A BIOGEOCHEMICAL COMPARISON OF SEA LOCH SEDIMENTS - MANGANESE AND IRON CONTENTS, SULFATE REDUCTION AND OXYGEN-UPTAKE RATES

The sediments of the upper basins of Lochs Goil, Fyne and Etive were h igh in both solid phase extractable manganese (up to 3.7% w/w), and hi gh in pore water manganese (up to 600 mu M), while Loch Linnhe sedimen ts were low in manganese. Solid phase manganese from the surface sedim ents at the deepest stations was highest in those lochs where the mean residence time of the bottom water is longest, indicating the importa nce of manganese cycling through the water column. Porewater iron conc entrations in the top 2 cm of sediment were highest near the heads of the lochs, i.e. near the main freshwater inputs. Within sediments of L ochs Goil, Fyne and Etive high rates of total sulphate reduction were associated with high relative rates of formation of acid volatile sulp hide, but this correlation did not occur in Loch Linnhe; here the form ation of pyrite was more important. Loch Linnhe sulphate reduction rat es were higher than those in Lochs Goil and Etive, but fixed sulphur c oncentrations in the sediments were lower, indicating a greater propor tion of the products of sulphate reduction were being reoxidised. The sulphide burial rate was high in Loch Etive and low in Loch Linnhe. Ox ygen uptake rates by sediments showed an increase near the heads of th e lochs, implying the presence of a component of the terrestrial organ ic input which was readily degradable by marine sediment bacteria.