DIATOM SUCCESSION TRENDS IN RECENT SEDIMENTS FROM LAKE-BAIKAL AND THEIR RELATION TO ATMOSPHERIC-POLLUTION AND TO CLIMATE-CHANGE

Recent environmental change in Lake Baikal has been attributed to anth ropogenic influences on the ecosystem, especially through pollution an d cultural eutrophication. These hypotheses are tested in this paper p rincipally by diatom analyses in 20 short sediment cores. Most of the cores were collected with a new type of box corer specifically designe d for use on Lake Baikal. Most cores contain a good sediment record bu t turbidites occur in some sediment profiles which may he best recogni zed using a combination of techniques, such as radiometric dating and percentage dry weight analyses. The most recent sediments, especially those in the southern basin and in the very north of Baikal, contain a record of anthropogenic contamination in the form of lead and spheroi dal carbonaceous particles, which confirms that the southern basin of Baikal is most affected by atmospheric sources of pollution. However, there is no sedimentary diatom evidence indicating offshore water qual ity deterioration in Baikal owing to air pollution or eutrophication. Small increases in diatoms which indicate nutrient enrichment (e.g. St ephanodiscus minutulus, Synedra acus v. radians and Synedra acus v. ac us) may reflect local eutrophication of the shallow waters close to th e Selenga Delta and certain coastal sites in the southern basin near t o the Baikalsk paper and pulp mill. By using numerical techniques, Lak e Baikal can be split into at least four regions on the basis of its s urface sediment flora: the south, middle and north basins, and the sha llow waters surrounding the Selenga Delta region. Diatom analyses reve al that the endemic flora of Lake Baikal has been constantly changing over at least the last 2000 years and that these fluctuations are prob ably responses to natural climatic variability. Recent sediments of Ba ikal may be affected by taphonomic processes (e.g. dissolution) and tu rbidite deposition, and these must be taken into account when interpre ting the sedimentary diatom record. The diatom flora of the lake is cu rrently dominated by several species, such as Aulacoseira baicalensis, A, islandica, Cyclotella minuta and Stephanodiscus binderanus v. baic alensis. All these species, except for C. minuta, have become more com mon in the lake in approximately the last 130 years, and we hypothesiz e that these changes may be attributed to a number of different proces ses linked to an ameliorating climate after the end of the Little Ice Age. The results presented here have important implications for this r ecently designated World Heritage Site, with regard to future pollutio n controls and catchment management policies.