Journal of Paleolimnology20: 151–162, 1998. 151c 1998Kluwer Academic Publishers. Printed in the Netherlands.

The spatial and temporal distribution of fossil-fuelderived pollutants in the sediment record of Lake Baikal,eastern Siberia�

N. L. Rose1, P. G. Appleby2, J. F. Boyle3, A. W. Mackay1 & R. J. Flower11 Environmental Change Research Centre, University College London, 26 Bedford Way, London, WC1H 0AP, UK2 Department of Mathematical Sciences, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK3 Department of Geography, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK

Received 2 December 1996; accepted 20 March 1997

Key words:atmospheric deposition, lake sediments, fly-ash particles, Lake Baikal

Abstract

Spatial and temporal patterns of spheroidal carbonaceous particles (SCP) extracted from lake sediments provide anunambiguousrecord of the distributions of fossil-fuel derived pollutants. When applied to sediment cores taken fromLake Baikal spatial patterns show good agreement with the distribution of industry, with the highest concentrationsfound in the southern basin nearest to Irkutsk. SCP were found to occur in all cores from all areas of the lake incontrast to metal results where anthropogenically enhanced deposition was only demonstrable in the southern basin.SCP distribution within the sediments of Lake Baikal is seen to be distinctly regional and therefore long distancetransport is not thought to be an important pathway for these pollutants. Temporal patterns of SCP show trends thatreflect the development of industry in the area since the 1940s. Settling rates in the 1600 m water column suggestthat the SCP sediment record may be approximately an order of magnitude more sensitive to depositional changesthan that of trace metals.

Introduction

Lake Baikal is internationally famous for its rich flo-ra and fauna with over 1 000 of the 2 500 identifiedanimal and plant species believed to be endemic. Thebiological uniqueness of the lake stems from both itsgreat age (current estimates vary between 25–50 mil-lion years) and size (over 1600 m deep and a volume of23 000 km3) and the fact that its waters are oxygenateddown to its greatest depths.

Threats to the ecosystem of the lake have result-ed from increased levels of pollution from industrialand domestic effluent, from atmospheric contamina-tion and from logging in the catchment. Although theseactivities have been recognised throughout the twen-tieth century, concern has increased since the 1970s

� This is the fourth in a series of seven papers published in thisspecial issue dedicated to the paleolimnology of Lake Baikal. Dr.Roger Flower collected these papers.

and recently been brought to more global attention asa consequence of the break-up of the former Sovi-et Union (Stewart, 1990a&b). Effluent from partiallytreated sewage enters Baikal directly in the far northat Severobaikalsk and factory waste products enter thesouth of the lake both directly and via rivers, espe-cially the Selenga River. However, the most notorioussources of pollution are the two pulp and cellulosemills, on the southern shore at Baikalsk and on theSelenga River at Selinginsk. Contamination of LakeBaikal via the atmosphere is a growing problem(Koko-rin & Politov, 1991) and, due to recent increases inindustrial emissions, may now pose a bigger threat tothe ecosystem than point source water pollution (Stew-art, 1990b). Sources of atmospheric pollution includenot only the two pulp and cellulose mills but also otherindustries in the Irkutsk region (see Figure 1), whichemit fly-ash, metals and sulphates to the atmosphere.However, the largest source of SO2 and particulates

15

2

Figure 1. Sediment coring sites in Lake Baikal together with the location of the main industries in the region. Size of circle corresponds to annual emission, subdivided to show the fractionrelating to particulates and SO2 (Politov, pers. comm.). N.B. These data were compiled by Sergey Politov (Institute of Global Ecology and Climate Change, Moscow) from unpublishedstatistical records at the Regional Committee for the Protection of the Environment and Natural Resources, Irkutsk.

153

in the region is the oil-fired power station at Angarskabout 50 km downstream of Irkutsk on the AngaraRiver. A number of smaller industries exist aroundthe south of Baikal at Shelekhov, Usolye-Sibirskoe,Cheremkhovo, Sludyanka, Ulan-Ude, and Kamensk(Figure 1). A small amount of industry is also present inthe north at Severobaikalsk and Nijneangarsk. Unlikeeffluents, whose effects are likely to be more localised,atmospheric pollutants can be carried long distancesand their presence has been recorded in even the moreremote regions of the Baikal area, for example theKhamar Daban mountains to the south-east (Flower etal., 1997).

