Chemical and physical analysis of laminated sediment formed in Loe Pool, Cornwall

• Main Author: Pickering, David Alan
• Published: University of Plymouth 1987
• Subjects: 551; Sediment formation in Loe Pool
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376677

Laminated and annually-laminated sediments are found in Loe Pool. The origins of such laminations are investigated and evidence for their conditions of formation are presented. In all sediment analysed the combustion residue was greater than 80%, and in the black and grey annually-laminated sediment the organic matter was less than 3%. This indicated that the sediment was dominated by a minerogenic input. The high lacustrine sediment concentrations of copper, zinc and other heavy metals together with evidence from analysis of magnetic variables which indicated high levels of haematite, confirmed that a major sediment source was effluent from mine waste. Analysis of individual black and grey annual laminations revealed increased concentrations of chlorophyll c, phaeopigments and perylene together with a lower C: N ratio in the black lamination. This indicated formation of the black layer in the summer months. From the high iron: manganese ratio and the low concentrations of calcium and carbonate in the black lamination as compared with the grey layer it was apparent that the black lamination was formed under conditions of oxygen shortage, and the grey lamination was formed when the bottom waters were fully oxygenated. It was concluded that from the analysis of selected physical and chemical properties of individual laminations it was possible to identify the principal sediment source, the likely season of deposition of each lamination and the palaeo-redox condition of the lake at that time. From this information a hypothesis of the formation of the laminated sediments in Loe Pool is proposed. It is suggested that a dominant factor controlling sediment composition was the redox conditions at the time of deposition. These conditions were primarily influenced by lake depth, lake mixing, input of allochthonous material and the oxygen demand of sedimenting material.