Diatom assessment of past environmental changes in lakes located near the Noril'sk (Siberia) smelters

Noril'sk, a major center for mining and smelting of high-sulphur nickel-cop per ores, is considered one of the most polluted regions on this planet. Ye t, long-term data on limnological changes in nearby lakes are lacking. Pale olimnological approaches were used to compare pre-industrial diatom assembl ages with recent assemblages in 17 Noril'sk-area lakes in order to assess t he effects of the metallurgical operations. Relative to other regions of in tense mining and smelting activities, the Noril'sk diatom assemblages have experienced relatively little change since pre-industrial times. The lakes are well protected against the effects of acidification due to their strong buffering capacities as a result of the surrounding bedrock and overlying glacial deposits. The alkaline nature of the lakes appears to have suppress ed the environmental availability of metals, as most likely formed insolubl e metallic complexes and became incorporated into the lake sediments. Chang es between recent and pre-industrial diatom assemblages were recorded for s ome lakes; however, the taxa contributing to the greatest amount of this ch ange were small, benthic Fragilaria species, and not acid and metal-toleran t taxa, as observed in similarly impacted regions. Emissions from mining ac tivities resulting in watershed disturbances, such as increased erosion, li kely accounted for shifts in these species over time.