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Review of Current Work on Loch Ness Sediment Cores

Reproduced with the permission of the Scottish Naturalist
Copyright: May be used for private research. All other rights reserved


REVIEW OF CURRENT WORK ON LOCH NESS  SEDIMENT CORES

By SENGA BENNETT
Department of Applied Science,
University of Staffordshire

ADRIAN J. SHINE
Loch Ness and Morar Project

The sediment mapping and coring programmes of the Loch Ness and Morar Project are now beginning to contribute to our understanding of Britain's greatest volume of fresh-water, so it is hoped that this short introductory review of sediment-coring work may make many aspects of its importance clear to the general reader.

Acidification of Lochs

To begin with, in Loch Ness it is very probably the sheer volume of water itself which has provided a buffer against acidification.  Many small lochs, particularly to the south of the Great Glen, have become very acidified, some of them losing their fish populations altogether.  Many of these lochs are at present being studied by a team lead by Professor R. Battarbee of the Environmental Change Research Centre at University College London (U.C.L.).

It is now well established that a significant cause of acidification is atmospheric contamination, and an indication of the degree to which a lake is subject to sulphur pollution is given by the numbers of microscopic 'carbonaceous particles' falling into it.  These spherical particles result from the burning of fossil fuels, especially oil, and have increased dramatically in sediments from about 1940, when this form of energy became increasingly used for power generation.

Loch Ness cores, taken in 1990 by the Loch Ness and Morar Project (L.N.M.P.) and analysed by Dr. Neil Rose at U.C.L. (pers. comm.) (Note 1), show typical concentrations of these particles, beginning between 1850 and 1870, increasing rapidly between 1949 and 1960, and reaching a peak in the 1970s.

Vol 105, The Scottish Naturalist: Review of Current Work on Loch Ness Sediment Cores p56

Diatom Record

The diatom record, as studied by Dr. Vivienne Jones of the U.C.L. team, permits reconstruction of pH.  Despite the sulphur contamination, acidity has remained relatively constant over the years since 1850, and agrees well with the current pH of 6.5 (Dr. Vivienne Jones, pers. comm.) (Note 1).  The silica frustules of diatoms remain intact within the sediments, and can be identified.  Since the requirements of many species are known with regard to temperature, nutrient richness, and pH, it is possible to reconstruct a quite detailed picture of conditions within the loch over this time.

 

Eutrophication

One of today's other great concerns is about the eutrophication of lakes.  Again the diatom record is the main indicator of change.  Until about 1970 the diatom community was dominated by benthic forms, presumably washed in from the shores and by rivers.  From then on, however, there is a dramatic increase of planktonic species, such as Aulacoseira subarctica and Asterionella formosa (Dr. Vivienne Jones, pers. comm.) (Note 1).  This situation is typical of the first impact of eutrophication in lakes throughout the world, even though studies of the loch's chemistry still show, for example, extremely low levels of phosphorus (Jenkins, 1993).  Thus, despite its great volume, Loch Ness is not entirely immune from change induced by man's activities within its catchment.

Pollen

Pollen grains from the loch catchment's vegetation also endure for thousands of years, locked in the sediments.  Dr. Sylvia Peglar, at the University of Bergen, has prepared pollen diagrams from cores taken by the Loch Ness and Morar Project, and these show events over the last three thousand years as tree pollens gradually give way to herbs and the cereals increase.  Finally the tree pollens increase again in the recent past, as new species of conifer were established in plantations (Dr. Sylvia Peglar, pers. comm.).

 

Isotopes

Although pollen is one example where historical sequences are well enough understood to provide a dating framework for the cores recovered, for recent events a higher resolution method is available to reveal the rate of sedimentation, and thus to date events within the core.  The method used by U.C.L. is based upon

Vol 105, The Scottish Naturalist: Review of Current Work on Loch Ness Sediment Cores p57

the relatively rapid decay (22.26 years half-life) of the naturally occurring radio-isotope 210Pb, and has dated Loch Ness cores back to 1830, thus covering almost all of the changes brought about by industrialisation.

The chronology can also be checked by the presence of the rather less natural caesium isotopes, such as 134Cs and 137Cs.  Thus the 1963 peak in nuclear bomb fall-out from atmospheric testing is faithfully recorded in the sediment at 9.0 cm down.  From the 3.0 cm mark on the graph, there points the long dark accusing finger of Chernobyl (Dr. P.G. Appleby, pers. comm.) (Note 1).

 

PCBs and PAHs

Other undesirable compounds, such as PCBs, PAHs and trace metals, are being studied by the Newcastle Research Group in Fossil Fuels and Environmental Geochemistry.  Mansfield (1992) and Bracewell (1993) show that the increase in these compounds peaks at about 1960.  The persistent pesticide DDT is still detectable in the upper sediments.  In the uppermost sediments there is evidence of some oil pollutants, probably derived from fuels used by vessels on the Caledonian Canal.  The work of Mansfield and Bracewell on the lipids shows that the bulk of the sediments are derived from terrestrial vegetation, rather than from productivity within the loch.  As will be seen, the catchment has great influence upon the loch's biology (see Sanders, Jones and Shine, 1993).

