The structure and periodicity of laminae in Holocene sediment cores from Loch Ness, Scotland.
The structure and periodicity of the laminations in the sediment of Loch Ness have been
investigated using material collected in sediment traps on the floor of Loch Ness and
suspended in the water column, and also from two ca 5 metre sediment cores. The study
of contemporary sedimentation processes using the sediment trap material has provided
useful insights into the processes that have created the Loch Ness sediment profile. The
combined use of sediment trap material and that in the cores has facilitated the
comparative study of modern and past laminae formation, and has allowed a hypothetical
model of sedimentary processes in the loch to be proposed.
The suite of analyses undertaken have been largely the same for both types of
sedimentary material and have included diatom, geochemical and particle size analysis.
Pollen analysis has also been carried out on material in the sediment traps from the floor
of Loch Ness.
Results from the diatom and geochemical analyses on sediment trap material have
provided evidence of low amplitude rhythmic sedimentation occurring at the sampling
location in the loch. The diatom analysis, in particular, has indicated rhythmic settling of
the diatom frustules to the bottom sediment and the geochemistry results demonstrated
identifiable chemical differences between the sediment layers in the sediment traps on the
floor of Loch Ness. However, results from the particle size analysis by laser diffraction
revealed only minor differences between the samples compared with visually observed
systematic differences carried out during laboratory sampling.
The analysis of the laminations in the sediment cores was undertaken after the individual
laminations were dissected from sections of the second five metre core, LNR4. The
diatom analysis of these laminae revealed no systematic differences between the
laminations in any given section and the inverse relationship between diatom species
eyclotella rossi and Achnanthes minutissima observed in the samples in the sediment
trap material was not apparent within the laminations in the core. Geochemical analysis
by ICP-AES analysis of dissected laminae (undertaken in collaboration with Dr M. Braun
ofDebrecen University, Hungary) again revealed no systematic differences.
The evidence from the research to date has revealed that the rhythmic deposition of
sediments observed in the sediment traps in Loch Ness, particularly the settling of diatom
frustules, is not identifiable in the cores. It is possible that the rhythmic deposition,
apparent in the traps, is being attenuated and masked within the cores because of the
oligotrophic nature of the loch, the very low sedimentation rate within the loch and the
subsequent sedimentary processes. The research would therefore suggest that rhythmic
deposition of laminated sediments in Loch Ness sediment cores cannot be confirmed by
the biological and geochemical analyses undertaken during the course of these