SEDIMENTARY RECORDS OF THE EXTENT AND IMPACT OF ATMOSPHERIC CONTAMINATION FROM A REMOTE SIBERIAN HIGHLAND LAKE

The Central Asian Khamar Daban Mountain Range (SE Siberia) is a remote region with softwater lakes that probably receive atmospheric polluti on from local industry as well as via long-distance transport. Palaeol imnological evidence of the impact of atmospheric pollution at one iso lated and otherwise undisturbed highland site in the Khamar Daban, Lak e Kholodnoye, was obtained. Shea sediment cores were analysed for radi o-isotopes, to establish a sediment chronology. The sediment accumulat ion rate in core KOL1 is slow (4 mg dry sediment cm(-2) yr(-1), or 0.3 mm yr(-1)) but trace metal (notably Pb and Zn) and spheroidal carbona ceous particle profiles show increases beginning at 2-cm (1920s) and 1 .3-cm (1940s) depth, respectively. The trace metal profiles are essent ially corroborated by KOL2, a replicate core analysed at a Russian lab oratory. Diatom analysis revealed no evidence of recent acidification or indeed of any marked floristic change during the twentieth century (upper 2.5 cm of sediment). Lack of catchment disturbance was indicate d by very uniform pollen frequencies throughout the core. Lake-water c hemistry indicated an excess of sulphate. Both the diatom and base cat ion stratigraphies showed a small but sustained change over the entire 28 cm of the core. Maximum floristic change in sedimentary diatom ass emblages occurred around 7 cm sediment depth, approximately dated to t he mid-eighteenth century. Small but gradual up-core increases in Na, K and Mg indicate a disturbance in the delivery of minerals from the c atchment to the lake. The sedimentary profiles of trace metals and sph eroidal carbonaceous particles show that the site is contaminated by l ow-level but nevertheless significant atmospheric pollution. This cont amination occurred during the twentieth century. Small changes in the diatom and other geochemical sedimentary records predate these industr ial impacts and so could reflect longer-term catchment weathering proc esses and/or indirect effects of climate change.