Sediment Character

The differing features of the loch's catchment have considerable influences upon the character of the sediments.  There is a pronounced rainfall gradient across the Highlands from west to east, which means that the bulk of the water enters the loch from the south-west end.  It seems that this brings with it the majority of the organic material derived from terrestrial vegetation, particularly peat and leaves.  Bennett (1993) has produced a sediment map prepared from the L.N.M.P.'s 'Short-Core' programme (Figure 1, 16K photo).  This clearly shows that each inlet contributes different characteristics to the sequences of sediment build-up.  Thus it has been confirmed that the rise in the bed opposite Foyers is composed of coarse mica sand brought down by the river, and the same is true off Invermoriston, although there is a much greater percentage of vegetable detritus there.  Clays are exposed at shallow sediment depth at the loch's northern end towards Dores.  Overall, sediments are focused towards the deeper water, where the contemporary rate of sedimentation exceeds 1.0 cm per year in the North Basin.

Vol 105, The Scottish Naturalist: Review of Current Work on Loch Ness Sediment Cores p60

 

Disturbance by the Great Flood

One feature of particular interest, discovered in 1990, was a disturbance in the rate of sedimentation, represented by a distinctive light grey clay layer, initially observed at 30-50 cm sediment depth throughout the dark brown organic deposits of the North Basin.  The 210Pb dating clearly suggests a major event in the latter part of the nineteenth century.

This feature was widespread within the loch, thus providing a clue to its origin.  In cores from the South Basin, instead of the characteristic thick clay layer, the same event appeared to be represented by much coarser material and layers of intact terrestrial vegetation.  This strongly suggests a major flood.

Throughout the summer of 1992 the layer was traced along and across the loch, and, in the North Basin, was tracked to the mouth of Urquhart Bay.  A transect of three cores showed the clay layer to be thickest nearest to the Bay, capping no less than 50 cm of coarse sand, before resumption of the normal pattern of deposition.  The sand layer tapered away with distance from the Bay, and the clay thinned to the north and south.  The transect results were quantified by particle size analysis by Miller (1993), who points to the great flood of 1868 (Anon., 1868; Barron, 1985) as the most likely cause of this huge outwashing of material.

On closer study of 27 short cores, Bennett (1993) noted the disturbance in sedimentation to be more complex than was initially observed.  In the deeper parts of the North Basin the grey clay layer overlies a fining upwards section of dark brown silts.  Bennett suggests that a turbidity current, triggered by the flood, plunged down the slopes of Urquhart Bay towards the deep North Basin.  The L.N.M.P.'s hydrographic surveys show two sub-lacustrine channels down the north wall at this point (Shine and Martin, 1988), and the current could have cut the small gully into the base of the 'wall' 200 m down (Young and Shine, 1993).

In the narrower South Basin, Bennett discovered that the coarser particles and vegetation were only part of a thicker sequence of material, each capped by a much thinner, but clear, light clay layer.  Here, similar powerful erosive currents, under the extraordinary conditions of the great flood of 1868, originated not only from rivers but also extended right across the loch bed from the Horseshoe Scree.  The particles of sand were deposited first, then the silts, twigs and vegetable matter, and finally, perhaps months later, the last of the fine clay particles settled to blanket the basin floors.

Vol 105, The Scottish Naturalist: Review of Current Work on Loch Ness Sediment Cores p61

 

Sediment Lamination

This spectacular event may well provide the key to the most interesting of the discoveries in the Loch Ness sediments, i.e. that they are laminated.  The >200 m depth of the loch provides an exceptionally stable resting place for silts and clays, which in shallower environments would be disturbed and resuspended.  Thus, characteristic light/dark 'couplets' are preserved.  The predominantly allochthonous origin of the sediment suggests the possibility that the laminae are precipitation controlled annual features; however, this has not been proved.  One Ph.D. thesis, funded by the University of Wolverhampton, has now been devoted to determining the nature and composition of the Loch Ness laminations.  The L.N.M.P.'s 'Project Hour-Glass' has been set up on the loch bed, to remain in place for a whole year, in order to aid this research.  The principle is to concentrate the sediment into a narrow tube, in order to emphasise any differences in the sediment's monthly character.

The quality of laminations establishes Loch Ness as a premier site for the study of climate change in Great Britain.  Once the basic language of the laminations is understood, each divided core will reveal a catalogue of information about the history of Loch Ness.  That history begins with glacial clays deposited by retreating ice some 12,000 years ago.  The 'Rosetta' project (L.N.M.P.'s 'Long-Core' programme; Note 2) is steadily being driven towards those clays.  Amongst other things, this will recover pollen and mineral records which will bear witness to such events as the general re-advance of the ice (often termed the 'Loch Lomond stadial'; see Sissons, 1979) to post-glacial bursts of productivity within the loch and its catchment, and to man's arrival in the Great Glen.