Lake Baikal supports the highest number of endem-ic species of any freshwater lake (Kozhov, 1963) andas a consequence it has been proposed as a World Her-itage Site by UNESCO. It is therefore imperative to beable to evaluate changes in the Lake Baikal ecosystemand in depositional regimes impacting the lake andits catchment. The palaeolimnological record is ableto provide evidence of temporal trends in ecologicalchange and pollutant deposition as well as contempo-rary spatial patterns.

Spheroidal carbonaceous particles (SCP) form anexcellent sedimentary record of pollution emissions.They are producedby the high temperature combustionof fossil-fuels and as such are unambiguous indicatorsof anthropogenic impact from atmospheric deposition.Their temporal distribution as recorded in dated lakesediment cores agrees closely with records of fossil-fuel combustion throughout Europe (Renberg & Wik,1984; 1985; Wik & Renberg, 1996; Rose et al., 1995)and the USA (Charles et al., 1990). SCP spatial distrib-ution has been shown to be closely linked with sulphurdeposition (Wik & Renberg, 1991; Rose & Juggins,1994) as well as with other pollutants such as poly-cyclic aromatic hydrocarbons (PAH) (Broman et al.,1990). SCP presence has been recorded in remote areasfar from industrial sources such as Svalbard (Rose,1995), Iceland and the Russian and Canadian Arctic(Rose, unpublished data) suggesting a possible hemi-spherical background level at these remote sites. Thispaper describes the spatial and temporal distributionof SCPs in Lake Baikal sediments, and from this evi-dence attempts to determine the extent of the impactfrom the various sources as well as the historical trendsof atmospheric deposition of fossil-fuel derived pollu-tants.

Methods

(i) Coring

A single sediment core (BAIK 6) was taken in Sep-tember 1992 from 1420 m depth using the Baikalbox-corer (Flower et al., 1995a) and in July 1993 afurther 29 sediment cores were taken using this boxcorer and a short gravity corer (Glew, 1991). Thesediment retrieved in the box corer was sub-sampledusing a wide diameter piston corer gently pushed intothe sediment, minimizing smearing and compaction.Disturbance effects were further reduced by trimmingeach slice on extrusion. These sub-cores were sec-tioned immediately upon retrieval; the 0–5 cm sectionin 2 mm intervals, 5–10 cm in 5 mm intervals and theremainder in 10 mm intervals. The samples were sealedin plastic bags. Despite precautions, some of the sed-iment cores showed signs of surface disturbance andthese were not analysed further. The locations of thesediment cores selected for SCP analysis are shown inFigure 1.

(ii) SCP analysis

The surface sediments from 26 cores were analysed forSCPs. In addition, the full SCP profile was determinedfor six 210Pb dated cores (BAIK6, 19, 22, 25, 29 and38). The SCP profile from BAIK6 has previously beenpublished in Flower et al. (1995b).

SCP analysis followed the method described inRose (1994). Dried sediment was subjected to sequen-tial chemical attack by mineral acids to remove unwant-ed fractions leaving carbonaceous material and a fewpersistent minerals. SCP are composed mostly of ele-mental carbon and although physically fragile arechemically robust. The use of concentrated nitricacid (to remove organic material), hydrofluoric acid(siliceous material) and hydrochloric acid (carbonatesand bicarbonates) therefore does them no damage. Aknown fraction of the resulting suspension was evapo-rated onto a coverslip and mounted onto a microscopeslide. The number of SCP on the coverslip were count-ed using a light microscope at�400 magnificationand the sediment concentration calculated in units of‘number of particles per gram dry mass of sediment’(gDM�1). The detection limit for the technique is 100gDM�1 and concentrations have an accuracy of�45gDM�1.

154

(iii) Sediment dating

Radiometric dates were obtained for the sediment coresby measuring210Pb,226Ra,137Cs and241Am by gammaspectrometry (Appleby et al., 1986).210Pb is a natu-rally occurring radionuclide of half-life 22.26 yearsand measurements of the down-core decline in210Pbactivity in excess of the supporting226Ra are used todetermine a chronology for the past 100–150 years.137Cs and241Am are artificial radionuclides first intro-duced into the environment on a global scale in 1954by the atmospheric testing of thermo-nuclear weapons.Fallout of137Cs from this source reached a maximumvalue in 1963 and then declined sharply following thetreaty in that year banning further atmospheric tests.Sediment records of this maximum can be used to con-firm the 210Pb defined 1963 level in the core. Indi-vidual chronologies of the Baikal sediment cores arediscussed in Appleby et al. (this volume).

