THE BEHAVIOR OF DISSOLVED MN, NI AND ZN IN THE FORTH, AN INDUSTRIALIZED, PARTIALLY MIXED ESTUARY

The distributions of dissolved Mn, Ni and Zn concentrations in the For th estuary are described, interpreted and discussed. The Forth estuary has a long flushing time and, in summer, is characterised by a pronou nced turbidity maximum and oxygen minimum in the upper estuary. Sampli ng throughout an annual cycle enabled the effects of riverine flow and varying hydrodynamic regimes to be assessed. Dissolved Mn profiles fo r the estuary show broad mid-estuarine maxima, indicating that reduced Mn is being added to the water column from the bottom sediments. Peak dissolved Mn concentrations are higher in summer (e.g. 2800 nM in Jun e) than in winter (e.g. 660 nM in January) when high freshwater flows and shorter Bushing times tend to mask the benthic source. Dissolved N i and Zn profiles in the Forth, like those for Mn, show broad mid-estu arine maxima. Significant correlations between dissolved Ni and Zn con centrations in summer suggest common sources for the elements. In summ er, Ni and Zn appear to be remobilised with Mn in the oxygen minimum z one of the upper estuary. Possible additional sources of Ni and Zn in May include release from disturbed bottom sediments or anthropogenic e missions.