Solid phase elemental analyses and dissolved metals and sulphate determinations were made on sediment samples and pore waters, respectively . A thin veneer of manganese and iron oxyhydroxide-rich material mantles the sediments in both basins. In Keogh, this layer appears to be at most 5 mm thick, in Benson, it may be slightly thicker. These data confirm that at the time of sampling there was no efflux of these metals to the overlying water in either basin. Profiles of the dissolved copper concentration in pore waters suggest that some Cu may be diagenetically cycled just below the sediment-water interface in the Keogh deposits.
Concentrations are low, however, and there was no indication of a benthic efflux of the metal.