Results and discussion

(i) Spatial distribution

The SCP concentrations from the 26 surface sedimentsamples (0–2 mm depth) distributed throughout thethree basins of Lake Baikal are shown in Figure 2.There is a distinct pattern to these concentrations. Thehighest are in the southern basin with a maximum of5 200 gDM�1 for BAIK39, the closest site to Irkut-sk. A cluster of sites in the southern basin BAIK 8,12, 33, 34 and 37 show concentrations greater than3 000 gDM�1 and concentrations decrease away fromIrkutsk both to the south of this area (BAIK 38) and tothe north towards the middle basin. The middle basinshows the lowest concentrations and is the area furthestremoved from industry. SCP concentrations in all sur-face sediments in this area are less than 1 000 gDM�1

(BAIK 20–25 inclusive) with higher concentrations inthe extreme south (BAIK20) and north (BAIK25) ofthe middle basin. These low concentrations are similarto those found in other remote areas of the northernhemisphere (e.g. Spitsbergen, Canadian Arctic) and ithas been suggested that such levels represent a hemi-spherical background concentration of SCPs in con-temporary sediments (Rose, 1995). If this is the case,then this indicates that industrial emissions from Irkut-sk in the south and other industry in the north are havinglittle impact on the sediments of the central basin ofLake Baikal. Concentrations increase northwards in

the northern basin with the highest SCP concentration(2 200 gDM�1) in BAIK 28 the furthest north sedimentcore. This implies that atmospheric deposition (aboveany hemispherical background level) to the northernbasin is from sources to the north of the lake.

Sediment accumulation rates vary however andthese can influence SCP concentrations making inter-core comparisons less reliable. Recent sediment accu-mulation rates for the six210Pb dated cores vary from0.017 (BAIK38) to 0.050 g cm�2 yr�1 (BAIK 22) butthese can be corrected for, to a certain extent, by con-verting the SCP concentrations to SCP accumulationrates. The highest SCP accumulation rate is BAIK6with 67 cm�2 yr�1, and, like the concentration trends,these decrease away from Irkutsk to the north. Howev-er, whereas for concentrations the lowest values werein the middle basin and then increased again north-wards, there is now less difference between the middleand northernbasins. The lowest SCP accumulation rateis for BAIK 25 (5.7 g cm�2 yr�1), an order of mag-nitude lower than for BAIK6, but rates for BAIK22to the south of BAIK25 and BAIK29 to the north arerelatively similar at 16 and 14 cm�2 yr�1 respectively.Conversion to SCP accumulation rate therefore high-lights the southern basin as the area of maximum par-ticle deposition and pollutant impact suggesting thatthe Irkutsk region is the major source of industrialatmospheric emissions affecting the lake. AlthoughBAIK28, the most remote coring site from Irkutsk, isover 460 km away it is not inconceivable that particu-late emissions from Irkutsk could be transported oversuch distances. However, as the northern basin con-centrations are higher than those in the middle basin,nearer to Irkutsk, and it is thought that these middlebasin concentrations represent a hemispherical back-ground, then it is probable that northern basin SCPconcentrations are elevated above this background dueto sources to the north of the lake, rather than due tolong-distance transport from Irkutsk.

These results are in good agreement with thosereported by van Malderen et al. (1996). Aerosols col-lected over Lake Baikal in 1992/93 and analysed byEPXMA revealed the northern and middle basins to besimilar and the southern basin to be most contaminatedby particles of industrial origin. However, a significantpercentage of particles collected over the north of thelake were found to be organic and these were thoughtto be from two sources, biogenic (pollen etc.) and fromfossil-fuel combustion at Severobaikalsk.

SCP analysis has also been undertaken on sedimentcores from two small mountain lakes in the Khamar

155

Figure 2. SCP concentrations in the surface sediments shown as proportional circles. Concentrations in ‘number particles per gram dry massof sediment’ (gDM�1).

