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