Journal of Conference Abstracts

Recent History of Two Subarctic Lakes in Lovozersky Alkaline Massif (Central Part of Kola Peninsula; Russia): Paleolimnological Evidence

Denis Yu. Smirnov¹ (smirnovd@alphais.inep.ksc.ru),
Valery A. Pobedonostsev² (felix@ksc-gi.murmansk.su) &
Ludmila Ya. Kagan¹ (root@ksc-inep.murmansk.su)

¹ Institute of North Ecology Problems, Kola Science Centre, Russian Academy of Sciences, Apatity, Russia.

² Institute of Geology, Kola Science Centre, Russian Academy of Sciences, Apatity, Russia.

These paleolimnological investigations were conducted to evaluate the history of recent changes of two subarctic alpine lakes situated within the Lovozersky alkaline massif (central part of the Kola Peninsula; Russia). Both lake catchments are located far from large sources of S, heavy metals (Ni, Cu, Co etc.), and atmospheric emissions - "Severonickel" smelter.

Loss on ignition (LOI), water content and element concentration were examined in four short sediment cores. Concentrations of 23 chemical elements were measured using AAS and XRF techniques. Sr/Ba ratio and some minerogenic elements (such as Li, La, Nb, Zr, Y, Rb, U, Th, Ce and Ba) indicate the proportion of slightly weathered clast materials in the sediments. Heavy metals such as Ni, Cu, Co have been used mainly as an indicator of anthropogenic pollution. Moreover, diatom analysis of one sediment core from Seidjavr lake was used for reconstruction of pH, trophic status, and paleogeographical conditions. The pH-index was estimated using the ratio of alkaliphilous and acidophilous species of the genera Aulacoseira dominated in phytoplanktonic community. Water and snow were sampled and pH and chemical composition were determined to estimate the present-day status of the lakes.

Sediment chemostratigraphy indicates that over the past 40 to 50 years Ilma lake has been contaminated by rare-element mining, which took place near the lake (Fig. 1). The contents of most elements (with the exception of Si and Cd) increase substantially toward the surface starting from 6 cm depth. The clear Sr/Ba decline in the topmost samples may be connected to increased inputs of mineral particles from mining. Light lantanoids (Ce, La), derived from loparite ores, are accumulated in surface layers more rapidly than heavy lantanoids (Y). Abrupt decline of silica concentrations and LOI increasing in the top part seem to be associated with some eutrophication and changes in phytoplankton community composition, probably due to inputs of P from mining waste and domestic sewage. However, geochemical and diatom sediment records from pristine Seidjavr lake illustrate that recent lake status changes could be properly interpreted as a result of natural processes, and that anthropogenic factors play a minor role (Fig. 1). Nickel, Cu, Co and Cr concentrations vary without any consistent pattern. The abundant input of fresh clast materials and corresponding minerogenic elements which have been occurring within 3-7 cm intervals in Seidjavr lake sediments possibly is a result of the lake shallowing during unusually dry and warm period (1940-1948; Yakovlev, 1961). The tendency of the pH-index to decrease was revealed at the top part of the core. The saprobity index, which characterises the trophic status of the lake has the opposite profile of the pH-index, indicating that the trophic status changes from oligosaprobity to ß-mesosaprobity zones towards top of the core. Some eutrophication and acidification of the lake might be caused by total warming after "Little Ice Age" which commenced on the Kola Peninsula 30,000 ybp. As a result of warming, the tree-line at the Kola Peninsula mountains moved up 70-150 m (Zhukova-Hovanskaya et al., 1985). Expansion of conifers and increased productivity offer one explanation for a decrease in pH of the lakes, due to acidification of precipitation and surface water during their infiltration through coniferous canopy and litter (Ushakova, 1979).

References

Ushakova, G.I. in Soil formation in biogeocenoses of Khibiny mountains (ed. Evdokimova, G.A.) 94-112 (Kola Branch of USSR Academy of Sciences, Apatity, 1979).

Yakovlev, B.A. Climate of Murmansk region , Murmansk (1961).

Zhukova-Hovanskaya, A.S. & Zhuchkova, V.K. in Engineering geography of Khibiny mountains 95-98, VINITI, Moskow, (1985).

Fig. 1. Some elements and Sr/Ba ratio vertical distribution, calculated pH-index and saprobity index in sediment cores from Ilma and Seidjavr lakes.