156

Daban mountains south-east of Lake Baikal. LakeKholodnoye and Lake Kvadratnoye were both cored in1992 and a more detailed description of the results ofthe sediment analyses are given in Flower et al. (1994).The SCP surface concentration of Kholodnoye is 2 800gDM�1 and that of Kvadratnoye is 2 550 gDM�1. Bothcores have been210Pb dated and surface SCP accumu-lation rates are 26.2 and 78.0 cm�2 yr�1 respectively.These SCP accumulation rates are in the same rangeas the cores in the southern basin of Baikal althoughthe surface SCP accumulation rate for Kvadratnoye ishigher than any of the dated Baikal cores. Kvadratnoyeis nearer to Irkutsk (the assumed source) than Kholod-noye but more distant than the Baikal southern basinsites. However, these lakes are at altitude and it may bethat there is some seeder/feeder enhancement to SCPdeposition at these sites. Concentrations of pollutantshave been reported as being five or six times more con-centrated in cap cloud than in rain (Dore et al., 1992).Cloud droplets formed in cap clouds are too small togrow into raindrop-sized particles, but can be washedout when ‘seeder’ raindrops from higher level cloudsfall through the ‘feeder’ cap cloud thereby producingelevated pollutant depositions at higher altitudes. Thismechanism for enhancing SCP concentrations has beensuggested as being possible at some lake sites in theU.K. (Rose & Juggins, 1994).

The high SCP accumulation rates of BAIK6 andKvadratnoye are still low in comparison to most Euro-pean mountain lakes, especially in central Europe andthe U.K. Sites in the Spanish Pyrenees studied aspart of the EC funded research programme AL:PE(unpublished data) show similar or lower SCP accu-mulation rates (Laguna Aguilo – 51.0 cm�2 yr�1;Laguna Redo – 22.9) as do Lac Noir in the FrenchAlps (63.0), and Laguna Caldera in the Sierra Nevada(54.3). In the U.K., only Loch Coire nan Arr in thenorth-west of Scotland shows a comparable contem-porary SCP accumulation rate (29.4), all others beingmuch higher. Sites in mid-Norway show SCP accumu-lation rates comparable to those in mid- and northernBaikal (Øvre Neadalsvatn – 12 cm�2 yr�1) and thelowest Baikal SCP accumulation rate, BAIK25 (5.7) isof similar magnitude to that of the remotest Europeansites, for example, Arresjøen on Svalbard (1.3 cm�2

yr�1), again suggesting that the mid-Baikal region isreceiving only background levels of pollutants.

(ii) Temporal distribution

Figure 3 shows the SCP profiles for the six210Pb datedsediment cores and the temporal patterns are broadlysimilar to those seen in Europe i.e. there is, in general,a long period of low SCP concentration followed by arapid increase to a maximum and a surface decline inthree of the six cores (Rose et al., 1995).

The longest SCP profile is for BAIK38 in the south-ern basin where the record appears to begin in the1850s (Figure 3). There was little industrial activity inthe area before 1940 (Politov, pers. comm.) and thisearly date could therefore be due to sediment smear-ing during coring or extrusion, despite the precautionsoutlined above. Small scale bioturbation or other phys-ical disturbance causing the SCP rich sediment fromupper levels to be moved down to lower sedimentdepths is also a possibility, although other measure-ments (see Appleby et al., this volume; Boyle et al.,this volume) suggest that large scale mixing has notoccurred. BAIK38 was taken from 600m depth com-pared to> 1000 m for the other cores and it may be thatthis core has been subjected to bioturbation to a greatersediment depth resulting in an apparently longer SCPprofile. The start of the record in BAIK38 does notpre-date the usual start of the SCP record in Europe(1850s–1860s) and could possibly be caused by longdistance transport of pollutants. However, the absenceof particles in the other Baikal cores at this time makesthis unlikely. The profile for BAIK19 shows a pres-ence of SCP as early as 1905 (�13 years), but thisagain is probably caused by smearing as the profilefalls to a concentration of 0 gDM�1 above this (1940s)and the upper ‘zero’ should probably be considered thestart of the SCP profile. BAIK6 and BAIK29 show thestart of the particle record to be in the 1920s/1930s asdoes the profile from Lake Kvadratnoye (Flower et al.,1994). This suggests that 1920s/1930s is the most like-ly date for the start of the SCP sediment record in theBaikal region. This is in agreement with coal miningstatistics for the Irkutsk area (Figure 4). This showsthat the amount of coal mined increased rapidly fromca.1930 to the mid-1980s (Office of Statistics, IrkutskDistrict, pers. comm) (Figure 4). Almost all the coalmined in the Irkutsk area is burned locally (Grachev,pers comm.) and therefore should be a good surrogatefor combustion statistics which are not available pri-or to 1954 (Irkutskenergo Co. pers. comm.). BAIK22and BAIK25 show later profile starts, 1979�2 andmid-late 1960s respectively. However, concentrationsin these short profiles are very low throughout suggest-

157

Figure 3. SCP profiles of the six210Pb dated sediment cores.

