Phosphorus and arsenic geochemistry

The similarities and the differences in geochemical properties of phosphorus and arsenic are reflected in the way these elements respond to diagenesis in the Saguenay Fjord (Mucci etal., 2000a). Both the elements are supplied to the sediment on settling particles, which appear to scavenge both P and As from 

Compared to the anoxic sediment, the oxic surface sediment is enriched in As (up to 345 nmol g-1). The enrichment is weak where the sedimentation rate is high, but enrichment becomes stronger with decreasing sedimentation rate. Phosphorus enrichment in the surface layer is evident only where the sedimentation rate is low. However, upon burial, both P and As are released from the solid phase to the pore water, irrespective of the sedimentation rate, and the distributions of both elements show subsurface maxima that correspond to the depth where the dissolution rates of solid phases of P and As are maximum. From the relative location of these maxima, it can be concluded that As is released to the pore water at shallower depths than at which phosphate is released. Mucci etal. (2000a) proposed that As is released upon the reduction of As(V) to soluble As(III), and that this takes place earlier than the reduction of Fe(III) to Fe(II) in the diagenetic sequence. In contrast, the 

---