 

Relationships

The northerly location of Loch Ness makes it possible to relate tephras (microscopic glass shards), enclosed within the sediments, to Icelandic volcanic eruptions.  The first depopulation of the Highlands, during the Bronze Age, was coincidental with one resultant 'volcanic winter', and potential relationships are being studied by Dr. Andrew Dugmore, of the Department of Geography at the University of Edinburgh.  On another topic, it may be possible, by looking for marine species of diatoms, to resolve the question of whether or not the sea entered Loch Ness, prior to isostatic and eustatic readjustments to the loch's present position of 15.8 m above sea level.  The cataclysmic release of water, from vanished ice-dammed lakes far up the Great Glen, proposed by Sissons (1979) to have been forced northwards through Loch Ness in a period of only 48 hours, should also be represented in the deep loch floor deposits.

Vol 105, The Scottish Naturalist: Review of Current Work on Loch Ness Sediment Cores p62

Radar pictures taken through the Antarctic ice cap have revealed water on the bedrock.  This offers the possibility that the very deep basin of Loch Ness may not have been completely scoured by ice.  It is therefore possible, if only marginally, that pockets of interglacial sediments lie preserved, and might be penetrated to reveal an even earlier history than has thus far been considered.

 

Conclusion
In conclusion, Loch Ness should not be seen as some untouched and pristine cul-de-sac.  It is very far from that; it is an open-ended time capsule, packed with the footnotes to very broad events, including the coming of man to the Great Glen and his activities here and further afield.  Sedimentary records have proved to be a remorseless treatise in cause and effect, and give dramatic confirmation of man's power to change his environment.

 

Notes

 1.  V. Jones and N. Rose (Environmental Change Research Centre, University College London) and P.G. Appleby (University of Liverpool):  The Recent History of Loch Ness.  Poster paper: displayed at British Ecological Society's winter meeting and A.G.M., University of Lancaster, 15th-17th December 1992; and at Scottish Freshwater Group's 50th Meeting, University of Stirling, 2nd-3rd February 1993.

 2.  The ROSETTA project (Recovery of Sediments Enabling Translations to Acoustics).  The 'Long-Core' programme is designed to complement the European Community REBECCA project (Reflection from Bottom, Echo Classification and Characterisation of Acoustic Propagation).  This is a seismic programme for which the British participant is Dr. Bryan Woodward of Loughborough University of Technology.

 

Acknowledgements

 

The authors would like to express their best thanks to all the L.N.M.P. sediment collaborators, and in particular to Mr. Alan Pike for his assistance with the pioneer coring work and for his subsequent technical advice and encouragement.

References

 

Anon.  (1868).  Great floods in the north.  Inverness Courier, 6th February 1868.

Barron, H.  (1985).  The County of Inverness.  Third Statistical Account of Scotland, Vol. 16.  Edinburgh: Scottish Academic Press.

Vol 105, The Scottish Naturalist: Review of Current Work on Loch Ness Sediment Cores p63

Bennett, S.  (1993).  Patterns and Processes of Sedimentation in Loch Ness.  B.Sc. Dissertation, University of Staffordshire.

Bracewell, C.E.  (1993).  A Geochemical Study of Natural and Pollutant Compounds in Loch Ness, Scotland.  M.Sc. Dissertation, University of Newcastle-upon-Tyne.

Jenkins, P.H.  (1993).  Loch Ness sediments:  a preliminary report.  Scottish Naturalist, 105: 65-86.

Mansfield, C.A.  (1992).  A Study of Biogenic and Anthropogenic Compounds in Sediment Cores from Loch Ness, Scotland.  M.Sc. Dissertation, University of Newcastle-upon-Tyne.

Miller, K.C.  (1993).  A Study of Sedimentary Markers within the Lacustrine Environment.  B.Sc. Dissertation, University of Edinburgh.

Sanders, G., Jones, K.C. and Shine, A.J.  (1993).  The use of a sediment core to reconstruct the historical input of contaminants to Loch Ness:  PCBs and PAHs.  Scottish Naturalist, 105: 87-111.

Shine, A.J. and Martin, D.S.  (1988).  Loch Ness habitats observed by sonar and underwater television.  Scottish Naturalist, 100: 111-199.

Sissons, J.B.  (1979).  The Loch Lomond Stadial in the British Isles.  Nature, 280: 199-202.

Young, I. and Shine, A.J.  (1993).  Loch Ness bathymetric and seismic survey, December 1991.  Scottish Naturalist, 105: 23-43.

 

Received June 1993

 Miss Senga Bennett, Loch Ness and Morar Project,
Loch Ness Centre, DRUMNADROCHIT, Inverness-shire IV3 6TU.

 

Mr. Adrian Shine, Loch Ness and Morar Project,
Loch Ness Centre, DRUMNADROCHIT, Inverness-shire IV3 6TU.

 

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