158

Figure 4. Historical statistics for mined coal (103 tons) and power station heat capacity (MW) for the Irkutsk area.

ing these late dates may be due to the limit of detectionof the SCP technique.

The start of the rapid increase in SCP concentration,usually a reliable indicator of the 1950s/1960s in theU.K. and Europe (Renberg & Wik, 1985; Rose et al.,1995), is less defined in the Baikal sediments. Thisfeature is usually allocated to the depth at which theintercept of the two gradients (pre- and post-gradientchange) occurs (Rose et al., 1995) and in the Baikalcores this varies from the mid-late 1960s (BAIK25)to the late-1980s (BAIK29), a period during whichboth coal mining and fossil-fuel combustion increasedcontinuously in the Irkutsk area (Figure 4). The SCPrapid increase in BAIK29 is much later than for anyof the sites in the southern basin and this is probablydue to the more recent development and increase inemissions from industries in the north compared withthose around Irkutsk. The low concentrations and shortprofiles for BAIK22 and BAIK25 make any assessmentof SCP profiles rather difficult, and it may be that thestart of the record in these cores represents the rapidincrease in SCP concentration in other Baikal profiles.The situation for BAIK22 is further complicated bythe presence of a turbidite layer at the beginning ofthe 1980s (Appleby et al., this volume) which mayaffect the bottom of the SCP profile in this core. Rapidsediment accumulation at this time could have caused

the SCP concentration to fall below the detection limitand hence the profile to show a zero concentration at amore recent date than would otherwise have been thecase.

A sub-surface SCP concentration peak followed bya surface decline is observed in three of the six cores(Figure 3), BAIK 19, 22 and 38. This decline is proba-bly due to the reduction in fossil-fuel consumption (asindicated by coal mining statistics – Figure 4), as par-ticle arresting equipment has not recently been intro-duced in the area. In two of the remaining cores, theabsence of the peak can be explained by low concentra-tions and short profiles (BAIK25) and a lack of sampleresolution for sediment levels from BAIK6. Where itexists the peak occurs at a similar date in all cores(1989�2 – 1991�2) and in this respect it is similarto the EuropeanSCP profiles where the SCP peak is thebest defined of dating features (Rose et al., 1995). Theremaining core, BAIK29, shows a surface maximum,but uniquely amongst the Baikal cores shows a slightsub-surface decrease just before it. The peak immedi-ately before this decrease also dates to 1990� 2 andtherefore may represent the feature present in the oth-er cores. If this is the case, then the SCP peak is theonly feature to occur at the same time throughoutBaikal and could therefore prove to be a useful sedi-ment marker.

159

An alternative interpretation could be that the sur-face maximum in BAIK29 is due to the developmentof more local industry at the northern end of the lakewhose impact is not observed in the southern basin.These interpretations rely on a single data point, themost recent, and so should be treated with caution.Future cores will need to be analysed to determinewhether these are continuing trends or whether theyare just artifacts of the sediment record. No surfacedeclines are observed in the sediment metal record,although a similar pattern is observed for Zn, Pb andSCP in BAIK29.

In the same way that SCP surface sediment concen-trations can be converted to SCP accumulation rates tocompensate for variations in sedimentation rate, so theSCP profiles can be converted to inventories cover-ing the full period of deposition. As the full profileis accounted for in the SCP inventory, these allow forchanges within each core and also allow comparisonsbetween cores on a ‘total deposition’ basis. Howev-er, variations between sites still may exist due to, forexample, the inwash of atmospheric pollutants fromcatchment sources and these can be compensated forby normalising the SCP inventories to the210Pb inven-tories for each core. The resulting SCP/210Pb ratio istherefore a ‘pollution index’ for the deposition periodand allows a better inter-site comparison for total SCPatmospheric deposition. These inventories are shownin Figure 5.

