Kinetics of manganese adsorption, desorption, and oxidation in coastal marine sediments

Ejection of excavated manganese (Mn)-laden particles from anoxic subsurface sediment onto an oxic sediment-water interface by infauna and by other physical disturbances triggers desorption and oxidation of reduced manganese species. These competing reactions determine whether adsorbed Mn(II) will be desorbed and escape into the water column or be oxidized to Mn(IV) and retained as an insoluble component of the sediment. Consequently, the net flux of Mn(II) to the water column depends on the relative rates of the two reactions. We determined the rates of Mn(II) adsorption, desorption, and oxidation by incubating slurries of natural anoxic sediment at 25 degrees C and monitoring the concentration of manganese in the aqueous phase of the slurry. The kinetics of adsorption, desorption, and oxidation were fitted to first-order rate laws. The first-order rate constants for adsorption (k'(ads) = 7.0 +/- 3.4 h(-1)) and desorption (k'(des) = 12.7 +/- 3.3 h(-1)) are more than two orders of magnitude greater than the first-order rate constant for oxidation (k'(ox) = 0.020 +/- 0.006 h(-1)). The combination of rapid desorption kinetics and slow oxidation kinetics allows dissolved manganese to be dispersed into the bottom water by turbulent diffusion and escape local reoxidation and retention at the sediment-water interface. Thus, advection of anoxic sediment to the sediment-water interface contributes to the overall flux of manganese from the sediment to the water column.

通过Infauna和其他物理障碍触发了解吸和氧化降低的锰物种的射精，从缺氧地下沉积物中发掘的锰（MN） - 淡颗粒颗粒从缺氧地下沉积物中射出。这些竞争反应决定了吸附的Mn（II）是否将被解吸并逃脱到水柱中或氧化为Mn（IV）并保留为沉积物的不溶性成分。因此，Mn（II）向水柱的净通量取决于两个反应的相对速率。我们通过在25度C下孵育天然缺氧沉积物的浆液并在浆液水相中监测锰的浓度，从而确定了MN（II）吸附，解吸和氧化的速率。将吸附，解吸和氧化的动力学拟合到一阶速率定律。吸附的一阶速率常数（k'（ads）= 7.0 +/- 3.4 h（-1））和解吸（K'（k'（des）= 12.7 +/- 3.3 h（-1））的数量级以上大于氧化的一阶速率常数（k'（ox）= 0.020 = 0.020 +/---0.006 h（-1006 h（-1））。快速解吸动力学和缓慢的氧化动力学的组合使溶解的锰可以通过湍流扩散并逃脱局部再氧化和在沉积物 - 水界面中分散到底部水中。因此，对沉积物 - 水界面的缺氧沉积物的对流有助于从沉积物到水柱的锰的整体通量。