Early diagenesis of arsenic in sediments of the Kalix River estuary, northern Sweden

Solid-phase As, Fe, Mn, S and Al and pore-water total As, Fe, Mn and S have been determined for two cores from the Kalix River estuary. At the same station, the depositional flux of arsenic was measured sediment traps. )-oxides persist in the anoxic zone of the sediment and act as a carrier for arsenic down to depths of 10–15 cm. The release of arsenic into the pore water is controlled by the reduction/dissolution of these oxides. As a result, internal cycling of arsenic, i.e. upward diffusion in pore water, re-adsorption onto Fe(III)-oxides in the oxidized surface layer and reburial occurs in the uppermost 10–15 cm. At the base of the arsenic cycling zone, solid-phase arsenic maxima (160–170 μg g−1) of probable diagenetic origin occur. antity of arsenic diffusing back towards the oxidized surface layer (2.2 μg cm−2 yr−1 As) is close to 75% of the quantity of arsenic being deposited due to sedimentation (2.9 μg cm−2 yr−1 As). However, a mass balance for the surface layer indicates that re-adsorption of arsenic onto Fe(III)-oxides may effectively prevent diffusion of dissolved arsenic back into the overlying water column. concluded that the interpretation of sedimentary arsenic profiles may be severely complicated due to post-depositional migration of arsenic.