The unmodified SCP inventories show similar val-ues for the two southern basin sites (BAIK38 andBAIK6) and then a decrease northwards throughBAIK19 to a consistent low value for BAIK 22, 25& 29, suggesting little or no impact from the northernindustries and that these values may be representingan SCP background figure. When normalised to210Pbinventories however, there are two main differences inthe pattern. First, there is a more obvious south to northtrend from BAIK 38 through to BAIK 22 in the middlebasin. The BAIK 38 SCP/210Pb ratio is now consider-ably higher than that of BAIK 6 and this may be due toits greater proximity to sources in Baikalsk, possiblythe pulp and cellulose mill, whereas sources in Irkutskand Angarsk may be more evenly distributed over thewhole southern basin (i.e. approximately equal con-tributions to both BAIK 38 and BAIK 6). If this isthe case, then this is significant evidence for the millhaving an impact on Lake Baikal from its atmosphericemissions in addition to the impact caused by directdischarge of waste into the lake. Van Malderen et al.(1996) reported that the highest abundances of sul-

phur rich (> 80% S as measured by EPXMA) parti-cles occurred in the atmosphere in the vicinity of theBaikalsk paper mill (6.4% abundance) and that low-er but similar abundances occurred in the middle andnorthern basins (3.7% and 3.9% respectively). Sec-ond, the sites in the northern basin have slightly higherSCP/210Pb ratios than the middle basin site and thisslight difference may be due to the influence of theindustries at Severobaikalsk and Nijneangarsk.

The SCP/210Pb inventory ratios for the southernbasin (2–3 000) are of a similar order to Europeanmountain lakes known to receive moderate pollutionloads. For example, Stavsvatn in southern Norway(2 950), Lac Noir in the French Alps (2 800) and LagoaEscura (Sierra da Estrela, Portugal) (2 600) show sim-ilar values (Rose & Appleby, unpublished data). Theratios for the middle (175) and northern basins (275–375) of Baikal are much lower and only have Euro-pean analogues in the cleanest and remotest sites (e.g.Arresjøen on Svalbard (125) and Øvre Neadalsvatn(550) in mid-Norway). This supports the hypothesisthat the middle basin is receiving only hemisphericalbackground levels of SCP and the sites in the northare only slightly more contaminated presumably dueto the industries to the north of the lake. The south-ern basin is seen to be reaching levels of atmosphericcontamination which would be considered moderate inEurope.

Comparisons with metals data

The results obtained from the palaeolimnologicalinvestigations of Lake Baikal using both trace met-als (Boyle et al., this volume) and SCPs are broad-ly similar. Metals only show enhanced supply in thesouthern basin with cores from the middle and north-ern basins showing no evidence for atmospheric depo-sition from anthropogenic sources. The SCP recordwhich is, to a certain extent, less ambiguous than themetal record due to the fact that SCP are derived solelyfrom atmospheric deposition of industrial emissions,also shows the southern basin to be the most conta-minated. Metals as, or attached to, very fine particu-lates will have longer atmospheric residence times thanthe larger SCP and should therefore be able to travellonger distances before deposition. Consequently, alarge source at the southern end of Baikal might beexpected to show a more widespread distribution formetals than SCP but this is the opposite to that whichis observed as analyses indicate a presence of SCP inall cores in all basins. The reason for this is that there

160

Figure 5. SCP inventories (105 particles m�2) and SCP/210Pb inventory ratios for the six210Pb dated sediment cores.

161

is a high pre-industrial baseline for metals and con-sequently any anthropogenic signal is lost as distancefrom the southern basin is increased.

The SCP in the northern basin are therefore mostlikely being produced from the industries in Sever-obaikalsk and Nijneangarsk although there are likelyto be small contributions from industries in the southand possibly even long-distance transport from sourcesoutside the region. SCP data in the northern and mid-dle basins show little enhancement over and above asupposed hemispherical background figure suggestingimpact from the northern industries is small and thatany anthropogenic metals signal from these sourcesis being obscured by background noise. Other studieshave shown the presence of aerosols containing heavymetals, most probably of anthropogenic origin to befound in all three basins (van Malderen et al., 1996),although abundances always constituted< 3% of thetotal aerosol.

Both SCP and metals data for a small mountain lakein the Khamar Daban mountains to the south-east ofBaikal (Flower et al., 1997) show good agreement withdata from the southern basin cores indicating that theimpact of atmospheric deposition from Irkutsk areasources is not confined to Lake Baikal but also to aconsiderable area around the south of the lake.

