k 2[ Mn(II)][ Mn p][ O 2] − d[ Mn(II)] dt = k[ Mn(II)][ Mn p][ O 2] The rate constants for both equations describe the oxidation in the Saguenay, in Loch Goil in Scotland, and in typical coastal seawaters equally well. Only the rate constants for the second equation, however, agrees well with field data from deep ocean waters. The manganese oxidation kinetics have been used to relate the vertical eddy diffusivity to the upwelling rate in deep water in the lower St Lawrence Estuary. In the upper St Lawrence Estuary, the kinetic model shows that net input of dissolved manganese by desorption from particles and release from sediments has comparable magnitude in April and August. The very different shapes of the dissolved manganese/salinity relationships at these two seasons are due to differences in the manganese oxidation rates.