56 Chapter 2 organic matter in the water column and surface sediments, hence the extended depth of the depletion of alternative electron acceptors such as sulfate (Figure 2). At Sites 3 and 5, a peak in dissolved Fe was observed directly below the sedimentwater interface, followed by a rapid decrease to values around zero. At Site 3, dissolved Fe concentrations increased again when sulfide was depleted at depth. Dissolved Fe was nearly absent at Site 7. A peak in dissolved Mn was observed near the sediment-water interface at all three sites, with maximum concentrations decreasing with increasingly reducing sediments from Site 3 to Site 5 to Site 7. At Site 3, dissolved Mn in the porewater increased again at depth after a subsurface minimum. Ammonium increased with depth at all sites, with the highest concentrations (up to 2.5 mmol L-1) and most rapid increase at Sites 5 and 7. NO x (nitrate and nitrite) concentrations ranged from 2.5 to 12.5 µmol L-1 in the bottom waters and decreased rapidly with depth in the sediment at all sites (Figure 2 and Supplementary Table 3).
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