Significant differences must exist between SCP andfine metal particulates with respect to the time takenfor changes in depositional regime to appear in thesediment record. Boyle et al. (this volume) suggestthat due to the extraordinarily long residence time offine particles in the 1600m water column, the heavymetal record is insensitive to changes in deposition ona smaller than decadal time scale. Stokes’ Law statesthat spherical particles of a given density settle throughwater at a rate directly proportional to the square oftheir radii. SCP are large and composed mainly ofelemental carbon. Theoretical calculation suggests thata SCP of radius 10�m would take in the order of75 days to settle through a column of water 1600mdeep. This is, of course, under ideal conditions with noresuspension, convection or current movement takeninto account. Despite these however, it is likely thatSCP will have a residence time in the Baikal watercolumn an order of magnitude less than that of metalsand likewise a comparable increase in response time todepositional changes in the sediment record.

The sediment record of SCP in Lake Baikal there-fore appears to be more sensitive to changes inatmospheric deposition than that of the metal record,especially on a short (< 10 year) time scale. Howev-

er, it has been suggested that for diatom frustules (ofthe same size order as SCP), temporary deposition onslopes can significantly increase the sediment responsetime (Grachev pers. comm.) and it maybe that SCP aresubject to the same processes and that the SCP responsetime discussed above is a minimum.

Since SCPs are only formed by high temperaturecombustion of fossil-fuels their only source is fromatmospheric deposition (directly or indirectly). Conse-quently, there can be no ambiguity about their prove-nance. In addition, once deposited, SCP do not sufferfrom remobilisation due to chemical changes in thesediment that can sometimes disturb the metal record.It is therefore suggested that SCP provide a morefaithful record of atmospheric deposition from anthro-pogenic sources than metals in Lake Baikal especiallywith regard to short term changes.

Despite this, on a broad time-scale, changes in thesediment record of both SCP and metals are seen tooccur at similar times (e.g. the Pb increase in the1950s/1960s in the southern basin) and the conclusionsdrawn by Boyle et al. (this volume) from the metalrecord that there is good spatial correlation between‘local’ pollution sources and distribution of pollutantsin the sediments is supported by SCP evidence. How-ever, whereas Boyle et al. suggest no anthropogenicenhancement to the metal record in the middle andnorthern basins, the SCP record shows low levels ofcontamination at all sites. This is probably due tothe atmospheric metal signal being lost in background‘noise’ whereas no comparable background for SCPexists and the presence of SCP is sufficient to indicateatmospheric deposition from industrial sources.

Acknowledgements

We would like to thank Prof. M. Grachev, Anna Kuz-mena, Dr Ye. Likhoshway and other members of theLimnological Institute in Irkutsk, the crew of the R.V.Titov and Don Monteith of the Environmental ChangeResearch Centre, University College London for theirsupport and help with the fieldwork. In addition wewould like to thank Dr Grachev for his useful com-ments on the manuscript and for supplying the coalmining and heat capacity data used in Figure 4. Weare grateful for the financial support received from theRoyal Society (BICER), the Leverhulme Trust (ProjectF134AZ) and ENSIS Ltd. (University College London)enabling the work to be undertaken. Cath Pyke in the

162

Cartographic Office of the Department of Geography,University College London produced the figures.

References

Appleby, P. G., P. Nolan, D. W. Gifford, M. J. Godfrey, F. Oldfield,N. J. Anderson & R. W. Battarbee, 1986.210Pb dating by lowbackground gamma counting. Hydrobiologia 141: 21–27.

Appleby, P. G., R. J. Flower, A. W. Mackay & N. L. Rose, thisvolume. Palaeolimnological assessment of recent pollution trendsin Lake Baikal: Sediment chronology.

Boyle, J. F., A. W. Mackay, N. L. Rose, R. J. Flower, P. G. Appleby& L. Z. Granina, 1998. Sediment heavy metal record in LakeBaikal: natural and anthropogenic sources. J. Paleolimnol. 20:135–150.

Broman, D., C. Naf, M. Wik & I. Renberg, 1990. The importance ofspheroidal carbonaceous particles for the distribution of particu-late polycyclic aromatic hydrocarbons in an estuarine-like urbancoastal water area. Chemosphere 21: 69–77.

Charles, D. F., M. W. Binford, E. T. Furlong, R. A. Hites,M. J. Mitchell, S. A. Norton, F. Oldfield, M. J. Paterson,J. P. Smol, A. J. Uutala, J. R. White, D. R. Whitehead & R. J. Wise,1990. Paleoecological investigation of recent lake acidification inthe Adirondack Mountains, N.Y. J. Paleolimnol. 3: 195–241.

Dore, A. J., T. W. Choularton & D. Fowler, 1992. An improved wetdeposition map of the United Kingdom incorporating the seeder-feeder effect over mountainous terrain. Atmos. Envir. 26A: 1375–1381.

Flower, R. J., S. Politov, N. Solovieva, N. L. Rose, R. W. Battarbee,B. Rippey, P. G. Appleby & C. L. Rose, 1994. A palaeolim-nological evaluation of the extent and impact of atmosphericcontamination and recent environmental change in two remotehighland lakes in SE Siberia. Final report for the NERC smallresearch grant GB9/1032. Environmental Change Research Cen-tre, Research Report, No. 9.

Flower, R. J., D. T. Monteith, A. W. Mackay, J. M. Chambers &P. G. Appleby, 1995a. The design and performance of a newbox corer for collecting undisturbed samples of soft subaquaticsediments. J. Paleolimnol. 14: 101–111.

Flower, R. J., A. W. Mackay, N. L. Rose, J. F. Boyle, J. A. Dearing,P. G. Appleby, A. E. Kuzmina & L. Z. Granina, 1995b. Sedi-

mentary records of recent environmental change in Lake Baikal,Siberia. Holocene 5: 323–327.

Flower, R. J., S. Politov, B. Rippey, P. G. Appleby, N. L. Rose& A. C. Stevenson, 1997. The extent and impact of atmospher-ic contamination and recent environmental change in a remotehighland lake in south-eastern Siberia. Holocene 7: 161–173.

Glew, J. R., 1991. Miniature gravity corer for recovering short sedi-ment cores. J. Paleolimnol. 5: 285–287.

Kokorin, A. O. & S. V. Politov, 1991. Wet deposition in the southBaikal region. Soviet Meteorology and Hydrology 1: 39–44.

Kozhov, M., 1963. Lake Baikal and its life. W. Junk. The Hague,Netherlands, 344 pp.

Renberg, I. & M. Wik, 1984. Dating of recent lake sediments bysoot particle counting. Verh. int. Ver. Limnol. 22: 712–718.

Renberg, I. & M. Wik, 1985. Carbonaceous particles in lake sedi-ments – pollutants from fossil-fuel combustion. Ambio. 14: 161–163.

Rose, N. L., 1994. A note on further refinements to a procedurefor the extraction of carbonaceous fly-ash particles from lakesediments. J. Paleolimnol. 11: 201–204.

Rose, N. L., 1995. Carbonaceous particle record in lake sedimentsfrom the Arctic and other remote areas of the Northern Hemi-sphere. Sci. Tot. Envir. 160/161: 487–496.

Rose, N. L. & S. Juggins, 1994. A spatial relationship betweencarbonaceous particles in lake sediments and sulphur deposition.Atmos. Envir. 28: 177–183.

Rose, N. L., S. Harlock, P. G. Appleby & R. W. Battarbee, 1995.Dating of recent lake sediments in the United Kingdom and Ire-land using spheroidal carbonaceous particle (SCP) concentrationprofiles. Holocene 5: 328–335.

Stewart, J. M., 1990a. Baikal’s hidden depths. New Scientist. 23June: 42–45.

Stewart, J. M., 1990b. ‘The Great Lake is in peril’. New Scientist.30 June: 58–62.

van Malderen, H., R. van Grieken, T. Khodzher, V. Obolkin &V. Potemkin, 1996. Composition of individual aerosol particlesabove Lake Baikal, Siberia. Atmos. Envir. 30: 1453–1465.

Wik, M. & I. Renberg, 1991. Recent atmospheric deposition inSweden of carbonaceous particles from fossil-fuel combustionsurveyed using lake sediments. Ambio. 20: 289–292.

Wik, M. & I. Renberg, 1996. Environmental records of carbonaceousfly-ash particles from fossil-fuel combustion. J. Paleolimnol. 15:193–206.